WO2013053614A1

WO2013053614A1 - Method to provide at least one patient specific device to be used for bone correction, a treatment kit, a method of operating a data-processing system, a computer program, and a correction and fixation device and a cutting assisting device for bone correction

Info

Publication number: WO2013053614A1
Application number: PCT/EP2012/069374
Authority: WO
Inventors: Johannes Gijsbertus Gerardus DOBBE
Original assignee: Academisch Medisch Centrum Bij De Universiteit Van Amsterdam
Priority date: 2011-10-14
Filing date: 2012-10-01
Publication date: 2013-04-18
Also published as: WO2013055203A1

Abstract

The invention relates to a method to provide at least one patient specific device to be used in a bone correction method, the method comprising the steps of obtaining a bone model and a target bone model; determining a treatment process including a cutting section for cutting the bone in a first and second bone portion and a relative target position of the first and second bone portion; and designing in the data processing system a correction and fixation device having a first positioning part having a first positioning surface tightly fitting to the first bone portion, a second positioning part having a second positioning surface tightly fitting to the second fitting surface, and a connection part connecting the first positioning part and the second positioning part, wherein the connection part is shaped to arrange the first bone portion and the second bone portion in the relative target position.

Description

METHOD TO PROVIDE AT LEAST ONE PATIENT SPECIFIC DEVICE TO BE USED FOR BONE CORRECTION, A TREATMENT KIT, A METHOD OF OPERATING A DATA- PROCESSING SYSTEM, A COMPUTER PROGRAM, AND A CORRECTION AND

FIXATION DEVICE AND A CUTTING ASSISTING DEVICE FOR BONE CORRECTION

FIELD OF THE INVENTION

The present invention relates to a method for providing at least one patient specific device to be used for bone correction, in particular osteotomy. The invention further relates to a treatment kit, a method of operating a data-processing system, a computer program, and a correction and fixation device and a cutting assisting device for bone correction.

BACKGROUND OF THE INVENTION

WO 2004/071309 discloses a method for treating malunited bones by osteotomy, the contents of which are herein incorporated by reference in its entirety. The method of WO 2004/071309 comprises the steps of: (A) obtaining a bone model representing a bone which is a subject of treatment; (B) obtaining a target bone model to which treatment aims; (C) determining a treatment process which is to be performed on the bone based on the bone model and the target bone model ; and (D) performing a surgical operation using the determined treatment process.

To improve the result of the treatment, the use of an osteotomy assisting member during the surgical operation is proposed. The osteotomy assisting member includes a fitting surface as a positioning element for indicating a position of the osteotomy assisting member which is to be attached to the bone; a slit as a cutting section indicating element for indicating a cutting section along which the bone is to be cut and divided; and guide holes each as an attachment position indicating element for indicating an attachment position of rods.

The fitting surface is formed to fit on a surface portion of the bone. The slit is provided so as to correspond to the cutting section of the bone. The cutting section is defined so as to be such a position that a post-correction bone shape and the shape of a normal bone are closest to each other.

The post-correction bone shape is obtained by dividing the bone along the cutting section into a proximal portion and a distal portion and moving and/or rotating the distal portion.

During the surgical treatment, the fitting surface of the osteotomy assisting member and the surface feature portion of the bone to be treated are made to fit each other, so as to fix the osteotomy assisting member in a closely fit manner. Thus, the osteotomy assisting member is uniquely positioned and attached to the bone. Rods are inserted into the guide holes, and the bone is pierced with the end of each rod so as to attach the rods to the bone.

Next, the bone is cut by moving a cutting jig such as a saw or the like along the slit, and the osteotomy assisting member is removed while leaving the rods in place. Then, the distal bone portion and the accompanying tissues are moved to a position at which the other end of each rod is insertable into a respective insertion hole of a correction block, and then the rod is inserted thereinto. This step puts the bone portions into the desired positional relationship.

Finally, the bone portions are joined to each other in this state using plate and screws or other fixing devices of a conventional type.

A drawback of the known method is that the final fixation of the two bone portions with a standard fixation plate may result in the introduction of stress into the assembly of the rods and the correction block and/or in the assembly of fixation plate and the bone portions. This stress may result in change of the relative position between the first bone portion and the second bone portion after the removal of the correction block and consequently in sub- optimal positioning of the bone portions with respect to each other. In addition, this method requires many steps, which makes it a time consuming procedure. This is a burden on the patients as well as on the healthcare team and makes it costly.

US 2010/0152782 A1 discloses open and closing wedge osteotomies using a patient specific alignment guide to a corresponding surface of a tibia of a patient for whom the alignment guide is customized during a pre-operative planning stage. It further discloses the method comprising removably attaching a patient-specific fixation plate to the implantable wedge. However, opening-wedge osteotomy is unsuitable for osteotomies that require rotational corrections or corrections involving shortening of the bone. Therefore, the number of bone corrections which may be treated using wedge osteotomy is rather limited.

US 2008/0195240 A1 discloses a method of designing an orthopedic plate by collecting digital information, which corresponds to a sample population for a particular anatomical site. A disadvantage of this approach is the fact that a standard plate does not fit on the bone geometry when the bone is deformed due to a malunion. In addition, locking screws may introduce a positioning error if the screws lock into the plate with different distances between each of the bone segments and the plate, compared to what was planned.

The aim of the present invention is to provide a device, which may improve the results of osteotomy surgery. SUMMARY OF THE INVENTION

The invention is set forth in the main claims, while the dependent claims describe other characteristics of the invention.

The purpose of the invention is to achieve a patient specific device, which can be used to correct positioning in a wide range of bone deformations, such as bone malunions, which require corrective osteotomy. Another purpose of the invention is to achieve a patient- specific device, which improves the accuracy and reproducibility of osteotomy surgery.

The present invention provides a method to provide at least one patient specific device to be used in a bone correction method, the method comprising the steps of:

- obtaining a bone model representing a bone which is a subject of treatment;

- obtaining a target bone model to which treatment aims;

- determining in a data processing system a treatment process which is to be performed on the bone, based on the bone model and the target bone model, said step of determining a treatment process at least comprising the steps of:

determining a cutting section for cutting the bone to be treated in a first bone portion and a second bone portion, and

determining a relative target position of the first bone portion and the second bone portion with respect to each other on the basis of a comparison of the bone model and the target bone model; and

- designing in the data processing system a correction and fixation device said step of designing comprising:

determining a first fitting surface on the first bone portion and a second fitting surface on the second bone portion; and

creating a correction and fixation device having a first positioning part having a first positioning surface tightly fitting to the first fitting surface, a second positioning part having a second positioning surface tightly fitting to the second fitting surface, and a connection part connecting the first positioning part and the second positioning part, wherein the connection part is shaped to arrange the first bone portion and the second bone portion in the relative target position when the correction and fixation device is fixed with the first positioning surface on the first fitting surface and with the second positioning surface on the second fitting surface.

The correction and fixation device according to the invention solves the problem of the standard anatomical plate, such as disclosed in US 2008/0195240 A1 , that a standard plate does not fit on the bone geometry when the bone is deformed due to a malunion. As a result, positioning with an anatomical plate may lead to considerable residual errors for individual cases that fall out of the generally accepted ranges in healthy subjects. These problems are solved by obtaining a bone model representing the bone to be treated rather than an 'averaged' bone model and obtaining a target bone model to which the treatment aims and design and determine the relative target position of the first bone portion and the second bone portion of the bone to be treated and create a patient specific correction and fixation device having a first positioning part having a first positioning surface tightly fitting to the first fitting surface, a second positioning part having a second positioning surface tightly fitting to the second fitting surface, and a connection part connecting the first positioning part and the second positioning part, wherein the connection part is shaped to arrange the first bone portion and the second bone portion in the relative target position when the correction and fixation device is fixed with the first positioning surface on the first fitting surface and with the second positioning surface on the second fitting surface. This connecting part serves a patient specific correction part, which enables a patient-specific correction in 6 degrees of freedom and therefore results in a higher positioning accuracy and is superior to that of the anatomical plate. Example 2 as described herein demonstrates the superiority of the advantages of the correction and fixation device according to the invention. The accuracy of positioning of anatomical plates is studied in Example 3, which is included herein for comparing the accuracy of the anatomical plate with the correction and fixation device according to the invention.

The concept of an anatomical plate, as exemplified in US 2008/0195240 A1 , assumes similar bone morphologies for the whole population. The anatomical plate is designed based on a group of individuals, i.e., a subpopulation. Figure 18a and 18b show two differently shaped volar distal radius plates as available from two manufacturers. The angle a (-20°) is indicative for the difference in correction angle (p_y (Fig. 16), which affects the radial inclination. The angle β (~12 °) is indicative for the difference in correction angle φ_ζ (Fig. 16), which affects the angle of rotation about the bone axis. Experimental evaluations of these plates in a small group of artificial bone specimens indeed confirm different positioning of angulation parameter φ_ζ (Fig. 17). The differences are evident from Fig. 16.

Different plates apparently provide different ways of positioning. These differences in plate definition are likely due to differences in the underlying subpopulations used by the manufacturers. The large differences between subpopulations are indicative for even larger differences between individuals. An anatomical plate may therefore perform very well for one patient but would be inadequate to use for another patient.

In case of bone deformities, such as in the case of bone malunion (Fig. 9a), the bone geometry is no longer 'anatomical', and utilization of an anatomical plate is very unlikely to result in adequate positioning.

The correction and fixation device according to the invention, however, exactly follows the contour of a patient's specific bone morphology while the presence of the 'connecting part which is shaped to arrange the first bone portion and the second bone portion in the relative target position when the correction and fixation device is fixed with the first positioning surface on the first fitting surface and with the second positioning surface on the second fitting surface' guarantees accurate positioning in six degrees of freedom, as shown by Fig. 12c-d.

The correction and fixation device according to the invention also improves the subjective plate placement compared to an anatomical plate. An anatomical plate aims on restoring the anatomical position of the bone segments with respect to one another, and uses the average anatomical shape to accomplish this task. However, subjective plate placement by surgeons, despite the manufacturer's instructions, introduces intra-surgeon and inter-surgeon variation (Fig. 16). The large variability ranges shown by this figure, (especially for the angulation parameters) are indicative for subjectivity in placement and yields suboptimal positioning for individual cases.

In Example 3, the accuracy of positioning of the anatomical plate was tested by two different physicians. By comparing the positioning error parameters with generally accepted differences due to bilateral asymmetry, it could be established that neither of the two physicians were able to correct all positioning parameters (six degrees of freedom) at the same time, to within their respective 95% confidence intervals (Table 1 ). This renders placement using an anatomical plate suboptimal.

The correction and fixation device according to the invention on the other hand, features objective placement to the bone by introducing predrilling and cutting with a cutting assisting device, according a preoperative plan. The custom plate snugly fits to the same patient-specific bone geometry and imposes positioning in 3-D space as planned. The small residual positioning errors as shown by Fig. 12c-d proof that correction and fixation device according to the invention is indeed superior to an anatomical plate.

The method of the inventions also solves the problems of US 2008/0195240 A1 , that wedge osteotomy is unsuitable for many types of malunions, because rotational corrections and corrections involving shortening or extreme lengthening cannot be performed with the methods described in US 2008/0195240 A1 . This problem is solved by determining a cutting section for cutting the bone to be treated in a first bone portion and a second bone portion and designing a correction and fixation device which enables corrections in 6 degrees of freedom and provides stability of the treated bone during the surgical procedure and the healing process.

The method of the invention provides a method to provide at least a correction and fixation device to be used in bone correction surgery, in particular in osteotomy.

The correction and fixation device which results of the method of the invention may be in the form of a three dimensional computer model, or in the form of a correction and fixation device manufactured on the basis of a computer model. The correction and fixation device resulting from the method of the invention comprises a first positioning part having a first positioning surface tightly fitting to the first fitting surface and a second positioning part having a second positioning surface tightly fitting to the second fitting surface.

The first fitting surface and the second fitting surface are based on three dimensional bone models and preferably selected such that the first and second positioning surface can only be placed in one unique position on the first fitting surface and the second fitting surface, respectively.

Since the first and second positioning surfaces are arranged, via the connection part, in a fixed relationship with respect to each other in six degrees of freedom, fixation of the correction and fixation device on the first and second fitting surface will result in a reliable positional relationship between the first bone portion and the second bone portion.

Furthermore, since the first and second positioning surface fit tightly to the first and second fitting surfaces stress free mounting of the correction and fixation device on the first and second bone portion is possible.

Designing the correction and fixation device comprises the following steps.

As a first step a three dimensional bone model of the bone to be treated and a three dimensional target bone model to which treatment aims are obtained.

The three-dimensional bone model of the bone to be treated and the target bone model can be obtained by any suitable method, for example by any method disclosed in WO 2004/071309, such as a model calculated on the basis of x-ray, CT or MRI images.

The three-dimensional model of the bone to be treated and/or the target bone model may be calculated as a step of the method of the invention on the basis of image data obtained from imaging the bone to be treated. However, the three dimensional bone model may also directly be obtained from another system for instance a 3D scanning system capable of directly calculating a three dimensional model that can be used in the method of the invention.

The three dimensional model of the target bone model may be based on calculations of the bone model of the bone to be treated or another bone model, but is preferably based on the healthy contralateral limb of the patient's body. An advantage thereof is, that a better reference is achieved compared to a reference based on e.g. merely population data.

Preferably corrections are included to compensate for bilateral differences, as data about contralateral differences in populations are acquired along this and other processes.

When the bone model and the target bone model are available in the data processing system, a treatment process can be determined. The treatment process comprises cutting the bone at a cutting section into a first and a second bone portion and repositioning the first and the second bone portions to optimally resemble the target bone model. The treatment process may include bone rotation, bone excision, insertion of a graft, and bone distraction or any combination thereof.

The determination of the relative position of the first and second bone portion after correction can be based on any suitable technique, such as a screw displacement method. The correction of the relative position of the first bone portion and the second bone portion may comprise translations and/or rotations to reposition the first bone portion and second bone portion in six degrees of freedom with respect to each other. A cutting section is determined for cutting the bone to be treated in a first bone portion and the second bone portion.

On the basis of the treatment process a correction and fixation device may be designed. As a first step a first fitting surface and a second fitting surface are determined on the bone. The first fitting surface is located on the first bone portion and the second fitting surface is located on the second bone portion. This first and second fitting surface are three dimensional surfaces selected such that any surface complementary to the first or second fitting surface can only be tightly arranged in one unique position with respect to the first and second fitting surface, respectively.

Since the relative target positions of the first bone portion and second bone portion after bone correction are determined as part of the treatment process, the relative target position of the first fitting surface and the second fitting surface after bone correction are also known. The selection of the locations of the first fitting surface and the second fitting surface may also be based on further criteria. The relative target positions of the first bone portion and the second bone portion may be based on the target bone model or another bone model and may also be based on further criteria, such as bilateral difference compensation. For example, the locations of the first fitting surface and the second fitting surface have to be suitable for fixation of the correction and fixation device. The bone material at these locations should be capable of holding fixation means such as screws or wires, and the presence of the fixation and correction device preferably has no or little negative effect on the functioning of soft tissues, such as tendons and muscles, surrounding the bone or on the kinematics of a joint.

The relative target position of the first and second fitting surface are used to design a correction and fixation device to be used in the actual bone correction surgery.

The connection part is shaped to arrange the first fitting surface and the second fitting surface in the relative target position when, after cutting the bone into the first bone portion and the second bone portion, the first positioning surface is arranged on the first fitting surface and the second positioning surface is arranged on the second fitting surface. Thus, fixation of the correction and fixation device will automatically arrange the first bone portion and the second bone portion in the relative target position with respect to each other. The method of claim 1 may be implemented as a method of operating a data processing system.

Since the correction and fixation device is configured to be implanted into a human body, the correction and fixation device is preferably a plate-shaped device made of implantable material. The correction and fixation device is further preferably designed to have high stiffness and low volume.

In an embodiment, the correction and fixation device comprises fixation locations to fix the correction and fixation device on the first bone portion and the second bone portion. These fixation locations may be in the form of one or more fixation holes each configured to receive a fixation means, such as a fixation screw, fixation wire or other fixation tool suitable to fix the correction and fixation tool on the respective bone portion.

In an embodiment, the fixation locations in the first positioning part are arranged in a first pattern with respect to the first fitting surface, and the fixation locations in the second positioning part are arranged in a second pattern with respect to the second fitting surface. This first pattern and second pattern can be selected to properly anchor the correction and fixation device on the first and second bone portion. The first and second pattern can for example be based on the locations where the bone is most suitable for anchoring the correction and fixation device.

The fixation locations may be planned dependent on the shape and state of the specific bone to be treated.

In an embodiment, the first fitting surface and the second fitting surface are adjacent to the cutting section. By selecting the first fitting surface and the second fitting surface adjacent to the cutting section, the distance between the first and second fitting surface after bone correction can be kept relatively low. As a result, less material and/or less stiff material is required to provide the correction and fixation device.

In an embodiment, the method further comprises the step of designing in the data processing system a graft model to be arranged between the first and second bone portion. In osteotomy procedures often use is made of grafts that are to be placed between the first and second bone portion. The graft is used for promoting the healing of the first and second bone portions to each other, and/or to support the bone.

The material with which the graft is made may be bone material obtained from the patient or from a donor. The graft material may also be made of other suitable biocompatible and/or biodegradable material, such as artificial bone material. The shape of the graft will depend on the space between the first and second bone portion after correction, and may for instance be substantially cylindrical or substantially wedge shaped.

In an embodiment, the method of the invention comprises the step of designing in the data processing system a cutting assisting device comprising a surface tightly fitting to the first fitting surface and to the second fitting surface and a cutting assisting element. A cutting assisting device can be used to assist in the cutting of the bone to be treated in a first and second bone portion. The cutting assisting element may be an element which assists in the cutting of the bone, such as an indicator indicating the location and/or orientation where the cut should be made. Preferably, the cutting assisting device comprises a slit in the cutting assisting device designed to receive a cutting device, for instance a cutting saw. The slit may act as a guide for the cutting device, therewith assuring cutting at the desired cutting section. The cutting assisting element of the cutting assisting member, for example a cutting slit may be designed and manufactured as "the template assisting member" disclosed in

WO2004/071309, the contents of which are herein incorporated by reference.

Since the surface of the cutting assisting device tightly fits on the first and the second fitting surface, the cutting assisting device can only be arranged in a single position with respect to the bone, and the cutting assisting element will reliably be positioned with respect to the desired cutting location. It is remarked that the surface of the cutting assisting device tightly fitting to the first fitting surface and the second fitting may be composed of two separate surface areas with for instance a cutting slit there between.

In an embodiment, the step of designing the cutting assisting device comprises the step of providing temporarily fixation locations in the cutting assisting device to temporarily fix the cutting assisting device to the bone to be treated. It is desirable to fix the cutting assisting device during cutting of the bone. Fixation locations may be provided for this reason. These fixation locations may be in the form of one or more fixation holes each configured to receive a fixation means, such as a fixation screw, fixation wire or other fixation tool suitable to fix the correction and fixation tool on the respective bone portion.

In an embodiment, the step of providing the cutting assisting device comprises the step of providing one or more holes in the cutting assisting device configured to assist in preparing the first bone portion and/or the second bone portion for fixation of the correction and fixation device on the first bone portion and/or the second bone portion. Since both the correction and fixation device and the cutting assisting device comprise surfaces tightly fitting to the first and second fitting surface, the correction and fixation device and the cutting assisting device can each only be placed in one unique fitting position on the first and/or second fitting surfaces.

Therefore, the cutting assisting device may be used to prepare the first bone portion and the second bone portion for the fixation of the correction and fixation device. In particular, holes may be provided in the cutting assisting device to prepare the first and second bone portion. For example, the holes may be holes configured to receive a drilling or tapping element to drill and/or tap a hole in the first bone portion and/or second bone portion. The resulting pre-drilled and/or tapped holes in the first and/or second bone portion can be used to receive fixation means to fix the correction and fixation device on the first and/or second bone portion, respectively. Instead of holes also other means to assist in the preparation of the bone for fixation of the correction and fixation device may be provided.

The holes may be configured to also receive a fixation means to temporarily fix the cutting assisting device to the bone to be treated. In this embodiment, the holes are also fixation locations for the cutting assisting device, and the holes may be used both for temporarily fixing the cutting assisting element and for preparing the fixation of the correction and fixation device to the first and/or second bone portion.

In such embodiment the locations of fixation in the bone portions resulting from the fixation locations of the cutting assisting device, e.g. holes drilled through the device into the bone portions, are also used as the locations for fixation of the correction and fixation device, as such bypassing the need of creating new, extra locations for fixation in the first and second bone portions.

In addition, or as an alternative, other fixation locations, for example fixation holes, may be provided for fixation of the cutting assisting device. In such embodiment, the cutting assisting device can first be fixed to the bone using the fixation holes. Subsequently, the holes configured to assist in preparing the bone for fixation of the correction and fixation device can be used to preparing the bone, for example for pre-drilling and/or tapping.

In an embodiment, the holes in the cutting assisting device configured to assist in preparing the first bone portion and/or the second bone portion for fixation of the correction and fixation are provided in a pattern corresponding with the first pattern with respect to the first fitting surface and with the second pattern with respect to the second fitting surface.

When using a cutting assisting device having holes with the same patterns as the correction and fixation device, the cutting assisting device can be used as a template for creating fixation locations in the first and second bone portions for fixing the correction and fixation device to the first and second bone portion. It is remarked that the pattern and the first and second pattern of fixation locations should be determined on the surface of the cutting assisting device and the first and second positioning surface, respectively.

Since the cutting assisting device may be removed from the bone after cutting of the bone, and will not remain in the body, the thickness of the cutting assisting device can be relatively large so that the fixation locations in the cutting assisting device provide a proper guidance of surgical saw and/or surgical drill or any other device to be used together with the cutting assisting device.

When the pattern of fixation locations on the cutting assisting device corresponds to the first and second pattern of fixation locations of the correction and fixation device, this guidance is less important when the correction and fixation device is fixed on the bone after removal of the cutting assisting device, since the locations for fixation in the bone are already prepared.

In an embodiment, the method further comprises the step of manufacturing the correction and fixation device and/or the step of manufacturing the cutting assisting device. Manufacturing of the patient specific correction and fixation device and/or the cutting assisting device may be performed by any suitable method, but is preferably carried out by a computer aided 3D manufacturing method such as 3D CAD/CAM or 3D printing. The correction and fixation device and the cutting assisting device can be made out of any suitable material. The material of the correction and fixation device is made of implantable material which is preferably stiff, and may be biodegradable. The correction and fixation device may for example be made of Titanium or Stainless Steel. The cutting assisting device can be made of biocompatible material.

The invention further provides a patient specific correction and fixation device to be used in a bone correction method, wherein the correction and fixation device comprises a first positioning part having a first positioning surface, a second positioning part having a second positioning surface, and a connection part connecting the first and the second positioning part, wherein the first positioning surface is configured to tightly fit on a first fitting surface defined on the bone to be treated and the second positioning surface is configured to tightly fit on a second fitting surface defined on the bone to be treated, and wherein the connection part is shaped to arrange the first fitting surface and the second fitting surface in a relative target position when the correction and fixation device is fixed on the first fitting surface and the second fitting surface.

The correction and fixation device may be part of a bone treatment kit. The bone treatment kit may further include a cutting assisting device and/or a graft. The bone treatment kit may also comprise fixation tools to fix the correction and fixation device and/or the cutting assisting device to the bone. Any other device or tool may also be part of the treatment kit.

The invention may also be applied as a method of operating a data-processing system comprising the steps of:

- obtaining a bone model representing a bone which is a subject of treatment;

- obtaining a target bone model to which treatment aims;

- determining a treatment process which is to be performed on the bone, based on the bone model and the target bone model, said step of determining a treatment process at least comprising the steps of:

determining a cutting section for cutting the bone to be treated in a first bone portion and a second bone portion, and determining a relative target position of the first bone portion and the second bone portion with respect to each other on the basis of a comparison of the bone model and the target bone model; and

- designing a correction and fixation device model, said step of designing comprising:

creating a correction and fixation device model having a first positioning part having a first positioning surface tightly fitting to the first fitting surface, a second positioning part having a second positioning surface tightly fitting to the second fitting surface, and a connection part connecting the first positioning part and the second positioning part, wherein the connection part is shaped to arrange the first bone portion and the second bone portion in the relative target position when the correction and fixation device is fixed with the first positioning surface on the first fitting surface and with the second positioning surface on the second fitting surface.

In an embodiment, the method is further adapted to perform the step of controlling a 3D manufacturing device, for example a 3D printer to form a correction and fixation device on the basis of the correction and fixation device model.

In an embodiment, the method comprises the step of designing a cutting assisting device comprising a surface tightly fitting to the first fitting surface and to the second fitting surface and a cutting assisting element.

The method of operating a data-processing system may further comprise any of the method steps of claims 2-14.

The invention may provide a computer program comprising software code adapted to perform the steps of the method of any of the claims 16-18.

The invention may also provide a correction and fixation device obtained by the method of any of the claims 1 -14 and a cutting assisting device obtained by the method of any of the claims 7-14.

Further, the invention may provide a bone correction method, comprising the steps of: - obtaining a bone model representing a bone which is a subject of treatment;

- obtaining a target bone model to which treatment aims;

determining a cutting section for cutting the bone to be treated in a first bone portion and a second bone portion, and determining a relative target position of the first bone portion and the second bone portion with respect to each other on the basis of a comparison of the bone model and the target bone model;

creating a correction and fixation device having a first positioning part having a first positioning surface tightly fitting to the first fitting surface, a second positioning part having a second positioning surface tightly fitting to the second fitting surface, and a connection part connecting the first positioning part and the second positioning part, wherein the connection part is shaped to arrange the first bone portion and the second bone portion in the relative target position when the correction and fixation device is fixed with the first positioning surface on the first fitting surface and with the second positioning surface on the second fitting surface,

carrying out the treatment process on the patient, comprising the steps of cutting the bone to be treated at the cutting section into a first bone portion and a second bone portion and fixing the first and second bone portions in their relative target position by fixation of the correction and fixation device with the first positioning surface on the first fitting surface and the second positioning surface on the second fitting surface.

In an embodiment, the bone correction method may comprise the step of designing a cutting assisting device comprising a surface tightly fitting to the first fitting surface and to the second fitting surface and a cutting assisting element, and, during the treatment process, the step of temporarily fixing the cutting assisting device on the bone to be treated and using the cutting assisting element to cut the bone to be treated at the cutting location.

In an embodiment, the bone correction method may further comprise the step of using locations of fixation in the bone portions resulting from fixation locations of the cutting assisting device, e.g. holes drilled through the cutting assisting device into the bone portions, as locations for fixation of the correction and fixation device on the bone portions.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the method according to the invention will now be described in further detail, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a bone model of a bone to be treated;

Figure 2 shows a target bone model to which treatment aims; Figure 3 shows a relative target position of the first bone portion and the second bone portion of the bone model of Figure 1 after dividing the bone in a first and second bone portion;

Figure 4 shows a cutting assisting device arranged on the bone to be treated;

Figure 5 shows the cutting assisting device in perspective view;

Figure 6 shows the correction and fixation device arranged on the first and the second bone portion; and

Figure 7 shows the correction and fixation device in perspective view. Osteotomy is a surgical operation whereby a bone is cut to shorten, lengthen, and/or change its alignment. The method of the invention proposes pre-operative planning of the treatment process for bone correction and design of a patient specific cutting assisting device and a preferably patient-specific correction and fixation device. The correction and fixation device is designed to be implanted into the patient temporarily or permanently. By fixating the correction and fixation device in the planned position on both the first bone portion and the second bone portion, the correction and fixation device automatically arranges the first and second bone portions in the desired target position.

The steps of the method and the correction and fixation device resulting from the method will now be described in more detail.

Figure 1 shows a three-dimensional bone model of a deformed bone. The bone model is indicated by reference sign 1 . It is desirable to correct the bone to position the ends of the bones in a normal position with respect to each other. To correct a bone to a normal position a target bone model is configured to define the desired positions of the ends of the bone after bone correction.

Figure 2 shows such three-dimensional target bone model 2. The target bone model shows the model to which treatment aims. The target bone model may be calculated on the basis of patient specific data, and for example be based on the corresponding bone of the contra lateral limb of the patient. The target bone model may also be based on any other suitable data, for example data obtained from a group of persons having similar build. It is also possible that the target bone model is completely calculated on the basis of the bone to be treated and physical structure of the patient.

The bone model and target bone model are provided as three dimensional computer models. These computer models are for example obtained by obtaining images on the basis of imaging techniques, such as x-ray, CT or MRI, and calculating a three-dimensional computer model on the basis of these images and possibly other data.

The computer models are preferably 3D CAD compatible models that can be used in 3D CAD software, such as "Solid works" or "Surgicase Connect", available from Materialise N.V., Leuven, Belgium. The computer models are preferably high resolution computer models that provide detailed information on the surfaces of the bone structure, at least at the relevant location, such as the first and second fitting surface to be discussed hereinafter.

By comparison of the bone model and target bone model a treatment process for the bone can be determined.

The treatment involves cutting the bone in a first bone portion and a second bone portion and repositioning the first and second bone portion to arrange the bone ends in a relative position optimally resembling the target bone model. It is remarked that in some treatments the bone may also be cut in more than two bone portions. For example, when the osteotomy involves shortening of the bone, the bone may be cut in three bone portions, whereby the central bone portion is taken out of the bone, and the two outer bone portions are fixed to each other to form a new bone structure.

Determining a treatment process comprises determining a cutting section where the bone is to be cut in a first bone portion and a second bone portion. After cutting the bone into a first and second bone portion, the first bone portion and the second bone portion can be positioned in the desired relative position by translation and/or rotation of the first bone portion and the second bone portion with respect to each other.

Figure 3 shows a three dimensional computer model of the deformed bone 1 of Figure 1 divided in a first bone portion 3 and a second bone portion 4, whereby the first bone portion 3 and the second bone portion 4 are arranged in their relative target position to resemble the target bone model of Figure 2.

Any suitable method may be used to determine the translation and/or rotation of the first and second bone portion required to position the first and second bone portion in the relative target position. The relative position may be determined in six degrees of freedom.

In determining the treatment process, the step of selecting a cutting section may be a start point to subsequently determine how the first and second bone portion should be positioned with respect to each other. In another embodiment the cutting section may be a result of the determination of the desired movement. For example, the cutting selection may be selected such that only rotation and/or translation in one or two directions is required to relocate the respective bone portion to the desired position. It is also possible that the determination of the cutting section comprises a number of iterative steps.

In an osteotomy procedure the relative positioning of a first and a second bone portion may be very difficult. To assist the surgeon during the bone correction operation a cutting assisting device 10 and a correction and fixation device 20 are designed

The cutting assisting device 10 is shown in Figure 4 arranged on the bone 1 to be treated. Figure 5 shows a perspective view of the cutting assisting device 10. The correction and fixation device 20 is shown in Figure 6 arranged on the first bone portion 3 and the second bone portion 4. Figure 7 shows a perspective view of the correction and fixation device.

The cutting assisting device 10 is designed to assist the surgeon in cutting the bone 1 to be treated at the cutting section 7 to obtain the first bone portion 3 and the second bone portion 4.

As a first step of designing the cutting assisting device 10 a first fitting surface 5 and a second fitting surface 6 are selected on the bone 1 . The first fitting surface 5 is located on the first bone portion 3 and the second fitting surface 6 is located on the second bone portion 4, as shown in Figure 3.

The cutting assisting device 10 comprises a surface 1 1 which tightly fits to the first fitting surface 5 and the second fitting surface 6 before the bone is cut into the first bone portion 3 and the second bone portion 4.

The cutting assisting device 10 further comprises a slit 12 which is configured as a cutting assisting element. The first fitting surface 5 and the second fitting surface 6 are selected such that the surface 1 1 can only be arranged in one fitting position with respect to the bone 1 , in which fitting position the surface 1 1 is in close contact with the first fitting surface 5 and the second fitting surface 6. As a result, the cutting assisting element 10 can only be arranged in one unique position on the bone 1 to be cut. The slit 12 is configured to guide a cutting saw or such during cutting of the bone such that the bone will be cut at the cutting section 7.

The cutting assisting device 10 comprises a number of fixation holes 13a, 13b for receiving fixation means such as fixation screws or fixation wires with which the cutting assisting device 10 can be fixed on the bone. The fixation holes 13a are arranged in a first pattern with respect to a first part of the surface 1 1 to be placed on the first fitting surface 5. The fixation holes 13b are arranged in a second pattern with respect to a second part of the surface 1 1 to be placed on the second fitting surface 6.

The fixation holes 13a, 13b may be designed to receive any fixation means, such as fixation screws or wires to fix the cutting assisting device to the bone to facilitate cutting of the bone at the desired location.

The cutting assisting device has a relative large thickness so that, during the operation, the resulting relative long fixation holes 13a, 13b provide a good guidance during cutting or drilling or such into the bone.

The correction and fixation device 20 is designed to assist the surgeon in

repositioning the first bone portion 3 and the second bone portion 4 with respect to each other, and to fix the first bone portion 3 and the second bone portion 4 to each other in this relative position so that the bone may heal with the first bone portion 3 and the second bone portion 4 in the desired relative position. The correction and fixation device 20 comprises a first positioning part 21 having a first positioning surface 22 tightly fitting to the first fitting surface 5 and a second positioning part 23 having a second positioning surface 24 tightly fitting to the second fitting surface 6. The first positioning part 21 and the second positioning part 23 are connected to each other with a connection part 25. The connection part 25 is shaped to position the first bone portion 3 and the second bone portion 4 in the desired relative position, when the first positioning surface 21 is arranged on the first fitting surface 5 and the second positioning surface 23 is positioned on the second fitting surface 6.

The patient specific correction and fixation device 20 has the advantage that no complex positioning system has to be provided to arrange the first bone portion 3 and the second bone portion 4 in their relative target location after cutting the bone. Also, since the correction and fixation device is used to fix the first and second bone portions 3, 4 to each other, there is no stress introduced by the correction and fixation device itself during the fixation of the first bone portion 3 and the second bone portion 4, and the bone portions will remain in the desired relative target position.

In the first positioning part 21 a number of fixation holes 26 are provided to fix the correction and fixation device 20 on the first bone portion 3, and in the second positioning part 22 a number of fixation holes 27 are provided to fix the correction and fixation device 20 on the second bone portion 4.

The fixation holes 26 are provided in the same first pattern as the fixation holes 13a on the cutting assisting device 10. The fixation holes 27 are provided in the same second pattern as the fixation holes 13b of the cutting assisting device 10. By providing the fixation holes 26, 27 in the correction and fixation device 20 in the same first and second pattern as the fixation holes 13a, 13b of the cutting assisting device 10, the existing holes in the bone that are caused by fixation of the cutting assisting device 10, can also be used for fixation of the correction and fixation device 20 to the first bone position 3 and the second bone portion 4. This has the advantage that no new holes have to be created, for instance drilled, for fixation of the correction and fixation device, and that the bone is not unnecessarily weakened by the temporarily fixation of the cutting assisting device 10. Furthermore, this adds to the precision and speed of the operational procedure.

In an alternative embodiment, the cutting assisting device may comprise further fixation locations, for example fixation holes, to temporarily fix the cutting assisting device on the bone to be treated, and the holes in a pattern corresponding to the patterns of the fixation holes of the correction and fixation device are used for assistance in preparing the bone for fixation of the correction and fixation device.

In such embodiment, different hole diameters can be used for either fixation of the cutting assisting device and/or for creating predrill holes for fixation of bone portions using the correction and fixation device model using fixation means, for example (bicortical) screws.

When the design of the cutting assisting device 10 and the correction and fixation device 20 is known, these designs can be used to create a cutting assisting device and a correction and fixation device in accordance with these models. The cutting assisting device and the correction and fixation device can be created by any suitable method, for example a 3D printing method or 3D CAD/CAM and with any suitable material.

The cutting assisting device and the correction and fixation device may be part of a patient specific treatment kit for bone correction. The treatment kit may further comprise a graft computer model or a graft, which graft is to be arranged between the first bone portion 3 and the second bone portion 4, to fill the space between the first bone portion 3 and the second bone portion 4. The graft model can be used to directly manufacture a graft, for example by a 3D manufacturing method such as 3D printing or 3D CAD/CAM. The graft may be manufactured from any implantable material, such as artificial bone material. The graft model may also be used as a guidance in adapting the shape of a bone part, for instance a bone part taken from the iliac crest of the patient to the desired shape for implantation. The graft may have any suitable shape such as a cylindrical or a wedge shape.

Figure 6 shows a graft model 30 which is designed to be arranged between the first bone portion 3 and the second bone portion 4.

Figure 8 shows The proximal segment and the distal segment are aligned with the mirrored contralateral bone. This provides transformation matrices Mp and Md that yield the

M = M 'M

correction matrix ^{c p d} , which brings the distal segment of the affected bone to the planned position.

Figure 9 shows steps for creating a patient specific device. A) Interactive selection of the cutting plane. B) Setting the virtual box for projecting a grid of points onto the bone surface. After tessellation between these points, the projected surface (red) is used to create a guide and plate by extrusion (towards plane normal, yellow arrow). C) Virtual cutting assisting device provided with one ore more holes for predrilling the bone and a slit for cutting the bone, attached to the bone. D) A temporary plate is created by extrusion of the projected bone surface and subsequent drilling of holes at the same position as for the cutting assisting device provided with one ore more holes. The temporary plate and affected bone are cut at the interactively indicated position and orientation (shown by line). E) After cutting, the distal bone and plate segments are repositioned using the correction matrix Mc. F) The missing piece is created by Bezier interpolation for smoothness, and concludes tailored plate design. Figure 10 shows a reference radius, which is constructed from the affected bone by adding a wedge-shaped insert to bring the distal end in alignment with the proximal segment, in agreement with the unaffected bone. Registration of the proximal (crossed pattern) and distal (striped pattern) segments with the reference bone (white) allow visualizing

malalignment (striped pattern segment position). Six malalignment parameters (translations: Δχ, Ay, Δζ; rotations: Δφχ, Acpy, Δφζ) are expressed in terms of an anatomical coordinate system.

Figure 1 1 shows an artificial bone specimen showing: A) cutting assisting device provided with one ore more holes attached to the affected bone. The cutting blade is inserted into the slit for demonstration purposes. B) Bone after utilization of a patient specific device showing a high degree of similarity with C) the reference bone.

Figure 12 shows in the top row the accuracy and reproducibility of positioning assessment, showing (A) the error of displacement assessment (B) the error of orientation assessment (n=4). In the bottom row is shown the accuracy and reproducibility of positioning using a patient specific device, showing (C) the residual displacement error and (D) the residual orientation error (n=5). The whiskers show the reproducibility represented by the SD.

Figure 13 shows A) creation of a plate insert by copying the cross section (Plane 0) to intermediate planes [0, N] showing smoothly varying orientations. B) The centroid of these planes follows a cubic Bezier curve defined by a starting point (P0), an end point (P3) and two control points (P1 , P2). C) Tessellation between consecutive points yields a smooth polygon mesh of the insert.

EXAMPLE 1 Preoperative planning for a radius osteotomy is based on a CT scan of the affected bone and the healthy contralateral bone. The contralateral bone is used as reference for restoring the affected bone. The affected bone is first segmented to create a 3-D polygon using "Surgicase Connect", available from Materialise N.V., Leuven, Belgium. A distal and a proximal segment are subsequently clipped, hereby excluding the fracture site. Next, the clipped segments are aligned with the mirrored image of the healthy contralateral bone. This yields two matrices: M_d, which aligns the distal segment with the reference bone, and M_p which aligns the proximal segment with the reference bone. These matrices can be combined to find the correction matrix, M_C=M_P ^"1 M_d, which brings the distal segment of the affected bone from its affected position to the planned position.

In this method intensity-based point-to-image registration may be used. To speed up the registration process, the affected bone is first segmented to find the polygon vertices describing the bone surface. These are used to resample the gray-level image 1 -mm towards the inside (bright voxels) and outside (dark voxels) of the bone. Using this double-contour polygon renders gray-level registration of the affected bone with the reference image very discriminative and accurate.

The affected bone is segmented using threshold-connected region growing followed by a binary closing algorithm to fill residual holes inside the object and at its surface. This intermediate segmentation result is used to initialize a Laplacian level-set segmentation growth algorithm which slightly adjusts the edges towards the highest intensity gradient of the bone image. A polygon is finally extracted from the segmented image, which is used to visualize the bone in 3-D. The vertices of this polygon are also used to determine the double- contour polygon for image registration, as described above.

During preoperative planning, the surgeon is enabled to interactively set the position and orientation of the cutting section. This cutting section is defined by the vector normal to the cutting section ( ^Hc ) and the distance (dc) of the plane to the origin of the coordinate system.

Then a piece of the affected bone polygon is clipped by interactively positioning a box and extracting the fitting surface inside that box. This fitting surface, which is patient specific and especially marked by the fracture, is used to create 1 ) a patient specific cutting assisting device for setting the actual osteotomy and for predrilling holes, and 2) a patient-specific correction and fixation plate for bone positioning and fixation.

The patient-specific cutting assisting device is created by extruding the clipped bone fitting surface towards the average surface normal vector, to create a 3-D mold that snugly fits to the bone surface. The extrusion length is set by the user, e.g. 30 mm. A slit with a user-defined width, e.g. a cutting blade thickness, is added at the position and orientation of the cutting section defined above. Then, the surgeon is enabled to add holes to the guide for fixation of the cutting assisting device itself using, e.g., Kirschner wires, and for predrilling the bone for subsequent fixation using the patient-specific correction and fixation plate with bicortical screws. Different hole positions, orientations and diameters can be chosen during this virtual planning step. In a final post-processing step, the cutting assisting device may be shaped by virtually cutting undesired pieces from the mold until it is conveniently shaped for surgical utilization. The actual cutting assisting device is created from a medical grade polyamide powder by stereolithography printing Materialise, Leuven, Belgium.

Creation of the patient-specific correction and fixation plate is done in a similar way as for the cutting assisting device although less user interaction is required. First the clipped bone fitting surface obtained above is again extruded towards the average surface normal vector, to create a template that snugly fits to the bone surface. The extrusion length is set by the user and corresponds to the desired plate thickness, e.g. 2 mm. Screw holes are added at the same predrill positions and orientations as defined for the cutting and drilling guide, although the hole diameters are adjusted to be in agreement with the required screw diameters. Next the affected bone polygon and the template polygon are cut using the defined cutting section and the distal bone and template segments are repositioned in 3-D space as planned using the correction matrix Mc. The missing piece between the two template segments, i.e. positioning parts, is created by linear or Bezier interpolation between corresponding points. Bezier interpolation results in a smooth connection part between the two positioning parts, altogether comprising the patient-specific correction and fixation plate.

The actual patient-specific correction and fixation plate is created from e.g. a medical grade titanium powder by stereolithography printing (Materialise, Leuven, Belgium).

After resection, the cutting assisting device is positioned at the first and second fitting surface and is fixated with Kirschner wires using the predefined holes. The cutting assisting device is subsequently used to insert predrill holes which are used for plate fixation using bicortical screws after osteotomy. The same cutting assisting device is subsequently used to position and orient the oscillating surgical saw for osteotomy through the slit. After osteotomy the cutting assisting device is removed and the patient-specific correction and fixation plate is first connected to the distal bone portion. It tightly fits to the fitting surface on the distal bone portion while the predrilled holes serve to further guide fixation of the plate to the distal bone portion using screws. The bone portions are distracted in order to align the proximal holes of the plate with the predrilled holes in the proximal bone portion. Fixation is then achieved by mounting the plate to the fitting surface of the proximal bone using bicortical screws.

EXAMPLE 2 Utilization of a patient specific device involved 1 ) planning the relative position of the bone segments in 3-D space using the contralateral bone, 2) creating a cutting assisting device provided with one or more holes, 3) creating a patient specific device, and 4) the intraoperative procedure.

Custom-made planning software [9] for finding the repositioning parameters was extended for designing the cutting assisting device and the patient specific device. This software enables interactive preoperative planning of the osteotomy cut, choosing a plate position, and choosing positions for the fixation screw holes. The thickness of the patient specific device, the diameter of the predrilling holes and the screw diameter are set by the user and are taken into account when designing both the cutting assisting device, and the patient specific device. The methods for guide and patient specific device design are detailed in the following sections. A correction and fixation device is designed by virtually cutting the bone and temporary plate at a user-defined location and by repositioning the distal plate segment using the correction matrix Mc. (Fig. 9e). The cross-section of the plate (Fig. 13a, Plane 0) is positioned repetitively within the gap such that it smoothly runs from the proximal plate segment to the distal plate segment. This is achieved by extracting the angles of rotation (φχ, cpy, φζ) from the rotation matrix that orients the cross-sectional points in "Plane 0" to

"Plane N" (Fig. 6a), and by linear interpolation of the rotation angles for intermediate planes. Positioning of these N planes within the gap is done using cubic Bezier interpolation between the starting point (P0), at the centroid of the cross-section points, and the end-point (P3 = McPO). The control points of this Bezier curve (P1 ) and (P2) are positioned at P1 = P0 + c T1 and P2 = P3 + c T2, with T1 and T2 the average tangent vector of the (transformed) cross- section points in the direction as shown by Fig. 13c. These control points define the curvature of the Bezier path. With this definition of the Bezier parameters (P0, P1 , P2, P3,), the centroids the cross-sectional planes P(i) (i = [0, N]) follow a cubic Bezier curve:

P( = (l-i)³P₀ + 3(l-i)²iP₁ + 2(l-i)(i)²P₂ + (^)³P₃, i e [0,N] (^A-¹ ) A polygon mesh of the insert is created by tessellation between neighboring points (Fig. 13c). 2.1 Preoperative planning

Preoperative 3-D planning is based on a CT scan of the affected bone and the healthy contralateral bone. The contralateral bone is used as reference for planning the reconstruction of the affected bone. The affected bone is first segmented (see below) to create a 3-D polygon, which is a virtual representation of the affected bone. A distal and a proximal segment are subsequently clipped, hereby excluding the malunited fracture region. Next, the clipped segments are aligned (by registration, see below) with the mirrored image of the healthy contralateral bone (Fig. 8). This yields two matrices: Md, which aligns the distal segment with the reference bone, and Mp, which aligns the proximal segment with the reference bone. These matrices can be combined to find the correction matrix, ^{Mc ~ Mp M}" , which brings the distal segment of the affected bone from its affected position to the planned position.

In the above-described method, the affected bone is first segmented using threshold- connected region growing followed by a binary closing algorithm to fill residual holes inside the object and at the bone surface [9]. This intermediate segmentation result is used to initialize a Laplacian level-set segmentation growth algorithm [14], which slightly adjusts the edges towards the highest intensity gradient of the bone image. A polygon is finally extracted from the segmented image, which is used for visualization in 3-D.

Intensity-based point-to-image registration is used for aligning the virtual

representation of the bone segments of the affected side with the mirrored image containing the contralateral bone. To this end, points are selected by sampling the gray-level image 0.3- mm towards the inside (bright voxels) and outside (dark voxels) of the segmented bone. This results in a double-contour polygon, which includes the gray-level value at each vertex.

Registration of these gray-level points with the gray-valued reference image renders bone alignment accurate.

2.2 Cutting assisting device

Patient-specific guides for cutting or drilling are increasingly used in surgery They enable accurate positioning of surgical instruments or implants with respect to the bone anatomy. In the present preoperative procedure, the surgeon is enabled to interactively set the position and orientation of the cutting plane (Fig. 9a).

Next, a virtual box is interactively positioned and a regular grid on the bounded plane formed by one side of this box (Fig. 9b) is projected onto the surface of the affected bone polygon. After tessellation between these points, this projected bone surface, which is patient specific and especially marked by the deformity, is used to create 1 ) a patient specific surgical guide for predrilling holes and for setting the actual osteotomy cut, and 2) a patient specific device for bone positioning and fixation.

The patient-specific cutting assisting device (Fig. 9c) is created by first extruding the projected bone surface towards the plane normal (Fig. 9b, arrow), to create a 3-D mold that snugly fits on the bone surface. The extrusion length defines the thickness of the guide. A slit with a user-defined width (cutting blade thickness) is added at the position and orientation of the cutting plane defined above. Then, the surgeon is enabled to add holes to the guide for fixation of the cutting guide itself and for predrilling the bone for subsequent fixation of the patient specific device with screws. Different hole positions, orientations and diameters can be chosen during this virtual planning step.

2.3 Correction and fixation device

Creation of the tailored correction and fixation device is done in a similar way as for the cutting assisting device although less user interaction is required. First the projected bone surface obtained above is again extruded in the same direction, to create a temporary correction and fixation device that snugly fits on the bone surface (Fig. 9d). The extrusion length defines the correction and fixation device thickness. Screw holes are added at the same predrill positions and orientations as defined for the cutting assisting device, although the hole diameters are adjusted to be in agreement with the required screw diameters. Next, the affected bone polygon and the temporary correction and fixation device polygon are cut using the defined cutting plane and the distal bone and temporary correction and fixation device segments are repositioned in 3-D space as planned using the correction matrix Mc (Fig. 9e). The missing piece between the two correction and fixation device segments (Fig. 9e) is created by Bezier interpolation (Fig. 9f) (Appendix) between corresponding points. Bezier interpolation results in a smooth insert between the two correction and fixation device pieces, altogether realizing the patient-tailored positioning and fixation correction and fixation device.

2.4 Surgical procedure In actual surgery, after resectioning, the surgical guide is positioned at the specific bone surface and is fixated with, e.g., Kirschner wires, using the planned fixation holes. The guide is subsequently used for predrilling screw holes, which are later used for correction and fixation device fixation. The same guide is subsequently used to position and orient the oscillating surgical saw for cutting the bone (osteotomy) through the guiding slit. After osteotomy, the guide is removed and the correction and fixation device according to the inventiondevice is first connected to the distal bone segment. It fits on the bone surface while the predrilled holes serve to further guide fixation of the correction and fixation device to the distal bone segment using screws. The bone segments are subsequently extracted in order to align the proximal holes of the correction and fixation device with the predrilled holes in the proximal bone segment. Positioning and fixation are then achieved by mounting the correction and fixation device to the proximal bone segment using screws.

To evaluate the method according to the invention, a CT scan was made of both arms of one single patient with a unilateral distal radius malunion, as shown in Fig. 9. Preoperative planning, as described above, yields surface descriptions of the affected bone, the planned position of the proximal and distal segments, the cutting assisting device (thickness 10 mm, slit width 1 mm), the correction and fixation device (thickness, 3.0 mm) and a reference bone (section 3.2). Five equal sets of the artificial bone of the affected radius, guides and correction and fixation devices are created of acrylonitrile butadiene styrene (ABS) by 3-D printing (SST1200es 3-D printer, Dimension Inc., Eden Prairie, MN). The resolution of this printer is 254μηι. In all experiments CT images are acquired with a Brilliance 64-channel CT scanner (Philips Healthcare, Best, The Netherlands) (isotropic voxel spacing of 0.45 mm) and included the whole radius.

Accuracy of position measurements

To test the accuracy and reproducibility of assessing positioning parameters, all five artificial affected radii were scanned before correction. One radius was segmented and a distal segment (10%) and a proximal segment (65%) were subsequently clipped for registration of the double-contour polygon with the remaining four radii images. The relative position of each distal segment with respect to its proximal segment was determined and the difference with the first bone (reference) yields the positioning error. This error value depends on manual initialization of the registration procedure, on the noise content of the images [9] and on possible shape differences due to 3-D printing.

3.2 Positioning accuracy of a correction and fixation device

To test the accuracy and reproducibility of positioning using a correction and fixation device, the affected bone specimens are corrected using the described methodology. The correction and fixation device is mounted to the bone segments using non-locking plastic screws instead of metal screws, to prevent image scattering in the evaluation scan. A reference bone is scanned together with these corrected bone specimens and serves to test the accuracy and reproducibility of positioning.

The end position is compared to the preoperatively planned position, in the same way as described in section 3.1 , although the correction and fixation device region was excluded for optimal registration (Fig. 10).

The reference bone (Fig. 1 1 c) is created by virtually repositioning the distal segment of the affected bone using the correction matrix Mc and by filling the gap between the bone segments using linear interpolation. Employing this reference bone to evaluate the accuracy of our method has the advantage of excluding positioning errors due to bilateral differences [33]. The reference bone is created using the same 3-D printer.

3.3 Data analysis

Positioning parameters are represented by displacements (x,y,z) along, and rotations (φχ, cpy, φζ; rotation sequence: y,x,z; the centroid of a bone segment serves as center of rotation) about three orthogonal axes of an anatomical coordinate system equally defined for each segmented radius (Fig. 10). The longitudinal gravitation axis is the z-axis. The x-axis is defined by the line perpendicular to the z-axis and passing through the tip of the radial styloid. The y-axis is perpendicular to the x- and z-axes according to the right-hand rule [33].

When evaluating residual displacement (d_err(x), d_err(y), d_err(z)), and orientation errors ((Perr(x), <Perr(y), (Perr(z)) of the positioning parameters (Fig. 10) from a series of measurements, the average parameter value is used to represent the accuracy; the standard deviation (SD) represents the reproducibility. Positioning errors are also expressed in a parameter called the mean Target Registration Error (mTRE) [15]. In this parameter, corresponding polygon points are evaluated in the planned position (target) and in the achieved position. The average distance (mTRE) represents the goodness of alignment. The achieved position is found by registration of the distal and proximal segment, obtained during preoperative planning, with a CT scan of the corrected bone.

4. RESULTS 4.1 Accuracy of position measurements

Figures 12a-b show the accuracy and reproducibility of displacement and orientation parameters (d_err < 0.06 ± 0.23 mm and φ_βΓΓ < 0.27 ± 0.28°). The mTRE in this experiment was 0.21 ± 0.10 mm.

4.2 Positioning accuracy of a correction and fixation device

After predrilling and cutting the plastic bone using the surgical guide (Fig. 1 1 a), the correction and fixation device snugly fits on the bone segments (Fig. 1 1 b). Correction using the correction and fixation devices was followed by CT analysis and yielded residual

displacement and orientation errors are shown in Figures 12c-d. It can be seen that both the relative displacements and orientations are achieved with high accuracy and reproducibility (derr < 1 .2 ± 0.8 mm and φ_βΓΓ < 1 .8 ± 2.1 °). The mTRE was 1 .6 ± 0.6 mm in this experiment. 5. DISCUSSION

Positioning using a correction and fixation device has shown to be very accurate and reproducible (d_err < 1 .2 ± 0.8 mm and cp_err < 1 .8 ± 2.1 °). The accuracy of our method is superior to that of related experimental studies that are based on 3-D techniques, such as the method described by Westphal et al. [34] who used a robot-assisted technique for bone fracture reduction. They reported a similar translational accuracy but a rotational deviation, which is relatively large (d_err < 1 -57 mm and φ_βΓΓ < 4.50°). The accuracy of our method is comparable to that of Croitoru and coworkers [6] (d_err < 1 .0 ± 2.1 mm and φ_βΓΓ < 4.0 ± 6.5°) who used a navigation system for positioning bone segments. The reproducibility of our method, however, is much better. Oka and coworkers [21 ] recently validated their technique using cadaver specimens [22]. In this method a first guide is used to insert parallel pin pairs in the proximal and distal bone segment. After osteotomy a second guide is used to align the pins pairs, hence the bone segments. Their experimental evaluation method shows similar accuracy and reproducibility results (d_err < 1 .1 ± 0.6 mm and cperr < 1 .1 ± 0.6 °) as our method. Dobbe et al. [9] used a similar method using parallel pin pairs but with a clamping tool for positioning the pin pairs in 3-D space. This method achieved comparable accuracy and reproducibility results (derr < 1 .2 ± 0.4 mm and cperr < 2.1 ± 1 .6°). However, the latter two experimental evaluation methods did not include plate fixation, which may deteriorate postoperative positioning. Miyake et al., [20] proposed preoperative computer simulation for surgery using a standard volar locking plate. During actual surgery, they used a similar drilling and cutting guide as we propose. Their radiographic evaluation showed average absolute differences with the unaffected side of 5° for the volar tilt (range [-2, 16] °) and 3 ° for the radial inclination (range [-3, 5] °). A disadvantage of their approach is the fact that a standard plate does not fit on the bone geometry when the bone is deformed due to a malunion. In addition, locking screws may introduce a positioning error if the screws lock into the plate with different distances between each of the bone segments and the plate, compared to what was planned. Reconsidering bilateral differences [33] described above, we can conclude that the correction and fixation device shows to be more accurate in translational positioning than what is possible based on bilateral differences. The residual orientation deficit is slightly larger than average bilateral differences suggest. However, the spread in this biological parameter is quite large. For most individual cases, the correction and fixation device will therefore position better than what is possible based on bilateral differences of the distal radius. Besides using the correction and fixation device for corrective distal radius osteotomy, the new method is equally accurate as methods reported for, e.g., femural or high tibial shaft malunion treatment [12,18] and for mandibular reconstruction after bone tumor resection [30,36].

In our experimental evaluation, artificial bones, guides and correction and fixation devices were used based on a single bone morphology, which is a limitation of the study. Deformation of the 3-D printed objects may have occurred, e.g., due to plastic deformation of the correction and fixation device when removing it from the heated printer chamber. Small errors may also have been introduced in drill-hole positioning due to plastic deformation of either the bone or the cutting assisting device provided with one ore more holes, since no coolant was used for drilling. This can be avoided either by using a coolant or by drilling through metal sleeve inserts. In addition, elastic deformation of the bone or correction and fixation device, by compressive forces that are due to screw fixation, may also have contributed to the positioning error. Actual implants will be made of, e.g., titanium, with a much higher elastic modulus than the ABS correction and fixation devices used for our experiments, which will reduce deformation by compressive forces. Finally, the thickness of the cutting assisting device provided with one or more holes was 10 mm in our experiments. Increasing this thickness may have further enhanced orienting the drill. In fact, the total positioning variance is the result of the sum of variances of aforementioned causes. Better dealing with these limitations may further enhance positioning using a correction and fixation device.

Actual surgery may introduce additional challenges, e.g., difficulties in placing the cutting assisting device provided with one or more holes due to the presence of ligaments, muscles and fascias, or unexpected bending of a correction and fixation device due to large soft tissue tensile forces. Insertion of a bone graft or bone substitute can also be made more difficult if the correction and fixation device is attached to the bone surrounded by soft tissue. On the other hand, it has been acknowledged that avascular wedges may (partially) be resorbed by the body [2]. Recently the use of a wedge is even considered not obligatory [35]. Actual surgery may benefit from using locking screws instead of compression fixation as used in our experiments. However, when using locking screws the surgeon needs to avoid a distance between the snugly fitting correction and fixation device and the bone, to prevent positioning errors as discussed above. Regarding to virtual planning of the osteotomy plane our method could benefit from using haptic control over mouse control for plane positioning as was proposed by Paul and coworkers [25].

Besides using the correction and fixation device for corrective distal radius

osteotomy, the method may be used for other types of bone corrections, including but not limited to: corrective osteotomy of other long bones, mandibular reconstruction and clavicular reconstruction as well. In all of these cases the contralateral side can equally be used as reference for reconstruction of the affected side. Even if a healthy reference is missing, the surgeon can plan the position of one (distal) bone segment with respect to another (proximal) bone segment in a manual fashion, e.g., guided by surrounding anatomy. A correction and fixation device can thus generally be used to fixate bone segments in a planned position.

The two-step method of predrilling and cutting using a surgical guide, followed by the utilization of a correction and fixation device for fixation and accurate 3-D positioning at the same time, seems very easy to utilize during surgery since it does not require complex navigation or robotic equipment nor tracking tools. Custom treatment with a patient tailored correction and fixation device may reduce the reoperation rate since repositioning is likely to be better than conventional malunion treatment using 2-D imaging techniques and a standard anatomical correction and fixation device. The patient-tailored plating technology is expected to have a great impact on future corrective osteotomy surgery.

6. REFERENCES OF EXAMPLE 2

1 . Athwal GS, Ellis RE, Small CF, Pichora DR (2003) Computer-assisted distal radius osteotomy. J Hand Surg, 28A(6):951 -958

2. Bilic R, Kovjanic J, Kolundzic R (2005) Quantification of changes in graft dimension after corrective osteotomy of the distal end of the radius. Acta Chirurgiae Orthopaedicae et Traumatologiae Cechosl, 72:375-380

3. Carelsen B, Jonges R, Strackee SD, Maas M, Van Kemenade P, Grimbergen CA, Her M, Streekstra GJ (2009) Detection of in vivo dynamic 3-Dmotion patterns in the wrist joint. IEEE Trans Biomed Eng, 56(4):1236-1244

4. Cartiaux O, Paul L, Docquier PL, Francq BG, Raucent B, Dombre E, Banse X (2009) Accuracy in planar cutting of bones: an ISO-based evaluation. Int J Med Robotics

Comput Assist Surg, 5:77-84

5. Ciocca L, De Crescenzio F, Fantini M, Scotti R (2009) CAD/CAM and rapid prototyped scaffold construction for bone regenerative medicine and surgical transfer of virtual planning: A pilot study. Comp Med Imag Graph, 33:58-62

6. Croitoru H, Ellis RE, Prihar R, Small CF, Pichora DR (2001 ) Fixation-based surgery: A new technique for distal radius osteotomy. Comp Aid Surg, 6:160-169

7. Cronier F, Pietu G, Dujardin C, Bigorre N, Ducellier F, Gerard R (2010) The concept of locking plates. Orthopaedics & Traumatology: Surgery & Research, 956:S17-S36

8. Cooney WP, Cobyns H, Linscheid RL (1980) Complications of Colles' fractures. J Bone Joint Surg, 62:613-619

9. Dobbe JGG, Strackee SD, Schreurs AW, Jonges R, Carelsen B, Vroemen JC, Grimbergen CA, Streekstra GJ (201 1 ) Computer-assisted planning and navigation for orrective distal radius osteotomy, based on pre- and intraoperative imaging. IEEE Trans Biomed Eng, 58(1 ):182-190

10. Dobbe JGG, Du Pre KJ, Kloen P, Blankevoort L, Streekstra GJ (201 1 ) Computer- assisted and patient-specific 3-D planning and evaluation of a single-cut rotational osteotomy for complex long-bone deformities. Med Biol Eng Comput, 49:1363-1370 1 1 . Hafez MA, Chelule KL, Seedhom BB, Sherman KP (2006) Computer-assisted total knee arthrosplasty using patient-specific templating. Clin Orth Rel Res, 444:184-192

12. Hankemeier S, Mommsen P, Krettek C, Jagodzinski M, Brand J, Meyer C, Meller R (2010) Accuracy of high tibial osteotomy: comparison between open- and closed-wedge technique. Knee Surg Sports Traumatol Arthrosc, 18:1328-1333 13. Hollevoet N, Van MG, Van SP, Verdonk R (2000) Comparison of palmar tilt, radial inclination and ulnar variance in left and right wrists. J Hand Surg, 25:431 -433

14. Ibanes L, Schroeder W (2003) The Insight Segmentation and Registration Toolkit, Software Guide, Clifton Park, NY: Kitware Inc., ISBN 1-930934-15-7

15. Van de Kraats EB, Penney, Tomazevic D, Van Walsum T, Niessen WJ (2005) Standardized evaluation methodology for 2D-3D registration. IEEE Trans Med Imag, 24(9) :1 177-1 189

16. Lozano-Calderon SA, Brouwer KM, Doornberg JN, Goslings JC, Kloen P, Jupiter JB (2010) Long-term outcomes of corrective osteotomy for the treatment of distal radius malunion. J Hand Surg, 35B:370-380

17. Menon MRG, Walker JL, Court-Brown CM (2008) The epidemiology of fractures in adolescents with reference to social deprivation. J Bone Joint Surg (Br), 90-B: 1482- 1486

18. Milner SA, Davis TRC, Muir KR, Greenwood DC, Doherty M (2002) Long-term outcome after tibial shaft fracture: Is malunion important? J Bone Joint Surg (Am), 84-A:971 -980

19. Murase T, Kunihiro O, Moritomo H, Goto A, Yoshikawa H, Sugamoto K (2008) Three- dimensional corrective osteotomy of malunited fractures of the upper extremity with use of a computer simulation system. J Bone Joint Surg Am, 90(1 1 ):2375-2389

20. Miyake J, Murase T, Moritomo H, Sugamoto K, Yoshikawa H (201 1 ) Distal radius osteotomy with ovlar locking plates based on computer simulation. Clin Orthop Relat

Res, 469:1766-1773

21 . Oka K, Murase T, Moritomo H, Goto A, Sugamoto K, Yoshikawa H (2010) Corrective osteotomy using customized hydroxyapatite implants prepared by preoperative computer simulation. Int J Med Robotics Comput Assist Surg, 6:186-193

22. Oka K, Murase T, Moritomo H, Goto A, Nakao R, Sugamoto K, Yoshikawa H (201 1 ) Accuracy of corrective osteotomy using a custom-designed devise based on a novel computer simulation system. J Orthop Sci, 16:85-92

23. Paley D (2005) Principles of Deformity Correction, 1 st edn, Springer-Verlag, Berlin, Heidelberg, New York, ISBN 3-540-41665-X

24. Patton MW (2004) Distal Radius Malunion. J Am Soc Surg Hand, 4(4):266-274

25. Paul L, Cartiaux O, Docquier PL, Banse X (2009) Ergonomic evaluation of 3D plane positioning using a mouse and a haptic device. Int J Med Robot Comp Ass Surg, 5:435- 443

26. Pearle AD, Kendoff D, Musahl V (2009) Perspectives on computer-assisted orthopaedic surgery: Movement toward quantitative orthopaedic surgery. J Bone Joint Surg, 92

Suppl 1 :7-12 Pichler W, Clement H, Hausleitner L, Tanzer K, Tesch NP, Grechenig W (2008) Various circular arc radii of the idstal volar radius and the implications on volar plate osteosynthesis. Orthopedics, 30(12):1 192

Prommersberger KJ, Froehner SC, Schmitt RR, Lanz UB (2004) Rotational deformity in malunited fractures of the distal radius. J Hand Surg, 29A:1 10-1 15

Rieger M, Gabl M, Gruber H, Jaschke WR, Mallouhi A (2005) CT virtual reality in the preoperative workup of malunited distal radius fractures: preliminary results. Eur Radiol, 15:792-797

Roser SM, Ramachandra S, Blair H, Grist W, Carlson GW, Christensen AM, Weimer KA, Steed MB (2010) The accuracy of virtual surgical planning in free fibula mandibular reconstruction: Comparison of planned and final results. J Oral Maxillofac Surg, 68:2824-2832

Simpson AL, Ma B, Slagel B, Borschneck DP, Ellis RE (2008) Computer-assisted distraction osteogenesis by llizarov's method. Int J Med Robotics Comput Assist Surg, 4:310-320

States RA, Pappas E (2006) Precision and repeatability of the Optotrak 3020 motion measurement system. J Med Eng Tech, 30(1 ):1 1 -16

Vroemen JC, Dobbe JGG, Jonges R, Strackee SD, Streekstra GJ (2012) Three- dimensional assessment of bilateral symmetry of the radius and ulna for planning corrective surgeries. J Hand Surg (Am), 37A:982-988

Westphal R, Winkelbach S, Wahl F, Gosling T, Oszwald M, Hufner T, Krettek C (2009) Robot-assisted long bone fracture reduction. Int Journal Robotics Res, 28(10):1259- 1278

Wieland AWJ, Dekkers GHG, Brink PRG (2005) Open wedge osteotomy for malunited extraarticular distal radius fractures with plate osteosynthesis without bone grafting. Eur

J Trauma, 31 :148-153

Zheng G, Su Y, Liao G, Jiao P, Liang L, Zhang S, Liu H (2012) Manible reconstruction assisted by preoperative simulation and transferring templates: Cadaveric study of accuracy. J Oral Maxillofac Surg, 70:1480-1485 EXAMPLE 3

Introduction Fixed-angled volar distal radius plates provide a stable fixation after radial fractures or corrective osteotomies of malunited fractures. (1 -4) The latest variation of this type of plate is the anatomical plate, which is pre-shaped to optimally fit the contour of the distal radius. The anatomical plate is designed to bring the distal radius to its original anatomical position.

In the last decade, several anatomical plates have been introduced to improve the results of open reduction and internal fixation (ORIF) of the distal radius. The manufacturers of anatomical plates claim that no intraoperative adjustment in terms of bending of the plate should be necessary, as the shape of the plate is already adapted to the contour of the bone. The shape of the plate can be used as an intraoperative guide to determine the correct position of the dislocated distal radius segment.

However, due to morphological variability, the contour of the plate may not always optimally fit the profile of the distal volar radius. In previous anatomical studies a statistically significant difference was observed in the morphology of the distal radius in 55% of the study population. This implicates that for these cases the application of the plate may lead to suboptimal plate positioning and a false position of the distal radius segment after plate fixation.

In addition, shape differences exist between anatomical plates among manufacturers. There is a considerable variation in ideal plate location among anatomical plates of different manufacturers. It is sometimes unclear where to place the anatomical plate. Erroneous plate positioning by the surgeon can cause complications such as tendon ruptures or loss of reduction.

Since accurate positioning is clinically important, we investigated the accuracy and reproducibility of distal radius positioning using two anatomical plate brands, placed by two physicians. This is done with the help of 3D imaging techniques, which have made a tremendous development in recent years. We have compared the residual errors observed in this study with naturally occurring bilateral differences in the radius found in healthy individuals (n=20).

Materials and Methods In this example we simulated distal radius fractures and correction of these fractures on plastic bone models of radii. To create artificial physical radii models with different morphology we used CT scans of five healthy individuals (3 women and 2 men; average age 23 years). CT images are acquired with a Brilliance 64 CT scanner (Philips, Cleveland, OH ; voxel size 0.45 x 0.45 x 0.45 mm, 120 kV, 1 50 mAs, pitch 0.6). The subjects had no history of wrist injury or other musculoskeletal disorders. The medical ethical committee of our hospital approved this study and we obtained informed consent from each subject. From the CT scans we segmented the right radius of each subject and we printed acrylonitrile butadiene styrene (ABS) 3D models of these five different radii using additive manufacturing (SST1 200es 3D printer, Dimension Inc., Eden Prairie, MN). The resolution of this printer is 254 μηι. We printed these five different radii (models 1 - 5) to investigate the effect of radius morphology on positioning (Fig. 14A). To separately investigate the reproducibility of placement by a single physician we made four additional copies of the first radius (models 14B - 14E).

We made high-resolution CT scans of these physical models that served as a reference in finding residual positioning errors after plate fixation. We simulated a defect by removing an arbitrary wedge shape from each of the nine artificial radii (Fig. 14B). Two different physicians performed a correction of these affected radii by placing the anatomical plates according to the instructions of the plate manufacturer. The distal part of the plate was placed at the best possible position against the watershed line. The proximal part of the plate was placed in line with the shaft of the radius. This plate was fixated with cyanoacrylate glue (Fig. 14C and 14D). The physicians performed this procedure with a Synthes Plate (2.4 mm LCP distal radius plate, 04.1 10.440, Solothurn, Switzerland) and an Acumed Plate (Acu-Loc standard distal radius VDR plate, PL-DR50R, Hillsboro, OR, USA). All radii were corrected in random order.

After plate fixation, CT scans were made of the corrected physical models with the plate in situ. This allowed calculating the residual positioning errors of the distal segment in relation to the unaffected artificial radii scanned earlier. The method of finding these residual positioning errors is previously described by Dobbe et al. (23) Using this method, the CT image containing the unaffected radius model was segmented to create a virtual 3D model of the radius. Subsequently, a distal part of this virtual bone model and a larger proximal part are selected and aligned with the CT image of the corresponding corrected radius by intensity-based image registration. Having the proximal segments aligned, the residual positioning error is then shown as the degree in which the poses of the distal segment differ. This allowed us to calculate the residual displacements (Δχ, Ay, Δζ) and rotations (Δφχ, Acpy, Δφζ, rotation sequence y, x, z) for aligning the corrected radius with each corresponding reference radius. To allow comparison of positioning results between radii of different morphology, an anatomical coordinate system is aligned with the virtual radius of each individual reference radius in the same way (Fig. 1 5). (23) Positioning parameters are expressed in terms of these anatomical coordinate systems. All image analysis steps described were performed with custom software.

We compared the residual errors observed in this study with naturally occurring bilateral differences in the radius found in healthy individuals (n=20). (22)

Statistical Methods

Due to small sample sizes, and possibly skewed distributions and outliers, statistical analysis was performed non-parametrically. Differences in positioning due to morphological variation between radii were assessed by using a Friedman test. To assess whether there were differences in positioning between physicians and between the Acumed and Synthes plate we used the paired Wilcoxon signed rank test. For all these tests we used the dataset of the models 1 - 5. The dataset of the models 1 , 1 B - 1 E was only to demonstrate the possible impact of the morphology of the radius. A p-value <0.05 was considered statistically significant.

Fig. 14 A Five artificial 3D radii with different morphology. B A defect is simulated by removing a wedge shape from the distal part of each radius. C and D In this example the affected radius is corrected with an Acumed plate and fixated with cyanoacrylate glue. Fig. 15 Anatomical coordinate system as defined for each individual reference radius.

Results

During the experiments, we experienced a good fit of the anatomical plates on the surfaces of the radii.

Figure 1 6 shows the results of positioning on the same bone morphology for 5 times (models 1 and 1 B - 1 E). Figure 1 7 shows the accuracy and reproducibility of positioning the distal radius segment in 5 different individuals (models 1 - 5) for an Acumed and a Synthes plate, by two physicians. Residual displacements along the axes of the anatomical coordinate system (Δχ, Ay, Δζ) are in the order of 0-2 millimeters while rotations around the axes (Δφχ, Acpy, Δφζ) can be up to 14 degrees in individual cases (Δφζ1 in Fig. 1 7).

According the effect of variety in morphology, we only observed a significant difference for positioning parameter Ay (p < 0.05) between the different physical models 1 - 5. Positioning using an Acumed plate was statistically significant different for parameter Acpy (p <0.05) compared to positioning using a Synthes plate. There were no statistically significant differences in positioning parameters between the two physicians. Table 1 shows the results of comparing residual positioning errors with naturally occurring bilateral differences in healthy individuals. These bilateral differences between the right and left radius are (Δχ, Ay, Δζ): -0.81 ± 1 .22 mm, -0.01 ± 0.64 mm and 2.63 ± 2.03 mm; and (Δφχ, Δφγ, Δφζ): 0.13 ± 1 .00 degrees, -0.60 ± 1 .35 degrees and 0.53 ± 5.00 degrees. (22) Table 1 displays the average ± two standard deviations as acceptable range. This enables judging which cases fall outside this range. In a considerable number of cases positioning is less accurate compared to what can be achieved when the contralateral bone is used as reference.

Table 1 . The ranges of bilateral asymmetry in the controlgroup (n=20) represent generally accepted ranges for the experiments in this study. For the Acumed and Synthes plates the results for the two observers together were used for the physical models 1 - 5 (n=10).

Fig. 16 shows the residual positioning errors for physician 1 and 2 for one single radius morphology, both for the Acumed plate and the Synthes plate. The whiskers indicate the entire range of values, including outliers. The box indicates the range between the 25th to the 75th percentile. The median is indicated by a horizontal line. Fig. 1 7 shows the residual positioning errors for physician 1 and 2 for multiple morphologies, both for the Acumed plate and the Synthes plate. The whiskers indicate the entire range of values, including outliers. The box indicates the range between the 25th to the 75th percentile. The median is indicated by a horizontal line.

Discussion

In this study we investigated the accuracy and reproducibility of distal radius positioning using an anatomical plate. We hypothesized that positioning may be influenced by 1 ) the different morphology between radii, 2) different contours of anatomical plates and 3) subjective placement of the plate by the physician.

1 ) An anatomically shaped plate should facilitate adequate bone positioning for every patient. When differences between bone morphologies exist, positioning errors may occur for individual patients. This study showed a large variation in positioning. This is mainly due to subjective placement by the physician. In this experimental evaluation we could not confirm malpositioning due to morphological differences. We found a small but statistically significant difference for parameter Ay (p < 0.05) between different radii, but not for the other positioning parameters. Due to the low power in this study, this might well be a type I error.

2) When comparing positioning parameters between Acumed and Synthes plates we clearly observe a difference (p < 0.05) for Acpy (see physician 1 , Fig. 3 and 4). This can be explained by the clearly visible shape differences between the Acumed and Synthes plates (Fig. 5). As seen in Fig. 5 angle a is likely to influence parameter Acpy, and angle β probably will have an influence on parameter Δφζ. It is unknown to us how the manufacturers defined the present shapes of the anatomical plates. We recommend conducting more anatomical research on morphology variations of the distal radius for improvement of fixation plates.

3) The large variability in positioning by both physicians is indicative for subjectivity in plate placement. Due to the low sample size, we were not able to establish a statistically significant difference in placement between different physicians. This is due to the high intra- observer spread.

In a considerable number of cases the result of our positioning experiments falls out of the range of acceptable parameters compared to the generally accepted standard based on bilateral differences in healthy subjects. If you look at all 6 positioning parameters at the same time for each experiment, 100% of the experiments has 1 or 2 positioning parameters that fall out of the range in healthy subjects.

In addition to the low power, another limitation of this study is that during the experiments, the physician had a clear view of the whole radius. During actual surgery, a physician will not have such a clear view and positioning errors may be even larger in a clinical setting than reported in this study. In the operating room, the physician can use the ulna as guide for positioning the distal radius along the bone axis. In performing the correction with the anatomical plate on the physical radius models, the physicians did not have this reference. Therefore, parameter Δζ has limited clinical relevance in this study. Furthermore, we did not include abnormal morphologies (e.g. a malunion of the radius) in this study. Deformities of the bone surface may not allow the anatomical plate to fit on the bone morphology. We anticipate that using an anatomical plate for corrective osteotomies of the malunited distal radius will introduce higher positioning errors.

This study was a pilot, a first onset to get an indication of the accuracy of anatomical plates. Future studies should be performed with more statistical power. Nevertheless, we can conclude that positioning with an anatomical plate may lead to considerable residual errors for individual cases that fall out of the generally accepted ranges in healthy subjects. Volar distal radius plate shapes are different among plate manufacturers. One plate may therefore perform better than the other for an individual patient.

Fig. 18 The Acumed plate on top of the Synthes plate shows an obvious difference in plate contours. Fig. 18A shows angle a, which is likely to influence parameter Acpy and Fig. 18B angle β which probably will have an influence on parameter Δφζ.

Reference List of Example 3

(1 ) Kilic A, Kabukcuoglu YS, Gul M, Sokucu S, Ozdogan U. Fixed-angle volar plates in corrective osteotomies of malunions of dorsally angulated distal radius fractures. Acta Orthop Traumatol Turc 201 1 ;45(5):297-303.

(2) Jakubietz MG, Gruenert JG, Jakubietz RG. Palmar and dorsal fixed-angle plates in AO C-type fractures of the distal radius: is there an advantage of palmar plates in the long term? J Orthop Surg Res 2012;7(1 ):8.

(3) Harness NG, Meals RA. The history of fracture fixation of the hand and wrist. Clin Orthop Relat Res 2006;445:19-29.

(4) Jupiter JB. Fractures of the distal end of the radius. J Bone Joint Surg Am 1991 ;73(3):461 -469.

(5) Brogren E, Hofer M, Petranek M, Wagner P, Dahlin LB, Atroshi I. Relationship between distal radius fracture malunion and arm-related disability: a prospective population-based cohort study with 1 -year follow-up. BMC Musculoskelet Disord 201 1 ;12:9.

(6) Pogue DJ, Viegas SF, Patterson RM, Peterson PD, Jenkins DK, Sweo TD, Hokanson JA. Effects of distal radius fracture malunion on wrist joint mechanics. J Hand Surg Am 1990;15(5):721 -727.

(7) McQueen M, Caspers J. Colles fracture: does the anatomical result affect the final function? J Bone Joint Surg Br 1988;70(4):649-651 .

(8) Mudgal CS, Jupiter JB. Plate and screw design in fractures of the hand and wrist. Clin Orthop Relat Res 2006;445:68-80.

(9) Downing ND, Karantana A. A revolution in the management of fractures of the distal radius? J Bone Joint Surg Br 2008;90(10):1271 -1275.

(10) Pichler W, Clement H, Hausleitner L, Tanzer K, Tesch NP, Grechenig W. Various circular arc radii of the distal volar radius and the implications on volar plate osteosynthesis. Orthopedics 2008;31 (12).

(1 1 ) Auerbach BM, Ruff CB. Limb bone bilateral asymmetry: variability and commonality among modern humans. J Hum Evol 2006;50(2):203-218. (12) Buzzell JE, Weikert DR, Watson JT, Lee DH. Precontoured fixed-angle volar distal radius plates: a comparison of anatomic fit. J Hand Surg Am 2008;33(7):1 144-1 152.

(13) Drobetz H, Bryant AL, Pokorny T, Spitaler R, Leixnering M, Jupiter JB. Volar fixed- angle plating of distal radius extension fractures: influence of plate position on secondary loss of reduction-a biomechanic study in a cadaveric model. J Hand Surg Am 2006;31 (4):615-622.

(14) Orbay JL, Touhami A. Current concepts in volar fixed-angle fixation of unstable distal radius fractures. Clin Orthop Relat Res 2006;445:58-67.

(15) Athwal GS, Ellis RE, Small CF, Pichora DR. Computer-assisted distal radius osteotomy. J Hand Surg Am 2003;28(6):951 -958.

(16) Bilic R, Zdravkovic V, Boljevic Z. Osteotomy for deformity of the radius. Computer- assisted three-dimensional modelling. J Bone Joint Surg Br 1994;76(1 ):150-154.

(17) Jupiter JB, Ruder J, Roth DA. Computer-generated bone models in the planning of osteotomy of multidirectional distal radius malunions. J Hand Surg Am 1992;17(3):406-415.

(18) Murase T, Oka K, Moritomo H, Goto A, Yoshikawa H, Sugamoto K. Three- dimensional corrective osteotomy of malunited fractures of the upper extremity with use of a computer simulation system. J Bone Joint Surg Am 2008;90(1 1 ):2375-2389.

(19) Rieger M, GabI M, Gruber H, Jaschke WR, Mallouhi A. CT virtual reality in the preoperative workup of malunited distal radius fractures: preliminary results. Eur Radiol 2005;15(4):792-797.

(20) Schweizer A, Furnstahl P, Harders M, Szekely G, Nagy L. Complex Radius Shaft Malunion: Osteotomy with Computer-Assisted Planning. Hand (N Y ) 2009.

(21 ) Zimmermann R, GabI M, Arora R, Rieger M. [Computer-assisted planning and corrective osteotomy in distal radius malunion]. Handchir Mikrochir Plast Chir 2003;35(5):333-337.

(22) Vroemen JC, Dobbe JG, Jonges R, Strackee SD, Streekstra GJ. Three-dimensional assessment of bilateral symmetry of the radius and ulna for planning corrective surgeries. J Hand Surg Am 2012;37(5):982-988. (23) Dobbe J, Strackee S, Schreurs A, Jonges R, Carelsen B, Vroemen J, Grimbergen C, Streekstra G. Computer-assisted planning and navigation for corrective distal radius osteotomy, based on pre- and intraoperative imaging. IEEE Trans Biomed Eng 2010.

Claims

1 . A method to provide at least one patient specific device to be used in a bone correction method, the method comprising the steps of:

- obtaining a bone model representing a bone which is a subject of treatment;

- obtaining a target bone model to which treatment aims;

2. The method of claim 1 , wherein the correction and fixation device comprises fixation locations to fix the correction and fixation device on the first bone portion and the second bone portion.

3. The method of claim 2, wherein the fixation locations comprise one or more fixation holes configured to receive a fixation means.

4. The method of claim 2 or 3, wherein the fixation locations in the first positioning part are arranged in a first pattern, and the fixation locations in the second positioning part are arranged in a second pattern.

5. The method of any of the claims 1 -4, wherein the first fitting surface and the second fitting surface are adjacent to the cutting section.

6. The method of any of the claims 1 -5, wherein the method further comprises the step of designing in the data processing system a graft model to be arranged between the first and second bone portion.

7. The method of any of the claims 1 -6, wherein the method further comprises the step of designing in the data processing system a cutting assisting device comprising a surface tightly fitting to the first fitting surface and to the second fitting surface and a cutting assisting element.

8. The method of claim 7, wherein the step of providing the cutting assisting device comprises the step of providing one or more holes in the cutting assisting device configured to assist in preparing the first bone portion and/or the second bone portion for fixation of the correction and fixation device the first bone portion and/or the second bone portion.

9. The method of claim 8, wherein the holes are holes configured to receive a drilling or tapping element to drill and/or tap a pre-drill hole in the first bone portion and/or second bone portion.

10. The method of claim 7 or 8, wherein the holes are further configured to receive a fixation means to temporarily fix the cutting assisting device to the bone to be treated.

1 1 . The method of claims 4 and 8, wherein the holes on the cutting assisting device are provided in a pattern corresponding with the first pattern and with the second pattern.

12. The method of any of the claims 1 -1 1 , wherein the step of obtaining a bone model representing a bone which is a subject of treatment and/or obtaining a target bone model to which treatment aims, comprises obtaining three-dimensional data.

13. The method of any of the claim 1 -12, wherein the method further comprises the step of manufacturing the correction and fixation device, wherein the correction and fixation device is preferably manufactured by a 3D printing or grinding or other 3D manufacturing method.

14. The method of any of the claims 7-13, wherein the method further comprises the step of manufacturing the cutting assisting device, wherein the cutting assisting device is preferably manufactured by a 3D printing or grinding or other 3D manufacturing method.

15. A treatment kit for bone correction at least comprising a patient specific correction and fixation device, wherein the correction and fixation device comprises a first positioning part having a first positioning surface, a second positioning part having a second positioning surface, and a connection part connecting the first and the second positioning part, wherein the first positioning surface is configured to tightly fit on a first fitting surface defined on the bone to be treated and the second positioning surface is configured to tightly fit on a second fitting surface defined on the bone to be treated, and wherein the connection part is shaped to arrange the first fitting surface and the second fitting surface in a relative target position when the correction and fixation device is fixed on the first fitting surface and the second fitting surface.

16. A method of operating a data-processing system comprising the steps of:

- obtaining a bone model representing a bone which is a subject of treatment;

- obtaining a target bone model to which treatment aims;

17. The method of claim 16, further adapted to perform the step of controlling a 3D manufacturing device, for example a 3D printer to form a correction and fixation device according to the correction and fixation device model.

18. The method of claim 16 or 17, wherein the method comprises the step of designing a cutting assisting device comprising a surface tightly fitting to the first fitting surface and to the second fitting surface and a cutting assisting element.

19. Computer program comprising software code adapted to perform the steps of the method of any of the claims 16-18.

20. A correction and fixation device obtained by the method of any of the claims 1 -14.

21 . A cutting assisting device obtained by the method of any of the claims 7-14.