CN112972076A

CN112972076A - Fitting method of knee joint prosthesis femoral component and femur and robot operation system

Info

Publication number: CN112972076A
Application number: CN202110169162.8A
Authority: CN
Inventors: M·杰森; 林必贵
Original assignee: Hangzhou Suwen Jiuzhou Medical Technology Co ltd
Current assignee: Hangzhou Suwen Jiuzhou Medical Technology Co ltd
Priority date: 2021-02-07
Filing date: 2021-02-07
Publication date: 2021-06-18
Anticipated expiration: 2041-02-07
Also published as: CN112972076B

Abstract

The invention provides a fitting method of a knee joint prosthesis femoral component and a femur, wherein the femoral component meets a preset constraint condition when being used as an implant and being jointed with the distal end of the femur in an aligned state. The method comprises the following steps: 1) generating a three-dimensional image model of the femur in a computer device, establishing a femur coordinate system based on the position information of the feature points on the femur, 2) obtaining an implant coordinate system, and setting an implant coordinate to be converted to the femur coordinate system as X; 3) based on the constraint conditions, solving a transformation matrix f (x) ═ Q + TX between the femoral coordinate system and the implant coordinate system to obtain a rotation vector T and a translation vector Q. The invention also provides a robotic surgery system comprising a manipulator end, a computer device for establishing a femoral coordinate system, a data acquisition device for acquiring an implant coordinate system of an implant to be implanted into a human body, and an implant implanted into the distal end of the femur based on the obtained rotation vector T and translation vector Q.

Description

Fitting method of knee joint prosthesis femoral component and femur and robot operation system

Technical Field

The invention relates to a method for fitting a prosthesis and a bone, in particular to a method for fitting a knee joint prosthesis femoral component and a femur for total knee joint replacement. The invention also relates to a robotic surgical system.

Background

Total Knee Arthroplasty (TKA) is a surgical procedure that may use an artificial knee prosthesis (hereinafter also referred to as an implant) to replace the surface of the knee. One of the bases for a successful TKA is to achieve mechanical alignment (also referred to as line-of-force alignment) of the implant.

Mechanical Alignment (MA) in TKA is intended to align the femoral and tibial prosthetic components (e.g., the medial base surface on which the implant component pegs are located) perpendicular to the mechanical axis of the respective bones, and to address joint space balancing to obtain normal lower limb force lines, i.e., to obtain the hip-knee-ankle angle (HKA) of the limb at 0 ° coronal (no varus deformity).

The mechanical axis of the lower limb is a line extending from the center of the femoral head to the center of the ankle joint and generally across the center of the knee joint. Wherein a line from the femoral head center to the femoral center of the knee joint is defined as the femoral mechanical axis, and a line from the proximal epiphyseal center of the tibia to the ankle joint center is referred to as the tibial mechanical axis.

For a normal lower limb, the two mechanical axes of the femur and tibia are at an angle of 0 ° in the coronal position (no varus deformity), and the mechanical axes of the femur, tibia and lower limb coincide when standing.

It is known to develop a method for fitting a prosthetic knee femoral component to the distal femur of a knee joint during pre-total knee resurfacing surgical planning. The method aims to obtain alignment of a knee joint prosthesis femur component and a femur CT image under the same physical coordinate system. To obtain the alignment, the following points are extracted from the CT image: the lateral posterior condylar point LP; medial posterior condylar point MP; knee joint femoral center K; the lateral epicondyle LE; medial epicondyle ME; a lateral distal condylar point LD; medial distal condyle point MD; the hip center H.

By definition, the line HK formed by the hip center H and the knee joint femoral center K defines the mechanical axis HK of the femur and is perpendicular to the transfemoral epicondylar axis TEA formed by the lateral epicondylar LE and the medial epicondylar ME connecting line LE ME, as shown in fig. 1.

As shown in fig. 2, a corresponding prosthetic knee femoral component is known to be formed from 5 medial surfaces A, B, C, D, E. By representing the model of the implant in a coordinate system, several vertices at the intersection between the medial side of the prosthesis and the edges of the faces and 3 points per face A, B, C, D, E may be obtained, where each 3 points define a plane.

For such knee joint prosthetic femoral components, the mechanical alignment of the implant with the femur must satisfy the following conditions.

The mechanical axis HK of the femur must be perpendicular to the C-plane of the implant;

TEA must be parallel to the line on the implant between points P1, P2 (the intersection between the boundary line of the B-plane and C-plane of the medial side of the prosthesis and the edge of the plane), i.e. line P1P 2;

after the posterior condylar osteotomy, the lateral posterior condylar point LP and the medial posterior condylar point MP must belong to the plane formed by the a-face of the implant;

the knee centre K must belong to a plane bisecting the implant medial blank area N and perpendicular to the line P1P 2;

after knee osteotomy, the MD and LD points of the femur must belong to the plane formed by the C-plane of the implant.

Disclosure of Invention

In order to satisfy these conditions, the present invention provides a fitting method for a knee joint prosthetic femoral component to a femur, which is capable of appropriately determining fitting vectors for mapping the implant coordinates to a coordinate system defining the femur, and thereby capable of using the obtained vector data for the operating steps of a robotic surgical system.

According to one aspect of the present invention, there is provided a method of fitting a femoral component of a knee joint prosthesis to a femur, the femoral component being formed as an implant with first to fifth surfaces (A, B, C, D, E) for engaging a distal end of the femur, the following constraints being satisfied when the femoral component is engaged in alignment with the distal end of the femur:

i) the mechanical axis (HK) of the femur is perpendicular to the third face (C) of the implant;

II) The Epicondyle Axis (TEA) of the femur is parallel to a first connection line (P1P2) on the implant, which is the connection line between the intersection line of the second face (B) with the third face (C) and the intersection point (P1, P2) between the respective face edges;

III) a lateral posterior condylar point (LP) and a medial posterior condylar point (MP) belong to a plane formed by said first face (A) after a posterior condylar osteotomy;

IV) the centre of the knee (K) belongs to a plane bisecting the intermediate void area (N) of the implant and perpendicular to the first line; and

v) the medial distal condyle point (MD) and the lateral distal condyle point (LD) of the femur belong to the plane formed by the third face (C) after knee osteotomy,

the method is characterized by comprising the following steps:

1) generating a three-dimensional image model of the femur in a computer device, establishing a femur coordinate system based on positional information of feature points on the femur,

wherein the feature points are selected from: lateral posterior condylar point (LP), medial posterior condylar point (MP), knee joint femoral center (K), Lateral Epicondyle (LE), Medial Epicondyle (ME), lateral distal condylar point (LD), medial distal condylar point (MD), hip center (H);

2) acquiring an implant coordinate system, and setting an implant coordinate to be converted to the femur coordinate system as X;

3) solving a transformation matrix F (x) Q + TX between the femur coordinate system and the implant coordinate system based on the constraint condition to obtain a rotation vector T and a translation vector Q,

where T is a 3 x 3 matrix allowing vector transformation from the implant coordinate system to the femoral coordinate system under the constraints described above; q is a 3 x 1 vector representing the necessary translation to match the point of the femur and the implant plane.

According to another aspect of the present invention, there is provided a robotic surgical system comprising a manipulator tip for assisting in osteotomy positioning and osteotomy operations, computer means for establishing a femoral coordinate system, data acquisition means for acquiring an implant coordinate system of an implant to be implanted into a human body, and by performing the fitting method described above, a rotation vector T and a translation vector Q are derived, the manipulator tip implanting the implant into a distal end of a femur based on the derived rotation vector T and translation vector Q.

The robot system according to the present invention has advantageous effects based on the same inventive concept as described below.

Drawings

FIG. 1 shows the mechanical axes and various markings of a femur;

fig. 2 shows a model of a femoral knee prosthetic femoral component.

Fig. 3 shows a schematic diagram of constraints in a fitted state.

Detailed Description

Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. The exemplary embodiments described below and illustrated in the figures are intended to teach the principles of the present invention and enable one skilled in the art to implement and use the invention in several different environments and for several different applications. The scope of the invention is, therefore, indicated by the appended claims, and the exemplary embodiments are not intended to, and should not be considered as, limiting the scope of the invention. Moreover, the terms "first" and "second," "step," and the like are intended to distinguish between different objects in a non-specific order.

In Total Knee Arthroplasty (TKA), the primary articular surface of the knee is replaced with a prosthetic component or implant, requiring the removal of worn or damaged cartilage and bone on the distal femur and proximal tibia, followed by replacement of the removed cartilage and bone with an artificial implant. The artificial implant is usually a metallic material with good biocompatibility, such as titanium alloy or cobalt chromium molybdenum alloy, to create a new joint surface.

The technical solution according to the present invention is described below by taking the distal femur as an example, but is not limited thereto, and may be applied to the proximal tibia or other joint parts, and is intended to provide a method for fitting a prosthesis to a bone by way of example.

< example >

The method according to this embodiment can be used to determine the correct fitting position between the femoral component of a knee prosthesis and the femur prior to total knee surface replacement surgery, and in particular can be applied to pre-operative planning by providing an accurate fitting method to ensure accurate final position and alignment of the prosthesis within the patient's knee joint, thereby improving long-term clinical outcomes and increasing the survival rate of the prosthesis.

< determination of femoral coordinate System >

In pre-operative planning, imaging data of the patient's femur is obtained using an imaging modality such as Computed Tomography (CT), ultrasound, or Magnetic Resonance Imaging (MRI). After the imaging data is transferred to a computer system in digital imaging, a 3D image model of the bone is generated. In particular embodiments, a patient's bone may be segmented manually, semi-manually, or automatically by a user to generate a 3D model of the bone.

For example, a three-dimensional (3D) model of the patient's skeletal anatomy may be generated by conventional interactive preoperative planning software based on a patient's Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) image dataset.

The CT image is often used as a reference for surgical planning, the CT image can be moved into a virtual space, and through the extraction of the same characteristic points, bones in the CT image can be superposed with structures of real bones in the virtual space, so that the whole structures of the bones in the CT image can be moved into the virtual space to replace the poses of the structures of the real bones in the virtual space. The main purposes of this process are: 1, displaying the integral structure of the bone in a virtual coordinate system; assisting the physician in surgical planning, allows the physician to place the implant into a 3D model of the bone anatomy to specify the optimal location and alignment of the implant on the bone. The surgical robot can be further assisted in performing accurate fitting between the femoral component of the knee joint prosthesis and the femur.

The resulting preoperative planning data may also be used to manufacture patient-specific instruments or be loaded and read by surgical equipment to assist the physician in intraoperatively performing the planning and even positioning the surgical robot to ensure the space of the robot into the desired surgical field.

In addition, the position of registration points (registration points) may also be collected with a registration probe to register the bare femoral structure to a computer-assisted surgery system.

The method and apparatus for establishing the femoral coordinate system are not the key points of the present invention, and are not described herein again, and can be implemented by the above-mentioned existing means.

Then, the following points are extracted from a 3D image model such as a CT image: the lateral posterior condylar point LP; medial posterior condylar point MP; knee joint femoral center K; the lateral epicondyle LE; medial epicondyle ME; a lateral distal condylar point LD; medial distal condyle point MD; the hip center H. Thereby, data information such as position coordinates of each point is obtained.

< implant model selection and constraint >

One of the primary goals of preoperative planning is to achieve precise alignment of the femoral component of the knee prosthesis with the femur, thereby providing guidance for subsequent surgery. Therefore, the present inventors have conducted extensive studies and have conducted reverse thinking to find the following method.

Here, a conventional knee joint prosthesis femoral component 1 (see fig. 2) in which 5 inner side surfaces A, B, C, D, E are integrally formed is used and fitted to a knee joint prosthesis tibial component 3 (see fig. 3) to be implanted in a knee joint of a patient as an implant.

When the knee joint prosthesis femoral component 1 (hereinafter referred to as an implant) is joined to the femur 2 by the medial pegs 11, 12 of the knee joint prosthesis femoral component 1 and mechanically aligned, the following constraints are necessarily satisfied.

The mechanical axis HK of the femur 2 must be perpendicular to the C-plane of the implant, i.e. the medial plane on which the medial pegs 11, 12 are located;

TEA must be parallel to the line on the implant between the points P1, P2 (the intersection between the boundary of the B and C faces and the face edge, which is the medial face of the prosthesis);

after the posterior condylar osteotomy, the lateral posterior condylar point LP and the medial posterior condylar point MP must belong to the plane formed by the a-plane of the implant;

< setting and obtaining of implant coordinate System >

As the surgeon or surgical instrument adjusts the position and orientation of the implant, a series of sequential rotations and translations can result in additional changes in the orientation of the coordinate system of the implant.

Therefore, in order to satisfy these constraints, the implant coordinates must be mapped to the femoral coordinate system and then the necessary translation performed in the femoral coordinate system.

Mathematically, this transformation can be defined as:

F(x)＝Q+TX

where T is a 3 x 3 matrix allowing vector transformation from the implant coordinate system to the femoral coordinate system under the constraints mentioned above; and Q is a 3 x 1 vector representing the necessary translation to match the points of the femur and the faces of the implant; x denotes the implant coordinates on which the transformation is to be performed.

The spatial position and rotation matrix at each sampling instant can be acquired by the registration tool using tracking measurements. The actual implant surface can be tapped by means of a three-dimensional measuring probe, and the three-dimensional position of the tapped point in the corresponding femoral coordinate system is measured and recorded.

At the moment, a high-precision optical motion tracking device or a surgical navigation system can be utilized to measure the space coordinates and the displacement of each trackable mark or target according to a certain sampling rate, and the three-dimensional space motion of the implant can be captured.

< solving coordinate transformation >

After research, the inventor finds that according to the above constraint conditions, the following conclusions can be drawn in the femur coordinate space:

if line P1P2 is parallel to TEA, the unit direction vector V of line P1P2₁Unit direction vector U equal to TEA₁。

If the mechanical axis of the femur is perpendicular to the plane C of the implant, the unit normal vector V to the plane C of the implant₂Unit direction vector U equal to line HK representing the mechanical axis of the femur₂。

Let V₃＝V₁×V₂And U₃＝U₁×U₂Then the transformation matrix T may be defined such that:

V_i·T＝U_iand therefore, the first and second electrodes are,

T＝U_i·V_i ^-1

wherein, V_iRefers to all V vectors, U_iAll U vectors are denoted by

i

1, 2, 3 … n, and n is a natural number.

Here, it is important to choose the V, U vector with the correct orientation so that the implant is oriented in the correct direction in which it must move to fit properly into the bone.

After the above-described transformation matrix is obtained in the above manner, an appropriate translation represented by the vector Q is further sought.

To determine the Q vector, it is only necessary to know that the LD and MD points of the resected femur belong to the C plane, the LP and MP points of the resected femur belong to the A plane, and the K point belongs to the plane bisecting the hollow-out N part of the middle of the implant. Under these sufficient conditions, a system of equations representing three unknowns for sufficient translation of the implant can be defined, such as Ax + By + Cz, where x, y, z are unknown variables.

By determining the transformation matrix T and the translation vector Q, each face or vertex of the implant can be mapped to the correct position in the femoral coordinate system.

< computer-aided navigation TKA System, Robotic surgery System >

Thus, in the surgical planning phase, predetermined parameters may be provided for coordinate calibration, transformation of a computer aided navigation system or robotic surgical system, including final implant to femur transformation according to the planned registration and execution of TKA.

Data collection of coordinates may include, but is not limited to, one or more binocular optical cameras, registration probes, targets, etc. marker holders.

When the femoral coordinate system is established, for example, the femoral coordinate system is established by using the collected measurement data of the medial epicondyle vertex, the lateral epicondyle vertex and the intercondylar notch center and the calculated coordinate information of the femoral head center.

The selected prosthesis model can be input into a computer software system in advance, the targets on the thighbone and the mechanical arm trolley base are identified through a binocular camera system, and the transformation relation from the robot coordinate system to the thighbone coordinate system is obtained: and describing the spatial position relationship between the robot coordinate system and the femur coordinate system by using the rotation matrix and the translation vector, and establishing the corresponding relationship between the robot coordinate system and the femur coordinate system by using the solved rotation matrix and translation vector to realize the accurate positioning of the femur component.

Therefore, the coordinates of each point in the robot coordinate system can be converted into the coordinates of the femur coordinate system, the coordinate conversion relation of the femur coordinate system and the robot coordinate system can be effectively and quickly solved, and accurate positioning of the femur component is realized.

< modification example >

Various anatomical references (e.g., mechanical axes) may also be determined, for example, by identifying anatomical landmarks on the femur and tibia, etc., when a user, such as a physician, plans a procedure manually or with the aid of an auxiliary device.

In the above embodiments, the goal of adjusting the position and orientation of the implant is the desired clinical varus-valgus in the coronal plane, and likewise, the desired clinical varus-valgus in the axial plane, and the desired flexion-extension in the sagittal plane.

According to the invention, CT scanning and the like can be firstly carried out on the knee joint (the distal femur or the proximal tibia), and a three-dimensional model of the knee joint is established; establishing a virtual imaging space in three-dimensional modeling software by using the obtained space position parameters; selecting each characteristic point specified by the conditions from the three-dimensional model of the knee joint to obtain corresponding position information; various planes for planning TKA, including coronal, sagittal, and axial planes, are also available. For example, the femoral coronal plane may be created through the femoral posterior condylar axis and the hip joint center.

This can provide a basis for aligning and positioning the implant component to the femoral model in a clinically established standard frame of reference.

The geometrical parameters of the femur can be selected and generated in computer aided drawing software (such as Solidworks).

The coordinate system may be established based on the hip joint center or the knee joint center of the lower limb. For example, the origin of the femoral coordinate system may be located at the knee joint center. The Y-axis direction of the femoral coordinate system is set from the knee joint center to the hip joint center. The Z-axis direction of the femoral coordinate system is set perpendicular to the femoral coronal plane and extends from the posterior to the anterior of the lower limb. The X-axis direction of the femoral coordinate system may also be set according to right-hand rules. In this way, a femoral coordinate system is established.

< advantages of the present invention >

According to the system of the invention, the transformation between implant and bone can be automatically output, which can be easily used by computer assisted surgery systems. Thereby achieving reliable implant alignment and post-operative clinical results.

Preferably, the converse derivation of the transformed coordinate relationship can be applied to automatic or semi-automatic operation of the surgical robot. Therefore, the robot surgical system can automatically plan the alignment target to achieve the expected result.

According to the system of the invention, the implant can be automatically aligned with the bone, and a doctor only needs to import the implant model into a computer system before operation to provide data of the position and the direction of the implant, so that the time for creating preoperative planning and intraoperative osteotomy positioning can be greatly reduced.

According to the system of the present invention, the implant can be automatically aligned to the bone with minimal user intervention. Allows placement of the implant relative to the bone in an orientation corresponding to a clinical alignment goal or clinical orientation, regardless of the pre-adjusted position and orientation of the implant.

According to the invention, the lower limb force line can be accurately recovered according to the anatomy and pathological changes of the lower limb of a patient, and the precise prosthesis implantation can be carried out. In the joint replacement operation, the artificial joint prosthesis can be correctly installed, and the contact and friction of the relative motion between the joint components are optimized.

The model of the prosthesis is selected according to the size of the femur, the preoperative scheme design can be carried out according to the shape of the prosthesis, the robot performs key operation in the operation, the operation precision is high, and postoperative recovery is smooth.

Furthermore, the implants described herein, as a whole or part that can be used to replace bone, correspond to implants or prostheses commonly referred to in orthopaedics, i.e. can be understood to include prostheses for knee replacement. The prosthesis may be used to internally secure fractured or damaged portions of a fracture.

In the above constraint, the case of halving the implant intermediate blank region N is defined, however, it should be understood that the "halving" in this document also includes two cases of dividing into two separately due to individual and family differences.

While the invention has been described with reference to various specific embodiments, it should be understood that changes can be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but that it will have the full scope defined by the language of the following claims. It is obvious to those skilled in the art that technical solutions that can be easily conceived based on the disclosure of the present invention should also be considered to be equivalent or equivalent and fall within the scope of the present invention.

Claims

1. A method of fitting a femoral component of a knee prosthesis to a femur, the femoral component having first to fifth surfaces (A, B, C, D, E) formed as an implant for engaging a distal end of the femur, the method satisfying the following constraints when the femoral component is engaged in alignment with the distal end of the femur:

the method is characterized by comprising the following steps:

2. Fitting method according to claim 1,

selecting a unit directional vector U equal to the Transfemoral Epicondyle Axis (TEA)₁Of the first connection line (P1P2) has a unit direction vector V₁Such that the first connection line (P1P2) is parallel to the Transfemoral Epicondyle Axis (TEA);

selecting a unit orientation vector U equal to a line (HK) representing the femoral mechanical axis₂To the third face (C) of the implant₂Such that the mechanical axis of the femur is perpendicular to the third face (C);

let V3 be V₁×V₂，U₃＝U₁×U₂，

Thus, the conversion matrix T ═ Ui · Vi is defined and obtained^-1，

Where Vi denotes all V vectors, Ui denotes all U vectors, i is 1, 2, 3 … n, and n is a natural number.

3. Fitting method according to claim 2,

the translation vector Q is determined by defining a system of equations representing three unknowns for sufficient translation of the implant.

4. Fitting method according to any of claims 1-3,

the feature points are extracted from a CT image or an MRI image of the femur.

5. A robot operation system comprises a mechanical arm tail end used for assisting the positioning and the bone cutting of the bone, a computer device used for establishing a femur coordinate system, a data acquisition device used for acquiring an implant coordinate system of an implant to be implanted into a human body,

characterized in that by performing the fitting method according to any one of claims 1-4, a rotation vector T, a translation vector Q are derived,

the manipulator tip implants the implant into the distal femur based on the derived rotation vector T, translation vector Q.

6. The robotic surgical system of claim 1,

the data acquisition device comprises a binocular optical camera, a registration probe and a target.