GB2519981A

GB2519981A - Sliding external fixator

Info

Publication number: GB2519981A
Application number: GB1319419.6A
Authority: GB
Inventors: Ali Abdullah Mohammed
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-11-02
Filing date: 2013-11-02
Publication date: 2015-05-13
Anticipated expiration: 2033-11-02
Also published as: GB201319419D0; GB2519981B

Abstract

The invention relates to a sliding external fixator in which a joint is stabilised with external metalwork that possesses a sliding mechanism that can adjust the metalwork to match the joint range of movement while being applied on the extensor surface without the need to radiologically identify the centre of rotation of the application. The invention comprises a device having first 12 and second 22 frame members hinged 20 together at their proximal ends 14, 24 with at least one base 40, 50 mounted on each member in a slidable arrangement. A plurality of half pins 72, 74, 82, 84 are mounted to each base to fix to a bone, and a bias spring means 90, 100 is arranged to allow the members and bases to slide without disengagement. A later embodiment relates to a method of stabilising a joint using said device.

Description

Sliding External Fixator

Field of the Invention

The present invention relates to a new technique in orthopaedic external fixation, in which a joint is stabilised with external metal work that possesses a sliding mechanism that can adjust the metal work to match the joint range of movement, while being applied on the extensor surface, without the need to radiologically identify the centre of rotation on application.

Backcjround External fixation in trauma and orthopaedics is well established practice for a variety of indications and a wide range of devices are available for this purpose. Taking for example the elbow, as a model to demonstrate the idea, it is useful to consider the mechanical structure of the elbow joint and the mechanical requirement for a device to stabilise it. What is referred to as the elbow is mainly two joints: (i) between the end of the humerus and the proximal aspect of the ulna, which allows flexion and extension, and (ii) between the proximal aspects of the radius and the ulna (excluding the articulation between the humerus and the radius), which allows twisting movement: supination -outward rotation of the forearm on its long axis,and pronation (inward rotation of the forearm on its long axis). If an elbow is to have an external fixator applied after for example dislocation, interpositioning arthroplasty or internal fixation, and if the elbow then has to be mobilized to maintain movement and to prevent stiffness while healing process takes place, there are many prior art external fixators which can be used, such as circular fixators like the llizarov frame circular fixator and the Compass external fixator, or monolateral ( one sided applied on the lateral aspect) ones, for example the Orthofix (RTM) galaxy fixation system.

Monolateral fixators are one sided and hence provide only one plane of stability and so provide a less rigid fixation system which works better in non-weight bearing joints such as in the upper limbs rather than the lower limbs.

In applying prior art circular or monolateral fixators the surgeon needs to position the centre of rotation correctly. Take for example the Orthofix (RTM) galaxy fixation for the elbow: the proximal part of the fixator needs to be fixed to the lateral aspect, that is the outer side, of the distal humerus, and the distal part of the fixator has to be fixed in the lateral aspect of the proximal ulna; the hinge between the two parts has to be placed laterally. (i.e on the outer side), and must match the centre of rotation.

This application therefore needs X-ray to locate the centre of rotation in the correct position. If the centre of rotation of the fixator is not aligned with the centre of rotation of the elbow joint the assembly will not work, i.e. the elbow will be disrupted on trying to achieve extension or flexion movements.

Furthermore, fitting of prior art fixators involves risk. Inserting pins in the proximal aspect of the ulna from the side may risk the posterior interosseous nerve while inserting pins in the distal aspect of the humerus there are three major nerves around the distal aspect of the humerus: the radial, medial and ulnar nerves. The radial nerve rotates around the humerus from back to front, so at the upper aspect of the upper arm it is essentially posterior medial, then posterior at the mid aspect (i.e. just behind the middle aspect of the humerus, about 12 cm proximal to theelbow joint), then moves to the lateral side ( about 8 cm proximal to the elbow), and then reaches anteriorly, so inserting pins is safer on the posterior aspect provided that the middle part of the humerus is avoided. However, this is mechanically difficult as a fixed hinge applied on the posterior aspect of the elbow will hinder movements: if it is applied in extension it will prevent flexion and vice-versa.

In order to be able to allow joint movement while applying the fixator on the posterior (extensor side) aspect of the joint, a self-adjusting hinge is needed. A fixator having such a hinge might be applied posteriorly with no need for X-ray, no need to meticulously identify the centre of rotation which is a demanding and time consuming process and with possibly lower risk of nerve damage, so would not need to be applied by an orthopaedic surgeon who is specialised in external fixation and instead might be easily applied by any general orthopaedic surgeon.

It is an object of the present invention to provide an improved external fixation device that overcomes the above described shortcomings of prior devices.

Summary of the Invention

According to the present invention there is provided an orthopaedic device comprising: first and second frame members hinged together at their proximal ends; at least one base mounted on each frame member in a slidable arrangement; plural fixing means mounted on each member to fix to a bone, and bias means arranged to allow the members and bases to slide without disengagement.

In use the orthopaedic device comprises: first and second frame members hinged together behind the specific joint; at least one base mounted on each frame member in a slidable arrangement; plural fixing means mounted on each member to fix to a bone, and bias means arranged to allow the members and bases to slide without disengagement.

The device thereby provides a hinging point that moves linearly, relative to the fixing points of the device to the limb as the limb is bent.

Through the device's ability to slide the device can be applied on the extensor surface of a joint, without the need to radiologically identify the centre of rotation on lateral views, which is a demanding step and crucial with external fixation systems known in current clinical practice.

In this way the device is fixed on the extensor surface of a joint, without requirement for x ray guidance to correctly position the hinging point over the joint's centre of rotation, wherein the limb is free to bend. In preferred embodiments the limb is biased straight by a spring bias and bent under tension through the bias. Ideally the spring tension level is capable of adjustment and may comprise an extension spring and for example a screwthread extension mechanism.

Preferably therefore the bias means acts linearly along the member, and has a maximum extension length.

In preferred embodiments the bases comprise elongated bar members, wherein the fixing means extends therefrom and is consequently provided with a stable grounding relative to the limb. Having the sliding members corresponding to what they slide in or on, ensures minima! twisting and consequently preferred stability. Typically the bias acts between the bases, or bases and members.

In one embodiment there is provided an orthopaedic fixator device comprising: a first and a second frame members each having a proximal end, and a distal end, and an axis between the two ends, the frame members being hinged together at their ends closer to the joint, and each comprising guide means aligned parallel to the axis to slide over a base; each base comprising a plurality of fixing means adapted to fix a half pin to the base; two or more half pins adapted to be fixed to the base and to be inserted into bone, and extension spring means associated with each frame member connecting it to the base member adjacent to it on either side of the joint.

In some embodiments the frame members are tubular ( having a cross section which accommodates the cross section of the corresponding base, and such cross section could be for example rectangular or any other configuration other than circular as that wouldn't be able to prevent rotation between the elements themselves) having an inner surface, the sliding base is mounted within the inner tubular space and the guide means comprises a portion of the inner surface of the frame member.

In some embodiments the guide means comprise one or more guide rails and the sliding bases are adapted to mount onto and be guided by the one or more guide rails. In some embodiments the sliding bases and guide rails are adapted such that the sliding base is retained on a guide rail against movement perpendicular to the axis. For example, in one embodiment the sliding base may comprise a recess having an overhang and a guide rail may comprise a portion adapted to fit underneath the overhang, so acting to retain the sliding base within the rail, as for example is known in the art of machine slides.

In this way the first base may be fixed to the bones of the upper arm and the second base may be fixed to the bones of the lower arm each by means of the pins such that the device is positioned at the extensor surface of the arm and the plane defined by the frame members angled apart is substantially aligned with the plane of bending of the elbow. When the elbow is bent, the hinge of the device is bent, the sliding bars move within the frames means away from each other and apply tension to the springs so exposing more of the bases out of the frames. The hinge stabilises the bending movement of the elbow into a single plane, the sliding bases are able to move only in the same plane, axially along the frame members. The resulting single allowed plane of bending of the device supports the elbow. The springs tension the device such that the sliding bases are pulled back towards one another within the frames, so pulling the device straight, when the elbow is straightened again, so the frames cover more of the bases.

In some embodiments the frame members and the sliding bases are substantially rectangular in cross-section, the sliding bases fitting within the frame members, so there is no rotational movement.

In some embodiments a frame member has one or more apertures through them in order for half pins mounted on the sliding bases to project through an aperture, so pins don't impede movement.

In some embodiments the device comprises a collar mounted over the exterior of a frame member so as to strengthen it and to hold the frame member in shape.

In some embodiments the device is adapted to be applied to the upper and lower arm in order to support the elbow joint. In some embodiments the device is adapted to be applied to the lower leg in order to support the knee joint. In some embodiments the device is adapted to be applied to support the wrist and in further embodiments the bones of the foot or hand.

In some embodiments the device is adapted to be applied to the upper and lower limb of a non-human animal, for example (but not limited to) a dog, cat or horse. In some embodiments the device is adapted to support joints of an animal body, such as the knee.

According to a further aspect the invention provides a method of stabilising a joint in a mammalian body using an apparatus as described herein comprising the steps of: fixing two or more half pins into the bone on each side of the joint: fixing the half pins to the corresponding sliding rod using the fixing means on each side of the joint.

In this way the device is mounted on the limb by at least a pair of half pins spaced a distance apart proximal to the joint and by at least a further pair of half pins spaced a distance apart distal to the joint. All the pins are in one longitudinal plane corresponding to the palpable subcutaneous border of the ulna. By anchoring each frame member over its corresponding bases the device establishes a single plane of bending and so stabilises the joint.

In a further embodiment the method comprises the further step of using the device as a template to determine the positions at which the half pins should be mounted on the bone.

Brief Description of Figures

Figure 1 shows an embodiment of the invention in a fully extended position; Figure 2 shows a sketch of a second embodiment of the invention; Figure 3 shows the embodiment of figure 1 in a first bent position; Figure 4 shows the embodiment of figure 1 in a second bent position; Figure 5 shows an exploded view of the embodiment of figure 1; Figure 6 shows the embodiment of figure 1 in position on a patient's arm in a fully extended position; Figure 7 shows the embodiment of figure 1 in position on a patient's arm bent at 70 degrees; and Figure 8 shows the embodiment of figure 1 in position on a patient's arm bent at the maximum angle of 120 degrees.

Detailed Description of Figures

Referring to figures ito 8, an embodiment 10 of the invention comprises a first frame member 12 and a second frame member 22 each having a proximal end 14, 24, and a distal end 16, 26, and an axis between the two ends, the frame members being hinged together at their proximal ends at the joint level, by means of a hinge 30 formed from a first hinge portion 18 on the first frame member and a second hinge portion 28 on the second frame member, the hinge portions being adapted to interfit to form the hinge. In this embodiment each hinge portion comprises a plurality of interfitting leaf portions 32 which act when assembled together to form a hinge that opens stably in a single plane and is resistant to torsional forces on the two frame members. The hinge is held together by a hinge pin 34 fitted into a central aperture 36.

Each frame member comprises guide means aligned parallel to the axis to receive a sliding base 40, 50. In this embodiment the frame members are tubular having an inner surface 42, 52 and a sliding base, for example 40 is mounted within the inner tubular space 42 and the guide means comprises the inner surface 42 of the frame members. Each frame member has a slot 44, 54 in the side of the frame member parallel to the axis of the hinge, extending along the axis of the frame member and through which a half pin mounted on the sliding base projects in use. In this embodiment each frame member has matching slots on both sides parallel to the axis of the hinge as shown in figures 1 to 5, and a collar 46. 56 mounted over the exterior of a frame member so as to strengthen it and to hold the frame member in shape.

Each sliding base 40, 50 has a proximal end 48, 58 nearest the proximal end of the frame member and a distal end 49, 59, each sliding base comprising a plurality of fixing means 60 adapted to fix a half pin 72, 74 82, 84 to the base. The embodiment further comprises two first half pins, 72 and 74, and two second half pins 82 and 84, mounted on the sliding bases. Each half pin is adapted to be fixed to the sliding base and to be inserted into bone by means of a threaded portion 76. The fixing means comprise an aperture 62 formed in the sliding base, a centring sleeve 64 sized to fit into the aperture 62 and having a central bore 66 adapted to receive the shank 68 of the half pin 74, and a grub screw 69 that fits into a threaded screw hoPe 63 orthogonal to the aperture 62 in order to fix the centring sleeve and the half pin in place to the sliding base. Such components are known for example in the product range of Smith and Nephew (UK) and examples will be described later herein.

Extension springs 90, 100 are associated with each frame member and the proximal end 92, 102 of each spring is connected to the frame member adjacent to its proximal end 14, 24, and the distal end of each spring 94, 104 is connected to the proximal end 46, 58 of each sliding base.

The frame members have a plurality of apertures 110 through their sides to allow access to the grub screws to allow positioning and fixing in place of the half pins.

Operation of the device is illustrated in figures Ito 4 showing progressive degrees of bending of the device. In figure 1 the device is shown fully extended, with the sliding bases located close to the hinge. In figures 2 to 4 the device is progressively further bent. If the half pins are fixed on either side of a joint, the sliding bases are drawn progressively further from the hinge axis, moving along the inside of the tubular frame members and extending the springs. At larger degrees of bend as shown in figures 3 and 4 the sliding bases may extend beyond the ends of the tubular frame members. HaLf pins 82, 84 move along the slot 54 and the corresponding slot on the opposite side of the frame member -not visible in figures ito 4-allowing the sliding base to move. Collar 56 is provided to stabilise and strengthen the frame member and in use presents a stop position for the half pin 62 as shown in figure 4.

The embodiment shown is able to achieve a flexure of 120 degrees, without becoming unstable, so allowing the patient to use the arm for normal, low-impact activities such as eating.

In some embodiments the dimensions and spring specifications are as set out below.

In some embodiments the springs should require a force to full extension of greater than 10kg force, and in some embodiments greater than 15kg force. In will be understood that different versions of the embodiment may be provided for different sizes and ages of patient, and the different versions may have spring extension forces chosen accordingly.

In some embodiments the total sliding distance is in the range 20 to 30 cm, preferably between 25 and 30 cm. In a typical embodiment the length of the guide means, that is the length of the tubular interior of the frame members as shown in figures 1 to 5, is in the range 20 to 35cm, more preferably in the range 25 to 30cm.

The length of the sliding base is preferably in the range 20-30cm, more preferably in the range 20 to 25cm.

It will be understood that larger device dimensions may be provided to accommodate patients who are large or obese. The spring parameters given above are suitable for some embodiments having dimensions in the ranges above. It will be understood by the skilled person that for a larger version of the device a higher force to fully extend the spring is desirable, and for a smaller version, for example for a child or for smaller joints such as metacarpophalangal (or knuckle) joints a lower force may be desirable.

The device is preferably made from a MRI-compatible material as known in the art, for example titanium.

One process for attaching the device in the embodiment as shown is as follows: Half pin application is by means of standard procedure and fixation through the apertures in the sliding bases is as per Smith & Nephews (RTM) fixation method, as known to those skilled in the art. The fixation method is only briefly described to give a description of the design of the sliding mechanism within the device.

The main items needed from Smith & Nephew (RTM) include the following catalogue items and catalogue numbers: 10-3455 Rancho Cubes (which in some embodiments may be used as the sliding bases) 12-2702 Half Pin, 4mm x 30mm.

10-3044 Drill Bit, 2.7mm 10-3045 Drill Bit, 3.8mm 10-3404 Centring Sleeves, 4mm.

11 -2727 Set Screws for Hex-Fix The above components and their use will be known to the skilled practitioner in the art, being suitable for the humerus, however the ulna would accommodate smaller half pins.

Steps in an example method of use comprise: Use the device as a template, pufting it on the posterior aspect of the arm when it is fully extended. Identify suitable positions for the pins to be drilled into the bone.

Identify suitable corresponding holes 62 in the sliding bases for the pins to be connected through.

On each side of the joint, for each frame member and sliding base: Starting with the nearest to the elbow joint, drill a 2.7mm location hole into the bone, followed by a 3.8mm hole.

Push the centring sleeve 64 into the chosen hole 62, followed by the half pin which is screwed into the bone.

Push the grub screw 69 into the corresponding side hole 63 on the sliding base and tighten it with a hex key.

Slide the supportive collar 46 over the sliding base and the frame member.

Repeat with the outer half pin, taking the size of the bone in consideration and choosing the appropriately sized half pin.

Cut the ends of the half pins so that they protrude only slightly from the frame members.

Flex the elbow joint to ensure the device is working correctly.

It will be apparent to a practitioner skilled in the art that the above steps may be carried out in the order and manner appropriate to the patient and the indication.

The invention has been described by way of examples only and it will be appreciated that variation may be made to the above-mentioned embodiments without departing from the scope of invention.

With respect to the above description then, it is to be realised that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.

Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as set out in the accompanying claims.

Claims

Claims 1. An orthopaedic device comprising: first and second frame members hinged together at their proximal ends; at least one base mounted on each frame member in a slidable arrangement; plural fixing means mounted on each member to fix to a bone, and bias means arranged to allow the members and bases to slide without disengagement.
2. An orthopaedic device according to claim I having a first and a second frame members each having a proximal end, and a distal end, and an axis between the two ends, the frame members being hinged together at their proximal ends, and each comprising guide means aligned parallel to the axis to receive a sliding bar base; a sliding base mounted on each frame member movable guided by the guide means, and having a proximal end nearest the proximal end of the frame member and a distal end, each sliding base comprising a plurality of fixing means adapted to fix a half pin to the base; two or more half pins adapted to be fixed to the sliding bar and to be inserted into bone, and extension spring means associated with each frame member connected to the frame member adjacent to its proximal end and connected to the proximal end of the sliding base.
3. A device according to claim 2 wherein the frame members are tubular having an inner surface, the sliding base is mounted within the inner tubular space and the guide means comprises a portion of the inner surface of the frame member.
4. A device according to claim 2 wherein the guide means comprises one or more guide rails and the sliding bases are adapted to mount onto and be guided by the one or more guide rails.
5. A device according to claim 3 wherein the frame members and the sliding bases are substantially rectilinear in cross-section, the sliding bases fitting within the frame members.

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6. A device according to any claim above wherein a frame member has one or more apertures through them in order for half pins mounted on the sliding bases to project through an aperture.
7. A device according to any claim above adapted to be applied to the upper and lower arm in order to support the elbow joint.
8. A device according to any claim above adapted to be applied to the upper and lower leg in order to support the knee joint.
9. A device according to any claim above adapted to be applied to support the wrist or hand joints.
10. A device according to any claim above adapted to be applied to the upper and lower limb of a non-human animal.
11. A method of stabilising a joint in a mammalian body using an apparatus as described herein comprising the steps of: fixing two or more half pins into the bone on each side of the extensor surface of a joint; fixing each half pin to their corresponding base using the fixing mean; wherein bases are held within corresponding frames so as to slide within the frames under spring bias.
12. A method according to claim 11 comprising the further step of using the device as a template to determine the positions at which the half pins should be mounted on the bone.Amendments to the claims have been made as follows: Claims 1. An orthopaedic device comprising: first and second frame members hinged together at their proximal ends; at least one base mounted on each frame member in a slidable arrangement; plural fixing means mounted on each base to fix to a bone, and bias means arranged to allow the members and bases to slide without disengagement from one another.2. An orthopaedic device according to claim 1 wherein the bias means allows the members and/or bases to slide without disengagement from the bias means.3. An orthopaedic device according to claim 1 or claim 2 having a first and a second frame members each having a proximal end, and a distal end, and an axis between the two ends, the frame members being hinged together at their proximal ends, and each comprising guide means aligned parallel to the axis to receive a sliding bar base; a sliding base mounted on each frame member movable guided by the guide means, and having a proximal end nearest the C\III proximal end of the frame member and a distal end, each sliding base comprising a plurality of fixing means adapted to fix a half pin to the base; two LI) or more half pins adapted to be fixed to the sliding bar and to be inserted into bone, and extension spring means associated with each frame member connected to the frame member adjacent to its proximal end and connected to the proximal end of the sliding base.4. A device according to claim 3 wherein the frame members are tubular having an inner surface, the sliding base is mounted within the inner tubular space and the guide means comprises a portion of the inner surface of the frame member.5. A device according to claim 3 wherein the guide means comprises one or more guide rails and the sliding bases are adapted to mount onto and be guided by the one or more guide rails.6. A device according to claim 4 wherein the frame members and the sliding bases are substantially rectilinear in cross-section, the sliding bases fitting within the frame members.7. A device according to any claim above wherein a frame member has one or more apertures through them in order for half pins mounted on the sliding bases to project through an aperture.8. A device according to any claim above adapted to be applied to the upper and lower arm in order to support the elbow joint.9. A device according to any claim above adapted to be applied to the upper and lower leg in order to support the knee joint.10. A device according to any claim above adapted to be applied to support the wrist or hand joints.11. A device according to any claim above adapted to be applied to the upper C\J and lower limb of a non-human animal. rLI) 12. A method of stabilising a joint in a mammalian body using an apparatus as 0 described herein comprising the steps of: fixing two or more half pins into the bone on each side of the extensor surface of a joint; fixing each half pin to their corresponding base using the fixing mean; wherein bases are held within corresponding frames so as to slide within the frames under spring bias.
13. A method according to claim 12 comprising the further step of using the device as a template to determine the positions at which the half pins should be mounted on the bone.