WO2017120645A1

WO2017120645A1 - A joint stabilisation method and apparatus

Info

Publication number: WO2017120645A1
Application number: PCT/AU2017/050027
Authority: WO
Inventors: Chris Arnold JEFFERY
Original assignee: Field Orthopaedics Pty Ltd
Priority date: 2016-01-15
Filing date: 2017-01-13
Publication date: 2017-07-20

Abstract

A wrist implant comprising: an implant body shaped to extend about at least part of carpal bones, and a fastening arrangement for fastening a joint prosthesis to the implant body for reducing undesirable loosening of the prosthesis from the carpal bones.

Description

A JOINT STABILISATION METHOD AND APPARATUS

CROSS-REFERENCE TO RELATED APPLICATIONS The present application claims priority to Australian Provisional Application No. 20169001 14 filed Jan. 15, 2016. The aforementioned application, including any drawings thereto, are hereby incorporated by reference in their entireties as if fully set forth herein. TECHNICAL FIELD

The present invention relates to methods and apparatus for the stabilization of a human or animal joint prior to implantation of a joint prosthesis. A preferred embodiment of the invention relates to a method and apparatus for the stabilization of a wrist joint and particularly the distal carpus.

BACKGROUND

The discussion of any prior art documents, techniques, methods or apparatus is not to be taken to constitute any admission or evidence that such prior art forms, or ever formed, part of the common general knowledge.

Arthritis presents a significant global burden documented to affect 1 in 7 Australians with prevalence increasing with the aging population. Common treatment modalities for severe arthritic disease in most joints of the body are via prosthetic replacement. In the hand however, despite being one of the most common collection of joints affected (up to 100 in 100,000) to date there has been minimal progress in the development of a physiologically equivalent implant.

Total wrist replacement/ arthroplasty involves the use of a surgical prosthesis that is designed to replace the diseased articulating surfaces of both the distal radius and the proximal carpal row in order to recreate the wrist joint and restore physiological function. To date the realization of a reliable implant has been less than ideal, due to limited survivability and failure from loosening of the distal implant. A wrist joint prosthesis basically comprises a first part (the proximal implant) which is usually attached to the radius and which has a socket or cup like portion, and a second part ( the distal implant) which is usually attached to the distal carpal and typically through to the metacarpals, the second part having a rounded portion for engagement with the socket.

In conventional wrist joint prosthesis designs the distal carpal row, whilst made up of four independent bones, has been assumed to be best simplified and considered as a rigid body with both experimental and retrospective studies confirming an increases in implant longevity with achievement of intercarpal fusion.

To date however mechanical fixation and stabilization of the distal carpal row has taken a very simplistic approach with fixation of the distal implant via a combination of one -to- three interosseous screws fixed into the distal carpal row or through to the metacarpals.

A problem with such a prosthesis is that, over time, the distal implant can become loose via loosening of the distal screw fixation. While not wishing to be bound by theory, it is proposed that this occurs through the persistence of micro motion in the vicinity of the bone-screw interface resulting in peri- implant wear and loosening.

It is an object of the present invention to address the problem of loosening of interosseous screws of a joint prosthesis and to provide a solution that improves the stability of the joint for implantation of a joint prosthesis. SUMMARY OF THE INVENTION

In a first aspect, the invention provides a wrist implant comprising:

an implant body shaped to extend about at least part of carpal bones, and

a fastening arrangement for fastening a joint prosthesis to the implant body for reducing undesirable loosening of the prosthesis from the carpal bones. In an embodiment, the implant body comprises a radial surface that extends radially relative to the bones.

Preferably, the implant further comprises a side wall extending transversely relative to the radial surface, the side wall extending circumferentially relative to the carpal bones, during use.

More preferably, the sidewall comprises a dorsal sidewall portion for directly supporting the carpal bones to assist in uniting the carpal bones as a solid body.

In an embodiment, the sidewall further comprises an anterior sidewall portion and/or opposed interconnecting sidewall portions.

Preferably, inner surfaces of the dorsal sidewall portion and the opposed interconnecting sidewall portions are arranged for directly supporting the carpal bones during use.

In an embodiment, the anterior side wall portion comprises a profiled portion for extending about a projecting carpal bone portion during use.

In an embodiment, inner surfaces of the one or more side wall portions are substantially concave, said concave side wall portions defining a cavity. In an embodiment, the side wall comprises an undulating edge portion defining an opening into the cavity.

Preferably, the undulating edge portion of the dorsal side wall portion is dissimilar to the undulating edge portion of the anterior side wall portion.

In an embodiment, the implant body defines an upwardly directed cup shaped cavity for extending about and supporting the carpal bones during use.

Preferably, the cup shaped cavity is defined by at least an in use upper portion of the side wall extending upwardly relative to the radial surface.

In an embodiment, the implant body further comprises a downwardly directed recessed cavity for receiving and fastening the joint prosthesis. Preferably, the recessed cavity is defined by at least an in use lower portion of the sidewall depending downwardly relative to the radial surface.

In an embodiment, the fastening arrangement allows at least a part of the joint prosthesis to be received into the recessed cavity and fastened to the implant body, during use.

In an embodiment, the fastening arrangement comprises one or more grooves located along an inner surface of the side walls, the grooves being adapted for engagement with the joint prosthesis, during use.

In an embodiment, the radial surface forms a wall comprising one or more openings to accommodate fixings of a distal implant.

In an embodiment, the implant body comprises an opening in the sidewall to accommodate a fixing to fix the implant to a bone.

In another aspect, the invention provides a wrist prosthesis comprising:

an implant body shaped to circumferentially extend about at least part of a distal row of carpal bones; a distal implant for attachment to the distal row of carpal bones; and

a fastening arrangement for fastening the implant body to the distal implant thereby reducing undesirable loosening of the prosthesis from the bones.

In one embodiment, the distal implant and the implant body are joined together. In an alternative embodiment, the distal implant and the implant body are separate components.

In an embodiment, the prosthesis further comprises a proximal implant. Preferably, the proximal implant comprises a stem portion for implantation into the radius bone.

In an embodiment, the prosthesis further comprises a coupling arrangement for coupling the proximal implant with the distal implant, and allowing motion of the wrist in at least one physiological direction during use.

In another aspect, the invention provides a method for reducing inter carpal micro movement between the distal row of carpal bones, the method comprising circumferentially retaining at least part of the carpal bones by positioning an implant.

In another aspect, the invention provides a method for the stabilization of a human or animal joint prior to implantation of a joint prosthesis, the method comprising providing an implant adapted to circumferentially extend at least part of the bones into which the prosthesis will be fixed thereby reducing undesirable loosening of the prosthesis from the bones. BRIEF DESCRIPTION OF THE DRAWINGS

The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows:

Figure 1 illustrates a dorsal view of the bones of a human wrist and fitted with a PRIOR ART prosthesis.

Figure 2 illustrates an in-use view of an implant 100 (in accordance with an embodiment of the present invention) surrounding and stabilizing the distal row of carpal bones. Figure 3 is a first perspective view of the implant 100.

Figure 4 is a second perspective view of the implant 100.

Figure 35is a third perspective view of the implant 100.

Figure 6 is a bottom view of the implant 100.

Figure 7 is a first side view (dorsal view) of the implant 100. Figure 8 is a top view of the implant 100.

Figure 9A is a second side view (anterior view) of the implant 100.

Figure 9B is a sectional view along section B-B (referring to Figure 9A). Figure 10A is an end view of the implant 100.

Figure 10B is a sectional view of the implant along A-A (referring to Figure 10A). Figure 1 1 A is an in-use end view of the implant 100.

Figure 1 1 B is a sectional view of the implant along A-A (referring to Figure 1 1A).

Figure 12A an in-use side view (dorsal view) of the implant 100.

Figure 12B is a sectional view of the implant 100 along C-C (referring to

Figure 12A). Figure 13 is an in-use top view of the implant 100. Figure 14 is a bottom view of the implant 100. Figures 15 to 17 illustrate in-use perspective views of the implant 100.

Figure 18 illustrates an in-use perspective view of the implant 100 in conjunction with a distal implant 13.

Figure 19 illustrates a top view of an implant 17 in accordance with a second embodiment of the invention.

Figure 20 is a top perspective view of an implant 17 in accordance with a second embodiment of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring to figure 1 , there is disclosed a hand 10 fitted with a wrist prosthesis 1 1 . The prosthesis typically comprises a proximal (or radial) component 12 and a distal component 13.

The proximal component 12 has a stem or peg (not illustrated) that attaches into the canal of the radius bone 14 and an upper cup 15 which forms the socket for the artificial wrist joint. The distal component 13 has a lower rounded part 16 shaped to fit into the cup 15. The distal component is fixed to the carpal and/or metacarpal bones using fixing screws and/or metal pegs that fit into the hollow bone marrow cavities (see, for instance figure 8).

This type of wrist prosthesis shown in Figure 1 is known and is described to provide a general background summary.

Figures 2-18 illustrate a first embodiment of the invention which comprises a wrist implant 100. The wrist implant 100 comprises a cup shaped implant body 1 17 that extends circumferentially about the distal row of the carpal bones 18 (best shown in Figure 2). As best illustrated in figures 3-10, the implant body 1 17 comprises an open topped cup shaped cavity 1 13 formed with a sidewall 1 19 that extends transversely relative to and a radial receiving surface 120 (shown in Figure 8). The radial surface 120 extends radially relative to the distal row of the carpal bones 18, during use. The radial surface 120 is provided with openings 121 , 122 and 123 that are adapted to allow fixings 24a-c (see exemplary figure 18) of the distal component 13 to pass through the openings 121 , 122 and 123 and into the carpal/metacarpal bones.

Referring to figures 3-4, the implant body 1 17 comprises a dorsal sidewall portion 126 (see figure 4), an anterior sidewall portion 127 (see figure 5), and interconnecting edge portions 28-29. The dorsal and edge portions 126, 128- 129 unite the carpal bones 18 as a solid body by providing three sides of direct abutting support. The anterior portion 127 comprises profiled edge portions 127A and 127B that extend about projecting carpal bone portion 30 and includes a forwardly extending portion 131 (See Figure 12).

The implant 100, in at least some embodiments, reduces the problem of survivability of the distal component 13 due to loosening of the distal screw fixation 24. As previously discussed, loosening has been thought to occur through the persistence of micro motion in the vicinity of the bone-screw interface resulting in peri-implant wear and loosening. A preferred approach to implantation of the distal carpus for the purpose of total wrist arthroplasty is via a three phase approach to maximise interosseous fusion and ridged fixation. An intra and extra carpal approach to fixation to support the entire distal carpus is adopted.

In a preferred embodiment the implantation procedure involves preparation of the distal carpus to promote primary fusion, though periosteal /cartilaginous abrasion. The abrasion is augmented by implantation of the implant 100 which is designed for providing circumferential cupping of the distal row of carpal bones 18. The HHA (human bone derived hydroxyapatite) coated interface of the implant body 1 17 defines a cavity that functions as a cradle for the carpus and opposes torsional forces to thereby reduce inter carpal micro movement. During use, inner surfaces of the dorsal sidewall portion 127 and the opposed interconnecting sidewall portions 128 and 129 directly support the carpal bones during use.

The inner surfaces of each of the side wall portions, namely the dorsal side wall portion 126, the anterior side wall portion 127 and the opposed interconnecting portions 128 and 129 are substantially concave. As a result these concave side wall portions defines a cup shaped cavity that circumferentially extends about the carpal bones 18. Each of the dorsal side wall portion 126 and the anterior side wall portion 127 comprises an undulating peripheral edge which is shaped for accommodating the carpal bones. As previously discussed, the anterior side wall portions 127 comprises profiled peripheral portions 171 which are shaped for supporting and accommodating projecting portions of the carpal bones 18 (located on an anterior side of the human wrist shown in Figure 12). Similarly, the dorsal side wall portion 126 also comprises undulating peripheral edge portions 173 that are shaped for supporting and accommodating projecting portions of the carpal bones 18 that are located on a dorsal side of the human wrist. As a result, the undulations on the dorsal side wall 126 are not similar to the undulations on the anterior side wall 127. Referring to Figures 4 to 6, 9 and 10 in particular, it is evident that the implant body 1 17 comprises side walls 1 19 that extend both upwardly and downwardly relating to the radial surface 120. A first upper portion 1 19A (shown in Figures 9B and 10B) of the side wall 1 19 extends upwardly relative to the radial surface 120 and defines the cup shaped cavity 1 13 that extends circumferentially relative to the carpal bones and provides support to the carpal bones, during use, in a manner as previously explained. A second lower portion 1 19B (shown in Figures 9B and 10B) of the side wall 1 19 extends downwardly relative to the radial surface 120 forming a downwardly directed recessed cavity 143 for receiving and fastening the joint prosthesis.

The recessed cavity 143 allows a distal portion of a wrist joint plant (such as implant 13 of figure 18) to be received and fastened into recessed cavity 143 of the implant 100. The peg 24b and screws 24a, 24c pass through the openings 121 to 123 that are formed through the radial surface 120 of the implant body 1 17. The central capitate porous peg 24b of the wrist joint implant 13 and two load angled radial and ulnar deviating screws 24a, 24c act to compresses the plate to the bone and resist inline forces. In at least embodiments, a fastening arrangement is provided for fastening the distal implant to the implant body 1 17. In some alternative embodiments, one or more grooves may also located along an inner surface of the side walls defining the recessed cavity 143. The grooves may be adapted for engaging the distal implant 13 during use. Whilst, the above description mainly relates to the use of the cup implant 100, it would be understood that in at least some embodiments, the invention also encompasses a wrist prosthesis which includes the implant 100, namely the implant body 1 17 having a fastening arrangement for fastening the distal implant 13 and a proximal implant 12 (shown in Figure 1 ). The proximal implant 12 comprises a stem portion for implantation into the radius bone during use.

Referring to Figures 19 and 20, a second embodiment of the implant, namely implant 17 is illustrated. The implant 17 comprises an open topped cup shaped implant formed with a sidewall 19 and an end wall 20. The end wall is provided with openings 21 -23 adapted to allow fixings 24a-c (see exemplary figure 8) of the distal component 13 to pass through the openings and into the carpal/metacarpal bones. Sidewall 19 has a further opening 32 for a fixing to fix the implant 17 in place.

Referring to figures 19 and 20, the implant 17 has a dorsal sidewall portion 26 (see figure 5) an anterior sidewall portion 27 (see figure 7), and interconnecting edge portions 28-29. The dorsal and edge portions 26, 28-29 unite the carpal bones 18 as a solid body by providing three sides of direct abutting support. The anterior portion 27 has a profile to extend about projecting carpal bone portion 30 and includes a forwardly extending portion 31 containing an opening 32 (shown in Figure 20) to enable the implant to be fixed to a carpal bone.

The implant 17 reduces the problem of survivability of the distal component 13 due to loosening of the distal screw fixation 24. As previously discussed, loosening has been thought to occur through the persistence of micro motion in the vicinity of the bone-screw interface resulting in peri-implant wear and loosening.

Once again, a preferred approach to implantation of the distal carpus for the purpose of total wrist arthroplasty is via a three phase approach to maximise interosseous fusion and ridged fixation. An intra and extra carpal approach to fixation to support the entire distal carpus is adopted.

As discussed earlier, the implantation procedure involves preparation of the distal carpus to promote primary fusion, though periosteal /cartilaginous abrasion. The abrasion is augmented by implantation of the distal carpal cupping prosthesis 17, which is designed with a circumferential cupping, HHA (human bone derived hydroxyapatite) coated interface to cradle the carpus and oppose torsional forces to thereby reduce inter carpal micro movement. The distal portion of a wrist joint implant (such as the implant 13 of figure 18) may be provided for engagement with the implant 17. The peg 24b and screws 24a, 24c pass through the openings 21 to 23 that are formed through the wall 20 of the cupping implant 17. The central capitate porous peg 24b of the wrist joint implant 13 and two load angled radial and ulnar deviating screws 24a, 24c act to compresses the plate to the bone and resist inline forces.

The implants 1 17 or 17 may be custom made for the patient or the patient can be fitted with a generalized off the shelf implant. A preferred method for making the implant 1 17 or 17 may commence with initially scanning a patient's hand using a computed tomographic (CT) scanner to provide an image (tomogram). The image is segmented into an STL (STereoLithography) format with the carpal bones part of the image being selected. This selected image is evaluated through surfacing techniques to find the specific geometry of the patients own proximal aspect of the distal carpal row. From this surface representation the distal implant 13 can be designed to accommodate the patient's native geometry to produce the custom made implant 17 or 1 17. Alternatively the patient may be retrofitted with a generalized off-the-shelf implant that approximates the patients geometry assessed by measuring the distal carpus width in the AP plan as well as the depth on the lateral cross sectional image. To compensate for the variability in this approach bone graph is utilised as a space filler between the carpus and the implant.

In the following passages, we have described a surgical procedure for surgically placing a wrist joint prosthesis into a human wrist.

The wrist joint is exposed via a longitudinal 20 cm incision directed over Lister's tubercle on the dorsum of the radius. The subcutaneous veins are ligated. The extensor retinaculum is divided in a "z" fashion from the second compartment to the fifth compartment. The digital extensor tendons are retracted to the ulnar side and the radial wrist extensor tendons retracted to the radial side. The dorsal wrist capsule is elevated as a distal based rectangular flap from the articular margin of the radius and TFCC over the ulna extending along the ECU tendon on the ulnar side and over the radial border of the scaphoid on the radial side of the wrist. The wrist is flexed and the proximal carpal row bones are excised preserving the volar extrinsic ligaments. The distal row is instrumented with a guide pin to establish the longitudinal and central axis by establishing the longitudinal and central axis of the capitates. The capitates is then prepared for the insertion of the porous peg of the implant by drilling and broaching. The proximal surfaces of the distal row bones are milled to prepare for the seating of the cupping implant 17 which is then seated thereon. The articulations between the capitate and hamate, between the capitate and trapezoid and between the trapezoid and trapezium are prepared for formal arthrodesis by debriding the adjacent cartilage surfaces.

The distal implant is placed and the radial and ulna load angulated drill holes made through the distal row bones. There is an option for a distal transverse compression screw to further fuse the distal carpus via horizontal compression.

The tension in the prosthesis is then checked with the additional trial components. The tension can be adjusted by placing thicker or thinner components.

Definitive implantation is then undertaken and stability and range of motion checked.

The capsule is closed loosely with an absorbable suture. The extensor retinaculum is repaired with absorbable suture. The skin is closed over a surgical drain with non-absorbable sutures. The wrist is placed in a well- padded bandage and postoperative hand therapy commenced after two to three days. Although a preferred embodiment of the invention has been described for use with the wrist, the invention is directly relevant for application to all joints of the body, as well as retrofitting into existing prosthesis to increase stability. Additionally whilst the preferred embodiment of the invention has been described in the context of human use it is also relevant for animal joints and for creation of artificial joints for robotic and bionic applications - wherever there is a requirement to artificially construct a stable joint. In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. The term "comprises" and its variations, such as "comprising" and "comprised of" is used throughout in an inclusive sense and not to the exclusion of any additional features.

It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art.

Claims

The claims defining the invention are as follows:

1 . A wrist implant comprising:

an implant body shaped to extend about at least part of carpal bones, and

a fastening arrangement for fastening a joint prosthesis to the implant body for reducing undesirable loosening of the prosthesis from the carpal bones.

2. The implant of claim 1 , wherein the implant body comprises a radial surface that extends radially relative to the bones.

3. The implant in accordance with claim 2 further comprising a side wall extending transversely relative to the radial surface, side wall extending circumferentially relative to the carpal bones, during use.

4. The implant of claim 3, wherein the sidewall comprises a dorsal sidewall portion for directly supporting the carpal bones to assist in uniting the bones as a solid body.

5. The implant of claim 3 or claim 4 wherein the sidewall further comprises an anterior sidewall portion and/or opposed interconnecting sidewall portions.

6. The implant of claim 5 when dependent upon claim 4 wherein inner surfaces of the dorsal sidewall portion and the opposed interconnecting sidewall portions for directly supporting the carpal bones during use.

7. The implant of claim 5 wherein the anterior side wall portion comprises a profiled portion for extending about a projecting carpal bone portion during use.

8. The implant in accordance with any one of claims 2 to 7 wherein inner surfaces of the one or more side wall portions are substantially concave, said concave side wall portions defining a cavity.

9. The implant in accordance with claim 7 or 8 wherein the side wall comprises an undulating edge portion defining an opening into the cavity.

10. The implant in accordance with claim 9 wherein the undulating edge portion of the dorsal side wall portion is dissimilar to the undulating edge portion of the anterior side wall portion.

1 1 . The implant in accordance with any one of the preceding claims wherein the implant body defines an upwardly directed cup shaped cavity for extending about and supporting the carpal bones during use.

12. The implant in accordance with claim 1 1 wherein the cup shaped cavity is defined by at least an in use upper portion of the side wall extending upwardly relative to the radial surface.

13. The implant in accordance with any one of the preceding claims wherein the implant body further comprises a downwardly directed recessed cavity for receiving and fastening the joint prosthesis.

14. The implant in accordance with claim 13 wherein the recessed cavity is defined by at least an in use lower portion of the sidewall depending downwardly relative to the radial surface.

15. The implant in accordance with claims 13 or 14 wherein the fastening arrangement allows at least a part of the joint prosthesis to be received into the recessed cavity and fastened to the implant body during use.

16. The implant in accordance with claim 14 or claim 15 wherein the fastening arrangement comprises one or more grooves located along an inner surface of the side walls, the grooves being adapted for engagement with the joint prosthesis, during use.

17. The implant as claimed in any one of claims 2 to 6, wherein the radial surface forms a wall comprising one or more openings to accommodate fixings of a distal implant.

18. The implant as claimed in any one of claims 3 to 6, comprising an opening in the sidewall to accommodate a fixing to fix the implant to a bone.

19. A wrist prosthesis comprising:

an implant body shaped to circumferentially extend about at least part of a distal row of carpal bones;

a distal implant for attachment to the distal row of carpal bones; and

20. A wrist prosthesis comprising:

an implant body in accordance with claim 1 to 18; and a joint prosthesis comprising at least a distal implant such that the distal implant is adapted for being fastened to the implant body during use.

21 . The prosthesis of claim 19 or claim 20, wherein the distal implant and the implant body are joined together.

22. The prosthesis of claim 20 or 21 , wherein the distal implant and the implant body are separate components.

23. The prosthesis of any one of claims 19 to 22 further comprising a proximal implant.

24. The prosthesis in accordance with claim 23 wherein the proximal implant comprises a stem portion for implantation into the radius bone.

25. The prosthesis in accordance with any one of claims 23 or 24 further comprising a coupling arrangement for coupling the proximal implant with the distal implant, and allowing motion of the wrist in at least one physiological direction during use.

26. A method for reducing inter carpal micro movement between the distal row of carpal bones, the method comprising circumferentially retaining at least part of the carpal bones by positioning an implant.

27. A method for the stabilization of a human or animal joint prior to implantation of a joint prosthesis, the method comprising providing an implant adapted to circumferentially extend at least part of the bones into which the prosthesis will be fixed thereby reducing undesirable loosening of the prosthesis from the bones.

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