Resorbable interposition arthroplasty implant

#The present invention relates to the field of implantable devices useful for joint repair and in particular to the field of such devices useful as interposition devices for the repair of small joints

#Arthritis is one of the most prevalent causes of adult impairment with the small joints of the hand and wrist commonly affected. Disability results from the pain produced by the grinding together of adjacent bones whose natural articular surfaces once covered with slippery cartilage have become rough from disease. Interposition arthroplasty is a common procedure where a biologic or synthetic material is interposed between the bones once the degenerated joint surfaces are removed. The interpositional material serves as a cushion to prevent bone to bone contact and to prevent the collapse of the adjacent bones into the surgically created void. One form of the disease, osteoarthritic degeneration of the thumb basal joint (which is also known as the trapeziometacarpal or carpometacarpal (CMC) joint) is particularly prevalent and debilitating, affecting as many as half of all post-menopausal women. The CMC joint is where the saddle-shaped trapezium bone articulates with the first metacarpal bone allowing motion like that of a mechanical universal joint. An arthritic CMC joint becomes painful enough to limit everyday activity such as grasping or pinching. Symptoms can often be treated with physical therapy, rest, splinting or anti-inflammatory medication. If pain persists surgery may be indicated to allow return to activities of normal daily living. Interposition arthroplasty, the most commonly performed surgical procedure for treating CMC arthritis, has been in use since the early 1970's.

#Surgical intervention for treatment of CMC arthritis begins with removal of the diseased tissue, usually the entire trapezium bone or a portion thereof. To prevent the collapse of the first metacarpal bone into the space thus created, a wire pin is often used to align the base of the first metacarpal bone with the base of the index metacarpal. The pin serves as a temporary stabilizer. A tendon, such as the palmaris longus or flexor carpi radialis is harvested from the forearm and rolled up, resembling a rolled "anchovy" or jelly-roll. The anchovy is then sutured to prevent unrolling and is interposed between the base of the thumb metacarpal and the scaphoid, the space previously occupied by the trapezium bone. In some cases a suspensionplasty is performed wherein a further piece of tendon is used to tie the base of the thumb metacarpal to the base of the index metacarpal, thereby "suspending" the thumb metacarpal. The wire pin is left in place for about 4 to 6 weeks while healing occurs. It is usually 8 weeks or more before patients are allowed unrestricted activity.

#FIG. 1 is an overview of the anatomy of the hand.

#FIG. 1A describes a close up view of the carpometacarpal joint.

#FIG. 2 shows a view of a tendon interposition repair procedure of the prior art.

#FIG. 1 is an overview of the bony anatomy of the human hand while FIG. 1A shows an enlarged view of the first carpometacarpal joint. As described by both of these figures, trapezium 11 articulates directly with the first metacarpal 13 which is the largest bone of the thumb. The trapezium 11 can be seen to have articulating surfaces which come in contact with the first metacarpal 13, scaphoid 15, trapezoid 17 and second metacarpal 19. It can be appreciated from FIG. 1A that the trapezium 11 is a complex shape with distal surface 21 (that articulates with the first metacarpal 13) being saddle-shaped to allow a high degree of mobility of the thumb.

#When the articulating surfaces of the trapezium are destroyed through disease or trauma, the bone is often removed and a tendon interposition is performed as illustrated in FIG. 2. Tendon interposition arthroplasty most often uses the flexor carpi radialis tendon 31. The autologous tendon 31 is split longitudinally as shown so that there is still some functioning tendon left intact. Half of the tendon is cut loose in the forearm, rolled up to create an "anchovy" 33 and placed in the space once occupied by the trapezium 11. The anchovy is often sutured in place to prevent migration. Although the illustration shows the use of the flexor carpi radialis other tendons such as the palmaris longus are also used.

#FIG. 3 describes an interposition arthroplasty procedure according to the present invention. The surgical procedure is similar to that for the conventional tendon arthroplasty procedure shown by FIG. 2 except that no tendon graft is harvested. After removal of the trapezium bone 11, resorbable, non-autologous implant material is provided, proportioned to roughly fit the space previously occupied by the trapezium 11. The proportioned resorbable implant 41 may be provided in a size and shape roughly similar to the native trapezium or optionally can be carved to the desired shape by the medical practitioner to accommodate the surfaces of the first metacarpal 13, the scaphoid 15, the trapezoid 17 and the second metacarpal 19. Because the material of the resorbable implant 41 is conformable due to its inherent compliance, any slight mismatch between the relative shapes of the implant and the adjacent bone surfaces will be accommodated as the implant 41 compresses locally to conform as necessary without causing damage to either the implant or the corresponding adjacent bone surfaces. This conformability allows the implant to accommodate to a substantial extent the variable bone shapes of different individuals.