Design of a Non-Constrained, Non-Cemented, Modular, Metacarpophalangeal Prosthesis

Abstract

A non-constrained, non-cemented, modular prosthesis for replacement of the metacarpophalangeal joints of the fingers has been developed. The prosthesis is of a surface design which is modular in construction and is implanted into the bones with a press fit. The prosthesis is designed to be implanted into patients with traumatic injuries, post-traumatic osteoarthritis and into patients with rheumatoid arthritis at an early stage in the disease where the muscles and ligaments that surround the joint are still functional and can provide joint stability.

Preliminary Results of Nonconstrained Pyrolytic Carbon Arthroplasty for Metacarpophalangeal Joint Arthritis

“…Three-dimensional models of the hand suggest that joint compressive forces can reach 6 times the externally administered force generated by pinch. 22 Older-generation MCP joint implants addressed stability through fully constrained or semiconstrained designs; however, the greater the constraint, the greater the transmitted stress through the prosthesis to the stem-bone interface, which can result in implant loosening. Nonconstrained designs such as the pyrolytic carbon implant (Ascension) require minimal bone resection and preserve the collateral ligaments.…”

Radiographic Assessment of the Relative Lengths of the Bones of the Fingers of the Human Hand

“…The centres of rotation of the metacarpophalangeal and interphalangeal joints change during flexion and extension (Beevers andSeedhom, 1995, Tamai et al, 1988). We were unable to find any references which described the locations of the centres of rotation of the finger joints in X-rays of the hand.…”

FEA analysis of silicone MCP implant

“…Flexible silicone MCP prostheses have a demonstrated place in MCP arthroplasty and can be effective in reducing joint pain and improving cosmetic appearance (Swanson, 1972(Swanson, , 1997Hagert et al, 1975;Goldner et al, 1977;Beevers and Seedhom, 1995a, b;McArthur and Milner, 1998). However, flexible silicone MCP prostheses are much less effective in establishing functional motion and functional strength.…”

“…Although considered as one the most stable and safest of implantable materials, silicone elastomer medical devices have failed in vivo (see, for example, Bass et al, 1996;Naidu, 1999;Beevers and Seedhom, 1995a, b). Failure of silicone elastomer in the use of a finger joint is related to the material's tear and fatigue strength properties.…”