IN VITRO WEAR PERFORMANCE OF MTP PROSTHESES EVALUATED ON A MULTISTATION METATARSOPHALANGEAL JOINT SIMULATOR

Abstract

The first metatarsophalangeal (MTP) joint is the key joint of the foot in terms of function during gait. Various replacement toe joint prostheses are commercially available but unlike other replacement joints such as the hip or knee, few simulator based studies have been conducted to evaluate the performance and reliability of these prostheses. Presented are results obtained using a newly developed and validated multi-station MTP joint test-rig that is able to simulate the natural biomechanics of the toe joint. The developed simulator is a multi-station computer controlled electro-pneumatic metataso-phalangeal joint simulator that applies dynamic loading and motions commensurate with the walking gait cycle. This involves the combination of plantar-dorsi flexion range of 32 degrees, 5 degrees of inversion/eversion and toe-off dynamic loading peaking at up to 820 N. Presented are the validation and in vitro test results of MTP joint simulations carried out on silastic and articulating metal and polymer designs of MTP prostheses. Despite being subjected to a reduced loading regime of 300 N peak force, the silastic prostheses were found to perform poorly in the simulator, ultimately failing due to a combination of fatigue crack growth and joint collapse. This behaviour and failure mode was consistent with that of ex vivo origin silastic MTP prostheses examined and provides confidence in the validity of the simulator.