The Mathys^_¯ finger joint replacement system offers a novel fixation method into the proximal and distal medullary canals and a semi-constrained articulation. This comprises a separable, form-fit joint with a distal/proximal play of 0.7 mm, a lateral excursion of 10°, and rotation of up to 6°. This has theoretical advantages of increased radio-ulnar stability, preventing ulnar drift in patients with rheumatoid disease, and enhanced osseointegration offering implant longevity. In our unit, however, high failure rates were noted, prompting a review of cases to quantify our suspicions.

Case notes of all patients who underwent finger joint replacement using the Mathys^_¯ implant between 1999 and 2005 were retrieved. Twenty-two devices were implanted by a single surgeon during this period. Four were in finger proximal interphalangeal joints, 17 in finger metacarpophalangeal joints and one in a thumb carpometacarpal joint (CMCJ).

Indications for joint replacement included sixteen for rheumatoid arthritis (RA) and five for post-traumatic joint problems. The only thumb CMCJ was replaced for primary osteoarthritis. Patients were reviewed regularly and implant performance assessed critically along with survival of the implant to revision, infection or death of the patient. Mean follow up was 30 months.

Sixteen implants failed including the only thumb CMCJ. Modes of failure were rotation (11), poor range of motion (two), infection (two) and dislocation (the CMCJ). Similar ball and socket designs for uncemented thumb CMCJ replacement, such as the Ledoux prosthesis, have previously shown poor survival and have been withdrawn from the market. Of the finger implants in RA patients (n=16), 12 implants failed of which ten were due to rotation. Time to failure ranged from two to 48 months (mean 15 months).

The authors do not recommend the use of this implant, especially in cases of rheumatoid arthritis.