In 80 % of patients with rheumatoid arthritis, the metacarpophalangeal (MP) joints are involved with increasing destruction and loss of function. Silicone arthroplasty of the MP joints leads to a limited range of motion, an increase in osteolysis and fractures of the implants. The cementless, unconstrained design of the HM prosthesis is a new concept for replacing the MP joints of rheumatoid patients. Short-term and midterm results are shown.
In a prospective study, 38 HM prostheses were implanted, 28 in patients with rheumatoid arthritis, four with osteoarthrosis, five with polyarthrosis and one after revision of a silicone implant. The patients were reexamined clinically and radiologically after an average follow-up of 16 months (6 - 37 months).
The average active range of motion for extension, flexion increased from 0/15/65 degrees before surgery to 0/9/65 degrees after surgery. The remaining ulnar drift was 12 degrees (preoperative 18 degrees ). The average grip strength after surgery was 80 % of the opposite side. Pain in the verbal analog scale improved from 2.3 to 1.7 postoperatively. One palmar subluxation of an implant of the little finger was recognized. No infection occurred. The X-rays showed complete osteointegration in all metacarpal components. Radiolucent zones were found in progress only at the basis on the phalangeal components without radiological signs of loosening or sinking.
The short- and midterm results after implantation of the cementless, unconstrained HM prosthesis show an improved hand function and pain relief. The design of the implant may solve the accepted postoperative problem of instability of the MP joints. Until now, no prosthesis had to be exchanged.