Polyurethane versus silicone for endoprosthetic replacement of the metacarpophalangeal joints in rheumatoid arthritis

In a prospective study 12 patients with rheumatoid arthritis underwent arthroplasty of four metacarpophalangeal joints. Two different implant materials were randomly used in each hand, polyurethane (Pellethane) or silicone (Silastic). Eleven patients with 44 (21 silicone; 23 polyurethane) implants were re-examined 4.5 years (range 3-5) postoperatively. No difference was found between the implant materials regarding pain, stability of the joint or recurrence of the ulnar drift. The mean range of motion was 41 degrees (range 20 degrees-70 degrees) in the polyurethane joints compared with 42 degrees (range 15 degrees-90 degrees) in the silicone joints. The extension deficit was more pronounced in the silicone (mean 11.4 degrees) than in the polyurethane (mean 5.8 degrees) joints, and clinical signs of synovitis around the implants were more common with the silicone arthroplasties. Radiographic analysis, performed with conventional radiography and computed tomography (CT) showed one implant fracture in each group. There was a more pronounced bone resorption around silicone implants, but more sclerosis around polyurethane implants. Bony spurs interfering with function of the implant were common with both materials.