The metacarpophalangeal joint is the most commonly involved joint when rheumatoid arthritis affects the hand. Many prosthetic implants have been designed for the replacement of this joint. Although studies of these implants have shown relief of pain, they have generally demonstrated a poor range of motion, progression of ulnar drift, and bone loss, as well as failure, fracture, and dislocation of the implant.
From December 1979 to February 1987, 151 pyrolytic carbon metacarpophalangeal implants were inserted in fifty-three patients. The implants had an articulating, unconstrained design with a hemispherical head and grooved, offset stems. Forty-four patients had rheumatoid arthritis; five, posttraumatic arthritis; three, osteoarthritis; and one, systemic lupus erythematosus. Three patients (eleven implants) were lost to long-term follow-up, and twenty patients (fifty-one functioning implants) died after the implant had been in situ for an average of 7.2 years. Eighteen implants (12 percent) in eleven patients were revised. Fourteen of the eighteen implants were replaced with a silicone-elastomer or another type of implant, and the remaining four were removed and a pyrolytic carbon implant was reinserted with the addition of bone cement or bone graft, or both. Twenty-six patients (seventy-one implants) were available for long-term review at an average of 11.7 years (range, 10.1 to 16.0 years) after implantation.
The implants improved the arc of motion of the fingers by an average of 13 degrees and elevated the arc by an average of 16 degrees. As a result, fingers were in a more functional, extended position. A complete set of preoperative, postoperative, and follow-up radiographs was available for fifty-three of the seventy-one implants that were followed long term. There was a high prevalence of joint stability: fifty (94 percent) of the fifty-three implants were in a reduced position postoperatively, and forty-one (82 percent) of those fifty implants were still in the postoperative reduced position at the time of long-term follow-up. Ulnar deviation averaged 20 degrees preoperatively and 19 degrees at the time of follow-up, with only the long finger having an increase in deviation. No adverse remodeling or resorption of bone was seen. Fifty (94 percent) of the fifty-three implants had evidence of osseointegration, with sclerosis around the end and shaft of the prosthetic stems. Radiolucent changes were seen adjacent to twelve implants. There was minimum-to-moderate subsidence (four millimeters or less) of thirty-four implants; most of the subsidence occurred immediately postoperatively. Survivorship analysis demonstrated an average annual failure rate of 2.1 percent and a sixteen-year survival rate of 70.3 percent. The five and ten-year survival rates were 82.3 percent (95 percent confidence interval, 74.6 to 88.2 percent) and 81.4 percent (95 percent confidence interval, 73.0 to 87.8 percent), respectively. None of the revised implants had any visible changes of wear or deformity of the surfaces or stems. Four instances of chronic inflammatory tissue and three instances of proliferative synovitis were noted histologically. Focal pigment deposits were seen in three fingers, one of which had removal of the implant two months after a fracture. No evidence of intracellular particles or particulate synovitis was found.
The results of this study demonstrate that pyrolytic carbon is a biologically and biomechanically compatible, wear-resistant, and durable material for arthroplasty of the metacarpophalangeal joint.