CLINICAL-EXPERIENCE WITH THE VARIABLE AXIS TOTAL KNEE REPLACEMENT

From 1975-1978, the variable axis total knee prosthetic system was implanted in 111 knees in 89 patients. Preoperative knee deformities ranged from 44.degree. of varus to 24.degree. of valgus angulation, with flexion contractures of as much as 34.degree.. Follow-up ranged from 24-60 mo. and averaged 36 mo. Most patients had significant pain relief (in 75% of the knees at rest and in 96% while walking) and improved function. Residual pain, which was usually mild and most commonly was located in the retropatellar region, caused no functional impairment. Complications included patellar dislocation in 6 knees, progressive collateral-ligament instability in 5, a loose tibial screw in 1, a tibiofemoral dislocation in 1, and a traumatic fracture of the methylmethacrylate in 1. There were no instances of component loosening, even though the alignment of the implanted prosthetic components in 20% of the knees deviated from the ideal by as much as 12.degree.. Radiolucent lines, which were less than 1 mm wide and did not progress, were observed at the bone-cement interface in 38% of the knees. Indications for implanting the variable axis prosthesis are broader than are generally recommended for semi-constrained designs. Correcting angular deformities by release of contracted ligaments has permitted use of the prosthesis in severely deformed knees. Although the absence of component loosening is encouraging, design modifications are advocated to prevent patellar dislocation and progressive instability. The variable axis prosthesis is recommended for most arthritic knees when the collateral ligaments are intact and correct realignment of the extensor mechanism is possible.