Ten- to 12-year followup of the Insall-Burstein I total knee prosthesis

The Insall-Burstein Posterior Stabilized knee prosthesis (Insall-Burstein I), developed at The Hospital for Special Surgery in 1978, has a metal-backed nonmodular tibial component. The polyethylene articular surface was directly molded. The purpose of the current study was to evaluate long-term wear with this design. The first 100 total knee arthroplasties (86 patients) performed by the senior author were followed prospectively. The average age of the patients at the time of surgery was 69.7 years (range, 45-89 years). The primary diagnoses were osteoarthritis in 77 knees (66 patients), inflammatory arthritis in 17 knees (14 patients), and posttraumatic arthritis in the remaining six knees (six patients). Thirty-eight knees (35 patients) had varus angulation, 14 knees (13 patients) had valgus angulation, and 48 knees (40 patients) had a 0 degrees to 10 degrees tibiofemoral angle preoperatively. All patients were evaluated at 10 to 12 years followup. Knee Society scores and radiographs were obtained. Thirty-six knees were in 30 patients who had died and two knees were in two patients who were infirm. Telephone evaluation only was available for eight knees (seven patients), leaving 54 knees (47 patients) for direct clinical and radiographic evaluation. No patients were lost to followup. The average Knee Society clinical score at latest followup was 91.6 points. The average function score was 69 points. One knee arthroplasty failed because of tibial loosening, one failed because of patella wear and fracture, two failed because of sepsis, and two failed because of nonspecific pain. There were seven patella fractures (7%) in the 100 knees. One of the fractures resulted in a total knee revision (noted above), two resulted in patellar component revision, and another resulted in patellar component removal. The remaining three patella fractures were discovered incidentally and were asymptomatic. There were no patellar dislocations. At long-term radiographic analysis, valgus alignment averaged 6 degrees (range, 0 degrees-11 degrees). Polyethylene wear averaged 0.40 mm. There was no catastrophic wear of tibial polyethylene. Thirty-two knees in 32 patients (65%) had radiolucencies in at least one zone; no lucency filled a zone, and none was wider than 2 mm. The absence of clinically significant tibial polyethylene wear at long-term followup is of particular interest. The performance of the molded, nonmodular polyethylene articulation is encouraging and needs to be analyzed critically against the more widely used machined, modular components used today.