Osteolysis after total knee arthroplasty: influence of tibial baseplate surface finish and sterilization of polyethylene insert. Findings at five to ten years postoperatively.

Background: Debris displaced from the articular and backside surfaces of the polyethylene inserts of modular tibial components is considered a chief cause of osteolysis at the sites of total knee arthroplasties. One design of total knee replacement featured changes, over time, in the proximal surface roughness of the tibial baseplate and the method of sterilization of the polyethylene insert. We hypothesized that polishing the baseplate surface and sterilizing the insert with means other than gamma radiation in air had reduced the prevalence of osteolysis.

Methods: Three hundred and sixty-five posterior cruciate ligament-retaining Anatomic Modular Knee primary total knee arthroplasties were performed in 300 patients from 1987 to 1998. Anteroposterior and lateral radiographs of the knees were made within a five to ten-year postoperative interval. Two arthroplasty specialists independently examined the radiographs for evidence of osteolysis (defined as any nonlinear region of cancellous bone loss with delineable margins).

Results: Osteolysis was identified in 34% (eighty-two) of 242 knees treated with an insert that had been gamma-irradiated in air and affixed to a rough baseplate surface, and it was identified in 9% (nine) of ninety-eight knees treated with an insert that had been gamma-irradiated in an inert gas, or had not been irradiated, and joined to a polished surface. Osteolysis was associated with six factors, including one related to the patient (male gender), one related to the tibial baseplate (the proximal surface finish), three related to the polyethylene insert (the material from which it was machined, the sterilization method, and the shelf age), and one related to the technique (hyperextension of the femoral component relative to the tibial component).

Conclusions: In this design of a total knee prosthesis, polishing the tibial baseplate counterface and implementing a more contemporary sterilization practice (as opposed to gamma radiation in air) noticeably diminished but did not eliminate osteolysis.