POLYETHYLENE WEAR IN UNICOMPARTMENTAL KNEE ARTHROPLASTY

From 1983 to 1989, 147 unicompartmental knee arthroplasties (UKA) were performed. Eighteen knees (13%) have required revision: there were 11 (37%) Porous Coated Anatomic (PCA), three (8%) Microloc, and four (17 %) Fibermesh UKAs. Retrieved implants were examined to determine the p attern and extent of polyethylene wear. Wear was severe in each series and was characterized by delamination, pitting, peripheral cracking, deformation, and abrasion. Polyethylene failure appeared to result fro m large localized stresses resulting from lack of conformity of the ar ticular geometries of the prostheses. Progressive subluxation of the i mplants occurred that produced very high localized contact stresses at the periphery of the tibial component where the polyethylene was thin nest. The progression of osteoarthritis in these knees, particularly t he attenuation of the anterior cruciate ligament, increased the tenden cy of these incongruous implants to subluxate. Although changes in the design and manufacturing of unicompartmental knee arthroplasties may increase the resistance of these implants to polyethylene wear, the pr ogression of osteoarthritis at an unpredictable rate is likely to be a ssociated with persistent polyethylene wear in this type of arthroplas ty.