Accurate in vivo measurement of polyethylene wear in total knee arthroplasty.

This study describes a new technique to evaluate accurate linear polyethylene wear and reports the in vivo annual linear wear rate in total knee arthroplasty. Patients (n = 69) were assessed using a single standing anteroposterior radiograph with 8 reference markers around the knee, where 3-dimensional (3D) locations of markers and 3D geometry of the implant were known. By matching the 3D locations of the markers and their projected points on the radiograph, 3D/2D transformation parameters were estimated. Using these parameters, the 3D coordinates of the implant were estimated from the projected x-ray silhouette. After calculating the femorotibial shortest distance, wear and creep deformity of the polyethylene was defined with an accuracy of 0.1 mm or better. Measured linear wear in the 69 knees varied from 0 mm (1 month postoperatively) to 2.71 mm (7 years postoperatively). The correlation of linear wear (Y) and year (X) was Y = 0.23 X -0.11 (P<.001). This study revealed that annual wear rate was 0.23 mm and 2 times greater than the average annual wear rate in total hip arthroplasties. Copyright 2002, Elsevier Science (USA).