O1244 AN IN VIVO STUDY OF THE WEAR RATE OF THE POLYETHYLENE TIBIAL INSERT IN TOTAL KNEE ARTHROPLASTY

Abstract

Aims: To compare the in vivo wear rates of the polyethylene inserts of different thicknesses in Freeman-Samuelson (F/S) total knee arthroplasties. Methods: Radiographs of 17 patients with F/S modular prostheses and 6mm thick inserts, 19 patients with 8mm inserts, and 6 patients with F/S1000 (more conformed medial femoral condyle) with 8mm inserts were studied. The distance (polyethylene thickness) between femoral and tibial components was measured from A-P radiographs at 6 months, 3 years and 5 years with correction for magnification and antero-posterior tilting of the tibial tray. Wear rates were calculated. Comparisons were made between the medial and lateral sides of the inserts, between the different thicknesses and between the two types of prostheses. Results: The difference in the wear rate between the medial and lateral side in the 3 groups of polyethylene inserts was shown to be 0.229, 0.054, and −0.044 mm/yr (p> 0.2 in all 3 groups). Between the two thicknesses in the F/SM group, the 6mm group had a higher wear rate than the 8mm group (diff = 0.072 mm/yr, p< 0.05) over 5 years, with the majority of wear occurring in the first 3 years (Diff = 0.098mm/yr, p< 0.05). Between the two types of prostheses used, the wear rate over 5 years was shown to be 0.006mm/yr (p> 0.5). Conclusions: The study showed that the 6mm polyethylene components had a significantly higher rate of wear than the 8mm ones, but there was no significant difference shown between the medial and lateral sides of the inserts and two versions of the prosthesis.