O1133 WEAR RATE IN POLYETHYLENE CUPS THROUGHOUT THE SERVICE TIME OF THE TOTAL HIP REPLACEMENT

Abstract

Aims: Although there have been theoretical expectations of increased polyethylene wear rate with the time a THR is in situ, wear rate is reported to slow down. We performed this study aiming to identify the relationship between wear rate and time of service for the prosthesis. Material and Methods: 45 intact polyethylene liners were retrieved from patients undergoing revision THR. The LWD was measured in the laboratory using the shadowgraph technique. Dividing LWD with time the prosthesis was in place allowed assessment of the Linear Wear Rate (LWR). A correlation between LWR and time of service was explored. Statistical analysis was performed using the SPSS® software package. Results: Linear Wear Rate (LWR) was not stable with time. There was a significant inverse correlation (p< 0.001) between the time that the prosthesis was in place and LWR. This relationship was stronger for the first 6 years of the THR service (p=0.005), while LWR does not change significantly after the 6th year of prosthesis implantation (p=0.060). Conclusions: The LWR is higher in the beginning either as result of the initial higher creep or because of initial lower conformity of the femoral head within the acetabular cup. As conformity increases, the LWR reduces to a more stable value.