Impact of Various Factors on the Polyethylene Wear Rate in Total Hip Arthroplasty

Purpose of the study-to determine the rate of polyethylene wear in hip arthroplasty depending on various factors and to evaluate a correlation of wear rate and activity level of the patients. Material and methods. 467 patients with degenerative pathology of the hip, 322 (35.8%) women and 145 (31.0%) men, were included in the study. Mean age of patients was 55.0 years without statistically significant differences in women and men (p = 0.743). Daily activity level of 167 patients (35.8%) was assessed using pedometer. The authors evaluated prosthesis head displacement in relation to the center of acetabulum and calculated the rate of polyethylene wear in MediCad. Modified Harris Hip Score and VAS parameters were evaluated for all patients. All data was analyzed and statistical processed. Results. Average level of activity level was more than 1.9 million steps per year. The overall rate of polyethylene wear depended on the follow up period, the Pearson correlation coefficient r = 0.297 (p< 0.001). Mean wear rate was 0,16 mm/ year (95% CI 0.15-0.17). At the same time wear rate significantly differed in the groups of standard and cross-link polyethylene, namely 0.18 mm/ year (95% CI 0.17-0.19) and 0.11 mm/ year (95% CI 0.1-0.11) (p< 0.001). The authors identified the following additional factors affecting wear rate in the present study: cup inclination angle, r = 0.241 (p = 0.002), and the level of activity level, r = 0.574 (p< 0.001). No evident correlation of wear rate to age, r = 0.14 (p = 0.859), and to BMI, r = -0.094 (p = 0.226), was identified, which apparently is due to a strong impact of confounding factors. Patients' satisfaction with treatment outcomes was assessed by VAS score and in average was 91,1 points (95% CI 90.3-91.9). Harris Hip Score parameters improved in average from 36.5 (95% CI 35.1-37.9) up to 91.6 points (95% CI 91.1-92.0). Conclusion. Out of the multiple factors affecting the polyethylene wear rate only the inclination angle of acetabular component and a higher level of patient activity level have proven to be statistically significant.