Longitudinal Assessment of Impingement Risk following Total Hip Arthroplasty through the Direct Anterior Approach.

Abstract

Component-on-component impingement following total hip arthroplasty (THA) can lead to postoperative complications, but its prevalence in non-failed hips remains unclear due to dynamic factors and limited measurement methodologies. Mechanisms of impingement are mostly thought to be due to component malalignment, such as acetabular cups placed outside of the Lewinnek safe zones, or component sizing, such as the use of large head sizes. However, it is known that early migration of implant components does occur following THA, which may potentially impact postoperative impingement risk. The objective of this study was therefore to evaluate component-on-component impingement risk in patients who have undergone THA over a 5-year postoperative timeline and to evaluate positional impact by comparing impingement risk in the supine and standing positions. There were 24 anterior approach THA participants who underwent radiostereometric analysis at multiple time points: on the day of surgery, at two weeks, four weeks, six weeks, three months, six months, one year, two years, and five years. Impingement risk was calculated as per a custom computational tool, which measures the closest distance between the femoral stem and the polyethylene liner based on the 3-dimensional poses extracted from radiostereometric analysis (RSA). A threshold of one mm was defined to classify impingement, with distances approaching one mm being considered at higher impingement risk. Supine distances remained stable, though standing measurements showed significantly lower mean distances (P < 0.001). Smaller femoral heads (32 mm) had lower distances than larger heads (36 mm; P < 0.0001). Offset stems had significantly greater (P-values = 0.016 to 0.046) neck-liner distances. There were no differences observed between collared and collarless stems. Our findings indicate that component-on-component impingement risk remains stable in the supine position, but increases in the standing position, suggesting that functional weight-bearing evaluations are critical for assessing postoperative impingement risk.