2019 Volume 38 Issue 1 Pages 1-8
Objective: We aimed to determine the risk factors and thresholds of cup protrusion for iliopsoas impingement (IPI) after total hip arthroplasty (THA).
Methods: This retrospective case-control study evaluated 633 primary THAs performed by a single surgeon in a single center. In all THAs, the cup was inserted with the assistance of the computed tomography (CT)-based navigation system. Twenty-seven patients with THAs (4.3%) were identified to have symptoms of IPI and were included in group I. Control group 1 (C1) comprised 606 THAs, whereas control group 2 (C2) was formed by recruiting three data-matched controls per patient in C1. Risk factors for IPI were assessed in group I and C1, respectively. Further analysis was performed in the group I and C2 to evaluate radiological data.
Results: Multivariate logistic regression analysis confirmed that the anterolateral approach was associated with a higher risk of IPI (odds ratio [OR], 2.77). There was no association found between the design of the acetabular component or the cup insert and IPI. Axial protrusion length≥12 mm (Odds ratio, 23.4; sensitivity=70.0; specificity=90.0) was determined as an independent predictor of IPI. In multiple linear regression analyses, higher native acetabular version and lower cup anteversion were related to cup protrusion.
Conclusion: This single center study determined the threshold of cup protrusion length for IPI and identified associated factors increasing cup protrusion. The results are useful for orthopedic surgeons in determining cup position and alignment when undertaking THAs.
