JAAOS - 2026-07-24 - Journal Article
Predictors of Iliopsoas Impingement after Total Hip Arthroplasty with Overhanging Acetabular Components.
Castagnini F, Galato G, Tassinari E, Poletto A, Dalla Rosa M, Traina F
Topics
Key Takeaway
Among THAs with cup protrusion, acetabular component oversizing (diameter mismatch +1.7mm vs -1.8mm, OR 1.33) was the only independent predictor of symptomatic iliopsoas impingement.
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Summary
This retrospective case-control study asked which CT-measured positional parameters differentiate protruding cups causing symptomatic iliopsoas impingement from asymptomatic protruding cups. Thirty-five CT-confirmed symptomatic THAs were compared to 17 asymptomatic THAs with comparable protrusion magnitude across cup anteversion, sagittal tilt, diameter mismatch, offsets, and leg length discrepancy. Firth penalized logistic regression identified acetabular diameter mismatch as the sole independent predictor (OR 1.33, 95% CI 1.09–2.26), with anteversion (19.8° vs 11.5°) and sagittal tilt (19.9° vs 11.2°) showing large univariate effect sizes but losing independence in the multivariate model.
Key Limitation
The asymptomatic control group (n=17) is too small and potentially biased by survivorship, as patients with mild symptoms may have been lost to follow-up or not referred for CT evaluation.
Original Abstract
BACKGROUND
Cup protrusion has been recognized as the most sensitive and specific radiological parameter to predict iliopsoas (IP) impingement after total hip arthroplasty (THA): it is a necessary but not sufficient factor. We aimed to investigate the following: (1) whether radiological differences exist between protruding cups associated with symptomatic IP impingement and asymptomatic ones; (2) which positional parameters correlate with symptomatic IP impingement in THA with cup protrusion.
METHODS
This retrospective case-control study included 35 noncemented THAs with CT-confirmed IP impingement (clinical, radiographic, and arthroscopic diagnosis) and 17 asymptomatic noncemented THAs with comparable protrusion and ≥5 years of follow-up. Postoperative CT scans were evaluated for cup protrusion in all planes, inclination, anteversion, cup tilt, femoral and acetabular offsets, eccentric reaming, leg length discrepancy (LLD), and stem antetorsion. Groups were comparable for age, sex, side, diagnosis, and protrusion magnitude.
RESULTS
Symptomatic hips showed markedly greater acetabular diameter mismatch (1.7 mm vs-1.8 mm; Cohen's d = 1.16), higher cup anteversion (19.8° vs 11.5°; d = 0.88), greater sagittal tilt (19.9° vs 11.2°; d = 0.81), and smaller LLD (1.4 vs 6.8 mm; d = 0.73). In the exploratory Firth penalized logistic regression model, acetabular diameter mismatch was the only variable associated with symptomatic IP impingement (OR 1.33, 95% CI, 1.09 to 2.26), whereas anteversion, tilt, and LLD did not retain independent associations.
CONCLUSION
Among THAs with comparable cup protrusion, cup oversizing showed the strongest and most consistent association with symptomatic IP impingement, whereas increased anteversion and sagittal tilt appeared to modulate the mechanical consequences of protrusion.
LEVEL OF EVIDENCE
Level of Evidence: III.