JOA - 2026-05-08 - Journal Article
Femoral Stem Collar Overhang Is Associated with Iliopsoas Impingement After Direct Anterior Total Hip Arthroplasty.
Vallabhaneni N, Ingawa HS, Gates KL, Kouzel-Martinez FA, Byrne RA, Volkmar AJ, Blackburn BE, Archibeck MA, Pelt CE
Topics
Key Takeaway
Femoral collar overhang ≥3 mm is associated with more than double the odds of iliopsoas impingement after direct anterior THA (OR 2.2, p=0.024), with IPI occurring in 4.8% of 985 hips.
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Summary
This single-center retrospective study asked whether femoral collar overhang on triple-tapered collared stems contributes to iliopsoas impingement (IPI) in direct anterior THA, independent of acetabular cup overhang. Among 985 primary THAs, 47 (4.8%) developed IPI; mean collar overhang was greater in the IPI group (1.90 vs 1.42 mm, p=0.036), and overhang ≥3 mm was present in 29.8% vs 13.7% of IPI vs non-IPI hips (p=0.003). Multivariable logistic regression confirmed collar overhang ≥3 mm independently doubled IPI odds (OR 2.2, p=0.024), while anterior cup overhang was minimal and non-contributory in either group.
Key Limitation
The 3 mm collar overhang threshold was derived by ROC analysis within the same dataset used to test it, creating overfitting risk and limiting external validity until validated in an independent cohort.
Original Abstract
INTRODUCTION
Iliopsoas impingement (IPI) is an underrecognized complication following total hip arthroplasty (THA), typically attributed to anterior acetabular component overhang. As modern implants have shifted toward collared stem designs, an overhanging femoral collar may also contribute to IPI. We aimed to determine whether the degree of femoral stem collar overhang is associated with IPI in direct anterior approach THA.
METHODS
We retrospectively reviewed 985 primary direct anterior THAs performed with triple-tapered collared femoral stems at a single academic center. All IPI cases were identified using diagnosis codes and surrogate markers (iliopsoas injections, metal artifact reduction sequence magnetic resonance imaging, or arthroscopic tenotomy),and then confirmed through chart review. Radiographic measurements included femoral collar overhang, neck height, and anterior cup overhang at six weeks, with collar overhang reassessed at one year. Collar overhang was analyzed continuously and dichotomously using a three-millimeter (mm) cutoff determined by receiver operating curve (ROC) analysis. Multivariable logistic regressions assessed the association of collar overhang with IPI, adjusting for age, sex, and body mass index (BMI).
RESULTS
Within one year of surgery, 4.8% of hips (47 of 985) met criteria for IPI. At one-year follow-up, mean collar overhang was significantly greater in the impingement group (1.90 versus 1.42 mm, P = 0.036), and a larger proportion had overhang ≥ three mm (29.8 versus 13.7%, P = 0.003). In multivariable analysis, collar overhang ≥ three mm was associated with more than double the odds of IPI (Odds Ratio [OR] 2.2, P = 0.024). Cup overhang was minimal and not significantly different in either group.
CONCLUSION
In direct anterior THA with collared femoral stems, increased collar overhang was associated with IPI. A threshold of greater than three mm may identify hips at elevated risk. Further research is needed to reduce IPI risk.