Iliopsoas impingement after THA: rethinking the 8 mm revision threshold

Design

Retrospective case series, level IV

Population

86 hips (83 patients) with iliopsoas impingement after primary THA

Primary outcome

Patient-reported outcomes, reoperation and revision by overhang

Effect

No significant PROM differences; reoperation 2.9% vs 10.5% (p = 0.21)

Persistent groin pain from iliopsoas impingement after total hip arthroplasty has traditionally been triaged by anterior acetabular overhang: more than 8 mm pointed to cup revision, less to tenotomy. That threshold came from open tenotomy outcomes.

A retrospective single-institution series reviewed 86 hips in 83 patients (mean age 63) treated with arthroscopic iliopsoas fractional lengthening between 2017 and 2024, followed for a mean of 2.5 years. Overhang was under 8 mm in 67 hips and 8 mm or more in 19. Pain, hip scores, activity, satisfaction and flexion strength did not differ significantly between groups. Reoperation was 2.9% against 10.5% and acetabular revision 1.5% against 5%, neither difference significant.

If these results hold, many patients with larger overhang could avoid a cup revision, a far bigger operation. The caveats are substantial: this is a retrospective level IV series, the large-overhang group was small, and the numerically higher reoperation rate in that group could be real but undetected.

• Consider arthroscopic iliopsoas fractional lengthening before cup revision for iliopsoas impingement that fails non-operative care.
• Overhang above 8 mm did not clearly predict a worse result after lengthening in this series.
• Counsel patients with large overhang that reoperation was numerically more frequent, 10.5% against 2.9%.
• Confirm the diagnosis first, for example with a diagnostic injection into the iliopsoas sheath.
• Measure overhang on a cross-table lateral radiograph to inform the discussion.

Why it matters

A rule that steers patients towards cup revision may be sending some to a bigger operation than they need.

Don't overread it

With only 19 hips over 8 mm, the study could miss a real difference in reoperation.

The statistics, in plain English

A non-significant p-value with 19 patients in one group means the study lacked power to detect differences, not that none exist. Reoperation of 10.5% against 2.9% is a gap worth watching.

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