Standardized CT Measurement of Cup Overhang and Its Link to Iliopsoas Impingement Post-THA

Overview

This study introduces a reproducible method for measuring cup overhang (CO) after total hip arthroplasty (THA) using multiplanar reformatted CT images. It demonstrates that increased overhang distance (OD) correlates with a higher incidence of iliopsoas impingement (IPI), an underrecognized cause of groin pain post-THA.

Background

Total hip arthroplasty is a common procedure with generally excellent outcomes, but iliopsoas impingement affects 2–7% of patients, causing persistent groin pain. Cup overhang, visible on CT as the cup extending beyond the acetabular bone, is a known risk factor for IPI. Prior measurement methods lacked standardization and did not account for pelvic rotation or acetabular inclination, limiting accuracy. This study aims to establish a standardized CT-based measurement of overhang and assess its relationship with IPI.

Data Highlights

Key Findings

• The proposed multiplanar reformation (MPR) method accounts for pelvic rotation and cup inclination, improving measurement accuracy of cup overhang.
• ODc (corrected overhang distance) measurements showed higher reproducibility and reliability compared to uncorrected sagittal measurements (ODu).
• Increased cup overhang distance correlates with a higher risk of iliopsoas impingement confirmed by clinical and imaging criteria.
• Diagnosis of IPI requires combined clinical assessment and imaging confirmation, including MRI or ultrasound evidence of iliopsoas tendinopathy or bursitis.
• Exclusion of confounding causes of groin pain (infection, loosening, fracture) is essential for accurate IPI diagnosis.

Clinical Implications

Clinicians should consider standardized multiplanar CT measurement of cup overhang when evaluating patients with groin pain after THA to identify iliopsoas impingement. Accurate measurement of overhang can guide diagnosis and potentially influence surgical planning or revision decisions to minimize IPI risk. Incorporating imaging confirmation with clinical assessment improves diagnostic confidence.

Conclusion

A standardized CT-based method for measuring cup overhang provides a reliable tool to assess risk of iliopsoas impingement after total hip arthroplasty. This approach may enhance diagnosis and management of persistent groin pain in THA patients.

References

1. Author/Source/Year -- Measuring Cup Overhang Following Total Hip Arthroplasty