Quantifying cup overhang after total hip arthroplasty: standardized measurement using reformatted computed tomography and association of overhang distance with iliopsoas impingement

Category	Detail
Condition	Iliopsoas impingement (IPI) after total hip arthroplasty (THA)
Key Mechanisms	Cup overhang (CO) causing iliopsoas tendon impingement and mechanical irritation during hip flexion
Target Population	Patients undergoing primary total hip arthroplasty
Care Setting	Orthopedic surgery and postoperative imaging assessment

Iliopsoas impingement occurs in approximately 2–7% of THA patients and is an underrecognized cause of persistent groin pain.
Cup overhang is measurable on CT scans and is a risk factor for iliopsoas impingement, but no consensus exists on symptomatic overhang distance.
A reproducible method using multiplanar reformation (MPR) of CT images was proposed to standardize measurement of cup overhang distance.

Diagnose IPI based on detailed patient history and physical examination including specific tests like the Thomas Test.
Use plain radiographs and CT scans to evaluate cup positioning and overhang.
Confirm diagnosis with imaging evidence of iliopectineal bursitis or iliopsoas tendinopathy on MRI or ultrasound.

Consider fluoroscopy-guided corticosteroid injections for confirmed cases of iliopsoas impingement.

Monitor patients post-THA with CT imaging to assess cup positioning and potential overhang.
Evaluate clinical symptoms of groin pain and correlate with imaging findings.

Oversized cups or version mismatch between cup and native acetabulum increase risk of cup overhang.
Female sex, leg length discrepancy, and retained cement or screw protrusion may also increase risk of iliopsoas impingement.

Patients undergoing primary total hip arthroplasty with postoperative groin pain

Fluoroscopy-guided corticosteroid injections can be used to treat confirmed iliopsoas impingement.

Use multiplanar reformation (MPR) of CT scans to accurately measure cup overhang distance accounting for pelvic rotation and cup inclination.
Perform blinded, independent image analysis by trained radiologists to improve measurement reliability.
Exclude patients with secondary osteoarthritis, revision THA, or other causes of groin pain to isolate iliopsoas impingement cases.
Correlate clinical findings with imaging evidence before confirming diagnosis of iliopsoas impingement.

Clinical Scorecard: Measuring Cup Overhang Following Total Hip Arthroplasty: A Standardized Approach Using Reformatted Computed Tomography and Its Relationship with Iliopsoas Impingement