Ultrasound and shear-wave elastography characteristics of the iliocapsularis muscle in pincer-type femoroacetabular impingement

Background: The iliocapsularis muscle is a structure of the anterior hip, which may play a key role in stabilizing the hip joint, but to our knowledge no studies exist describing ultrasound (US) and shear-wave characteristics of this muscle.

Objectives: To investigate the anatomic dimensions and elasticity of the iliocapsularis muscle in patients with pincer-type femoroacetabular impingement (FAI) and normal hips using gray-scale US and shear-wave elastography (SWE).

Design: Case-control study.

Setting: Sports medicine and ultrasound department within a tertiary hospital.

Participants: Thirty-three patients (33 hips) with pincer-type FAI and 37 healthy volunteers (37 hips).

Interventions: Not applicable.

Main outcome measures: US parameters (anteroposterior diameter, transverse diameter and circumference) of the iliocapsularis muscle in patients with pincer-type FAI and volunteers. Shear-wave velocity and Young's modulus of the iliocapsularis muscle in patients with pincer-type FAI and volunteers in both neutral and external rotation positions.

Results: Significant differences were not observed in the anatomic dimensions of the iliocapsularis muscle between patients with pincer-type FAI and volunteers. The iliocapsularis muscle in patients with pincer-type FAI had significantly lower shear-wave velocity and Young's modulus than the volunteers (p < .05). The cutoff value of the maximum velocity in the external rotation position was 3.35 m/s, which separated pincer-type FAI patients from volunteers and revealed the highest accuracy with sensitivity, specificity, and accuracy of 78.8%, 48.6%, and 64.3%, respectively.

Conclusion: The anatomic dimensions of the iliocapsularis muscle in pincer-type FAI patients and volunteers were similar; however, iliocapsularis stiffness in patients with pincer-type FAI was significantly lower than that of the volunteers. SWE can demonstrate altered muscle stiffness of the iliocapsularis muscle in pincer-type FAI patients, which might be used to help make clinical decisions.