Reduced Hip Mobility Correlates with Increased Alpha Angle in Chronic Hip/Groin Pain

Overview

This study found that in patients with longstanding hip and groin pain, reduced passive hip range of motion (ROM) is associated with higher alpha angles, a radiographic marker of cam morphology. Specifically, internal rotation with 90° hip flexion showed the strongest negative correlation with alpha angle, supporting its use in clinical assessment.

Background

Chronic hip and groin pain is prevalent among young to middle-aged adults and significantly impacts quality of life and activity levels. Femoroacetabular impingement syndrome (FAIS), particularly cam-type morphology characterized by an increased alpha angle, is a common cause of hip-related pain and may predispose to osteoarthritis. While cam morphology is common even in asymptomatic individuals, greater deformities are linked to symptoms and reduced hip range of motion, especially in internal rotation. Clinical diagnosis of FAIS relies on symptoms, physical examination, and imaging, but access to imaging can be limited and carries risks, highlighting the need for reliable clinical indicators of cam morphology.

Data Highlights

Key Findings

• Higher alpha angles (≥60°) correlate with significantly reduced passive hip range of motion, especially internal rotation at 90° hip flexion.
• Internal rotation with 90° flexion (IRF) showed the strongest negative correlation with alpha angle, supporting its diagnostic value.
• Patients with cam morphology demonstrated lower scores on the Copenhagen Hip and Groin Outcome Score (HAGOS), indicating greater symptom burden.
• Clinical assessment of hip ROM can aid in identifying patients likely to have cam morphology and guide decisions on radiographic referral.
• ROM restrictions are common in symptomatic patients with cam morphology but are not exclusive to this group, necessitating comprehensive clinical evaluation.

Clinical Implications

Measurement of passive hip internal rotation at 90° flexion is a valuable clinical tool to identify patients with cam morphology who may benefit from further imaging. Incorporating ROM assessment into routine evaluation of patients with chronic hip and groin pain can improve diagnostic accuracy and optimize referral pathways. Clinicians should consider ROM limitations alongside patient-reported symptoms to guide management.

Conclusion

Reduced passive hip mobility, particularly internal rotation at 90° flexion, is associated with increased alpha angle in patients with chronic hip and groin pain. These findings support the use of targeted ROM assessment in clinical evaluation to identify cam morphology and inform management strategies.

References

1. Clohisy et al. -- Alpha Angle Measurement Method
2. Systematic Review 2023 -- Alpha Angle Cut-off of 60°
3. HAGOS Validation Studies -- Patient-Reported Outcome Measures