Femoroacetabular impingement and classification of the cam deformity: the reference interval in normal hips

Area of Science:

• Orthopedics
• Radiology
• Biomechanical analysis

Background:

• Femoroacetabular impingement (FAI) often involves cam deformity, quantifiable by alpha angle and anterior offset ratio (AOR).
• Limited knowledge exists regarding "normal" values for alpha angle and AOR.
• Establishing population-based reference intervals is crucial for accurate diagnosis and research.

Purpose of the Study:

• To define reference intervals for alpha angle and AOR in a general population with normal hips.
• To provide thresholds for classifying hip morphology in studies of FAI and osteoarthritis (OA).
• To assist clinicians in evaluating young adults with hip pain.

Main Methods:

• Radiographic and clinical review of 157 individuals from the general population.
• Exclusion of 74 individuals with hip disease or osteoarthritis (OA), resulting in 83 normal hips.
• Measurement of alpha angles and AORs from cross-table lateral radiographs; validation through cadaver and reliability studies.

Main Results:

• The 95% reference interval for alpha angle was 32-62 degrees; for AOR, it was 0.14-0.24.
• Mean alpha angle was 48 degrees in men and 47 degrees in women; mean AOR was 0.19 for both sexes.
• Validation confirmed measurement reliability and resistance to positional variations.

Conclusions:

• Normal hips can exhibit alpha angles and AORs previously considered abnormal.
• The established reference intervals aid in classifying individuals in longitudinal FAI and OA studies.
• These thresholds are valuable for clinicians assessing hip pain in young adults.