What is Femoroacetabular Impingement (FAI)?
Femoroacetabular impingement (FAI) syndrome is an intra-articular hip joint disorder where abnormal bone contact between the femoral head-neck junction and the acetabular rim during hip motion causes groin pain, labral tears, chondral damage, and potentially early osteoarthritis. 1
Pathophysiology and Anatomical Abnormalities
FAI results from structural bone deformities that create abnormal mechanical contact during hip movement 1, 2:
- Cam morphology: A non-spherical osseous prominence at the femoral head-neck junction that creates abnormal contact 1, 3
- Pincer morphology: Acetabular overcoverage of the femoral head (lateral center-edge angle >40°) 1, 3
- Mixed pattern: Combination of both cam and pincer abnormalities 1
The repetitive mechanical loading from these abnormalities progressively damages the acetabular labrum, chondrolabral junction, and articular cartilage, predisposing patients to early hip osteoarthritis 1, 4, 2
Clinical Presentation
Patient Demographics
FAI syndrome typically affects young to middle-aged active adults between 20-50 years old, particularly athletes and individuals with repetitive hip flexion activities 1, 5
Pain Characteristics
- Primary location: Groin pain is the hallmark symptom and essential for diagnosis 1, 5
- Pain pattern: Motion-related pain worsened by hip flexion, adduction, and internal rotation 1
- Radiation: May extend to the back, buttock, or thigh 1
- Quality: Chronic, deep, or aching anterior groin pain, most common when sitting or during/after activity, with occasional sharp pains during movement 3
Physical Examination
- FADIR test (flexion-adduction-internal rotation): A positive test indicates FAI syndrome, while a negative test helps rule out hip-related pain 1, 5, 2
- Range of motion: Limited hip internal rotation and flexion are common findings 1
- Additional symptoms: Clicking, catching, buckling, stiffness, and giving way sensations 2
Diagnostic Approach
Initial Imaging
Start with AP pelvis and lateral femoral head-neck radiographs (Dunn, frog-leg, or cross-table views) to evaluate osseous morphology and exclude fractures, arthritis, and dysplasia 1, 5
Advanced Imaging
MRI or MR arthrography is used when radiographs are negative, equivocal, or nondiagnostic to assess 6, 1:
- Labral tears (frequently associated with FAI)
- Chondral damage and cartilage delamination
- Ligamentum teres pathology
MR arthrography with intra-articular gadolinium injection is superior to CT arthrography and noncontrast MRI for evaluating labral tears, though high-resolution 3 Tesla MRI may obviate the need for intra-articular contrast 6
Critical Diagnostic Pitfalls
Lumbar spine pathology must be excluded in all hip pain evaluations, as radicular pain can mimic FAI 1, 5. Perform a comprehensive lumbar spine and pelvis examination to exclude concurrent conditions 5
FAI morphology is extremely common in asymptomatic individuals as incidental findings—clinical correlation is mandatory 1. The presence of bony abnormalities on imaging without corresponding symptoms does not constitute FAI syndrome 1
Treatment Algorithm
Conservative Management (First-Line)
Initiate a 3-6 month trial of 1:
- Activity modification
- Physical therapy focusing on hip strengthening and range of motion
- NSAIDs for pain control
Surgical Indications
Consider surgery when 1:
- Conservative management fails with persistent symptoms after 3-6 months, OR
- MRI confirms labral/chondral damage in symptomatic patients
Advanced chondral wear and pre-existing osteoarthritis are major contraindications for hip preservation surgery and the strongest predictors of poor surgical outcomes 4, 7. Hip arthroscopy is the preferred surgical approach to correct bony abnormalities and repair labral lesions 2, 7
Prognosis
Early recognition and intervention are critical to alleviating morbidity and preventing FAI progression to osteoarthritis 3, 8. Behavioral modification (profession, sports activities) or surgery may reduce the rate of osteoarthritis due to FAI when identified early 8