Residency · Residency · Physical Medicine Rehabilitation
Hip Pain in the Young Adult: Femoroacetabular Impingement and Labral Tears
Anatomy of the Hip Joint
Osseous Structures
Ball-and-socket joint with inherent bony stability (deeper socket than glenohumeral joint). Acetabulum: formed by the ilium, ischium, and pubis; faces anterolaterally and inferiorly. Femoral head: covered by articular cartilage except at the fovea centralis (ligamentum teres attachment). Femoral neck-shaft angle: normal ~125 degrees; coxa vara (<120) and coxa valga (>135) alter mechanics. Femoral anteversion: normal ~10-15 degrees in adults; increased anteversion predisposes to impingement.
Labrum
Fibrocartilaginous structure attached to the acetabular rim. Deepens the acetabulum by ~20%, increasing joint stability. Creates a suction seal maintaining negative intra-articular pressure. Has a limited blood supply (primarily from the capsular side).
Anterosuperior labrum is the most common site of tearing (watershed zone, highest mechanical stress). Contains free nerve endings -- labral tears can be a significant pain source.
Capsule and Ligaments
Three major capsular ligaments: iliofemoral (Y ligament of Bigelow -- strongest), ischiofemoral, pubofemoral. Iliofemoral ligament resists extension and external rotation. Zona orbicularis: circular fibers encircling the femoral neck.
Musculature
Hip flexors: iliopsoas (primary), rectus femoris, sartorius, TFL. Hip extensors: gluteus maximus, hamstrings. Abductors: gluteus medius (primary), gluteus minimus, TFL. Adductors: adductor longus, brevis, magnus, gracilis, pectineus.
External rotators: piriformis, obturator internus/externus, gemelli, quadratus femoris. Internal rotators: gluteus medius/minimus (anterior fibers), TFL.
Femoroacetabular Impingement (FAI)
Definition
Abnormal mechanical contact between the femoral head-neck junction and the acetabular rim during hip motion. Results in damage to the labrum and adjacent cartilage. Recognized as a significant risk factor for early hip osteoarthritis.
Types of FAI
Cam Morphology
Aspherical femoral head-neck junction (bony bump on the anterolateral femoral head-neck). Alpha angle >55-60 degrees on imaging indicates cam morphology. More common in young athletic males. Mechanism: during flexion and internal rotation, the aspherical prominence shears into the acetabulum. Causes cartilage delamination (outside-in pattern) and labral detachment. Associated with aggressive cartilage damage.
Pincer Morphology
Acetabular over-coverage (global or focal). Lateral center-edge angle >40 degrees (global over-coverage). Acetabular retroversion (focal over-coverage): crossover sign, ischial spine sign, posterior wall sign on AP pelvis radiograph. More common in middle-aged women.
Mechanism: labrum is crushed between the over-covered rim and the femoral neck. Causes labral degeneration/ossification and limited cartilage damage (initially). Contrecoup cartilage lesion on the posterior-inferior acetabulum.
Mixed Morphology
Most common presentation (~85% of surgical cases). Combination of cam and pincer features. Both femoral and acetabular contributions to impingement.
| Feature | Cam | Pincer | Mixed |
|---|---|---|---|
| Morphology | Aspherical femoral head-neck | Acetabular over-coverage | Both |
| Imaging marker | Alpha angle >55-60° | CE angle >40° or crossover sign | Both findings |
| Demographics | Young athletic males | Middle-aged women | Most common (~85%) |
| Cartilage damage | Delamination (outside-in) | Initially limited; contrecoup posteroinferior | Combined pattern |
| Labral injury | Detachment | Crush/degeneration | Both patterns |
Risk Factors
High-impact sports during skeletal development (hockey, soccer, basketball). Repetitive hip flexion activities. Slipped capital femoral epiphysis (SCFE) history. Legg-Calve-Perthes disease. Male sex (cam), female sex (pincer). NOTE: Cam and pincer morphology is also found in asymptomatic individuals (~25%).
Labral Tears
Etiology
FAI-related: most common cause in young adults. Traumatic: sports injury, hip dislocation. Degenerative: associated with early OA, capsular laxity. Hypermobility/Dysplasia: acetabular dysplasia creates excessive labral stress.
Location
Anterosuperior labrum: most common (FAI-related). Posteroinferior: traumatic or dysplasia-related. Classification: Seldes Type 1 (detachment from acetabular rim) vs. Type 2 (intrasubstance cleavage).
Clinical Evaluation
History
Anterior groin pain is the hallmark (C-sign: patient cups hand around greater trochanter and groin). Deep, aching pain, possibly sharp with certain movements. Pain with prolonged sitting, getting in/out of car, squatting. Mechanical symptoms: clicking, catching, locking (suggest labral tear).
Pain with pivoting and twisting movements. Insidious onset, often bilateral. May have a history of groin strain that failed to resolve.
Physical Examination
Observation and ROM
Gait: antalgic gait or Trendelenburg sign (indicates abductor weakness). ROM: typically decreased internal rotation in flexion; painful arc. Log roll test: gentle internal and external rotation in extension -- most specific test for intra-articular pathology.
Provocative Tests
FADIR (Flexion-Adduction-Internal Rotation): hip flexed to 90 degrees, adducted and internally rotated; reproduces anterior impingement pain (sensitivity ~95%, specificity ~10%). FABER (Flexion-Abduction-External Rotation / Patrick test): positive if groin pain (intra-articular) or posterior/SI pain (SI joint); compare distance of knee from table bilaterally. Anterior impingement test: same as FADIR. Posterior impingement test: hip extension with external rotation.
Resisted straight leg raise (Stinchfield test): hip flexion against resistance reproduces deep groin pain. Fitzgerald test: combined flexion-ER to extension-IR (click with labral tear). Thomas test: assess hip flexor contracture. Ober test: assess iliotibial band/TFL tightness.
Key Differentials to Examine For
Greater trochanteric pain syndrome (lateral hip pain, tenderness over trochanter). Iliopsoas tendinopathy/snapping hip (anterior snapping with flexion-extension). Athletic pubalgia (sports hernia). Stress fracture (femoral neck -- urgent diagnosis). Lumbar radiculopathy (L2-L3). Sacroiliac joint dysfunction.
Imaging
Radiographs (Essential First Step)
AP pelvis: standardized (coccyx 1-3 cm above pubic symphysis). Lateral center-edge angle (normal 25-40 degrees; <20 = dysplasia, >40 = over-coverage). Tonnis angle (acetabular inclination). Crossover sign, posterior wall sign, ischial spine sign (retroversion).
Joint space width (>2 mm normal). Dunn view (45 or 90 degrees) or frog-leg lateral: best for visualizing cam lesion. Alpha angle measurement (>55-60 degrees = cam morphology). False profile view: anterior coverage assessment.
MRI / MR Arthrography
MR arthrography (MRA): gold standard for labral tear detection (sensitivity ~90%, specificity ~90%). Contrast distends the joint, outlining labral tears and cartilage delamination. 3T MRI without contrast: improving sensitivity, may approach MRA for labral tears. Assess cartilage status (delamination, chondral defects). Assess paralabral cysts, subchondral edema.
Diagnostic Injection
Image-guided intra-articular lidocaine injection: >50% pain relief confirms intra-articular source. Essential when clinical and imaging findings are ambiguous. Helps differentiate intra-articular pathology from extra-articular sources.
Management
Conservative Management
Activity Modification
Avoid deep flexion, pivoting, impact loading. Modify sport participation during acute flares. Ergonomic adjustments (seat height, workstation).
Physical Therapy (First-Line)
Hip stabilization program: gluteus medius and minimus strengthening. Core strengthening: lumbopelvic stability. Flexibility: hip flexor stretching (iliopsoas, rectus femoris), piriformis stretching. Avoid: excessive hip flexion, deep squats, aggressive stretching into impingement positions.
Neuromuscular control: single-leg balance, proprioceptive training. Aquatic therapy: for pain-limited patients. Progressive loading: gradual return to sport with load management.
Pharmacologic
NSAIDs for pain and to facilitate participation in therapy. Acetaminophen as adjunct. Intra-articular corticosteroid injection: short-term pain relief, diagnostic value; limit repeated use (cartilage concerns).
Surgical Management
Indications
Failed 3-6 months of structured conservative management. Significant labral tear with concordant symptoms and positive diagnostic injection. Symptomatic cam or pincer morphology limiting function. No or minimal existing osteoarthritis (Tonnis grade 0-1).
Arthroscopic Hip Surgery
Cam resection (osteochondroplasty): reshaping the femoral head-neck junction. Labral repair (preferred over debridement): suture anchor fixation. Labral reconstruction: if labrum is irreparable (using iliotibial band or allograft). Pincer resection: acetabular rim trimming.
Capsular closure: important to prevent iatrogenic instability. Microfracture / cartilage restoration: for focal cartilage defects.
Post-Arthroscopy Rehabilitation
Weight-bearing restrictions: 2-4 weeks partial weight-bearing (procedure-dependent). CPM or early PROM. Hip precautions: limit flexion, avoid active SLR for 2-4 weeks (protect labral repair). Progressive strengthening: 6-12 weeks. Return to sport: 4-6 months (full competitive return may take 6-9 months).
Prognostic Factors for Arthroscopic Surgery
Good outcomes: minimal arthritis, normal joint space, isolated labral/cam pathology. Poor outcomes: Tonnis grade 2+ OA, joint space <2 mm, age >40 with significant cartilage damage.
<image>Anterior view of the hip joint showing three inset diagrams comparing normal hip morphology, cam morphology (aspherical femoral head-neck junction with a bump at the anterolateral head-neck junction, alpha angle measurement shown exceeding 60 degrees), and pincer morphology (acetabular over-coverage with lateral center-edge angle exceeding 40 degrees). Show the labrum in each diagram, with the cam diagram demonstrating cartilage delamination and the pincer diagram showing labral crush injury.</image>
<image>Clinical examination illustration demonstrating the FADIR test (Flexion-Adduction-Internal Rotation): patient supine, clinician flexing the hip to 90 degrees then adducting and internally rotating while watching for reproduction of groin pain. Adjacent illustration shows the FABER test (Patrick test): patient supine with ankle on opposite knee, clinician pressing the knee toward the table while stabilizing the contralateral pelvis. Label the direction of force and the expected pain location for positive tests.</image>
<image>AP pelvis radiograph illustration showing key measurements for FAI evaluation: lateral center-edge angle drawn from the center of the femoral head vertically to the lateral acetabular rim (normal 25-40 degrees), crossover sign indicating acetabular retroversion (anterior wall line crossing posterior wall line), and a Dunn view inset showing alpha angle measurement from center of femoral head along the axis of femoral neck to the point where the head-neck junction exceeds the radius of the femoral head.</image>
Clinical Pearls
Groin pain is the hallmark of intra-articular hip pathology -- lateral hip pain points to extra-articular causes (greater trochanteric pain syndrome). FADIR is sensitive but not specific; a negative FADIR makes intra-articular hip pathology unlikely. Always obtain standardized AP pelvis and Dunn views as the first imaging step before ordering MRI. Cam morphology is extremely common in asymptomatic young athletes; imaging alone does not indicate surgery.
A diagnostic intra-articular injection providing >50% pain relief is one of the most important diagnostic tools for confirming intra-articular pathology. Hip dysplasia (center-edge angle <20 degrees) must be identified as it requires different surgical management (periacetabular osteotomy, not arthroscopy). Labral repair has better outcomes than labral debridement for most tears. The evidence for hip arthroscopy vs. structured physiotherapy (UK FASHIoN trial, Australian HIPARTI trial) shows modest benefits from surgery, supporting informed shared decision-making.
References
- Griffin DR, et al. Hip arthroscopy versus best conservative care for the treatment of femoroacetabular impingement syndrome (UK FASHIoN): a multicentre randomised controlled trial. Lancet. 2018;391(10136):2225-2235.
- Reiman MP, et al. Diagnostic accuracy of clinical tests of the hip: a systematic review with meta-analysis. Br J Sports Med. 2013;47(14):893-902.
- Ganz R, et al. The etiology of osteoarthritis of the hip: an integrated mechanical concept. Clin Orthop Relat Res. 2008;466(2):264-272.
- Nepple JJ, et al. Clinical and radiographic predictors of intra-articular hip disease in arthroscopy. Am J Sports Med. 2011;39(2):296-303.
- Mosler AB, et al. The Doha agreement meeting on terminology and definitions in groin pain in athletes. Br J Sports Med. 2015;49(12):768-774.
