# Femoroacetabular Impingement > Femoroacetabular impingement for NEET-PG Orthopaedics: cam and pincer morphology, alpha angle, labral tears, C-sign and arthroscopic osteochondroplasty. - Canonical URL: https://prepelephant.com/topics/neet-pg/orthopaedics/femoroacetabular-impingement - Exam / course: NEET-PG · Subject: Orthopaedics - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Femoroacetabular Impingement", PrepElephant, https://prepelephant.com/topics/neet-pg/orthopaedics/femoroacetabular-impingement ## Direct answer A young athletic man's groin pain that deepens with sitting, pivoting and deep squats — often localised with the C-sign, a hand cupped over the hip because patients point to the side, not the groin — characterises femoroacetabular impingement, abnormal contact between the femoral head-neck junction and the acetabular rim during terminal hip motion. Two morphologies produce it: cam impingement, a non-spherical femoral head with an aspherical anterosuperior neck bump (alpha angle above roughly 55 degrees) that shears the chondrolabral junction, typical of young athletic males; and pincer impingement, acetabular over-coverage that crushes the labrum directly, more typical of women — with combined cam-pincer the commonest real pattern. The anterior impingement test (flexion-adduction-internal rotation) provokes it, MRI arthrography shows the labral tear, and arthroscopic femoroplasty with rim trimming and labral repair addresses symptomatic pathology after activity modification and physiotherapy fail. ## What you must remember - **Cam morphology:** aspherical head-neck junction with diminished offset, quantified by alpha angle above about 55-60 degrees; produces shear delamination of cartilage at the chondrolabral junction in young men. - **Pincer morphology:** focal or global acetabular over-coverage — centre-edge angle above about 40 degrees, crossover sign, protrusio — pressing the labrum, which fails first; more common in women. - **Clinical tests:** anterior impingement test — flexion, adduction and internal rotation reproduces groin pain; FABER distance supplements; the sitting and deep-squat aggravation history is nearly as diagnostic. - **Imaging pathway:** standing pelvic radiograph for crossover sign, centre-edge and Tonnis angles; MRI arthrogram for labral tear and cartilage delamination; CT with 3D reconstruction for offset mapping before femoroplasty. - **Treatment logic:** morphology alone is not disease — asymptomatic cam is common; first-line is activity modification and hip-focused physiotherapy; persistent symptomatic impingement with confirmed labral pathology goes to arthroscopy for femoroplasty, rim trimming with labral refixation, and capsular closure. - **Secondary causes to exclude:** slipped capital femoral epiphysis sequelae, Perthes deformity, coxa vara and post-traumatic deformity — treat the mechanics, not just the bump. - **Natural history caution:** impingement morphology is a risk factor for early osteoarthritis, but prophylactic surgery on asymptomatic hips is not supported — a favourite viva boundary. ## A typical case from bike seat to arthroscope A 26-year-old state-level hockey player has eight months of right groin pain — worst after matches and long drives, improved sitting with the leg dropped open — and he grips his hip with a cupped hand when asked to localise it. Internal rotation at 90 degrees flexion is painful, the anterior impingement test is positive, and FABER shows 6 cm of knee-to-table distance. Radiographs reveal a pistol-grip deformity with a crossover sign; the alpha angle measures 64 degrees, and MRI arthrogram demonstrates an anterosuperior labral tear with a paralabral cyst. Management proceeds in two phases. He first undergoes a structured 12-week programme — avoiding terminal-range flexion and rotation, strengthening gluteal and deep rotator groups, modifying training — because a proportion of impingement pain is soft-tissue overload rather than structural necessity. Symptoms persist through the season, so he proceeds to hip arthroscopy: femoral osteochondroplasty resecting the cam bump, rim trimming with labral refixation using suture anchors, chondroplasty of the delaminated flap, and capsular plication — followed by staged rehabilitation over 3-4 months before return to pivot sport. Counselling includes realistic expectations: pain relief is the goal, arthritis prevention plausible but unproven. ## Where students slip Two confusions dominate. First, labral tear versus impingement as the diagnosis: a labral tear is the injury, impingement the mechanism, and treating the tear without correcting the bony morphology recurs — the answer that pairs refixation with femoroplasty scores over the one that stops at labral debridement. Second, number-free morphology talk: the exam expects alpha angle thresholds and centre-edge angles as the quantitative backbone, and candidates who cannot attach numbers to the two shapes lose the image-interpretation marks. The C-sign earns its place as the bedside giveaway that pain is truly intra-articular. A final boundary: finding cam morphology on an asymptomatic hip is not an indication for surgery, and differentiating FAI groin pain from the adductor, iliopsoas and sports-hernia cluster is the diagnostic discipline the exam probes. ## Frequently asked questions ### How do cam and pincer impingement differ mechanically? Cam is an aspherical head-neck junction that shears the chondrolabral junction in flexion (young men, alpha angle over 55-60 degrees); pincer is acetabular over-coverage that directly crushes the labrum (centre-edge angle over 40 degrees, women) — combined lesions commonest. ### What is the anterior impingement test? Passively flexing the hip to about 90 degrees, adducting and internally rotating it; reproduction of the familiar groin pain indicates anterior impingement, often with labral pathology. ### What does the C-sign indicate? The patient cups a hand over the hip, thumb posterior and fingers anterior — localising true intra-articular hip pain better than pointing, a bedside discriminator from lumbar referred pain. ### Which imaging confirms labral pathology? MRI arthrography — contrast distends the capsule and shows labral tears, paralabral cysts and cartilage delamination; radiographs and CT define the bony alpha angle and coverage first. ### Why is prophylactic surgery not done for asymptomatic cam morphology? Bony morphology is common in asymptomatic hips and osteoarthritis prevention from surgery is unproven; intervention is reserved for symptomatic impingement after conservative failure.