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Femoroacetabular Impingement

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Other Names

  • FAI
  • Femoral Acetabular Impingement


  • This page refers to femoroacetabular impingement (FAI) of the hip


  • Originally described by Ganz[1]


  • Challenging to estimate prevalence, incidence
    • Radiographic and clinical findings do not always match up
  • Frank et al estimates in asymptomatic individuals[2]
    • Prevalence of cam deformity: general (23.1%), athletes (54.8%)
    • Prevalence of pincer deformity: general (67%)
  • In symptomatic individuals
    • Nepple et al: FAI in 94% of NFL combine athletes[3]
    • Mascarenhas et al: prevalence of cam impingement 49%[4]


  • Dynamic phenomenon of unclear etiology that leads to hip joint damage
    • Related to abnormal hip morphology, motion
    • Exact etiology remains unclear
  • Cam-type lesions (femoral head-neck junction)
    • Refers to femoral head based pathology
    • Cause impingement to due to abnormal shaped femoral head rotating within the acetabulum
    • Particularly worse during forced flexion
    • Produces shearing forces of the Acetabular Labrum, most commonly anterior-superior
    • Worsened by by increased α angle
    • Large cam lesions associated with increased acetabular cartilage, labral damage[5]
    • More common in young, mostly male athletes
  • Pincer-type lesions (acetabular rim)
    • Characterized by acetabular overcoverage
    • Can be described as local (acetabular retoversion) or global (coxa profunda or protrosio)[6]
    • Impingement occurs due to abnormal contact of the acetabular rim, femoral head-neck junction
    • Leads to labral injuries initially, subsequent chondral injuries
    • More common in active, middle aged women
  • Mixed pathology
    • Combination of cam- and pincer-type deformity is most commonn[7]
    • Can occur individually, but less commonly so
  • Radiographic studies
    • Murray et al: athletes participating in "aggressive athletic activities" at a younger age more likely to have proximal femoral deformities[8]
    • Sienbrock et al: increased alpha angle on MRI of elite basketball players with open physes compared to controls[9]
    • Agricola et al: Among adolescent soccer players, prevalence of cam lesion increased from 7.1% to 22.2%, and normal appearing head-neck junction decreased from 84.1% to 43.2% over 2.4 years of follow up[10]
  • Developmental
    • Sienbrock et al: physeal abnormalities could alter femoral head-neck relationship[11]

Associated Injuries


  • Hip Joint
    • Acetabulum formed by confluence of ischium, ilium, pubic bones
    • Femoral Head sits on neck, antiverted 15° in relation to femoral condyles

Risk Factors

  • Genetic
    • Risk increases 2.0-2.8 in sibling studies[12]
  • White race[13]
  • Sports
    • Hockey (10 fold)[14]
    • Basketball (4 fold)
    • Soccer[15]
    • Football[16]

Differential Diagnosis

Clinical Features



  • Standard Radiographs Hip
    • Should include a PA, lateral view
    • Consider frog leg, cross table lateral
    • 45 degree Dunn lateral provides most information for FAI[19]
  • Alpha angle (for cam deformity)
    • Most commonly used quantitative measurement for cam impingement
    • Determined by fitting a circle to the femoral head and connecting a line from the center of this circle to the center of the femoral neck[20]
    • Second line drawn from center of circle to superior head-neck junction outside the circle
    • No standardization of normal, ranges from 42-63°
    • No agreement of threshold for pathology, ranges from 50-62°
    • Increasing threshold to 60° increased specificity to 74%, sensitivity 76.5%[21]
  • Pincer deformity
    • Look for detection of retroversion, focal overcoverage, and global overcoverage[22]
    • Crossover sign: anterior rim of the acetabulum crosses the line of the posterior aspect of the rim before reaching the lateral edge of the sourcil[23]
    • Posterior wall sign: center of the femoral head is lateral to the posterior wall[24]
    • Lateral center-edge angle: AP view, angle is calculated by a line through the center of the femoral head, perpendicular to the transverse axis of the pelvis and a line from the center of the head through the most superolateral point of the weight bearing zone of the acetabulum[25]


  • Helpful to evaluate cartilage, labrum
  • Degree of chondral injury predictive of patient outcomes and satisfaction[26]


  • Helpful to better clarify osseous architecture
  • Useful for surgical planning, especially with 3D surface rendering


  • General
    • Head-neck junction (cam lesion)
    • Acetbular rim (pincer lesion)
    • Both or mixed



  • Palmer et al: Patients with symptomatic FAI referred to secondary or tertiary care achieve superior outcomes with arthroscopic hip surgery than with physiotherapy and activity modification.[27]


  • Indications
    • Minimally symptomatic or no mechanical symptoms
  • Activity modification
    • Individualized to patients athletic demands and symptoms
    • Exacerbating movements and activities should be avoided


  • Khan et al systematic review[28]
    • US guidance better tolerated than fluoroscopic guidance
    • Lack of response strong predictor of poor surgical outcome
    • Corticosteroid Injection: improvement in only 15% of patients at 6 weeks
    • Hyalouronic Acid provided relief at up to 12 months, superior to CSI


  • Indications
    • Symptomatic
    • Failure of non-op
    • Non-arthritic joint
  • Technique
    • Arthroscopic osteoplasty (preferred)
    • Open osteoplasty
    • Periacetabular osteotomy
    • Total hip arthroplasty

Rehab and Return to Play


  • No universal protocol
  • Directed at improving hip muscle strength, mobility
  • Also work on posture, body control, core strength

Return to Play

  • Needs to be updated


See Also


  1. Ganz R, Parvizi J, Beck M, et al. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop. 2003;417:112–120.
  2. Frank JM, Harris JD, Erickson BJ, et al. Prevalence of femoroacetabular impingement imaging findings in asymptomatic volunteers: A systematic review. Arthroscopy. 2015;31:1199–1204.
  3. epple JJ, Brophy RH, Matava MJ, et al. Radiographic findings of femoroacetabular impingement in national football league combine athletes undergoing radiographs for previous hip or groin pain. Arthroscopy. 2012;28:1396–1403.
  4. Mascarenhas VV, Rego P, Dantas P, et al. Imaging prevalence of femoroacetabular impingement in symptomatic patients, athletes, and asymptomatic individuals: a systematic review. Eur J Radiol. 2016;85:73–95.
  5. Johnston TL, Schenker ML, Briggs KK, et al. Relationship between offset angle alpha and hip chondral injury in femoroacetabular impingement. Arthroscopy. 2008;24:669–675.
  6. anz R, Leunig M, Leunig-Ganz K, et al. The etiology of osteoarthritis of the hip. Clin Orthop. 2008;466:264–272.
  7. Beck M, Kalhor M, Leunig M, et al. Hip morphology influences the pattern of damage to the acetabular cartilage: femoroacetabular impingement as a cause of early osteoarthritis of the hip. J Bone Joint Surg Br. 2005;87:1012–1018.
  8. Murray RO, Duncan C. Athletic activity in adolescence as an etiological factor in degenerative hip disease. J Bone Joint Surg Br. 1971;53:406–419.
  9. Siebenrock K, Ferner F, Noble P, et al. The cam-type deformity of the proximal femur arises in childhood in response to vigorous sporting activity. Clin Orthop Relat Res. 2011;469:3229–3240.
  10. Agricola R, Heijboer MP, Ginai AZ, et al. A cam deformity is gradually acquired during skeletal maturation in adolescent and young male soccer players: A prospective study with minimum 2-year follow-up. Am J Sports Med. 2014;42:798–806.
  11. iebenrock K, Wahab KA, Werlen S, et al. Abnormal extension of the femoral head epiphysis as a cause of cam impingement. Clin Orthop. 2004;418:54–60.
  12. Pollard TC, Villar RN, Norton MR, et al. Genetic influences in the aetiology of femoroacetabular impingement: a sibling study. J Bone Joint Surg Br. 2010;92:209–216.
  13. Hoaglund FT, Shiba R, Newberg AH, et al. Diseases of the hip. A comparative study of Japanese oriental and American White patients. J Bone Joint Surg Am. 1985;67:1376–1383.
  14. Nepple JJ, Vigdorchik JM, Clohisy JC. What is the association between sports participation and the development of proximal femoral cam deformity? A systematic review and meta-analysis. Am J Sports Med. 2015;43:2833–2840.
  15. Gerhardt MB, Romero AA, Silvers HJ, et al. The prevalence of radiographic hip abnormalities in elite soccer players. Am J Sports Med. 2012;40:584–588.
  16. Kapron AL, Anderson AE, Aoki SK, et al. Radiographic prevalence of femoroacetabular impingement in collegiate football players: AAOS exhibit selection. J Bone Joint Surg Am. 2011;93:e111.1–e111.10.
  17. Clohisy JC, Knaus ER, Hunt DM, et al. Clinical presentation of patients with symptomatic anterior hip impingement. Clin Orthop. 2009;467:638–644.
  18. Wyss TF, Clark JM, Weishaupt D, et al. Correlation between internal rotation and bony anatomy in the hip. Clin Orthop Relat Res. 2007;460:152–158.
  19. Meyer DC, Beck M, Ellis T, et al. Comparison of six radiographic projections to assess femoral head/neck asphericity. Clin Orthop Relat Res. 2006;445:181–185.
  20. Notzli HP, Wyss TF, Stoecklin CH, et al. The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement. J Bone Joint Surg Br. 2002;84:556–560.
  21. Sutter R, Dietrich TJ, Zingg PO, et al. How useful is the alpha angle for discriminating between symptomatic patients with cam-type femoroacetabular impingement and asymptomatic volunteers? Radiology. 2012;264:514–521.
  22. Nepple JJ, Prather H, Trousdale RT, et al. Diagnostic imaging of femoroacetabular impingement. J Am Acad Orthop Surg. 2013;21:S20–S26.
  23. Egger, Anthony C. MD; Frangiamore, Salvatore MD; Rosneck, James MD Femoroacetabular Impingement: A Review, Sports Medicine and Arthroscopy Review: December 2016 - Volume 24 - Issue 4 - p e53-e58
  24. Clohisy JC, Carlisle JC, Beaule PE, et al. A systematic approach to the plain radiographic evaluation of the young adult hip. J Bone Joint Surg Am. 2008;90(suppl 4):47–66.
  25. Clohisy JC, Carlisle JC, Beaule PE, et al. A systematic approach to the plain radiographic evaluation of the young adult hip. J Bone Joint Surg Am. 2008;90(suppl 4):47–66.
  26. Saadat E, Martin SD, Thornhill TS, et al. Factors associated with the failure of surgical treatment for femoroacetabular impingement: review of the literature. Am J Sports Med. 2014;42:1487–1495.
  27. Palmer Antony J R, et al. Arthroscopic hip surgery compared with physiotherapy and activity modification for the treatment of symptomatic femoroacetabular impingement: multicentre randomised controlled trial BMJ 2019; 364 :l185
  28. Khan W, Khan M, Alradwan H, et al. Utility of intra-articular hip injections for femoroacetabular impingement: a systematic review. Orthop J Sports Med. 2015;3:2325967115601030.
Created by:
John Kiel on 21 July 2020 23:59:32
Last edited:
5 October 2022 13:06:01