Femoroacetabular Impingement

Key Points:

  • FAI is a clinical syndrome of hip pain, limitation in range of motion and abnormal mechanical contact of the femoral head/neck and the acetabulum
  • FAI can play a role in the development of osteoarthritis
  • There is a high prevalence of morphologic abnormalities found in asymptomatic individuals


  • Characterized by abnormal mechanical contact between the rim of the acetabulum and the upper femur
  • Clinical syndrome of hip pain, limitation of movement, and joint damage
  • Two types: CAM and pincer


  • Prevalence remains unknown
  • There is some association between FAI and athletic adolescents
  • There is a high prevalence of morphologic abnormalities associated with FAI in asymptomatic individuals

Clinical Findings:

  • Insidious onset hip pain, usually localized to the groin
  • May be precipitated by activities requiring hip flexion
  • Physical examination:
    • Painful limitation of hip flexion
    • Limited range of motion, especially hip flexion and internal rotation
    • Anterior impingement test
      • Classic provocative maneuver
      • Pain elicited by flexion, adduction, and internal rotation of the affected hip
    • Other provocative maneuvers include resisted straight leg raise, 
posterior impingement test

Imaging Studies:

  • X-rays:
    • CAM type:
      • Frog lateral, cross table lateral or Dunn lateral views can be used
      • Reliability depends on location of deformity and rotation of limb during x-rays
    • Pincer type:
      • AP radiograph usually demonstrates acetabular-sided over coverage
      • Coverage assessed with lateral center edge angle (LCEA)
        • Hips with LCEA >40 deg at risk for impingement
      • Focal over coverage assessed with crossover sign
        • Anterior acetabular wall crosses over posterior acetabular wall on properly oriented AP radiograph
  • MRI:
    • Radial reconstructions more accurately assess head-neck junction
    • Alpha angle of Notzli: estimates the degree at which the radius of curvature of the femoral head begins to increase (larger angle indicates more aspherical head)
    • Intra-articular contrast enhances ability to detect an associated labral tear and chondral injury


  • Abnormal contact between the femoral head/neck and acetabulum leads to supraphysiologic stress
    • Results in tear of labrum and avulsion of the underlying cartilage region
    • Eventually results in arthritis
  • FAI morphology may result from early exposure to high-impact sports and therefore is likely a developmental process
  • Two types:
    • CAM (femoral-sided): 
      • Aspherical epiphyseal extension
      • Produces characteristic bump at femoral head-neck junction
      • Damage pattern:
        • Labral distortion and shear forces peripherally 
        • Detachment of labrum from the acetabular rim 
        • Delamination injuries of the cartilage within the joint
    • Pincer (acetabular-sided):
      • Includes: global over coverage, focal over coverage, and acetabular retroversion
      • Damage pattern:
        • Characteristic trough located in the femoral neck
        • Labrum crushed between the bony acetabular rim and femoral neck
        • Peripheral acetabular cartilage becomes detached and frayed
    • Hips may have a mixed-type impingement with features of both CAM and pincer


  • Nonoperative management:
    •  Usually warranted as an initial step
    • Includes physical therapy, anti-inflammatories, and lifestyle modifications
  • Surgical management:
    • Surgical dislocation:
      • Performed through a lateral Gibson approach to the hip 
      • Trochanteric osteotomy and anterior-based arthrotomy
      • Allows for rim resection, labral repair, acetabular chondroplasty, femoral osteochondroplasty
      • Complete visualization and access to both acetabulum and femoral head
    • Anterior arthrotomy:
      • Standard anterior approach
      • Can be supplemented with arthroscopy
      • Allows for femoral osteochondroplasty, labral debridement, and limited acetabular rim resection
      • Treatment of acetabular rim lesions and labral repair are difficult
      • Incomplete access to posterior hip joint and acetabular rim
    • Arthroscopy:
      • Typically performed with patient supine or lateral using a combination of peritrochanteric, midanterior, and anterior portals
      • Smallest amount of surgical dissection
      • Requires advanced arthroscopic skills to address all FAI lesions
      • Limited access to posterior regions of the hip joint and acetabular rim


  • Variable outcomes based on patient-related factors including lifestyle, work and sports demands, patient expectations, and duration of symptoms
  • FAI can predispose to later development of arthritis in certain patients
    • CAM lesion in isolation is not sufficient to cause clinically significant osteoarthritis
    • Insufficient evidence to confirm association between pincer deformity and clinical or radiographic osteoarthritis


  1. Anderson LA, Peters CL, Park BB, et al.  Acetabular cartilage delamination in femoroacetabular impingement.  Risk factors and magnetic resonance imaging diagnosis.  J Bone Joint Surg Am 2009;91(2):305-13.
  2. Clohisy JC, Knaus ER, Hunt DM, et al.  Clinical presentation of patients with symptomatic anterior hip impingement.  Clin Orthop Relat Res 2009;467(3):638-44.
  3. Ganz R, Leunig M, Leunig-Ganz K, et al.  The etiology of osteoarthritis of the hip: an integrated mechanical concept.  Clin Orthop Relat Res 2008;466(2):264-72.
  4. Ito K, Leunig M, Ganz R.  Histopatholgic features of the acetabular labrum in femoroacetabular impingement.  Clin Orthop Relat Res 2004;429:262-71.
  5. Kennedy MJ, Lamontagne M, Beaule PE.  Femoroacetabular impingement alters hip and pelvic biomechanics during gait walking biomechanics of FAI.  Gait Posture 2009;30:41-4.
  6. Leunig M, Podeszwa D, Beck M, et al. Magnetic resonance arthrography of labral disorders in hips with dysplasia and impingement.  Clin Orthop Relat Res 2004;418:74-80.
  7. Notzli HP, Wyss TF, Sotecklin CH.  The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement.  J Bone Joint Surg Br 2002;84:556-60.
  8. Parvizi J, Leunig M, Ganz R.  Femoroacetabular impingement.  J Am Acad Orthop Surg 2007;9:561-70.
  9. Sankar WN, Matheney TH, Zaltz, I.  Femoroacetabular impingement: current concepts and controversies.  Orthop Clin N Am 2013; 44:575-89.

Top Contributors:

Rachel Goldstein MD