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

Description:

  • 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

Epidemiology:

  • 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

Etiology:

  • 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

Treatment:

  • 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

Complications:

  • 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

References:

  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