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, 

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

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

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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.

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