Femoroacetabular Impingement

Topic updated on 02/08/16 9:34am
  • A common cause of 
    • early onset hip dysfunction
    • secondary osteoarthritis 
  • Epidemiology
    • Cam impingement
      • refers to femoral based disorder is usually in young athletic males and includes
        • decreased head-to-neck ratio
        • aspherical femoral head
        • decreased femoral offset
        • femoral neck retroversion
          • can be due to previous SCFE deformity
    • Pincer impingement
      • refers to acetabular based disorder usually in active middle-aged women and includes
        • anterosuperior acetabular rim overhang
        • acetabular retroversion
        • acetabular protrusio
        • coxa profunda
    • combined Cam/Pincer impingement
      • can include both patient populations
        • refers to combinations of above (up to 80%)
  • Mechanism
    • result of impingement of the femoral neck against anterior edge of acetabulum
  • Pathoanatomy
    • proximal femur abuts acetabulum with range of motion, especially in flexion
      • occurs if femoral head/neck bone is too broad in Cam impingement
      • occurs if acetabular bone/labrum overhang is too broad in Pincer impingement
  • Associated injuries
    • labral degeneration and tears
    • cartilage damage and flap tears
    • secondary hip osteoarthritis
  • Symptoms
    • activity related groin or hip pain, exacerbated by hip flexion
    • difficulty sitting
    • mechanical hip symptoms
    • can present with gluteal or trochanteric pain
      • due to aberrant gait mechanics
  • Exam
    • limited hip flexion (<90 degrees), especially with internal rotation (<5 degrees)
    • anterior impingement test (flexion, adduction, internal rotation) elicits pain 
    • externally rotated extremity
      • can be due to post-SCFE deformity
  • Radiographs
    • radiographic views
      • false profile view 
        • to assess anterior coverage of the femoral head
        • standing position at an angle of 65° between the pelvis and the film 
    • characteristic findings
      • asphericity and contour of femoral head and neck
        • pistol grip deformity 
          • indicates Cam impingement
      • examine for acetabular protrusio, retroversion, and coxa profunda
        • crossover sign
          • indicates acetabular retroversion in Pincer impingement
    • measurements
      • alpha angle  
        • method
          • measured frog-leg lateral radiograph
          • first line is drawn connecting the center of the femoral head and the center of the femoral neck.
          • second line is drawn from the center of the femoral head to the point on the anterolateral head-neck junction where prominence begins
          • the intersection of these two lines forms the alpha angle
        • normal values
          • values of >42° are suggestive of a head-neck offset deformity
      • head-neck offset ratio  
        • method
          • measured from lateral radiographs
          • a
            line #1 is drawn through the center of the long axis of the femoral neck
          • line #2 is drawn parallel to line 1 through the anteriormost aspect of the femoral neck
          • line #3 is drawn parallel to line 2 through the anteriormost aspect of the femoral head
          • the head-neck offset ratio is calculated by measuring the distance between lines 2 and 3, and dividing by the diameter of the femoral head
        • normal values
          • If the ratio is <0.17, a cam deformity is likely present
  • CT
    • can be used as adjunct to assess for structural abnormalities
  • MRI
    • best modality to evaluate for articular cartilage, and labral degeneration and tears
    • can assess anatomy of femoral head/neck junction abnormalities
  • Nonoperative
    • observation
      • indications
        • minimally symptomatic patient
        • no mechanical symptoms
  • Operative
    • arthroscopic hip surgery 
      • indications
        • symptomatic patient
        • mechanical symptoms
      • outcomes
        • recent literature supports arthroscopy shows equivalent results to open hip surgery
    • open surgical hip dislocation 
      • indications
        • gold standard for management of FAI for patients with clinical signs and structural evidence of impingement and
        • preserved articular cartilage, correctable deformity, reasonable expectations
      • contraindications
        • age >55, morbid obesity, advanced joint disease
    • periacetabular osteotomy 
      • indications
        • structural deformity of acetabulum with poor coverage of femoral head
      • technique
        • osteotomy and fixation
    • total hip arthroplasty
      • indications
        • age >60 years and end-stage hip degeneration
  • Arthroscopic hip surgery
    • approach
      • arthroscopic approach to the hip 
    • technique
      • trim femoral head/neck in Cam impingement 
      • acetabular rim labral debridement vs repair 
        • isolated labral debridement will not solve problem without treatment of underlying pathology
  • Open surgical hip dislocation 
    • approach
      • anterior (Smith-Peterson) approach
        • best for isolated femoral head/neck pathology due to limited exposure, although it is possible that acetabular side could be treated
        • acetabular treatment involves take down of rectus femoris reflected head
        • femoral osteotomy and fixation
    • technique
      • uses a "trochanteric flip" for safe access to proximal femur and acetabulum
        • provides best visualization for hip surgery
        • preserves all external rotators and blood supply to femoral head (medial circumflex femoral artery)
          • no increase in AVN risk
        • provides wide exposure of femoral head and acetabulum
  • Femoral neck fracture
    • at risk during open or arthroscopic debridement of Cam lesions
    • risk is minimized by limiting depth of femoral head-neck osteochondroplasty to <30% of femoral neck diameter


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Qbank (1 Questions)

(OBQ11.259) In the radiographic evaluation of femoroacetabular impingment (FAI), which of the following views is obtained with a standing radiograph and an angle of 65 degrees between the pelvis and the film? Topic Review Topic

1. AP pelvis
2. Inlet
3. Outlet
4. Frog lateral
5. False profile


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