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What Is Femoroacetabular Impingement (FAI)?

  • The normal hip is a highly congruent ball-and-socket joint 
  • FAI occurs when there is a structural mismatch between the ball (femur) and the socket (acetabulum) of the hip joint
  • Abnormal contact (impingement) at extremes of hip range of motion leads to dysfunction and damage
  • A small deformity may become symptomatic with high-level activities while symptoms with routine activities may occur with larger deformities or more advanced damage
  • Damage is usually the result of cumulative effects of repetitive abnormal contact

ball and socket image

Types

  • Cam Impingement
    • Ball (femoral head) is not completely round
    • May be a prominent bump or the ball may be elliptical in shape
    • Damage occurs when the out-of-round area of the ball rotates into the round socket (square peg in a round hole)
    • Pain occurs with hip flexion, inward rotation, squats, etc. 
    • More common in men
  • Pincer Impingement
    • Overhanging rim of socket decreases clearance during hip motion
    • May be caused by a socket that is too deep or not facing forward (retroversion)
    • Damage occurs when the neck collides with the rim of socket
    • Pain with hip flexion, stairs, abduction, etc.
    • More common in women
  • Mixed or Combined
    • Having elements of both cam and pincer FAI

Cam image

Pincer image

Management

  • Key Concepts to Consider:
    • FAI is a dynamic problem—It occurs because the hip is under stress from the activities to which it is exposed
    • A high percentage of people have hips that would meet X-ray criteria for FAI, but only a small percentage become symptomatic, and an even smaller percentage require intervention
    • A high percentage of people with FAI have similar findings on the other hip but do not have symptoms
  • Fundamental to management is returning the hip to the presymptomatic state by reducing inflammation and optimizing the mechanics around the pelvis
  • Rest and avoiding the inciting activity will improve symptoms and allow healing
  • Anti-inflammatory medicines (ibuprofen, naproxen, etc.) decrease swelling and inflammation
  • A cortisone injection may help to calm inflammation in the joint
  • Physical therapy is essential to improving pelvic mechanics and stabilizing gait
  • Most cases of FAI improve without surgery 

hip impingement x-ray image

Arthroscopic Surgery for FAI

  • The goal is to correct the bony abnormality underlying the impingement
  • A small (4 mm) video camera is inserted into the hip joint and highly specialized instruments are used to perform surgery
  • Traction is required to separate the ball from the socket
  • Cam FAI – The ball is recontoured to improve congruity
  • Pincer FAI – The rim is trimmed to increase clearance
  • Secondary damage (labral tears, cartilage damage) is fixed or cleaned up
  • Recovery takes 4 to 6 months and requires rigorous therapy to restore hip function
  • Potential complications include traction-related injury, nerve damage, progression of labral tearing and/or arthritis, abnormal bone formation in muscles around the hip, blood clots, incomplete correction, and residual pain

arthroscopic surgery for FAI image

Cam and Pincer Correction Images