Joseph Norris, MD
Orthopedic Surgeon Sports Medicine

Femoroacetabular Impingement Syndrome (FAI)

    Femoroacetabular Impingement Syndrome (FAI)

  • Femoroacetabular impingement or FAI is a condition where the bones of your hip joint come too close and pinch tissue or cause too much friction.
  • Usually the ball of the hip joint (femoral head) sits on the femoral neck similar to ice cream sitting on a cone. The pinching and friction occurs when the femoral head and neck contact the socket (acetabulum), creating damage to the hip joint. 
  • The pinching or friction may cause damage to the labrum (a fibrous cartilage that lines the outer edge of the socket) and/or the articular cartilage (the white covering over the bony surfaces that allows smooth surface gliding of the joint).

Femoroacetabular Impingement Syndrome (FAI)Causes

  • FAI generally occurs as two forms: Cam and/or Pincer. 
  • The Cam form describes the femoral head and neck relationship as aspherical or not perfectly round. This loss of roundness contributes to abnormal contact between the head and socket as the hip goes through a range of motion. 
  • The Pincer form describes the situation where there is over coverage of the socket or acetabulum relative to the ball or femoral head. This over-coverage typically exists along the front-top rim of the socket (acetabulum). 
  • The end result is that the labral cartilage gets "pinched" between the rim of the socket and the front part where the femoral head meets the femoral neck. 
  • The Pincer form of the impingement is typically the result of "retroversion", where the socket is pointed backwards a bit (rather than the usual situation where it is angled forwards), or where the socket is too deep.
  • Very often, the Cam and Pincer forms exist together and the exact cause of these bony variations is not known at this time, but thought to be an anatomic predisposition (you were just born this way).


  • FAI is associated with articular cartilage damage and labral tears and may result in hip arthritis at a younger age  


  • Pain or aching (usually located at the inner hip, or groin area), usually after walking, or prolonged sitting (such  as in a car)
  • A locking, clicking or "catching" sensation within the joint (may indicate labral tear)
  • Pain with deep hip flexion
  • It is often confused with other sources of pain, such as hip flexor strain or pain from the low back
    • Hip pain usually does not go past the knee and is felt more in the groin or thigh
    • Back pain usually is sharp, burning in quality and can have associated numbness and tingling and can go all the way down the leg


  • History and physical exam where the hips and legs are moved in different positions to assess range of motion and evaluate the positions where the hip hurts. 
  • X-rays of the hip
  •  A special type of magnetic resonance imaging (MRI) called magnetic resonance arthrogram (MRA) is commonly used
  • X-rays show bones well, but the MRI is particularly good at showing the non-bony structures of the body, such as the labrum and articular cartilage
  • During a MR- arthrogram, dye (contrast material) is injected into the joint space to help make images more clear.  Frequently, local anesthetic (numbing medicine) is added to the contrast material to help determine if the pain is coming from inside the joint (typically called an MR arthrogram with lidocaine challenge)



  • Lifestyle modifications and a commitment to maintaining hip strength
  • A good physical therapy program focusing on hip strengthening instead of stretching may be beneficial
  • Anti-inflammatory medications can also be attempted
  • Hip injections (steroid)


  • Surgery for FAI can be performed using hip arthroscopy
  • The results of surgery are clearly better when there is no articular cartilage damage (typically younger patients are better candidates 45 yrs and younger) 
  •  In hip arthroscopy, the hip is distracted and an arthroscope (a videocamera about the size of a pen) is used to look in the joint to see and treat damage that is found using small incisions
  • Often, all of the components of FAI such as the labral tear, and bony changes between the ball and socket can be treated with the assistance of the arthroscope. 
  • Repair of a torn labrum as well as stimulating new cartilage growth (microfracture) are often possible with the arthroscopic approach.
  • This is done as an outpatient surgery (go home the same day)

Recovery from Surgery

  • Recovery from hip arthroscopy is anywhere from 3-6 months
  • Patients are usually toe-touch weightbearing with crutches for 4 weeks
  • After the 4 week mark patients are allowed to weightbear as tolerated (WBAT)
  • Patients will also start physical therapy (PT) about 3-5 days after surgery for just some gentle range of motion exercises
  • At around the 6-8 week mark patients begin strengthening their hip and progress at their own rate until fully recovered at the 3-6 month mark
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