Femoroacetabular impingement

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[edit] Discussion of Femoroacetabular impingement

  • Femoroacetabular impingement (FAI) is a relatively newly described etiology for hip pain and early onset osteoarthrosis.

[edit] Etiology

  • Patients are predisposed to developing FAI due to their intrinsic (congenital or acquired) anatomy.
  • The impingement in FAI is caused by abnormal anatomic features of the proximal femur or the acetabulum.

[edit] Sequelae

  • Impingement can lead to labral tears, cartilage lesions, and eventually premature osteoarthrosis.

[edit] Predisposing factors

[edit] Symptoms

  • Hip pain most significant with internal rotation.
  • The symptoms of impingement are usually unilateral.
  • Worse after prolonged periods of sitting or when significant stress is placed on the hip.

[edit] Physical examination

  • Loss of internal rotation out of proportion to the loss of range of movement at other positional extremes.
  • Osteoarthosis will usually produce a universal limited range of motion.
  • A grinding and popping sensation can be felt when the femur is externally rotated when the hip is maximally abducted.

[edit] Pincer FAI

  • “Acetabular” FAI
  • Abnormal acetabulum contacting a normal femur.
  • Usually presents in elderly women.
  • This can be due to increased acetabular anteversion or coxa profunda.
  • Acquired causes can be acetabular protrusio or postsurgical prominent anterosuperior acetabulum.
  • Acetabular retroversion: may be seen as a result of trauma or as part of acetabular dysplasia (either in isolation or part of a complex).

[edit] Pathophysiology

  • The acetabular labrum is the first structure to be effected.
  • The repetitive impact results in degeneration of the labrum with intrasubstance ganglion formation or ossification of the acetabular rim.
  • Ossification can lead to further deepening of the acetabulum and therefore more overcoverage of the femoral head by the acetabulum.
  • When cartilage lesions do occur with pincer impingement they are typically focal and involve small areas of the acetabular rim.

[edit] Treatment

  • Reduction of anterior acetabular coverage of the femoral head by an excision of the osseous prominence at the acetabular rim.

[edit] Cam FAI

  • "Femoral" FAI
  • Abnormal morphology of the anterior femoral head–neck junction.
    • Prominence of the femoral head-neck junction in the anterior/anterosuperior portion of the proximal femur is known as the “pistol grip deformity"
  • Younger males.

[edit] Pathophysiology

  • Prominence femoral head-neck junctions produces intermittent and consistent stress (the cam effect) on the associated articular cartilage
  • The shear forces cause damage to both the acetabular labrum and the articular cartilage of the femoral head and acetabulum.

[edit] Treatment

  • Excision osteoplasty of the femoral neck.

[edit] Imaging Findings for Femoroacetabular impingement

[edit] Pincer type

[edit] Plain films

  • Coxa profunda
  • Acetabular protrusio
  • Acetabular rim ossification
  • Acetabular retroversion
    • Crossover sign: The anterior acetabular rim is projected laterally relative to the same point of the posterior rim in the superolateral aspect of the acetabulum.

[edit] CT

  • Same as plain films

[edit] Femoral type

[edit] Plain film

  • Anteroposterior radiographs may show the “pistol grip deformity.”
  • The lateral view may also be helpful to show the decreased femoral head-neck ratio.

[edit] CT

  • α angle : objective representation of the prominence of the anterior femoral head-neck junction.
    • A section through the narrowest portion of the femoral neck is selected
    • A best-fit circle is drawn around the femoral head to determine the head-neck junction
    • A line down the center of the femoral neck and the head-neck junction.
    • A second line that extends from the intersection of the first line and the center of the femoral head to the point where the osseous anterior femoral head intersects the circle.
  • An angle greater than 55 degrees has been shown to be closely associated with symptomatic cam-type femoroacetabular impingement.
  • The larger the α angle, the more the predisposition for impingement.

[edit] Images

Patient #1

[edit] See Also

[edit] External Links

[edit] References for Femoroacetabular impingement

  • Beall DP, Sweet CF, Martin HD, Lastine CL, Grayson DE, Ly JQ, Fish JR. Imaging findings of femoroacetabular impingement syndrome. Skeletal Radiol. 2005 Nov;34(11):691-701.
  • Kassarjian A, Yoon LS, Belzile E, Connolly SA, Millis MB, Palmer WE. Triad of MR arthrographic findings in patients with cam-type femoroacetabular impingement. Radiology. 2005 Aug;236(2):588-92.
  • Blankenbaker DG, Tuite MJ. The painful hip: new concepts. Skeletal Radiol. 2006 Jun;35(6):352-70.