FAI (Femoro-acetabular Impingement)

Definition

  • [Delee] process by which a misshapen hip joint secondarily leads to breakdown of the intraarticular structures causing pain and associated dysfunction, followed by the premature development of osteoarthritis
  • [Campbell] abnormal contact between proximal femur and  acetabulum during terminal motion. This abnormal contact leads to damage of the acetabular labrum and articular cartilage and may lead to what was previously thought of as idiopathic osteoarthritis of the hip

Three types of FAI have been identified:

pincer type — excessive prominence of  anterolateral rim of the acetabulum = abnormal acetabular coverage

Full size image for 'Femoroacetabular Impingement in Athletes'

A, Bony overcoverage of the anterior labrum sets the stage for pincer impingement. B, With hip flexion, the anterior labrum gets crushed by the pincer lesion against the neck of the femur. Secondary articular failure occurs over time. In normal circumstances, clearance is adequate for the labrum during hip flexion.

cam type — cam effect caused by a nonspherical femoral head rotating inside the acetabulum

Full size image for 'Femoroacetabular Impingement in Athletes'

A, The cam lesion is characterized by the bony prominence centered on the anterolateral femoral head-neck junction. B, Cam impingement occurs with hip flexion as the nonspherical portion of the femoral head (cam lesion) glides under the labrum, engaging the edge of the articular cartilage and resulting in progressive delamination. Initially the labrum is relatively preserved, but secondary failure occurs over time.

 

combined impingement

 

Clinical presentation

  • Sharp or Ache: Groin > Lateral hip > Anterior thigh > Buttock > Knee
  • Insidious onset
  • Mechanical symptom: Catching
  • Activity related:
    • Prolonged sitting
    • Sexual intercourse (คนไข้มักไม่บอก)
  • Miss บ่อย

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