Femoroacetabular Impingement Syndrome (FAI) (Hip Impingement)

Altered morphology of femoral neck and/or acetabular causes abutment of the femoral neck on the edge of the acetabulum during movement (usually flexion, adduction, and internatal rotation)

Aetiology

  • Occurs because the hip bones do not form normally during the childhood growing years

Pathophysiology

Types of FAI

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CAM type impingement
  • The femoral head is not round and cannot rotate smoothly inside the acetabulum
  • A bump forms on the edge of the femoral head that grinds the cartilage inside the acetabulum
  • Usually young athletic males
  • Can be related to previous SUFE
Pincer type impingement
  • Occurs because extra bone extends out over the normal rim of the acetabulum
  • The labrum can be crushed under the prominent rim of the acetabulum
  • Usually seen in females
Mixed impingement
  • Combination of CAM and pincer type

Consequences

  • Damage to the labrum and tears
  • Damage to cartilage
  • OA in later life

Clinical presentation

Symptoms

  • Activity related pain in the groin, particularly in flexion and rotation
  • Difficulty sitting

Signs

  • C sign positive
  • FADIR provocation test positive

Investigations

  • X-ray
  • CT
  • MRI - better for visulising damage to labrum and bony oedema

Management

  • Observation in asymptomatic patients
  • Try conservative measures before surgery
  • Arthroscopic/open surgery to remove CAM/debride laral tears
  • Peri-acetabular osteotomy/debride labral tears in pincer impingement
  • Arthroplasty/total hip replacement in older patients with secondary OA