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

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