In the normal hip there is smooth gliding motion of the round femoral head within the acetabulum socket. FAI is a condition where the gliding motion is disturbed. Impingement occurs if there is a block or restriction to the normal hip motion.

This can occur if the head of the femur is not entirely round, in which case there is a jamming (cam impingement) when the abnormal part of the head is squeezed into the socket as the hip is bent.

A second type of impingement (pincer impingement) occurs if the front edge of the acetabulum (socket) is too prominent. This allows the femur to bump into the rim of the acetabulum during normal hip movement.

• Cam impingement is caused by a squeezing or jamming of an abnormally shaped femoral head and head-neck junction into the acetabulum (socket) during certain types of motion, such as tying one's shoe, or riding a bike.
• Pincer impingement occurs when there is direct contact between the femoral head-neck junction and a section of the acetabular rim

Impingement of the hip can also be caused by conditions such as Legg-Calve-Perthes disease, slipped capital femoral epiphysis, misshapen femoral head, abnormally tilted head with bump on the femoral neck, or post traumatic deformities, such as Coxa Vara.

Your physician may diagnose femoro acetabular impingement after a complete medical history, physical examination and imaging studies. Imaging studies may include one or more of the following diagnostic procedures.

• x-ray - a diagnostic test which uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film.
• magnetic resonance imaging (MRI) - a diagnostic procedure that uses a combination of large magnets, radiofrequencies, and a computer to produce detailed images of organs and structures within the body.
• CT scan - A computerized compilation of many small x-rays taken at slightly different angles. A CT scan allows useful imaging of the interior bones and joints.