Hip impingement (femoral acetabular impingement) is a disorder of the hip that is becoming more recognized as a cause of hip pain in the active adult. It is also thought to be a previously unrecognized cause of arthritis in the young adult.
Causes of Hip Impingement
Hip impingement is caused by lack of room or clearance between the neck of the femur at the top of the thigh bone, and the rim of the socket (acetabulum). This lack of room may originate on the femoral neck, acetabulum, or both. The head of the femur may not be sufficiently offset from the neck of the femur to allow room when the hip is flexed. This can be caused by childhood disorders or from wear over time stimulating new bone to be laid down on the front of the femoral neck. The acetabulum may be the cause of the impingement by covering too much of the femoral head in the front of the hip joint. There may also be multiple causes in the same hip.
This lack of clearance causes the neck and rim of the socket to jam together as the hip is flexed (as in sitting or running). This contact between the femoral neck and socket leads to damage of the contacting structures. This damage may be a tear of the cartilage around the socket (acetabular labrum) to more advanced cartilage damage and degenerative arthritis of the hip.
Symptoms of Hip Impingement
Typically the person with hip impingement complains of pain in the groin region during hip flexion activities such as running or jumping. There may also be symptoms after prolonged sitting. During most of these activities, the hip is placed in a flexed position, although pain may also occur with standing and walking when irritation of the hip is more generalized.