In 2003, Ganz et al. introduced the concept of femoroacetabular impingement syndrome (FAI). Hip impingement syndrome is a group of hip syndromes caused by dysplasia, childhood femoral head necrosis, femoral head slippage, acetabular impingement, trauma, surgical overcorrection and other causes, mainly presenting as intermittent or persistent pain in the groin area in adolescent and middle-aged patients, induced or aggravated during hip flexion movements such as squatting, bending, leg lifting and climbing, accompanied by some degree of hip mobility restriction. Some patients show weakness, playing softness and pseudo-interlocking of the hip. After playing soccer and other sports, prolonged walking, sitting on a low stool for a long time and driving for a long time may be the triggering factors. The main clinical signs are limited internal rotation of the hip joint, pain can be induced by flexion and internal rotation of the hip (positive anterior medial hip impingement sign), and pain can be induced by extension and external rotation of the hip in individual patients (positive posterior lateral hip impingement test). The disorder can lead to glenoid labral injury and cartilage damage in the corresponding part of the hip joint, and osteoarthritis can develop in the late stage. There are three categories based on clinicopathology: pincer (Pincer), cam (Cam), and mixed. Hip impingement caused by excessive acetabular coverage is called pincer impingement. Its main factors are overcoverage, such as posterior acetabular tilt, internal acetabular impingement, and internal acetabular protrusion. Acetabular hypoplasia, slipped femoral epiphysis, trauma, and surgical overcorrection can cause retroversion of the acetabulum, which can be seen as a “crossed sign” in the anterior-posterior border of the acetabulum on standard pelvic orthopantomographs. Hip impingement caused by lateral femoral neck augmentation is known as cam-type impingement. The main factor is the lack of eccentric distance at the femoral head-neck junction, such as an unrounded femoral head and hyperplasia of the head-neck junction area. The hyperplasia of the cephalocervical junction area caused by femoral head necrosis, slipped femoral epiphysis and flattened hip in children makes the cephalocervical junction impingement with the outer upper edge of acetabulum when the hip is flexed and internally rotated at the same time, and the bone fullness, protrusion and cystic changes of the outer edge of the cephalocervical junction area can be seen in the conventional frontal and lateral x-ray of the hip joint. On oblique films of direct MRI angiography of the hip through the femoral neck, an increased Alpha angle is demonstrated. The coexistence of the pincer and cam type is called mixed hip impingement. Treatment is divided into conservative treatment and surgical treatment. Surgical treatment can be further divided into arthroscopic surgery and incisional surgery. The main goal is to remove the bony prominence of the acetabular rim and the craniocervical junction, repair the glenoid lip and cartilage, remove the cause of impingement, and relieve symptoms. Patients with advanced osteoarthritis need to undergo artificial hip replacement surgery. Currently, this disorder is not uncommon in China and is more frequently reported in Europe and the United States.
In young patients, the disease needs to be differentiated from acetabular labral injury, acetabular dysplasia, hip synovitis, hip muscle ligament injury, ankylosing spondylitis, and femoral head necrosis; in middle-aged and elderly patients, it needs to be differentiated from other hip osteoarthritis, femoral head necrosis, rheumatoid hip osteoarthritis, and so on. MRI of the hip joint is of great value in the diagnosis and treatment of this disorder.