Femoroacetabular Impingement (FAI), or hip impingement syndrome, may affect the hip joint in young and middle-aged adults and occurs when the ball shaped femoral head rubs abnormally or does not permit a normal range of motion in the acetabular socket. Damage can occur to the articular cartilage, or labral cartilage (soft tissue bumper of the socket), or both. Treatment options range from conservative to arthroscopic to open surgery.
FAI has been speculated as a cause of premature hip osteoarthritis and is characterized by abnormal contact between the proximal femur and rim of the acetabulum (hip socket). In most cases, patients present with a deformity in the femoral head, or acetabulum, a poorly positioned femoral-acetabular junction, or any or all of the foregoing. A combination of certain factors may predispose to some form of FAI, predominantly, a marginal developmental hip abnormality together with environmental factors such as activities involving recurrent motion of the legs within a supraphysiologic range.
Three types of FAI are recognized. The first involves an excess of bone along the upper surface of the femoral head, known as a Cam deformity (abbreviation for camshaft which the shape of the femoral head and neck resembles). The second is due to an excess of growth of the upper lip of the acetabular cup and is known as a 'Pincer' deformity. Colloquially, these are referred to as 'Cam' and 'Pincer'. The third is a combination of the two, generally referred to as 'Mixed'. Studies have suggested that 'Cam' deformities are more common in the male, while 'Pincer' deformities are more common in females. However, the most common situation, approximately 70%, is a combination of both. A complicating issue is that some of the radiographic findings of FAI have also been described in asymptomatic subjects. Consequently, the true frequency of femoroacetabular impingement is currently under debate, but the ultimate result is increased friction between the acetabular cup and femoral head which may result in pain and loss or reduction of hip function.
FAI-related pain is often felt in the groin, but may also be experienced in the lower back or around the hip. The diagnosis, often with a co-existing labral tear, typically involves physical examination in which the range of motion of the hip is tested. Limited flexibility leads to further examination with x-ray, providing a two-dimensional view of the hip joints. Additional specialized views, such as the Dunn view, may make x-ray more sensitive. Subsequent imaging techniques such as CT or MRI may follow producing a three-dimensional reconstruction of the joint to evaluate the hip cartilage, demonstrate signs of osteoarthritis, or measure hip socket angles (e.g. the alpha-angle as described by Nötzli in 2-D and by Siebenrock in 3-D). It is also possible to perform dynamic simulation of hip motion with CT or MRI  assisting to establish whether, where, and to what extent, impingement is occurring.
The treatment of FAI varies. Conservative treatment includes reducing levels of physical activity, anti-inflammatory medication and physiotherapy. Physical therapy may optimize alignment and mobility of the joint, thereby decreasing excessive forces on irritable or weakened tissues. It may also identify specific movement patterns that may be causing injury.
Due to the frequency of diagnosis in adolescents and young adults, various surgical techniques have been developed with the goal of preserving the hip joint. Surgery may be arthroscopic or open, peri-acetabular or rotational osteotomies being two common open surgical techniques employed when an abnormal angle between femur and acetabulum has been demonstrated. These primarily aim to alter the angle of the hip socket in such a way that contact between the acetabulum and femoral head are greatly reduced, allowing a greater range of movement. Femoral sculpting may be performed simultaneously, if required for a better overall shape of the hip joint. It is unclear whether or not these interventions effectively delay or prevent the onset of arthritis. Well designed, long term studies evaluating the efficacy of these treatments have not been done.
A 2011 study analyzing current surgical methods for management of symptomatic femoral acetabular impingement (FAI), suggested that arthroscopic method had surgical outcomes equal to or better than other methods with a lower rate of major complications when performed by experienced surgeons.
Notable persons who suffered hip impingements:
- Charlie Morton, American baseball pitcher
- Devin Mesoraco, Cincinnati Reds catcher
- Isaiah Thomas, American basketball guard
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- http://www.clinicalgraphics.com Dynamic motion simulation for hip impingement.
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- Femoroacetabular Impingement (FAI) on OrthoInfo
- Hip Impingement Awareness website written by ex FAI patient, Louisa Weeks Browning
- Hip Preservation Awareness, information and support for hip impingement, hip dysplasia, and related issues in young adults (12-adult)
- IMPAKT-HiP (Investigations of Mobility, Physical Activity, and Knowledge in Hip Pain) Study by the Arthritis Research Centre of Canada