(Left) Pincer impingement. (Center) Cam impingement. (Right) Combined impingement.
Three types of Femoroacetabular Impingement (FAI) are recognised. The first involves an excess of bone along the upper surface of the femoral head, known as a Cam deformity. The second is due to an excess of growth of the upper lip of the acetabular cup and is known as a 'Pincer' deformity. The third is a combination of the two. 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 FAI 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 specialised 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. 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 optimise 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.
Schreiber, Mary L. Evidence-Based Practice. Neurovascular Assessment: An Essential Nursing Focus. MEDSURG Nursing (MEDSURG NURS), Jan/Feb2016; 25(1): 55-57.
The American Academy of Orthopaedic Surgeons (2016) “preeminent provider of musculoskeletal education to orthopaedic surgeons and others” Available online at: <https://orthoinfo.aaos.org/en/diseases--conditions/femoroacetabular-impingement> Accessed on 14 November 2016.