The third is a combination of the two, generally referred to as mixed. The most common type seen, approximately 70% of the time, is the mixed type. A complicating issue is that some of the radiographic findings of FAI have also been described in asymptomatic subjects.Current literature suggests that the cam type of impingement is associated with the development of hip osteoarthritis. Thus far, no correlation has been seen between the pincer type and development of hip osteoarthritis. Anatomy
The hip joint is classified as a ball and socket joint. This type of synovial joint allows for multidirectional movement and rotation. There are two bones that make up the hip joint and create an articulation between the femur and pelvis. This articulation connects the axial skeleton with the lower extremity. The pelvic bone, also known as the innominate bone, is formed by three bones fused together: the ilium, ischium, and pubis. The musculature of the hip is divided into anterior hip muscles and posterior hip muscles. The major nerve supply that runs through the hip joint is the femoral nerve and the sciatic nerve. Diagnosis
Clinical evaluation is the first step in diagnosis, but will rarely lead to the diagnosis on its own, due to inconsistent and vague nature of the pain. Childhood and current activity should be inquired about. Physical exam should also involve assessing passive internal rotation of the hip during flexion, as range of motion is reduced in proportion to the size of a cam lesion.
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. The cause of FAI is currently unknown, but both congenital and acquired etiologies have been put forth. Studies have shown an increased incidence in siblings, suggesting a genetic component. At least one study has also shown a predilection in the white population. It has also been reported to be more common in males. However, there is no concrete evidence to suggest a genetic trait and instead, the most favored theory currently supports that FAI (the cam type in particular) is due to repetitive movements involving the hip (e.g. squatting) in young athletes. Aggravating activities that are commonly reported include repetitive or prolonged squatting, twisting movements of the hip, like pivoting during athletics, getting in and out of cars, and even sitting for prolonged periods. A combination of these factors may also predispose to a form of FAI; predominantly, a marginal developmental hip abnormality together with environmental factors such as recurrent motion of the legs within a supraphysiologic range.Three types of FAI are recognized (see title image). 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.