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The prevalence of cam-type femoroacetabular impingement deformity is higher in men as well as in individuals with decreased internal rotation. Defining what represents a normal head-neck contour is important for establishing treatment strategies in patients presenting with prearthritic hip pain.

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Femoroacetabular impingement (FAI) is a recently proposed mechanism causing abnormal contact stresses and potential joint damage around the hip. In the majority of cases, a bony deformity or spatial malorientation of the femoral head or head/neck junction, acetabulum, or both cause FAI. Supraphysiologic motion or high impact might cause FAI even with very mild bony alterations. FAI became of interest to the medical field when (1) evidence began to emerge suggesting that FAI may initiate osteoarthritis of the hip and when (2) adolescents and active adults with groin pain and imaging evidence of FAI were successfully treated addressing the causes of FAI. With an increased recognition and acceptance of FAI as a damage mechanism of the hip, defined standards of assessment and treatment need to be developed and established to provide high accuracy and precision in diagnosis. Early recognition of FAI followed by subsequent behavioral modification (profession, sports, etc) or even surgery may reduce the rate of OA due to FAI.

Level I, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Femoroacetabular impingement is a cause of hip pain in adults and is potentially a precursor of osteoarthritis. Our aim in this study was to determine the prevalence of bilateral deformity in patients with symptomatic cam-type femoroacetabular impingement as well as the presence of associated acetabular abnormalities and hip pain. We included all patients aged 55 years or less seen by the senior author for hip pain, with at least one anteroposterior and lateral pelvic radiograph available. All patients with dysplasia and/or arthritis were excluded. A total of 113 patients with a symptomatic cam-impingement deformity of at least one hip was evaluated. There were 82 men and 31 women with a mean age of 37.9 years (16 to 55).Bilateral cam-type deformity was present in 88 patients (77.8%) while only 23 of those (26.1%) had bilateral hip pain. Painful hips had a statistically significant higher mean alpha angle than asymptomatic hips (69.9° vs 63.1°, p < 0.001). Hips with an alpha angle of more than 60° had an odds ratio of being painful of 2.59 (95% confidence interval 1.32 to 5.08, p = 0.006) compared with those with an alpha angle of less than 60°. Of the 201 hips with a cam-impingement deformity 42% (84) also had a pincer deformity.Most patients with cam-type femoroacetabular impingement had bilateral deformities and there was an associated acetabular deformity in 84 of 201 patients (42%). This information is important in order to define the natural history of these deformities, and to determine treatment.Femoroacetabular impingement (FAI) has recently been described as a cause of pain in the hip in young adults and of osteoarthritis (OA) of the hip 1,2 with two modes of impingement being described, pincer and cam-type.

Insufficient femoral head-neck offset is common in femoroacetabular impingement (FAI) and reflected by the alpha angle, a validated measurement for quantifying this anatomic deformity in patients with FAI. We compared the alpha angle determined on magnetic resonance imaging (MRI) oblique axial plane images with the maximal alpha angle value obtained using radial images. The MRIs of 41 subjects with clinically suspected FAI were reviewed and alpha angle measurements were performed on both oblique axial plane images parallel to the long axis of the femoral neck and radial images obtained using the center of the femoral neck as the axis of rotation. The mean oblique axial plane and mean maximal radial alpha angle values were 53.4 degrees and 70.5 degrees, respectively. In 54% of subjects, the alpha angle was less than 55 degrees on the conventional oblique axial plane image but 55 degrees or greater on the radial plane images. Radial images yielded higher alpha angle values than oblique axial images. Patients with clinically suspected FAI may have a substantial contour abnormality that can be underestimated or missed if only oblique axial plane images are reviewed. Radial plane imaging should be considered in the MRI investigation of FAI.

Femoroacetabular impingement (FAI) causes abnormal contact at the anterosuperior aspect of the acetabulum in activities requiring a large hip range of motion (ROM). We addressed the following questions in this study: (1) Does FAI affect the motions of the hip and pelvis during a maximal depth squat? (2) Does FAI decrease maximal normalized squat depth? We measured the effect of cam FAI on the 3-D motion of the hip and pelvis during a maximal depth squat as compared with a healthy control group. Fifteen participants diagnosed with cam FAI and 11 matched control participants performed unloaded squats while 3-D motion analysis was collected. Patients with FAI had no differences in hip motion during squatting but had decreased sagittal pelvic range of motion compared to the control group (14.7 ± 8.4°versus 24.2 ± 6.8°, respectively). The FAI group also could not squat as low as the control group (41.5 ± 12.5% versus 32.3 ± 6.8% of leg length, respectively), indicating the maximal depth squat may be useful as a diagnostic exercise. Limited sagittal pelvic ROM in FAI patients may contribute to their decreased squatting depth, and could represent a factor amongst others in the pathomechanics of FAI. Level of Evidence: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.