Femoral head-neck junction deformity is related to osteoarthritis of the hip

Abstract

Background: Primary or idiopathic osteoarthritis (OA) of the hip has increasingly been attributed to the presence of presumably minor femoral or acetabular deformities that are not routinely identified. The alpha angle reflects one such deformity of the femoral neck and reflects a risk for femoroacetabular impingement, which in turn reportedly is associated with OA. If impingement is in fact associated with OA, then one might expect the mean alpha angle to be greater in patients with presumed idiopathic hip OA.

Questions/purposes: We therefore compared the alpha angle among a group of elderly patients with idiopathic OA with that in a control group of elderly individuals without OA.

Patients and methods: We measured the alpha angles in 50 individuals (72 hips) with a mean age of 70 years (range, 60-84 years) with apparently idiopathic OA and compared their angles with those from a control group of 56 individuals without OA. The alpha angle was measured by means of radiographs of their hips using the Dunn view at 45 degrees flexion.

Results: The patients with OA had a greater percentage with abnormal alpha angles than did the normal subjects: 82% versus 30%, respectively. The mean alpha angle in the group with OA was larger than in the control subjects: 66.4 masculine (range, 28 degrees -108 degrees ) versus 48.1 masculine (range, 34 degrees -68 degrees ).

Conclusions: Hips with presumably idiopathic OA had more abnormalities at the femoral head-neck junction than did the control hips without OA and may relate to the risk of OA developing.

Level of evidence: Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Fig. 1A–B

Dunn radiographic views at 45° flexion produced by positioning the patient in dorsal decubitus with (A) 45° flexion of the hip that is to be evaluated, and with (B) neutral rotation and 20° abduction are shown; the center beam is regulated at 90° centered on the hip. The source-to-film distance should be 1 m.

Fig. 2A–B

The alpha angle was defined as the acute angle between the neck axis and the line connecting the center of the femoral head with the point where the cortical surface of the head-neck junction first exited a perfect circle drawn around an ideally spherical femoral head. (A) A right hip with severe osteoarthritis (OA), with an increased alpha angle, and (B) a right hip without OA, with a normal alpha angle are shown.