The relationship between hip joint space width, center edge angle and acetabular depth

Radiographic parameters used to define acetabular dysplasia may be related to anthropological characteristics independent of dysplasia. The goal of the present study was to investigate the relationship between the minimal joint space width (JSW) of the hip and the parameters that define acetabular dysplasia, in clinically normal subjects.

One hundred and eighteen patients who underwent supine abdominal radiography for non-rheumatological indications and had no hip pain or history of hip arthritis were evaluated. JSW was quantified manually using dial calipers, and center edge (CE) angle and acetabular depth were measured for each hip.

CE angle, but not acetabular depth, correlated (inversely) with the minimal hip JSW (r=-0.26 and -0.20, P=0.005 and 0.038, R (right) and L (left) hips, respectively). CE angle inversely correlated with the pelvic width (r=-0.27 and 0.27, P=0.003 and 0.004, R and L hips, respectively) and acetabular depth correlated with subject's height (r=0.27 and 0.42, P=0.008 and <0.001 R and L hips, respectively) and leg length (r=0.27 and 0.45, P=0.008 and <0.001, R and L hips, respectively). Also, pelvic width correlated significantly with the JSW (r=0.27 and 0.20, P=0.003 and 0.033, for R and L hips, respectively).

The radiographic parameters used to define acetabular dysplasia, CE angle and acetabular depth, are strongly associated with anthropological variables and CE angle is associated with minimal JSW of the hip. It is important to recognize that height and limb length variability may affect radiographic parameters of acetabular dysplasia, and thus may falsely suggest the presence of anatomic abnormalities in some patients.