The normal hip joint space: variations in width, shape, and architecture on 223 pelvic radiographs

Abstract

Objectives: To determine the range of normal radiographic joint space width (JSW) values and the shape of the normal hip, and the influence of age, sex, dysplasia, coxa profunda, and acetabular roof curve abnormalities on these values.

Methods: On routine conventional pelvic radiographs taken in the supine position in patients with no history of hip or lumbar pain, JSW was measured at three points (superolateral, apical, superomedial), together with the VCE, HTE, and neck shaft angles; acetabular depth; and femoral head diameter.

Results: 223 radiographs (446 hips) from 127 women and 96 men (mean age 51.3 years) were examined. Interindividual variations in JSW were large (apical site: 4.19 (0.92) mm; range 2-7). Mean JSW values were higher at the superolateral site than at the apical and superomedial sites in nearly 80% of cases. Women had lower JSW values than men. JSW values did not fall with age. Marked right/left JSW asymmetry was seen in 13/221 (5.9%) subjects. Eight cases of acetabular dysplasia (7 unilateral) and 16 cases of coxa profunda were found, but no cases of acetabular protrusion. The JSW was thicker in dysplastic hips, and thinner in hips with coxa profunda. A roof curve abnormality was found in 96/446 (21.5%) hips.

Conclusions: Normal JSW values vary widely; the JSW is commonly narrower at the superomedial site than at the apical site, and is sometimes asymmetric. The roof curve is dysmorphic in about 20% of patients. These findings may have important implications for epidemiological studies and early diagnosis of osteoarthritis of the hip.

Figure 1

Normal hip joint space. Location of the three sites of JSW measurement. From right to left: the superolateral, the apical, and the superomedial sites (point of arrow).

Figure 2

(A) The VCE, HTE, and NSA (indicated as CC¹D, 140°) angles; (B) acetabular depth: segment "ad" stretches from the deepest point of the acetabulum and the line EP, drawn from the lateral extremity of the acetabular roof to the superior pubic angle.

Figure 3

Sketch of the three main types of acetabular roof dysmorphia: (A) excessively arched roof; (B) excessively flat roof; (C) roof with a prominent segment (angular roof).

Figure 5

Acetabular roof dysmorphias. The three main types: (A) excessively arched roof: the radius of the curve is smaller than that of the femoral head; (B) excessively flat roof: the radius of the curve is larger than that of the femoral head; (C) angular roof; note the prominent segment in the superolateral part.

Figure 4

Cybernetics of the growing cartilage regulating (negative) feedback. The system input is the pressure (in the standing position) exerted on cellular receptors (chondrocytes of the deep layer). These cells build the matrix, which is the outcome. The thicker the matrix (acting as a "cushion"), the lower the pressure exerted on deep chondrocytes. At a certain point, matrix secretion stops through a lack of stimulation. Thus, the higher the pressure (/cm² in hip dysplasia), the thicker the matrix.