Comparison of Joint Space Measurements between Supine and Weightbearing Anteroposterior Pelvis Radiographs for Patients Undergoing Hip Arthroscopy

OBJECTIVES: Osteoarthritis and joint space narrowing of the hip have been correlated with poor outcomes and conversion to arthroplasty after hip arthroscopy. However, a standardized protocol for radiographic measurement of minimal joint space width of the hip has not been developed. We hypothesized that minimal joint space width would be significantly lower on the affected side in weightbearing anteroposterior pelvis radiographs versus supine radiographs. We also hypothesized that radiographs with single-leg stance would show the lowest minimal joint space width. METHODS: Thirty-one consecutive adult patients with hip pain were prospectively enrolled and each had single-leg and double-leg weightbearing and supine anteroposterior pelvis radiographs in a standardized position. Two independent investigators determined minimal joint space width. Differences between minimal JSW as well as intra- and interobserver reliability were calculated. One and 2-way analyses of variance (ANOVA) were used to compare the measurements. Power analysis determined that recruitment of 30 patients was necessary to achieve 90% power. P<0.05 was considered significant. RESULTS: No significant differences in joint space width were found between supine or weightbearing radiographs for any pelvis site (Figure 1). Comparing those under 50 years of age to those older than 50 years of age, mean joint space width was 3.5±0.5 vs. 3.0±0.9 in the supine position, 3.2±0.8 vs. 3.0±1.0 during double-leg stance, and 3.5±0.5 vs. 3.0±1.1 during single-leg stance (P=0.002). CONCLUSION: Our data showed no significant difference in joint space width among anteroposterior single-leg or double-leg weightbearing or supine radiographs at any location measured. These findings suggest that either weightbearing or supine radiographs can be used to evaluate hip joint space width and that all locations provide a similar indication of joint space width. These findings support the use of a single view for the evaluation of JSW in patients with hip pain, which may allow for a less burdensome clinical workflow.