A quantitative analysis of hip capsular thickness

Purpose The purpose of this study was to provide a comprehensive quantitative analysis of capsular thickness adjacent to the acetabular rim in clinically relevant locations. Methods Dissections were performed and hip capsular measurements were recorded on 13 non-paired, fresh-frozen cadaveric hemi-pelvises using a coordinate measuring device. Measurements were taken for each clock-face position at 0, 5, 10 and 15 mm distances from the labral edge. Results The capsule was consistently thickest at 2 o’clock for each interval from the labrum with a maximum thickness of 8.3 at 10 mm [95 % CI 6.8, 9.8] and 15 mm [95 % CI 6.8, 9.7]. The capsule was noticeably thinner between 4 and 11 o’clock with a minimum thickness of 4.1 mm [95 % CI 3.3, 4.9] at 10 o’clock at the labral edge. Direct comparison between 0 and 5 mm between 9 and 3 o’clock showed that the hip capsule was significantly thicker at 5 mm from the labrum at 9 o’clock ( p = 0.027), 10 o’clock ( p = 0.032), 1 o’clock ( p = 0.003), 2 o’clock ( p = 0.001) and 3 o’clock ( p = 0.001). Conclusions The hip capsule was thickest between the 1 and 2 o’clock positions for all measured distances from the acetabular labrum and reached its maximum thickness at 2 o’clock, which corresponds to the location of the iliofemoral ligament.