Left-right difference in acetabular articular cartilage surface area and the quantification of acetabular fractures.

X-ray computer tomography scans were carried out on 11 female and 9 male dry bony pelvises. A 512 x 512 image matrix was used with a slice thickness and separation of 2 mm. Images were transferred onto a computer and the articular cartilage marked on each relevant image. The points were connected to form a triangle mesh and the total articular cartilage area calculated by summing the area of each triangle. There was a highly significant difference (p < 0.001) between the male and female acetabular areas, 25.4 ± 2.7 cm² and 19.5 ± 2.0 cm², respectively. The mean left-right difference was 0.2 ± 0.9 cm² for males and-0.2 ± 0.47 cm² for females. When the sign of the differences are removed, the mean and standard deviations of the differences is 0.5 ± 0.46 cm² (2.3% ± 1.8%) for males and females, 0.66 ± 0.61 cm² for males and 0.4 ± 0.27 cm² for females. Each articular surface was outlined twice in order to assess the repeatability of the technique. The left-right variation in articular surface area was found to be similar to the variation in repeatability, suggesting that if any left-right difference does exist it is too small to be reliably detected by this technique. This enables the area of articular cartilage of the fragments of a fractured acetabulum to be compared directly with surface area of the contralateral intact acetabulum. Acetabular fractures can therefore be quantified by measurement of the articular surface area of the fracture components. Comparison with the clinical results will enable surface area to be developed as a prognostic factor in the management of acetabular fractures.