Posterior acetabular fracture-dislocations: fragment size, joint capsule, and stability.

In acetabular fractures, the size of a significant posterior wall fragment remains undefined as it affects joint stability. The purpose of this study was to quantitatively evaluate fragment size and hip stability in cadaveric specimens after serial osteotomies. Also, the role of the posterior capsule, in the various osteotomies, was evaluated for changes in hip stability. We found that fragments involving 25% or less of the acetabulum are insignificant, i.e., do not affect joint stability, while fragments involving 50% or more are significant. The significance of transitional fragments (25-50% of the acetabulum) is determined by the posterior capsule.