Stability of posterior fracture-dislocations of the hip. Quantitative assessment using computed tomography.

The treatment of a posterior fracture-dislocation of the hip is strongly influenced by the surgeon's assessment of stability of the hip after the dislocation has been reduced. Stability is inversely related to the size of the posterior acetabular fragment. Computed tomography was used to measure the size of the fracture fragment in nine cadavera of adults. Progressive increments of bone were removed from the posterior part of the acetabular wall in sixteen hips. After each osteotomy, the hip was tested for stability and was measured by computed tomography until it became unstable. All hips from which less than 20 per cent of the posterior part of the acetabular wall was removed were stable, while those from which more than 40 per cent was removed were unstable.