Acetabular alterations in untreated congenital dysplasia of the hip: computed tomography with multiplanar re-formation and three-dimensional analysis.

The alterations in acetabular morphology that occur in untreated congenital hip dysplasia (CDH) were evaluated in 29 prehistoric and four modern hemipelvis specimens using inspection, sectioning, conventional radiography, CT, and multiplanar re-formation with three-dimensional image reconstruction. Three major patterns of acetabular morphology were recognized, each reflecting a different grade of severity of dysplasia. Type I (positionally unstable or subluxatable) hips were characterized by acetabular deepening with prominent circumferential ossification within the transverse acetabular ligament and everted limbus. Type III (dislocated) hips demonstrated definite false acetabula separated from triangular remnants of the true acetabula by ossified inverted limbi. Type II (subluxated) hips revealed an intermediate pattern, with acetabular elongation and ossification of deformed limbi, but without definite pseudoacetabula. Computed tomography, particularly with three-dimensional analysis, was extremely useful in characterizing the abnormal acetabular morphology of untreated CDH. An awareness of the secondary osseous alterations of this disorder facilitates understanding the spectrum of hip instability and its soft tissue abnormalities.