In cases of severe postdysplastic coxarthosis, it seems to be impossible to recognize acetabular geometry and the real femoral position on a plain X-ray because the real diameters and angles can be disfigured when projected. Computed tomography (CT) provides important information to the surgeon about the concavity, shape and stereotomy of the acetabulum.

It is quite difficult to correctly evaluate severely changed hips. CT displays more precise acetabular diameters and angles than a plain radiograph. Because of the high density of bony tissue, the CT makes it easy to produce a three-dimensional display of the hip.

From September 1995 to December 1998, 224 patients (148 female, 76 male) underwent arthroplasty using a non-cemented prosthesis according to Zweymüller. A total of 236 hip joints were operated and classified as Crowe Group I (76 hips), Crowe Group II (149 hips), and Crowe Group III (11 hips). There were no Crowe Group IV hips.

A total of 96 patients were examined by 3D CT in preoperative planning. Based on CT results, four joints were not recommended for an operative solution.

CT protocol: scanner Elscint TWIN II, slice 2.5 mm, 120 kV, 285 mAs, matrix 3402,

No. of slices: 40–50, incremental dual acquisition. Postprocessing: axial images, multiplanar reconstructions, 3D SSD.

Acetabular stereometry: superoinferior diameter, anteroposterior diam., depth, bottom thickness, femoral neck anteversion angle and subtrochanteric marrow diameter.

A three-dimensional CT of the hip is a very effective tool for preoperative assessment.