Abstract
Three-dimensional computed tomography (CT) is the method of choice in understanding the morphological changes after periacetabular osteotomy in children. We studied different parameters and compared aspects of operated hip (OH) with non-operated hip (NOH) to define the maneuver that promotes normalization of the hip during repositioning of the acetabulum. A total of 22 patients with 25 OHs underwent CT control scans an average of 4 years after surgery. The patients, with a mean age of 6.8 years, had either Legg-Calvé-Perthes disease (12 cases) or dysplasia (10 cases).The measurements included the anterior and posterior coverage angles of the hip and version of the acetabulum on axial CT views. The 3D reconstructed images measured the inclination of the antero- and postero-lateral lips, the external rotation and the anterior inclination of the acetabulum. The mean anterior coverage angle was 27 degrees for OHs, 31 degrees for NOHs, and 12 degrees versus 10.3 degrees for the posterior coverage angle. Acetabular anteversion was 2 degrees for OHs (6.3 degrees in the dysplastic OHs) and 6 degrees for NOHs. The mean angle of inclination of the antero-lateral lip was 37 degrees for OHs, 47 degrees for NOHs, and the postero-lateral lip inclination was 56 degrees for OHs and 67 degrees for NOHs. Inferior 3D views showed a mean internal acetabular rotation of 1.5 degrees (4.8 degrees in the dysplastic OH), 3 degrees for NOH. The anterior acetabular inclination angle measured with lateral 3D views was 6 degrees for OHs, 11 degrees for NOHs. Our analysis demonstrated a mean anteversion of the acetabulum despite normalization of the anterior coverage of the hip, particularly in the dysplastic group, in which the osteotomized fragments had anteversion superior to NOH. The unexpected external rotation used to improve anterior coverage of a coax magna in Legg-Calvé-Perthes disease was responsible for the retroversion and the decrease of the posterior coverage.
Highlights
Many different pelvic osteotomies have been used to improve femoral head coverage; all focused on the restoration of a more normal hip morphology
If the goal of the pelvic osteotomy is to normalize the anatomy of the hip, it is more interesting to compare the aspect of the operated hip (OH) with that of the nonoperated hip (NOH)
Particular attention has been devoted to the results of dysplastic hips, in a series including Legg-Perthes disease, in order to determine whether greater correction of anterior or lateral deficiencies promotes deficiencies in other parameters, at the version of the acetabulum
Summary
Many different pelvic osteotomies have been used to improve femoral head coverage; all focused on the restoration of a more normal hip morphology. J Child Orthop (2007) 1:357–363 provides a powerful means of precisely measuring and assessing critical factors; of better understanding the concept of coverage in 3D; and of avoiding over or insufficient mobilization of the acetabular fragment, or a maneuver promoting morphological disorders [1,2,3,4]. The postoperative assessment of 3D changes evaluates the appropriate maneuver for displacement of the osteotomized fragment to avoid unintended positions of the acetabulum, such as excessive external rotation and retroversion of the acetabulum or insufficient posterior coverage of the hip. Particular attention has been devoted to the results of dysplastic hips, in a series including Legg-Perthes disease, in order to determine whether greater correction of anterior or lateral deficiencies promotes deficiencies in other parameters, at the version of the acetabulum
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