Acetabular deficiency in spastic hip subluxation

Background: The direction of spastic hip subluxation is generally agreed to be posterolateral; however, the location of acetabular deficiency is still controversial. This study aims to define the degree and location of acetabular deficiency that is crucial in choosing acetabuloplasty method. Methods: Twenty-five children with spastic cerebral palsy, average aged 7.1 years (range, 4.4 to 9.6 y), underwent 3-dimensional computed tomography (CT) studies of the pelvis. Mean Reimers migration percentage of the 50 hips was 32.6% (range, 16% to 66%). Twenty-eight hips were nonsubluxated and the other 22 hips were subluxated (migration percentage >30%). The 3-dimensional image of pelvis was realigned and a series of 9 section planes were formed to represent the whole iliac root. The CT acetabular indexes were measured and compared to define the deficiency. The data of 5 children without hip problem was retrieved as control. Results: Spastic nonsubluxated hips had similar CT acetabular indexes to normal hips. The differences between spastic subluxated hips and normal hips, from anterosuperior to posterosuperior aspects of acetabulum, were 14.8 degrees (A60 degrees), 11.2 degrees (A45 degrees), 10.8 degrees (A30 degrees), 9.9 degrees (A15 degrees), 9.7 degrees (0 degree), 9.5 degrees (P15 degrees), 9.8 degrees (P30 degrees), 9.8 degrees (P45 degrees), and 5.3 degrees (P60 degrees). The differences were significant in all directions and greater in the anterior aspect of the acetabulum. Conclusions: The definition of pathology is defined by the deviation from normal physiological status. Acetabular dysplasia in spastic hip subluxation is global and more apparent in the anterior aspect. Level of evidence: Diagnostic II.