To analyze the acetabular wall defects of cerebral palsied hips using 3 dimensional computed tomography (3D CT).

56 hips of 28 cerebral palsy patients with hip instability were included and contralateral hips of unilateral LCP patients were used as a control. We categorized the instabilities into dislocation and subluxation, and described the location of acetabular defects qualitatively. Anterosuperior, lateral, and posterosuperior acetabular indices were measured on the quantitative base by multi-planar reformation, and acetabular volume was calculated.

In qualitative study, posterior defect was the most predominant in subluxation group, whereas global defect was predominant in dislocation group. All three indices in both subluxation and dislocation group increased when compared with those of control (p<0.05). On the other hand, lateral index increased in dislocation group when compared with subluxation (p<0.05). The acetabular volume was largest in control group, while the volume of dislocation group was least, and that of subluxation was between the two (p<0.05).

Subluxated hips mainly represent posterior acetabular wall defects. As dislocation progresses, global wall defect was noticeable and acetabular volume decreased. Gross visual wall defects was not always consistent with true wall defect. So, quantitative measurement should be considered when determining the acetablular defects.