Acetabular shape and orientation of the spastic hip in children with cerebral palsy

Aim To see if three-dimensional (3D) methods could bring new understanding to acetabular changes in shape and orientation in the spastic hip and in which direction(s) acetabular orientation might change, which is crucial for planning appropriate hip correction surgery. Method We performed a retrospective study of pelvic computed tomography (CT) examinations in 20 consecutive patients (10 females, 10 males). The mean age of patients was 12 years 9 months (SD 2y; range: 9-16y) at the time of the CT examination. The control group consisted of 18 consecutive pelvic CT examinations (36 acetabula) of deceased individuals (six females, 12 males) aged 4 to 17 years (mean age: 10y 6mo; SD 5y 2mo) whose whole-body CT scans were taken shortly after their death. We compared 3D CT reconstructions of 28 unstable and dislocated hips in children with bilateral cerebral palsy (Gross Motor Function Classification System levels IV and V) with the unaffected side and typically developing controls to assess spatial orientation (inclination, anteversion, and tilt), acetabular volume, and surface area. Additionally, we analysed the multiple factors that may lead to structural and spatial changes of the acetabulum. Results Patients with dislocated and spastic hips had significantly lower anteversion (-3.2 degrees and -1.4 degrees respectively, p<0.001), increased inclination (85.2 degrees and 85.3 degrees respectively, p<0.001), and decreased tilt (24.6 degrees [p=0.014] and 20.7 degrees [p=0.013] respectively) compared with typically developing individuals. Regarding acetabular volume and surface area, dislocated and unstable hips had significantly lower volume (17.6ml vs 31.5ml respectively, p<0.001) and surface area (28.9cm(2) vs 36.2cm(2) respectively, p<0.001) than unaffected hips. Among several factors, only Reimer's migration index had an influence on acetabular orientation (i.e. anteversion, p=0.01), volume (p<0.001), and surface (p=0.004). Interpretation Acetabula in patients with spastic hip disease were severely retroverted with increased steepness; acetabular orientation was distorted superoposteriorly. In rare cases, acetabular orientation was distorted only superiorly or superoanteriorly.

Automated summary

In this study, 3D CT reconstructions were used to analyze acetabular changes in patients with spastic hip disease. The results showed that these patients had significantly altered acetabular orientation, volume, and surface area compared to typically developing individuals. Factors like Reimer's migration index were found to have an influence on acetabular orientation, volume, and surface area. These findings suggest the importance of considering these changes in planning hip correction surgery.