O2114: Comprehensive Three-dimensional Proximal Femoral Morphology in Cerebral Palsy

Background: Neuromuscular hip dysplasia affects nearly one-third of all children with cerebral palsy (CP), the most common cause of motor disability in childhood. While radiographs are the current gold standard for hip surveillance in CP, three-dimensional computed tomography (3D-CT) may better represent the nuanced changes of the proximal femur in CP. The aim of this study is to comprehensively characterize the 3D morphology of the proximal femur in children with CP using 3D-CT.

Methods: Over a 12-year period at a single tertiary care institution, a consecutive sample of 285 children with CP were retrospectively identified across all GMFCS levels (age range: 3-22 years, age average: 9.3±3.5 years, 43% females; GMFCS I: n=12, GMFCS II: n=48, GMFCS III: n=55, GMFCS IV: n=92, GMFCS V: n=78). Patients with other neuromuscular conditions or prior hip surgery were excluded.

Using a validated automatic segmentation and anatomy measurement program (VirtualHip), 3D femur models from CT scans were developed to measure femoral version, neck-shaft angle (NSA), head-shaft angle (HSA), migration percentage (MP), neck diameter, and neck length on both hips of each patient. Analysis of variance (ANOVA) with Dunnet posthoc were used to compare all values between GMFCS levels.

Results: Femoral version was significantly higher in GMFCS levels III, IV, and V compared to GMFCS level I, indicating increased anteversion at greater GMFCS levels (all P< 0.05; Figure 1). Both NSA and HSA were also significantly higher at all GMFCS levels above GMFCS I, demonstrating coxa valga with increasing GMFCS levels (all P< 0.05; Figure 1). MP was significantly higher for GMFCS IV and V compared to GMFCS I (P < 0.001; Figure 1), denoting greater hip subluxation and dislocation with higher GMFCS levels. Finally, increasing GMFCS was significantly associated with decreased femoral neck length in GMFCS III, IV, and V (P < 0.05; Figure 1), with a trend toward decreased femoral neck diameter as well.

Conclusion: Abnormal morphology of the proximal femur contributes to hip subluxation, dislocation, and disability in children with CP. In our large cohort, we conclude that children with greater functional limitations (higher GMFCS levels) tend to have increased femoral anteversion, coxa valga, femoral head valgus, dislocation, and decreased neck length. There was also a trend toward smaller femoral neck diameter with greater GMFCS levels. This study validates previous population-based plain film investigations of the hip in CP but illustrates additional complex anatomic subtleties captured on 3D-CT. Clinicians are recommended to consider the added value of 3D-CT scans for hip surveillance and pre-operative evaluation.