Deformities of proximal femur in spastic hip displacement: A reconstructed three-dimensional computed tomography model approach

Background/Purpose: Spastic hip displacement is a common musculoskeletal problem in cerebral palsy (CP), leading to further complications in daily life. Deformities of the proximal femur were regarded as a factor in hip displacement, and therefore, femoral osteotomy is often recommended. This study aims to identify the relationship between hip displacement and femoral deformities. Methods: We retrospectively collected preoperative radiography and three-dimensional computed tomography (3D-CT) images from 19 nonambulatory CP children with unilateral hip displacement (average age: 8.4 years; range: 4.4-13.6). The 3D image of femur was reconstructed for measuring the femur anteversion angle (FAA) and true femoral neck-shaft angle (NSA). The association among migration percentage (MP), acetabular index (AI), FAA, and NSA between nondisplaced and displaced hips was analyzed by paired t test and its correlations were identified. Results: The FAA and AI are significantly greater in displaced hips (42.7° vs. 36.3° and 32.8° vs. 22.7°, respectively, p<0.001). However, the NSA is similar between displaced and nondisplaced hips. The AI and FAA have significantly positive correlations with MP between nondisplaced hips and displaced hips (0.69 and 0.57, respectively). Conclusion: Using reconstructed 3D-CT images we can directly measure and prove these femoral deformities. We found that AI has a positive correlation with MP (0.69), which is consistent with the results of previous studies. The displaced side has greater femur anteversion (42.7° vs. 36.3°), and coxa valga is common in these nonambulatory patients, irrespective of whether or not these patients underwent hip displacement. In addition, the severity of AI and anteversion angle will be affected by the MP.