Progression of Hip Displacement during Radiographic Surveillance in Patients with Cerebral Palsy

Abstract

Progression of hip displacement is common in patients with cerebral palsy (CP). We aimed to investigate the rate of progression of hip displacement in patients with CP by assessing changes in radiographic indices according to Gross Motor Function Classification System (GMFCS) level during hip surveillance. We analyzed the medical records of patients with CP aged < 20 years who underwent at least 6 months interval of serial hip radiographs before any surgical hip intervention, including reconstructive surgery. After panel consensus and reliability testing, radiographic measurements of migration percentage (MP), neck-shaft angle (NSA), acetabular index (AI), and pelvic obliquity (PO) were obtained during hip surveillance. For each GMFCS level, annual changes in radiographic indices were analyzed and adjusted for affecting factors, such as sex, laterality, and type of CP. A total of 197 patients were included in this study, and 1,097 radiographs were evaluated. GMFCS classifications were as follows: 100 patients were level I-III, 48 were level IV, and 49 were level V. MP increased significantly over the duration of hip surveillance in patients with GMFCS levels I-III, IV, and V by 0.3%/year (P < 0.001), 1.9%/year (P < 0.001), and 6.2%/year (P < 0.001), respectively. In patients with GMFCS level IV, NSA increased significantly by 3.4°/year (P < 0.001). Our results suggest that periodic monitoring and radiographic hip surveillance is warranted for patients with CP, especially those with GMFCS level IV or V. Furthermore, physicians can predict and inform parents or caregivers regarding the progression of hip displacement in patients with CP.

Keywords: Cerebral Palsy; Hip Displacement; Hip Surveillance; Progression.

Fig. 1

Inclusion and exclusion criteria. CP, cerebral plasy; MP, migration percentage; NSA, neck-shaft angle; AI, acetabular index; PO, pelvic obliquity; LMM, linear mixed model.

Fig. 2

Hip internal rotation view. For the right hip, migration percentage (MP) was calculated by dividing the width of the femoral head lateral to Perkin's line (A) by the total width of the femoral head (B). For the left hip, neck-shaft angle (NSA) was defined as the angle between a line passing through the center of the femoral shaft and another line connecting the femoral head center and the midpoint of the femoral neck. Femoral head center was the center of the largest best-fitting circle inside the femoral head.

Fig. 4

Serial hip radiographs obtained during the duration of hip surveillance. (A) Radiographs of a 5-year-old girl with Gross Motor Function Classification System (GMFCS) level III. The left hip seemed to have displacement, but there was no acetabular dysplasia or hip displacement at the last follow-up, 6 years after the initial radiographs were obtained. Migration percentage (MP) decreased throughout the duration of hip surveillance. (B) Radiographs of a 7-year-old boy with GMFCS level V. Left hip displacement progressed by a lateral migratory course. Initial MP was 14%, but increased to 50% at the last follow-up, 5 years after the initial radiographs were obtained.

Fig. 3

Estimation of the progression of migration percentage (MP) by a linear duration of hip surveillance effect according to Gross Motor Function Classification System (GMFCS) level.