Range of hip abduction after preventive and reconstructive surgery in cerebral palsy: a longitudinal registry study of 307 children.

Background and purpose - Hip dislocation in cerebral palsy (CP) is caused by altered muscle forces on the joint during typical hip positioning in adduction-flexion-inward rotation. Preventive surgery includes adductor-psoas lengthening (APL) or varus derotation osteotomy (VDRO) of the proximal femur. We assessed the changes in the hip abduction range after these operations. Patients and methods - Data were obtained from the Swedish Surveillance Programme for CP. The range of hip abduction before and up to 18-36 months after surgery was assessed for all children who underwent APL or VDRO. Data for 1 hip per child was assessed. Ordinary linear regression was used. Results - In the 150 children who underwent APL, the mean range of abduction increased from 29° (95% confidence interval [CI] 28-32) preoperatively to 37° (CI 35-39) at 18-36 months. In the 157 children who underwent VDRO, the respective mean values were 30° (CI 29-32) and 29° (CI 28-31). The mean difference in preoperative abduction between sides was greater in children who underwent unilateral (9.4°, CI 7.8-11) than bilateral (5.5°, CI 3.4-7.6) VDRO. At 18-36 months postoperatively, the differences between sides were almost unchanged. Interpretation - The range of hip abduction increased after APL but remained unchanged after VDRO. This may explain the normal development of hip displacement after these operations. Differences in abduction between sides were not substantially affected by whether VDRO was performed uni- or bilaterally.