Children with unilateral spastic cerebral palsy have smaller and weaker tibias in the spastic limb compared to the non-spastic limb.

Cerebral palsy (CP) is associated with poor bone architecture. It is unclear if abnormal bone architecture is localized to the area affected by spasticity and whether these deficiencies are dependent on physical activity. This study aimed to examine differences in tibial bone architecture between the spastic and non-spastic limbs in children with unilateral spastic CP and the association between physical activity habits with spastic limb bone architecture. Twenty-four ambulatory children with CP (13 females, 11 males; 7.8 ± 1.7 years) completed bilateral high-resolution peripheral quantitative computed tomography (HR-pQCT) at the distal tibia metaphysis. The frequency of participation (FPS), bone specific physical activity questionnaire (BPAQ), and dynamic participation survey (DPS) were used to assess physical activity habits. Differences between limb architecture were assessed with paired t-tests. Linear regressions were performed on FPS/BPAQ/DPS scores with each HR-pQCT outcome separately. HR-pQCT data without significant motion artifacts were available for eighteen participants. The spastic limb had less total area (p = 0.013, 95%CI 4.87-35.13mm2), trabecular area (p = 0.035, 95%CI 1.22-29.96mm2), cortical area (p = 0.008, 95%CI 1.35-7.63mm2), cortical perimeter (p = 0.012, 95%CI 0.52-3.60 mm), cortical thickness (p = 0.046, 95%CI 0.001-0.112 mm), stiffness (p = 0.012, 95%CI 2065-13,429 N/mm), and failure load (p = 0.008, 95%CI 128-747 N) than the non-spastic limb. Only BPAQ was associated with limb length (p = 0.011, R = -0.584). The distal tibia metaphysis of the spastic limb had similar bone density but was smaller and weaker compared to the non-spastic limb. Differences in bone geometry likely accounted for between-limb differences in estimated bone strength.