Jump Loading Mechanics In Children With Cerebral Palsy And Its Relationship With Areal Bone Mineral Density

Cerebral palsy (CP) is a nonprogressive movement disorder associated with muscle weakness, limited physical activity, and poor bone health. Jumping is a valuable skill that can increase bone strength in children. Unfortunately, children with CP have limited jumping ability. PURPOSE: To determine if children with CP demonstrate atypical loading of the lower extremities during countermovement jumps that is related to their areal bone mineral density (aBMD). METHODS: Thirty children with spastic CP were matched with 30 typically developing control children by age and sex. Maximum jump height was determined using 3D motion capture. Ground reaction forces at takeoff and landing, rate of force development during take-off, and loading rate during landing were determined using dual force plates. The distal femur aBMD of the non-dominant limb was assessed using dual-energy X-ray absorptiometry. RESULTS: Groups did not differ in age, height, body mass, or BMI (p > 0.05). Compared to controls, children with CP had lower jump height (d = 2.27, p < 0.001). Joint reaction force (d = 0.77, p = 0.004), loading rate (d = 0.93, p = 0.001), and rate of force development (d = 0.61, p = 0.024) were lower in the nondominant limb of children with CP. On the other hand, joint reaction force (d = 0.85, p = 0.002), loading rate (d = 1.40, p < 0.001), and rate of force development (d = 1.10, p < 0.001) were higher in the dominant limb of children with CP (all p < 0.05). Children with CP had lower aBMD Z-score (d = 0.65, p = 0.015) in the subregion closest to the metaphyseal plate of the distal femur as determined from the high-resolution scan. In children with CP, take-off ground reaction force was inversely related to aBMD Z-score (r = -0.375, p = 0.041). No relationships between measures of loading and aBMD Z-score were observed in controls. CONCLUSION: Children with CP exhibit impaired jump performance and rely more on the dominant limb during the jump cycle which may contribute to low bone development in their nondominant limb. Supported by: This study was funded by National Institutes of Child Health and Human Development (R01HD090126) and the University of Georgia Athletic Association.