Compromised Midfemur Strength In Individuals With Hemiplegic Cerebral Palsy Is Associated With Low Quadriceps Femoris Mass

Abstract

The action of skeletal muscle on bone is recognized as a major stimulus for bone development. The study of individuals with hemiplegic cerebral palsy (CP), a movement disorder in which poor muscle accretion and bone development occur primarily on one side of the body, may further our understanding of site-specific muscle-bone relationships. PURPOSE: To determine the muscle group most strongly related to the compromised bone development in the involved lower extremity of individuals with hemiplegic CP. METHODS: Magnetic resonance images of the thighs and hips were collected from adolescents and young adults with hemiplegic CP (n = 23; 13 to 23 y) using a Phillips 1.5 Tesla scanner. Cortical bone volume and bone strength [i.e., section modulus (Z) and polar moment of inertia (J)] of the middle third of the femur (midfemur) and mass of the quadriceps femoris, hamstring and hip adductor muscle groups were estimated using custom software designed with Interactive Data Language (Research Systems, Boulder, CO). Multiple regression analysis was used to determine whether the side-to-side differences in midfemur cortical volume, Z and J were best predicted by the side-to-side differences in quadriceps, hamstring or hip adductor mass. RESULTS: Midfemur cortical bone volume, Z and J were 6, 7 and 9 % lower, respectively, in the involved side vs. the uninvolved side of children with CP (all p < 0.01). In addition, quadriceps femoris mass, hamstring mass and hip adductor mass were 23, 16 and 21 % lower, respectively, in the involved side vs. the uninvolved side (all p < 0.001). When all three muscle groups were included in a regression model, the side-to-side differences in Z and J were significantly related to quadriceps femoris mass (part r = 0.56, p = 0.007). No other significant muscle-bone relationships were observed (p > 0.05). CONCLUSIONS: The findings suggest that the lower midfemur strength observed in the involved lower extremity of children with hemiplegic CP is partly due to the poor accretion of quadriceps femoris mass. Future studies are needed to determine the effect of a quadriceps femoris strengthening program on midfemur bone structure and strength in individuals with hemiplegic CP. Supported by FoU Kärnsjukhuset Skövde Sweden and the NIH (HD 50530).