Bone strength is related to muscle volume in ambulant individuals with bilateral spastic cerebral palsy

- To investigate bone strength and local muscle volume in cerebral palsy (CP)
- Bony geometry and the volume of nine lower limb muscles were measured using MRI.
- The polar section modulus (Zp) and CSA were used to estimate bone strength.
- In the distal femur, Zp was related to thigh muscle volume and height.
- Femoral cortical CSA is dependent on diagnosis and thigh muscle volume.

ObjectiveThe aim of this study is to investigate how bone strength in the distal femur and proximal tibia are related to local muscle volume in ambulant individuals with bilateral spastic cerebral palsy (CP).MethodsTwenty-seven participants with CP (mean age: 14.6 ± 2.9 years; Gross Motor Function Classification System (GMFCS) levels I-III) and twenty-two typically developing (TD) peers (mean age: 16.7 ± 3.3 years) took part in this study. Periosteal and medullary diameter in the distal femur and cortical bone cross-sectional area (CSA) and thickness (CT) in the distal femur and proximal tibia were measured along with nine lower limb muscle volumes using MRI. Additionally, the polar section modulus (Zp) and buckling ratio (BR) were calculated to estimate bone bending strength and compressional bone stability respectively in the distal femur. The relationships of all measured parameters with muscle volume, height, age, body mass, gender, and subject group were investigated using a generalized linear model (GZLM).ResultsIn the distal femur, Zp was significantly positively related to thigh muscle volume (p = 0.007), and height (p = 0.026) but not significantly related to subject group (p = 0.076) or body mass (p = 0.098). BR was not significantly different between groups and was not related to any of the variables tested. Cortical bone CSA was significantly lower in the CP group at both the distal femur (p = 0.002) and proximal tibia (p = 0.009). It was also positively associated with thigh muscle volume (p < 0.001) at the distal femur, and with subject height (p = 0.005) at the proximal tibia.ConclusionsBending and compressional strength of the femur, estimated from Zp and cortical bone CSA respectively, is associated with reduced thigh muscle volume. Increasing muscle volume by strength training may have a positive effect on bone mechanics in individuals with CP.