Muscle strength and walking ability in diplegic cerebral palsy: implications for assessment and management

Muscle weakness is a recognised problem in children with Cerebral Palsy (CP). Changes in the understanding of motor control, and progress in the treatment of spasticity, have led to a greater appreciation that spastic muscles are also weak. In recent years weakness has been identified in isolated muscle groups, but studies quantifying the degree and distribution of weakness in multiple muscles remain limited. This study evaluated isometric lower limb muscle strength in 50 ambulant children with CP/Spastic Diplegia (mean age 11 years 7 months) at GMFCS levels I (n=14), II (n=26) and III (n=10). Muscle strength was compared with 15 control children (mean age 11 years 1 month) using the same protocol. Six muscle groups in both lower limbs were measured using a digital dynamometer. All lower limb muscles were significantly weaker in the CP children than in healthy children (p<0.05) except for the hip extensors. Muscle strength ranged from 43% to 90% of control values depending on the muscle group, with the knee extensors measured at 30° being the relatively weakest group. There was a significant difference in strength between GMFCS levels in 4/6 muscle groups with a progressive reduction in strength in all muscle groups with increasing walking difficulty from GMFCS levels I to III. The greatest difference in strength between independent walkers and those dependent on walking aids was in the hip abductors and knee extensors at 30°, which are key muscle groups in sagittal and coronal plane walking stability. This has implications in targetting strength training to maximise functional outcomes.