Forearm Flexor Muscles in Children with Cerebral Palsy Are Weak, Thin and Stiff

Abstract

Children with cerebral palsy (CP) often develop reduced passive range of motion with age. The determining factor underlying this process is believed to be progressive development of contracture in skeletal muscle that likely changes the biomechanics of the joints. Consequently, to identify the underlying mechanisms, we modeled the mechanical characteristics of the forearm flexors acting across the wrist joint. We investigated skeletal muscle strength (Grippit®) and passive stiffness and viscosity of the forearm flexors in 15 typically developing (TD) children (10 boys/5 girls, mean age 12 years, range 8–18 yrs) and nine children with CP Nine children (6 boys/3 girls, mean age 11 ± 3 years (yrs), range 7–15 yrs) using the NeuroFlexor® apparatus. The muscle stiffness we estimate and report is the instantaneous mechanical response of the tissue that is independent of reflex activity. Furthermore, we assessed cross-sectional area of the flexor carpi radialis (FCR) muscle using ultrasound. Age and body weight did not differ significantly between the two groups. Children with CP had a significantly weaker (−65%, p < 0.01) grip and had smaller cross-sectional area (−43%, p < 0.01) of the FCR muscle. Passive stiffness of the forearm muscles in children with CP was increased 2-fold (p < 0.05) whereas viscosity did not differ significantly between CP and TD children. FCR cross-sectional area correlated to age (R2 = 0.58, p < 0.01), body weight (R2 = 0.92, p < 0.0001) and grip strength (R2 = 0.82, p < 0.0001) in TD children but only to grip strength (R2 = 0.60, p < 0.05) in children with CP. We conclude that children with CP have weaker, thinner, and stiffer forearm flexors as compared to typically developing children.

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“…The growth of muscles in children with CP is impaired compared to that in TD children, as shown in several cross-sectional studies [42,48,190]. Skeletal muscle associated with CP is not only thinner and weaker, but also stiffer [44], all three important contributors to the reduced range of motion observed [56]. The anabolic response of skeletal muscle and their development of hypertrophy is largely dependent on the number of ribosomes they contain [84,85], which essentially determines the rate of protein synthesis [81].…”

“…Skeletal muscle of children with CP differs from that of TD children in a variety of ways. Their total muscle mass is reduced and the muscles in their affected arms and legs are weak, short and thin [42][43][44]. Furthermore, there is more variability in the size of muscle fibers [45,46] and a lower capillary density in muscles of children with CP [47].…”

“…Approximately one third of children with CP develop contractures in the arms [57]. The passive stiffnes, secondary to an upper motor neuron lesion [58][59][60] is altered in both plantar flexors and forearm muscles [44].…”

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“…Skeletal muscle contractures develop as the child grows. In addition to a reduced range of motion of involved joints, children with CP have short, hypoplastic, and thin muscles in affected limbs . Children with CP have a reduced muscle mass in comparison to typically developing (CON) children, and slowed muscle growth rate has been described as preceding the development of contractures .…”

“…In addition to a reduced range of motion of involved joints, children with CP have short, hypoplastic, and thin muscles in affected limbs. 4,5 Children with CP have a reduced muscle mass in comparison to typically developing (CON) children, 6 and slowed muscle growth rate has been described as preceding the development of contractures. 7 With advancing age and progressive contracture formation, sarcomere length is increased in children with CP due to a reduction in the number of sarcomeres arranged in series.…”