Contributing factors to muscle weakness in children with cerebral palsy

Abstract

The aim of this study was to determine the extent of ankle muscle weakness in children with cerebral palsy (CP) and to identify potential causes. Maximal voluntary contractions of plantar (PF) and dorsiflexors (DF) were determined at optimal angles in knee flexion and extension in both legs of 14 children with hemiplegia (7 males, 7 females) and 14 with diplegia (8 males, 6 females). Their results were compared to 14 age‐ and weight‐matched control participants (5 males, 9 females). Muscle cross‐sectional areas of soleus, posterior, and anterior compartment muscles were determined from MRIs in 14 children with CP (eight diplegia, six hemiplegia) and 18 control children. Specific tension (torque/unit area) of PF and DF was determined from torque and cross‐sectional area results. Muscle volumes of PF and DF were also determined in both legs of five control children and five with hemiplegia. Muscle EMG was recorded from soleus, medial gastrocnemius, and tibialis anterior during each maximal voluntary contraction. Mean amplitude was significantly reduced in PF and DF in both CP groups and significantly higher levels of coactivation of antagonists were found compared to control participants. Strength of PF and DF was significantly reduced in both CP groups, but more importantly the muscles were found to be weak based on significantly reduced specific tensions. The PF were most affected, particularly in the group with hemiplegia. It is believed that an inability to maximally activate their muscles contributed to this weakness. A combination of incomplete activation and high levels of PF coactivation are thought to have contributed to DF weakness.

A method for quantifying dynamic muscle dysfunction in children and young adults with cerebral palsy

“…Data were analysed for 17 children and young adults with spastic diplegic cerebral palsy (mean age 11.3 years, range [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. The muscle strength for these children (CP) was assessed using the Oxford/MRC scale from five for full strength to zero for no contraction [11]: 4.06 AE 0.24 for the hip flexors and extensors, 3.84 AE 0.44 for the knee flexor and extensors, and 3.09 AE 1.43 for the ankle dorsiflexors and plantarflexors.…”

Reliability and validity of trunk accelerometry-derived performance measurements in a standardized heel-rise test in elderly subjects

“…PF muscle performance has been evaluated with manual muscle testing (testing the ability to move against gravity or against a force applied by the examiner) [5], isokinetic devices for the measurement of isometric peak torque [6], and handheld dynamometers for the measurement of isometric peak force [7]. However, due to the short lever arm (length of the foot), the unilateral standing HR test, commonly quantified by the number of repetitions rather than by the amount of force produced, has been repeatedly recommended over the use of manual resistance [8].…”

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

“…The significantly reduced lower limb muscle volume in this group [19][20][21][22][23][24][25][26] results in reduced mechanical loading experienced by the bones, stimulating bone growth less than in their TD peers. However, contrary to the hypothesis, tibial cortical bone CSA and CT were not significantly related to muscle volume.…”

“…However, measurements of muscle strength in CP are unreliable and may underestimate the maximum force generating capacity of muscle due to poor selective voluntary motor control and coactivation of antagonists [21,36,37]. However, muscle volume is reflective of the total number of sarcomeres and is linearly related to muscle power [38].…”

“…Longitudinal growth increases the length of lever arms and bending moments leading to greater forces experienced by the bone [15], with bending and torsional forces being the predominant loading factors in the long bone diaphysis [16,17]. Muscle weakness [18] and reduced muscle volume [19][20][21][22][23][24][25][26] in individuals with CP is well documented. Therefore, in individuals with CP, the reduced bone strength and increased fracture rate may be due to the reduced mechanical loading applied to the bones by the local musculature.…”