Abstract
Botulinum NeuroToxin-A (BoNT-A) injections to the medial gastrocnemius (MG) and lower-leg casts are commonly combined to treat ankle equinus in children with spastic cerebral palsy (CP). However, the decomposed treatment effects on muscle or tendon structure, stretch reflexes, and joint are unknown. In this study, BoNT-A injections to the MG and casting of the lower legs were applied separately to gain insight into the working mechanisms of the isolated treatments on joint, muscle, and tendon levels. Thirty-one children with spastic CP (GMFCS I-III, age 7.4 ± 2.6 years) received either two weeks of lower-leg casts or MG BoNT-A injections. During full range of motion slow and fast passive ankle rotations, joint resistance and MG stretch reflexes were measured. MG muscle and tendon lengths were assessed at resting and at maximum dorsiflexion ankle angles using 3D-freehand ultrasound. Treatment effects were compared using non-parametric statistics. Associations between the effects on joint and muscle or tendon levels were performed using Spearman correlation coefficients (p < 0.05). Increased joint resistance, measured during slow ankle rotations, was not significantly reduced after either treatment. Additional joint resistance assessed during fast rotations only reduced in the BoNT-A group (−37.6%, p = 0.013, effect size = 0.47), accompanied by a reduction in MG stretch reflexes (−70.7%, p = 0.003, effect size = 0.56). BoNT-A increased the muscle length measured at the resting ankle angle (6.9%, p = 0.013, effect size = 0.53). Joint angles shifted toward greater dorsiflexion after casting (32.4%, p = 0.004, effect size = 0.56), accompanied by increases in tendon length (5.7%, p = 0.039, effect size = 0.57; r = 0.40). No associations between the changes in muscle or tendon lengths and the changes in the stretch reflexes were found. We conclude that intramuscular BoNT-A injections reduced stretch reflexes in the MG accompanied by an increase in resting muscle belly length, whereas casting resulted in increased dorsiflexion without any changes to the muscle length. This supports the need for further investigation on the effect of the combined treatments and the development of treatments that more effectively lengthen the muscle.
Highlights
Cerebral palsy (CP), the most common childhood disability, is caused by an injury to the developing brain that occurs prior to, or shortly after, birth
We found that the reduction in hyperactive stretch reflex in the lateral gastrocnemius following casts was associated with an increase in tendon length
This study presents initial findings on treatment response in a heterogeneous group of children with spastic CP
Summary
Cerebral palsy (CP), the most common childhood disability, is caused by an injury to the developing brain that occurs prior to, or shortly after, birth. Recent literature indicates that hyperactive stretch reflexes, commonly labeled as spasticity, are considered to have less impact [2, 3] Instead, alterations such as reduced muscle volume and atrophy, cellular and genetic factors have been related to the increased joint resistance [4,5,6]. The effectiveness of BoNT-A in correcting gait deviations, and passive joint ROM on the short-term, has been shown to improve when BoNT-A is combined with casting [7,8,9] The rational of this treatment combination is that paralysis, followed by passive immobilization in a neutral position, results in tissue elongation through physiological adaptation to prolonged stretch. Results are inconclusive and whether the improved joint ROM occurs due to muscle remodeling or at the expense of other soft tissues, is not wellunderstood [19]
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