Effects of High-Velocity Passive Stretch on Spasticity, Function, and Muscle Structure in Spastic CP Children

Cerebral palsy (CP) is characterized as a neurodevelopmental disorder resulting in enduring deficits in mobility and posture owing to non-progressive injury to the infant or developing brain. CP is the predominant etiology of physical impairment observed in children. Research indicates a global prevalence of 1.6 per 1,000 live births in developing nations and 3.4 per 1,000 in low- and middle-income countries. Ninety percent of all CP patients demonstrate spasticity as a symptom. Spasticity is characterized by a speed-dependent augmentation of excessive stretch reflexes, stemming from the hyperexcitability of these reflexes due to upper motor neuron injury. Management of spasticity includes physical therapy techniques, antispasmodic medication, botulinum toxin administration, orthotic devices, therapeutic exercises, and surgical interventions. Stretching exercises constitute one of the initial therapeutic interventions and have been employed for numerous years. Certain studies indicate that the impact of conventional stretching on joint range of motion and spasticity is constrained. If spasticity is not appropriately managed, it may hinder motor learning and the development of movement abilities, leading to various functional impairments such as joint contractures and gait issues over time, while also causing changes in muscle architecture. Muscle architecture denotes the configuration of fibers or fascicle bundles within the muscle. It encompasses the fascicle length and pennation angle.

The length of a muscle fiber or fascicle correlates with the muscle's maximal excursion and contraction velocity, reflecting the number of sarcomeres arranged in series. The physiological cross-sectional size of a muscle is directly related to its maximum force production capability and the quantity of sarcomeres arranged in parallel. Numerous investigations have documented a reduction in fascicle length in the afflicted limbs of children with cerebral palsy. The extension of fascicle length can beneficially impact children's functional capabilities by improving the muscle's length-tension and force-velocity properties. Consequently, the extension of fascicle length is crucial for enhancing children's motor functions and functional capabilities. Ultrasonography of the musculoskeletal system serves as a potential instrument for assessing alterations in in vivo muscle architecture. It has been utilized in numerous research studies, including the pediatric population, to elucidate muscle anatomy. One study indicated that high-speed passive stretching may enhance muscle fascicle length in spastic muscles.

The hypothesis of the study is that rapid stretching exercises administered to children with cerebral palsy who have undergone BoNT-A treatment will yield superior outcomes in spasticity, functional status, and muscle architecture compared to conventional speed stretching.

Method:

Study Design and Participants:

The present study is designed as a prospective, single-blind, randomized controlled trial. It investigates the effects of high-velocity and standard ankle stretching exercises, added to a standard physical therapy program, on functional status, muscle architecture, and spasticity in children with cerebral palsy. Furthermore, it evaluates the contribution of these parameters to gait. The minimum required number of extremities per group was calculated as 23. Considering a 10% potential dropout rate, 26 extremities (17 children) per group were allocated. Accordingly, a total of 52 extremities from 34 children aged between 2 and 8 years were planned for inclusion.

All participants receive botulinum toxin-A (BoNT-A) injections into the gastrocnemius muscle in accordance with clinical indications and the guidelines of the Health Implementation Communiqué (SUT). Participants scheduled for BoNT-A injections and presenting to the Physical Medicine and Rehabilitation outpatient clinic of Erciyes University Faculty of Medicine undergo standardized clinical history, physical examination, anthropometric measurements, observational gait analysis, and ultrasound assessments.

Following BoNT-A administration, all participants undergo a standardized physical therapy and rehabilitation program delivered by the same physiotherapist three times a week for four weeks. The intervention group receives a high-velocity passive stretching protocol, while the control group follows a standard stretching protocol. Treatment protocols are explained to families during the hospital-based therapy period to ensure accurate implementation.

After completing the four-week in-hospital therapy, all participants continue with a home-based exercise program until the 6th month. These exercises are performed by families and are designed to replicate the stretching routines taught during hospital sessions, particularly in terms of velocity and technique. Adherence to the home program is monitored through telephone follow-ups at the 2nd, 4th, and 5th months.

Participants are randomly assigned to either the high-velocity stretching or standard stretching protocol group, both combined with the standardized physical therapy regimen. Assessments are conducted at baseline (pre-injection) and at the 1st, 3rd, and 6th months post-injection. The eligibility criteria and detailed participant selection process are described in the Eligibility section.

Randomization:

Participants will be assigned to intervention and control groups using stratified randomization based on GMFCS staging. The website "https://www.randomizer.org/" will be used for the randomization process. The randomization procedure will be conducted by an independent research assistant who will store the randomization codes and will not be involved in the study process. The evaluator will be completely blinded to group assignments and will have no information regarding the treatment process. The physiotherapist administering the treatment will not be blinded to the treatment methods but will not participate in the evaluation stages. This approach ensures impartiality in randomization and evaluation processes.

Interventions:

• Standard Rehabilitation Protocol: Participants in both groups undergo a one-hour physical therapy program including strengthening exercises, weight-bearing, balance, proprioception, and walking training.
• Stretching Protocol: Stretching will be applied in the same position for participants in both groups. Participants lie supine on a foam mat, and the physiotherapist positions beside the participant, opposite the leg to be stretched. The starting position for stretching is achieved by lifting the leg to 90° knee flexion. To stretch the gastrocnemius muscle, the physiotherapist's hand is placed flat on the foot with a smartphone fixed around the heel and the palm flat against the foot. The knee is supported and brought into full extension, with pressure applied to the proximal tibia for stabilization. Once the knee is locked in full extension, the ankle is dorsiflexed, and pressure is applied to the plantar surface, stretching the muscle until maximum dorsiflexion is reached. Standardization for both groups is provided using smartphone applications. The metronome app standardizes start, end, and rest intervals. Speed measurements are standardized using the Phyphox application. Angular velocity data taken with a smartphone fixed to the plantar region of the foot are transferred to an Excel file. The data are in radians/sec and will be converted to degrees/sec in Excel.

In the intervention group, stretching starts as described above, first at a slow speed (V1) for 5 minutes, followed by fast stretching (V3) for 10 minutes (to induce the catch sensation), as per Tardieu's method. A 1-minute rest period is provided after each stretch. This protocol is performed three times a week for four weeks under physiotherapist supervision, after which families continue the exercises as home exercises without speed measurements for up to 6 months. In the control group, standard stretching is applied with 10 repetitions of 60 seconds and 30 seconds of rest intervals for each leg, three times a week for a total of 15 minutes per session. Similarly, families continue exercises at home for 6 months after the 4-week period.

Outcome Measures:

Detailed in the Outcome Measurements section.

Power Analysis:

Sample size was determined using G*Power software (version 3.1.9.7), based on Kavano et al.'s study. Their study found that 12 weeks after botulinum toxin injections to the gastrocnemius, fascicle length increased by approximately 6% (at rest) and 14% (at maximum dorsiflexion). Assuming a similar difference in fascicle length between intervention and control groups in the current study, with a standard deviation of 3.6, 80% power, and a Type I error of 0.05, at least 23 limbs per group were calculated as necessary. Considering a 10% dropout rate, 26 limbs per group (17 children) were planned, totaling 34 patients.

Statistical Analysis:

All statistical analyses will be conducted using SPSS version 22.0. Normality of the data will be tested using the Shapiro-Wilk test. Baseline (pre-intervention) numerical data from both groups will be compared using independent samples t-tests (if normally distributed) or Mann-Whitney U tests (if not normally distributed). Primary (fascicle length) and secondary outcomes (pennation angle, muscle thickness, spasticity scores, OGA scores, GMFM-66 scores, and ROM scores) will be analyzed for intra-group and inter-group (intervention vs. control) differences across different time points (pre-treatment, post-treatment at 1 month, 3 months, and 6 months) using repeated measures mixed-model ANOVA. Bonferroni correction will be applied to determine specific time points of significant differences. Linear regression analysis will assess the relationship between changes in fascicle length and independent variables (group, time, spasticity score, etc.). Chi-square or Fisher's exact tests will be used for categorical variables. A significance level of p<0.05 will be considered.