Introduction

Cerebral palsy (CP) is defined as a collection of movements and postural dysfunctions resulting in restrictions in functional abilities [1]. The lesion in the immature brain in children with CP leads to improper nerve signals to the musculoskeletal system, causing muscular tone abnormality and a decrease in the control of body movements. This results in a decrease in balance, muscle weakness, and disturbance of functional capacity [2].The prevalence of CP is about 1.5 to 4/1000 live births [3].

Balance is the capacity to keep and maintain equilibrium. It is classified into static and dynamic balance [4]. CP gives rise to disturbances in balance, motor functions, activity, and participation.

The production of movement requires stability of the spine and relies on the core muscles to attain sufficient power, endurance, and strength. The core muscles can be clarified as a muscular box with the diaphragm as the roof of the muscular box, the hip girdle and pelvic floor muscles as the bottom, the abdominals in the front, and gluteal and paraspinal muscles in the back [5]. Muscles of this box assist in controlling the movement and position of the central body portion and also provide the basis for extremities movements. Strengthening and core stabilization programs can be done for children with CP to improve both balance and stability [6].

Rebound therapy is the therapeutic use of rebound and rebound-like devices to provide the opportunity for subjects with functional limitations to do recreational activities [7]. It was suggested that rebound therapy help in improving balance, gross motor abilities, and coordination in addition to enjoyment and satisfaction during the treatment sessions [8]. Multiple studies suggested using rebound therapy as a rehabilitation modality for children with CP to increase strength, balance, and functional mobility [7, 8]. The elastic tension that is produced by the springs forms an unstable surface. The movements on unstable surfaces offer an active base upon this movement. Also, the changeable surface can be organized to enhance symmetrical weight bearing, leading to balance improvement [9]. Germain and his colleagues added that rebound therapy enhances the strength of lower limbs, improves functional strength, motor performance, and balance with a high degree of performance with no adverse effects in children with CP [8].

To the extent of our awareness, until now there is no study comparing the effect of core stabilization and rebound therapy on balance in children with CP. The current study aimed to compare the effect of core stabilization and rebound therapy on dynamic standing balance in children with hemiplegic CP. It was hypothesized that there is no difference between the effect of core stabilization compared to rebound therapy on dynamic standing balance in children with hemiplegic CP [10].

Methods

Participants

Fifty-two children with hemiplegic CP from the Faculty of Physical Therapy, Cairo University (25 boys, 27 girls) enrolled in this study and complied with the following inclusion criteria: can follow instructions given to them, their chronological age ranged from 5 up to 8 years, muscle tone grade of their lower limbs ranged between 1+ and 2 in the Modified Ashworth scale (MAS), and they were classified as Level II & III of gross motor function in Gross Motor Function Classification System Expanded and Revised (GMFCS E&R). Children were excluded in case of significant problems in vision or hearing, botulinum toxin injection or orthopedic surgery 6 months before the study in the lower limbs, children suffering from epilepsy, osteoporosis, contracture, deformity and/or tightness in upper or lower limbs, recent fracture, vertigo or dizziness.

Study design

The current study is a comparative, single-blinded randomized controlled study design, performed between November 2022 and May 2023. Children with hemiplegic CP were randomized by a simple random sampling system into two groups; core stability and rebound therapy using closed sealed envelopes. Recruitment for this study included sixty-two children with hemiplegic CP; parents of three children refused their study participation and seven children did not meet the inclusion criteria. The Consolidated Standards of Reporting Trials (CONSORT) diagram (Fig. 1) displays the study design.

Fig. 1
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Participants’ flow chart

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Intervention

Interventions were described according to the TIDieR checklist, Tables 1 and 2. A designed physical therapy program in conjunction with core stability exercises was applied to one group, Tables 1 and 3, while the other group applied the same designed physical therapy program in conjunction with rebound therapy, Tables 2 and 4.

Table 1 Core stability intervention group exercise program according to TIDieR criteria
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Table 2 Rebound therapy intervention group exercise program according to TIDieR criteria
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Table 3 Core stability prescribed exercises
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Table 4 Rebound therapy prescribed exercises
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Measurements

Biodex balance system (BBS) was used as a measurement for dynamic standing balance which was considered the primary outcome of this study, while a hand-held dynamometer and a 6-min walk test (6MWT) were used as secondary outcome measures for assessing knee extensor strength and functional capacity respectively.

The BBS is a sophisticated reliable and objective assessment device for balance (BBS; Biodex Medical Systems, Inc, Shirley, NY). It has a platform that can shift in medial, lateral, anterior, and posterior directions to assess the overall stability index (OASI), mediolateral stability index (MLSI), and anteroposterior stability index (APSI) [11]. Instructions have been given to all children about how to perform the test before starting the evaluation. According to the child’s height, handrails had to be adjusted to obtain safety for all children while using the device but they were not allowed to use them during testing. Standing on a platform barefoot with arms beside the body and looking forward at an adjustable display screen for visual biofeedback was required. The Dynamic Balance operation was chosen as a method of assessment and the child was required to keep the cursor at the middle of the screen during the platform movement. BBS has eight stability levels; level 1 represents the level with the least stability and level 8 represents the level with the most stability. In this study, the measurements were conducted at level 6 because it was suitable for all participating children [12, 13]. Three trials were performed for each child, each one lasted 30 s and the mean value was used while analyzing the data. Higher scores indicated poorer balance.

A handheld dynamometer is an objective, valid and reliable instrument in children with CP for measuring isometric muscle strength (Nicholas Manual Muscle Test system, Model 01163; Lafayette Instrument Company, Lafayette, IN) [14]. It was selected in this study for measuring the affected knee extensors strength. It was set to read force in pounds. From sitting position with knees and hips flexed 90° while stabilizing the pelvis and the other non-tested limb, all children were instructed to perform maximal isometric contraction against dynamometer resistance which was placed at the anterior side of the distal tibia, 10 cm above the lateral malleolus [15]. Three attempts were recorded. The application of the first attempt was for familiarization, and the second and third attempts were averaged to obtain the score. One minute rest between trials was allowed to avoid possible fatigue.

Six-minute walk test is a submaximal, valid, and reliable test that is used to evaluate endurance and aerobic capacity in children with CP [16]. Evaluation procedures occurred in a straight corridor with a flat hard surface of 30 m long, without any obstacles. Children were asked to wear comfortable clothing. During the test procedure, verbal instructions and encouragement were given to all participants. Children were asked to walk as far as they could for a period of 6 min. After ending the test, the distance that the children covered was recorded in meters [17].

Statistical analysis

Calculation of the sample size prior to the study was done using the statistical software “G*POWER” (version 3.1.9.4; Franz Faul, Universitat Kiel, Germany) using large effect size, β = 0.2, α = 0.05. The detected sample size for our study was N = 52; with 26 children for each group. 62 children were recruited for possible dropouts.

The statistical package for social studies (SPSS) version 25 for Windows (IBM SPSS, Chicago, IL, USA) was selected to conduct the statistical analysis. The t-test was selected to analyze the characteristics of subjects between groups. Chi-square test was selected to analyze the comparison of affected side distribution and sex between groups. The Shapiro–Wilk test was selected for checking if the data are normally distributed, and Levene’s test was selected for testing between groups homogeneity. Mixed repeated measures MANOVA was used for comparing within and between treatment effects for all outcomes. For subsequent multiple comparisons, multiple tests were performed using the Bonferroni correction. “p < 0.05” was used to set the level of significance for all statistical tests.

Results

The subject characteristics are shown in Table 5. Age, height, weight, the distribution of sex, and affected side showed no significant difference between groups (p > 0.05).

Table 5 Comparison of participants’ baseline characteristics between core stability and rebound therapy groups
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Effect of treatment on stability indices, knee extensors strength, and 6MWT

A significant interaction of treatment and time was detected as revealed by Mixed MANOVA (η2 = 0.38; F (5,46) = 5.7, p = 0.0001). A significant main effect of treatment was detected (η2 = 0.393; F (5,46) = 5.96, p = 0.0001). A significant main effect of time was detected (η2 = 0.98; F (5,46) = 756.2, p = 0.0001).

Comparison within the group

A decrease in all stability indices was significantly detected post-treatment in both groups, when compared to pre-treatment values (p < 0.0001). In addition, an increase in knee extensor strength and 6MWT was significantly detected post-treatment when compared to pre-treatment values (p < 0.0001) in both groups as shown in Table 6.

Table 6 Changes in stability indices, knee extensors strength, and 6MWT within and between groups
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Comparison between groups

Comparison between groups is shown in Table 6. No significant difference was observed between core stabilization and rebound therapy groups in all outcome measures pre-treatment (p > 0.05). A significant decrease in all stability indices of the core stability group compared with that of the rebound therapy group post-treatment was detected (p < 0.0001) as shown in Fig. 2, while there was a non-significant difference in the strength of knee extensors and 6MWT when comparing the two groups post-treatment (p > 0.05) as shown in Fig. 3.

Fig. 2
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Comparison of post-treatment mean values of different balance outcomes between groups

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Fig. 3
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Comparison of post-treatment mean values of knee extensors strength and 6 MWT between groups

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Discussion

The objective of the current study was to compare the effect of core stabilization exercises and rebound therapy on balance in children with hemiplegic CP. The hypothesis was rejected and there was a significant difference between core stability exercises and rebound therapy in favor of core stability.

Maclennan and coworkers defined CP as a heterogeneous condition. Since there are numerous causative pathways and different types and degrees of dysfunction within the CP clinical spectrum, CP might be better described as "the cerebral palsies." [18]. The neurological subtype of CP is a powerful predictor of functional status in children with CP [19]. Children with hemiplegic type of CP typically exhibit higher gross motor function scores. As a result, they have less activity restrictions than the other types. [20]. Specifying type of CP was shown in different balance studies for homogeneity of the cases [21,22,23]. In addition, diplegic patients exhibited weaker postural balance compared with hemiplegic CP patients in other studies [24, 25]. For these reasons, only spastic hemiplegic CP children with levels II &III of GMFCS were selected to be included in our study.

A significant improvement of both groups in all types of stability indices was shown post-treatment in comparison with their pre-treatment results. The core stability group’s stability indices results showed significantly better dynamic balance than the rebound therapy group.

The core stability group in our study showed a significant improvement in balance post-treatment in comparison with pre-treatment results. The main reason for this improvement might be related to improving the trunk muscle strength after core stability training programs as core stabilization improve the strength and the control of the trunk's stabilizing muscles which is directly linked to balance in children with spastic CP [26]. Core stability training activates the trunk musculature by proprioceptive stimulation. In addition, the somatosensory control of the vestibular system is also stimulated during the core stability exercise [27]. Improvement of balance in the core stability group in our study has been supported by the findings of the study by Rana and his colleagues which concluded that the stability of the trunk is a significant core element of coordination and balance in children with CP [28]. Our findings are also supported by previous studies which studied trunk stability exercises and their effect on children’s balance in different disabilities including diplegic and hemiplegic children with CP [29], children with ataxic CP [27], children with Down syndrome [30], and also, in normal children [31].

The trunk muscles activities are clearly correlated with the lower extremity function and movement. The core stability program can improve the postural activity of the extremities by stimulating the feed-forward system [32]. Thus, improving both lower limbs’ muscle strength and their functional activities which can justify the improvement in the strength of knee extensors and functional capacity in the core stability group after core stability exercises. These results are consistent with Hoppes and his colleagues who stated that 8 weeks of a core stabilization program can improve endurance [33]. Core stability problems were identified as potential risk factors for injuries of the lower extremity [32]. Güngör and his colleagues stated that both home and supervised Pilates-based core stability exercises could improve postural sway and lower extremity muscle strength in patients with multiple sclerosis [34].

Rebound therapy creates situations that improve both static and dynamic balance mechanisms via vestibular and proprioceptive stimulation that enhances balance and postural stability and decreases the risk of falling [35]. It was proven to improve hip moment generation resulting in increasing dynamic stability [36] which can illustrate the significant balance improvement which is detected in the rebound therapy group.

The current study results were supported by Abd-Elmonem and Elhady results who studied the rebound therapy effect on balance in 40 children with diplegic CP whose balance was evaluated using the dynamic test in BBS. Their study revealed a significant improvement in balance after the rebound therapy exercise program [37]. Our results are also supported by previous studies, which examined the rebound therapy effect on balance in children with different disabilities including autism spectrum disorder [38], and Down syndrome [39].

Skin, muscle, and joint receptors as well as the vestibular system can be stimulated by rebound exercises, resulting in muscle co-contraction, modulation of muscle tone, and increase the knee extensor moments leading to an increase in knee joint stability [40]. The current study revealed that the strength of knee extensors and functional capacity were significantly improved after rebound therapy. These results may be based on the biomechanical effect of rebound therapy on joint range of motion and stretch reflex [39].

Our results came in agreement with a study by Azab and his colleagues who reported that trampoline-based stretch–shortening cycle exercises have distinct effects on muscle strength in children with Down syndrome [39]. Claesson and his colleagues also conducted a study that revealed the effect of somatosensory training using rebound therapy and showed a significant improvement in balance and functional capacity using Berg Balance Scale and 10-min walk test respectively [41].

The current study has many limitations; only one type of CP (hemiplegic type), specific age group (from 5 up to 8 years), and two levels of GMFCS (level II and III) were allowed to be included in this study. So, additional studies are required to be performed on children with different levels of GMFCS, different ages, and other types of CP. Also, absence of follow-up for participants. So, future studies are recommended to detect and illustrate the maintenance of the improvement gained.

Conclusion

In this study, a significant dynamic standing balance improvement of the core stability group when compared to the rebound therapy group was revealed when comparing the two intervention groups after 12 weeks intervention. The current study concluded that including both core stability and rebound therapy during the rehabilitation of children with hemiplegic CP is helpful when the treatment plan aims to improve their balance. However, core stabilization produces significantly more favorable effects on balance than rebound therapy when added to a designed physical therapy program in those children.