INTRODUCTION
Cerebral palsy (CP) is defined as a permanent impairment of motor and postural development resulting from non-progressive brain damage in the fetus or infant after birth (Rosenbaum et al., 2007). Spastic CP is characterized by problems such as loss of selective motor control, spasticity, muscle weakness, and co-contraction and can be classified into unilateral and bilateral CP (Bax et al., 2005).
Unilateral CP is difficult with voluntary movement due to neuromuscular imbalance resulting from unilateral brain damage. Increased anterior pelvic tilt during gait (Park et al., 2019), retraction of the pelvis on the affected side in the transverse plane (O’Sullivan et al., 2007; Park et al., 2006), and Trendelenburg sign in the coronal plane appear (Metaxiotis et al., 2000). This causes trunk imbalance due to asymmetrical weight bearing and increased postural sway, affecting balance and gait (El Shemy, 2018). Abnormal pelvic movements and body asymmetries on the affected side of children with unilateral CP are important to consider as they affect movement.
Trunk control is maintained by antigravity activation of the trunk muscles, which are involved in balance when sitting. Therefore, appropriate trunk muscle activity is necessary to perform voluntary movements (Lee et al., 2022). Coordination of movements between the trunk and pelvis is essential for controlled leg movements during walking (Sung et al., 2012). Children with spastic unilateral CP have impaired trunk control (Heyrman et al., 2013). Specifically, force production is reduced, proprioception around the core is weakened, core muscle coordination is insufficient, and the ability to coordinate coupling between the trunk, pelvis, and hip stabilizers is reduced, leading to decreased movement proficiency (Heyrman et al., 2013). Therefore, strengthening trunk muscles and improving pelvic movement are important factors in children with unilateral CP.
Previous studies have focused on improving the function of the paralyzed limbs of children with unilateral CP (Barati et al., 2020; Hoare et al., 2019; Hung et al., 2017; Surana et al., 2019). Weakness of the trunk muscles and problems with pelvic movement are important factors affecting the functional limitations of children with unilateral CP. There have been many cross-sectional studies on pelvic movement to understand the characteristics of children with unilateral CP, but studies on trunk muscles are rare. Furthermore, there are few studies that examine changes in these factors as a result of interventions. Improving trunk muscles and pelvic movements involved in asymmetry may play an important role in improving motor function in children with spastic unilateral CP. Therefore, this study aimed to investigate the effects of abdominal muscle strengthening and pelvic control exercises on trunk control, abdominal muscle thickness change rate, and pelvic movement in children with unilateral CP.
MATERIALS AND METHODS
Participants
Participants were children who used the Sky Children Development Center in Yangsan. The general characteristics of the target children are shown in Table 1. The inclusion criteria were as follows: (1) children diagnosed with unilateral CP aged 4–12 years, (2) children corresponding to gross motor function classification system (GMFCS) levels 2–3, (3) children who could follow simple verbal instructions from the researcher, (4) children who provided information to parents and children and obtained voluntary consent. The exclusion criteria were as follows: (1) children with autism, (2) children with acute inflammation or fever, (3) children with visual and auditory problems, and (4) children with uncontrolled seizures.
We randomly divided 14 children with unilateral CP into two groups by drawing colored balls; the white ball corresponded to the experimental group, and the black ball corresponded to the control group. The experimental group (n=7) applied abdominal muscle strengthening and pelvic control exercises, and the control group (n=7) applied general physical therapy for 30 minutes per session, twice a week for a total of 8 weeks, respectively. We measured trunk control, abdominal muscle thickness, and pelvic movement before and after the intervention. We explained the content and purpose of this study to the participants and their guardians and obtained their consent. This study was approved by the research ethics committee of Kyungnam University (1040460-A-2023-017).
Intervention
The experimental group performed abdominal muscle strengthening and pelvic control exercises for 15 min each. The abdominal muscle strengthening exercise was performed by repeatedly lifting the head in a hook-lying position with the back on the floor and rotating the trunk to raise the head. If it was difficult, the participant rested for 1 min. The pelvic control exercise was performed by repeatedly moving the pelvis on the affected side up and down according to the therapist’s in a hook-lying position, and resting for 1 min if it was difficult. In the control group, weight maintenance and weight shifting were applied for 10 min each in sitting and standing positions, and gait training was applied for 10 min.
Trunk control
We used the trunk control measurement scale (TCMS) to measure trunk control. It consisted of static sitting balance (5 items), dynamic sitting balance (7 items), and equilibrium (3 items), and the total score was 58 points. The intraclass correlation coefficient (ICC) for the intrarater reliability of the TCMS was 0.98, and the ICC for test-retest reliability was 0.97 (Mitteregger et al., 2015; Pham et al., 2016).
Abdominal muscle thickness change rate
Ultrasonography (SONON, Healcerion Co., Ltd., Seoul, Korea) was used to measure abdominal muscle thickness change rate. The examiner placed a 10-MHz linear probe horizontally at the point where the midaxillary line meets the iliac crest in B mode and scanned the thickness of the external oblique (EO), internal oblique (IO), and transversus abdominis (TrA) muscles corresponding to the lateral abdominal muscles. For resting thickness measurements, we measured during expiration with the participant lying comfortably in the hook-lying position. To measure thickness during activity, we measured during expiration when the participant was looking at the knees with the head raised in the hook-lying position, as instructed by the examiner. Muscle thickness was measured using a built-in caliper by connecting the endpoints of each line between the upper and lower borders of the fascia, and recorded in mm. We measured twice and used the average value, and the abdominal muscle thickness change rate was calculated using the following formula (Koppenhaver et al., 2009).
Pelvic movement
A wearable gait analysis system (BTS G-Walk, BTS Bioengineering S.p.A., Garbagnate Milanese, Italy) was used to measure pelvic movement. The examiner placed the device between the 5th lumbar vertebra and the 1st sacrum of the participants. The participant walked 6-m straight from the starting position according to the examiner’s instructions, turned the turning point, and returned to the starting point. The pelvic movement during walking consists of pelvic tilt, obliquity, and rotation range, and the measured data were transmitted to the computer via Bluetooth. We measured twice and used the average value. The ICC for test-retest reliability was 0.799 to 0.977 (Yazıcı et al., 2022).
Statistical analysis
We used IBM SPSS Statistics ver. 21.0 (IBM Co., Armonk, NY, USA) for statistical analysis. After normality testing using the Shapiro-Wilk test, the Mann–Whitney U-test was used to examine differences between groups, and the Wilcoxon signed-rank test was used to examine differences within the group. Statistical significance for all statistical analyses was set at P<0.05.
RESULTS
Comparison of trunk control
In the experimental group, there were significant differences in dynamic sitting balance, equilibrium, and total within the group (P<0.05). There was a significant difference in the difference values (pre-post) of dynamic sitting balance and total between the groups (P<0.05), which means that trunk control was improved in the experimental group (Table 2).
Comparison of abdominal muscle thickness change rate
On the nonaffected side, EO had significant differences between the groups after the intervention (P<0.05), and IO had significant differences between the groups in the difference values (post-pre) (P<0.05). On the affected side, TrA had significant differences between the groups before the intervention (P<0.05), and the difference values (post-pre) of EO and IO had significant differences between the groups (P<0.05). In the control group, TrA significantly decreased within the group (P<0.05) (Table 3). This means that the change rate of deep muscles such as IO and TrA on the affected side increased in the experimental group, but the change rate decreased in the control group.
Comparison of pelvic movement
There was a significant difference between the groups in the rotation range of the nonaffected side after the intervention (P<0.05). There was a significant difference between the groups in the difference value (post-pre) of the rotation range of the affected side (P<0.05) (Table 4). The decrease in rotation range in the experimental group means that it is approaching the normal range.
DISCUSSION
Decreased trunk control is one of the main problems observed in children with unilateral CP, and trunk and postural control are very important for them (Panibatla et al., 2017). We investigated the effects of abdominal muscle strengthening and pelvic control on trunk control, pelvic movement, and abdominal muscle thickness change rate in children with unilateral CP.
The trunk plays an important role in developing limb movement control, balance, and functional mobility (Hsieh et al., 2002). One of the most important motor deficits in children with CP is inadequate trunk control (Panibatla et al., 2017). Strengthening trunk muscles can improve proximal control and further affect limb activity. Elanchezhian and SwarnaKumari (2019) reported that Swiss ball training improved trunk control and balance in children with unilateral CP. Afifa et al. (2022) reported that applying traditional physical therapy and trunk exercises to children with unilateral CP was effective in improving trunk control, balance, and walking mobility. Bilek and Tekin (2021) reported that the combination of extracorporeal shock wave therapy (ESWT) and neurodevelopmental treatment improved postural control and balance in unilateral CP; the application of ESWT to the paraspinal muscles reduced stiffness and increased trunk control and balance by more actively using trunk muscles, thereby increasing spinal stability. In this study, the experimental group showed significant increases in dynamic sitting balance, equilibrium, and total within the group. We believe that improving trunk stability through abdominal strengthening affected improving trunk control. In particular, it is thought that strengthening the deep abdominal muscles through the head-raising movement in hook-lying affected trunk control. Pereira et al. (2011) reported that the EO on the nonaffected side showed greater activity when lifting the leg from the supine position in stroke hemiparesis patients; they said it was a method to achieve pelvic stability by compensating for muscle weakness on the affected side. In the present study, there was a significant difference in the IO difference value between the groups. The increase in the IO change rate on the nonaffected side of the control group is thought to be compensation for the weak abdominal muscles, and the increase in the IO change rate in the experimental group is thought to be the result of strengthening the deep abdominal muscles. Therefore, we suggest that strengthening the deep abdominal muscles affects the contraction of the deep abdominal muscles on the affected side and improves postural control.
In normal gait, the pelvis rotates in all three planes. In children, the range in the frontal, sagittal, and transverse planes is 4º, 7º, and 8º, respectively (Schwartz et al., 2008). Pelvic protraction and retraction are movements that occur in the transverse plane, and pelvic retraction is considered to be a consequence of primary neurological deficits resulting from central nervous system lesions (Park et al., 2019). Excessive pelvic retraction is observed in approximately 46% of children with unilateral CP (O’Sullivan et al., 2007). Since the pelvis is a single segment, increased protraction on one side may lead to increased retraction on the other side (Böhm et al., 2012). The retraction of children with unilateral CP is increased compared to typically developing children because the tightness of the gastrocnemius and soleus causes a compensatory pattern of the pelvis (Aminian et al., 2003; O’Sullivan et al., 2007). In this study, there was a significant difference between groups on both the affected and nonaffected sides in the rotation range after the intervention. The control group showed an increased rotation range after the intervention, although not significantly, while the experimental group showed a range closer to the normal range. These results suggest that direct pelvic control had an effect on improving the pelvic movement and that reducing distal spasticity through strengthening abdominal muscles (Abd-Elfattah and Aly, 2021) had an effect on reducing excessive contraction of the pelvis. However, there was no difference between groups in pelvic tilt and obliquity range. These results only considered GMFCS level when recruiting participants and did not consider gait characteristics. It is assumed that this led to limitations in identifying differences in overall pelvic movement.
In summary, abdominal muscle strengthening and pelvic control exercises applied to children with unilateral CP affected deep abdominal muscle contraction and thus trunk control. This also affected the change rate of IO on the affected side and reduced the rotation range of pelvic movement closer to normal. Therefore, we suggest that abdominal muscle strengthening and pelvic control exercises are effective methods for improving trunk control and pelvic movement in children with unilateral CP.
The limitations of this study were the small number of participants and the rather short intervention period, making it difficult to generalize the results. In addition, the daily environment of children with unilateral CP could not be controlled, and functional movements such as gait and upper limb movements were not considered. Research that complements these limitations will be proposed as an intervention that can improve asymmetry by improving abdominal muscle contraction and pelvic movement in children with unilateral CP.
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