Cerebral palsy (CP) refers to a disorder of movement and posture with “non-progressive, but often changing motor impairment syndromes secondary to lesions or anomalies of the brain, arising in the early stages of its development [1,2].” The three subtypes of CP are named after the types of motor dysfunction: spastic, dyskinetic, and ataxic [3].

Spastic CP is observed in 70%–80% of patients with CP [4]. Spasticity has long affected patients’ quality of life, hampering their basic activities of daily living [1]. Various methods, including both medical and surgical treatments, have been introduced to ease the pain and burden of patients with CP. Oral medications, including benzodiazepines, dantrolene, gabapentin, alpha-2 adrenergic agonists, and baclofen, have been commonly used to control spasticity [5]. Along with oral medication, posterior rhizotomy and intrathecal baclofen (ITB) pump insertion have been utilized as neurosurgical interventions to control spasticity in children with CP [6].

The ITB pump was first devised in the 1980s [7]. In addition to CP, ITB pump insertion can be considered in various disease groups, including stroke, spinal cord injury, brain injury, and multiple sclerosis [8]. Compared to oral baclofen, intrathecal pumps had a direct effect on gamma-aminobutyric acid receptors in the spinal cord, which enabled a significantly lower dosage to be used [7].

There are no accurate statistical data with regard to the use of ITB in CP. In Vender et al. [9]’s paper, two surgeons performed ITB pump insertions on 108 children with CP over 5 years. In a meta-analysis, which includes 48 papers, selective dorsal rhizotomy (SDR) was performed in 54% and ITB pump was performed in 29% for the purpose of controlling spasticity in children with CP [10].

Although there are complications, such as infection, wound dehiscence, cerebrospinal fluid leakage, and overdose or withdrawal symptoms of baclofen, baclofen pump has been used so far to alleviate spasticity. Along with the pump’s effect on spasticity, ITB pump insertion has been shown to reduce the probability of additional orthopedic surgery [11,12].

Until now, the ITB-related meta-analysis in CP was limited to the comparison of the influence on spasticity and superiority with rhizotomy rather than on the risk of scoliosis progression [10,13-16]. In terms of spasticity, there were studies that showed that it was helpful in CP patients, and there were no uniform studies on long-term effect [15]. When compared with SDR and extracorporeal shockwave therapy, ITB was a less invasive method for treating spasticity in children with CP [14]. As the number of cases using ITB pump in CP increased, studies on various effects and side effects caused by the pump began. The impact on scoliosis after pump insertion had controversial conclusions, with some studies suggesting that ITB pumps accelerate scoliosis progression and others suggesting the opposite [17-24].

Regarding the fact that the prevalence of scoliosis in CP patients reaches as high as 76% [12] and the rate of scoliosis progression varies with the growth of children, it is important to identify how ITB pump insertion affects scoliosis in determining its usefulness. Therefore, given that two theories coexist with regard to the influence of an ITB pump on scoliosis, this study aimed to analyze how ITB pumps affect the progression of scoliosis in patients with CP.

The Preferred Reporting Items for Systematic Review and Meta-Analyses checklist was used in this study (Supplementary Material) [25].

The four studies [19,20,22,23] included in this meta-analysis were divided into two groups with conflicting conclusions. In two studies [19,20], ITB pump insertion accelerated scoliosis, while no statistically significant difference in annual Cobb’s angle change was found in the remaining two [22,23]. The current meta-analysis included a total of 181 and 197 children with and without ITP pump insertion, respectively. Children with CP and ITB pump insertion showed greater annual changes in the Cobb’s angle than those with CP without ITB pump insertion. Data synthesis and meta-analysis showed that the four studies were homogeneous, and a funnel plot confirmed that there was no publication bias.

Until now, the available systematic review of ITB pump in children with CP has focused mainly on whether there is an improvement in spasticity. In 2000, the American Academy for Cerebral Palsy and Developmental Medicine performed a systematic analysis of 17 studies after screening papers from 1956 to March 2000 [26]. Twentysix out of the 32 measures of spastic signs, such as muscle tone, range of motion, and functional level, showed improvement after ITB pump application. In particular, ITB pump was found to be more effective in controlling spasticity in the lower extremities; however, its effect was not yet clear in the upper extremities. The functional level and caregiver burden improved. Complications were also described in this systematic review, most of which were medical problems, such as hypotonia, device-related events, seizure, and headache, whereas there was no mention of scoliosis [26].

There have been limited studies showing the relationship between spasticity and ITB pump in CP children, but studies on the factors that may affect scoliosis acceleration in CP children are abundant. In children with CP, Willoughby et al. [27], using Gross Motor Function Classification System (GMFCS) 1 as the reference value, reported that GMFCS 4 had odds ratio (OR) of 15.3 (95% CI, 6.6–35.5) and GMFCS 5 had OR of 23.4 (95% CI, 9.9–55.6). Also, 18% of GMFCS 4 and 48% of GMFCS 5 children had scoliosis, with Cobb’s angle being larger than 40 degrees. In a population-based study including 962 CP patients [28], GMFCS 4 showed a hazard ratio of 15 (95% CI, 9–30), GMFCS 5 of 53 (95% CI, 28–100) when compared to GMFCS 1 and 2. These large population-based studies [27,28] suggest that GMFCS is an important prognostic factor for scoliosis progression. In the four papers included in the current meta-analysis, all children had GMFCS levels of 4 and 5; thus, we ruled out the impact of GMFCS level on the progression of scoliosis. Given that age and GMFCS level of patients were similar in the four studies, homogeneous and meaningful conclusions could be drawn.

Further, in another study by Gu et al. [29] with 110 nonambulatory spastic tetraplegic CP children, age and Cobb’s angle >40 degrees at age 12 years were correlated with aggravation of scoliosis in a multivariate regression model. Given that Walker et al. [20] found no significant difference in age at last follow-up and the other three papers [19,22,23] also reported no significant difference in age at baseline, we ruled out the impact of age on scoliosis progression and ITB pump insertion. Three out of the four studies [20,22,23] reported no statistical difference between ITB pump and non-ITB pump groups with regard to the initial Cobb’s angle. In the remaining one study [19], the initial Cobb’s angle was more severe in the control group (35.1±20.7) than in the ITB pump insertion group (22.0±17.2). We predicted that the control group would show acceleration of scoliosis, but in reality, the rate of acceleration of scoliosis was faster in the ITB pump group. In addition, since the initial cobb’s angle was less than 40 degrees in all studies, with age under 12 years [19,20,22,23], we could rule out the effect of Cobb’s angle at presentation on scoliosis progression. Thus, we concluded that ITB pump insertion was the only variable in our study with greater clinical significance. Therefore, this meta-analysis has been a clinically significant study in analyzing the effect of pump insertion on scoliosis progression.

The association between ITB pump insertion and scoliosis has not yet been clearly elucidated. In addition, it is unclear how to distinguish between the natural course of scoliosis progression and the effect of the ITB pump. A possible mechanism is that hypotonia caused by baclofen increases instability and worsens scoliosis [30,31]. Therefore, it is meaningful to compare a control group without ITB insertion and an ITB pump insertion group, as in this meta-analysis. This study demonstrated that pump insertion resulted in the acceleration of scoliosis.

This study has some limitations. In this study, since Cobb’s angle was measured annually in patients with CP who were mainly about to undergo surgery, most of them progressed in the direction of aggravating scoliosis. Since the study was conducted on children with GMFCS levels of 4 or 5 and most of the patients who underwent baclofen pump insertion generally presented poor clinical manifestations, the annual scoliosis progression rate recorded by the Cobb’s angle might have been higher than that in the natural course of the disease. In addition, although a significantly larger number of procedures is currently performed than in the 1980s, the total number of patients who underwent pump procedures in this systematic review was limited to 181 due to the procedure’s invasiveness and the inclusion criteria. Despite these limitations, this systematic analysis is meaningful as it analyzed the effect of ITB pump insertion from a new perspective of scoliosis rather than spasticity, with Cobb’s angle as an objective indicator.

Our study supports the view that ITB pumps may accelerate the rate of scoliosis progression in children with CP. Managing scoliosis is clinically important because it affects the maintenance of a sitting or standing posture, the performance of activities of daily living, and the caregiver burden [31,32]. Future studies are needed to reveal the clinical and long-term effects and mechanisms of scoliosis of the ITB pump through case-control studies with a larger sample size. In the meantime, the ITB pump should be carefully applied to appropriate patients at the right time, considering its advantages and disadvantages between spasticity control and scoliosis exacerbation.