The effectiveness of nonsurgical treatment for PE with the VB was evaluated through a cross-sectional study using questionnaires conducted at Hunan Children's Hospital in Hunan, China. This study received approval from the Institutional Ethics Committee of Hunan Children's Hospital (No. HCHLL-2024-83), and informed consent was obtained from all participants and their parents.

The questionnaires were distributed to the parents between September and October 2021. Parents whose children received VB treatment from January 2018 to December 2019 were included in this study. Inclusion criteria comprised of: VB treatment for PE, age ≥1 year, treatment duration ≥6 months, and consent provided by the patient's father, mother, or guardian for accessing their data for research purposes. Exclusion criteria consisted of: absence of chest sinking determination at the start of treatment, osteogenic syndrome presence, and withdrawal from clinical follow-up.

The parents were invited to participate in the study and complete online questionnaires 6 months to one year after the commencement of the research. The caregivers provided reports on daily VB usage (average duration in minutes and frequency per day), treatment duration (accumulated months of use), vacuum pressures (kPa), among other factors. Apart from subjective assessment, we also used the CT scan and 3D scanner to record treatment outcomes. After approval, every patient underwent initial CT scan upon ordering of a VB and later follow-ups every 3 months to half a year during use of the device. The 3D scanner was used to acquire body surface data on the standing position, which was used to record treatment outcomes, the collected body surface data were used for deformity documentation in order to compare with follow-up scans during the course of treatment.

The primary variables were analyzed using descriptive statistics and frequencies. Continuous data with a normal distribution were presented as mean ± standard deviation, while non-normally distributed data were reported as median and interquartile range. Categorical data were expressed in frequencies and percentages. Univariate analysis and multivariate logistic regression were conducted to analyze the therapeutic effect and identify factors associated with its effectiveness. Statistical analysis was performed using SPSS 27.0 (SPSS Inc., Chicago, IL, USA, 2020) software for Windows.

A total of 77 questionnaires were distributed, and 65 valid responses were obtained (Figure 2). In this study, a cohort of 65 children (50 males, 15 females) was enrolled. The mean age was (6.37 ± 3.28) years, the average height was (120.18 ± 20.20) cm, and the mean weight was (23.80 ± 10.22) kg (Table 2).

The mean duration of VB usage was 23.20 ± 9.86 months. Regarding complications, petechiae was reported by 29 patients (44.6%) during VB use, while blistering was reported by 14 patients (21.5%), along with some cases of pain and/or discomfort. All symptoms resolved after a short pause in treatment, without any permanent sequelae from side effects. In terms of effectiveness, based on subjective evaluations by caregivers, the majority considered the therapeutic effect to be moderate (27 patients; 41.5%) or good (30 patients; 46.2%), while 8 patients (12.3%) rated it as excellent, resulting in an overall effective rate of 100% for VB treatment. Among the participants, 52 patients (80%) continued using the VB unless instructed otherwise to pause or terminate its use, whereas 39 patients (60%) experienced at least one pause lasting more than two weeks (Table 3).

The objective of our study was to investigate the therapeutic efficacy and influencing factors of VB therapy in pediatric patients with PE. Our findings demonstrate a 100% effective rate for VB therapy, with an average duration of vacuum bell usage being (23.20 ± 9.86) months. Patients who experienced reduced incidence of petechiae complications were more likely to achieve favorable treatment outcomes, suggesting that proactive complication prevention and intensive management may be necessary in these individuals.

The non-surgical conservative treatment of PE with VB therapy was initially described by Schier et al. in 2005 (6). Since then, it has gained increasing popularity as a viable alternative to surgical intervention for carefully selected patients (15–17). However, the efficacy of VB therapy heavily relies on patient compliance and motivation. Therefore, it is crucial to conduct rigorous follow-up assessments to evaluate the long-term stability of correction achieved through VB therapy (17). Obermeyer (10) reported that nearly one third of their patients were either lost to follow-up or exhibited poor compliance.

In our study, all patients expressed satisfaction with the use of the VB, although subjective assessment of improvement in PE varied among individuals. The subjective evaluation questionnaire revealed a 100% effective rate for VB therapy, with 41.5% showing moderate correction, 46.2% showing good correction, and 12.3% showing excellent correction. These findings are consistent with Haecker's (18) results from a study involving 133 patients, where sternum flattening was observed in 79%, despite a treatment discontinuation rate of 10%. However, the effectiveness rate in our study was significantly higher than the reported range of successful corrections in literature (13.5%–43.6%) (9, 10, 18). This discrepancy may be attributed to variations in evaluation tools used; some studies employed absolute depression depth measurements that did not account for patient body size or necessitated specialized measurement tools to quantify correctness, while others utilized Haller Index, Correction Index or modified percentage depth (19). In our questionnaire-based assessment conducted by caregivers who monitored long-term home treatments without hospital visits or during review intervals, treatment effectiveness was subjectively evaluated based on improvements in the degree of depression, though this approach is subjective it does provide insights into treatment progress and efficacy.

Contrary to previous literature, this study found no statistically significant association between age at treatment and outcomes. Obermeyer et al. reported better results in children under 11 years of age, possibly due to inclusion of both adult and pediatric patients (10). Therefore, the variation in complete correction rates among different age groups may be attributed to differences in chest wall flexibility. Our study included children with a mean age of (6.37 ± 3.28) years, all younger than 10 years. As children grow older, chest wall becomes stiffer and less flexible, which can influence treatment outcomes. All patients with available follow-up data demonstrated improved chest appearance as objectively and subjectively confirmed. Thus, the impact of age on the treatment outcome was limited in our study.

The effects of height, weight, duration of usage (months), duration per time and negative pressure on the treatment outcome were not statistically significant. This finding is consistent with Dengke Luo (8), who reported that daily usage time, initial negative pressure, sex, comorbidities, and family history also did not show statistical significance in relation to the treatment outcome.

The identification of influencing factors on treatment outcomes in this study has direct clinical applicability. Side effects, such as petechiae, blistering, discomfort or pain were reported at a similar rate to that found in literature. The occurrence of side effects may be attributed to excessive negative pressure regulation; however, all observed side effects were reversible and resolved by reducing suction pressure or pausing treatment for no more than two weeks (20). The utilization of VB was discontinued due to the occurrence of complications, which had the potential to impact treatment efficacy. This highlights the importance of educating patients and their families on managing complications throughout the entire treatment process, such as providing one-to-one guidance via Wechat, which proves to be an effective approach.

Another factor influencing therapeutic efficacy is equipment maintenance, which involves returning it to the manufacturer. As VB therapy is relatively new in the hospital where the study was conducted, there may be instances of equipment damage due to factors such as device malfunctions or improper use during treatment. Repairing the equipment requires time for it to be sent back and forth from the manufacturer, potentially affecting treatment effectiveness. In future treatments, we will establish communication with the manufacturer to ensure strict control over VB quality, thereby reducing product quality issues and minimizing treatment interruptions caused by objective reasons.

The limitations of this study include its retrospective design and the presence of patients lost to follow-up or with incomplete data. Additionally, it is important to note that the survey subjects were excluded from a single tertiary pediatric hospital, resulting in a relatively small sample size. Moreover, the self-reported questionnaire data on daily usage and pressure may be susceptible to memory-related or other errors. Furthermore, due to the young age of our patients and their exposure to winter during treatment, several pauses occurred for weeks or even months. Although parents were required to report these pauses, there is a possibility of errors when calculating the total duration. Furthermore, while treatment outcomes were assessed based on caregivers' measurements, aspects such as quality of life and changes in self-belief were not evaluated. Future studies should incorporate patient evaluations of outcomes and measure chest depression.