Early-onset scoliosis (EOS) is a complex condition defined as scoliosis with an onset before the age of 10 years, irrespective of etiology [1]. Because of their favorable risk–benefit ratio, conservative treatments, such as casting, bracing, and traction, are often preferred as initial interventions for patients with EOS [2,3]. However, surgical intervention becomes necessary when patients are noncompliant with conservative treatments or when complications such as skin ulcers arise. In patients with severe EOS, characterized by a Cobb angle exceeding 80°, surgery is often unavoidable [4]. The spinal fusion techniques used in adolescent and adult patients can result in spinal shortening and reduced thoracic cavities in patients with EOS due to incomplete skeletal development. Fortunately, growing rod technology has been used since the introduction of the Harrington rod in the early 1960s [5,6]. Growing rod technology is an effective treatment for EOS that involves limited spinal fusion at the cephalad and caudal ends, with rods spanning these fused segments linked by connectors. To accommodate spinal growth and curve progression, patients require multiple rod-lengthening surgeries. This technique maintains the corrective effects of the initial surgery while allowing near-normal spinal growth, although periodic rod lengthening is necessary. According to Akbarnia et al. [7], rod-lengthening surgeries are scheduled based on the patient’s age, sitting height, and curve progression and typically occur every 6 months. Thompson et al. [8] emphasized that, regardless of the curve progression, patients should undergo rod lengthening every 6 months. However, in practice, various factors often delay these surgeries beyond the 6-month interval. In a global survey of 265 patients undergoing growing rod surgeries, Yang et al. [9] found that despite the consensus among most physicians (12/17) on the necessity of 6-month intervals, the actual average interval was 8.6±5.1 months. Several studies have also reported intervals significantly exceeding 6 months [10–12]. At Beijing Chaoyang Hospital, particularly among patients from high-altitude regions, economic and transportation challenges often result in rod-lengthening surgeries being performed annually or even less frequently. Clinically, we observed an increased incidence of complications in patients who did not undergo rod lengthening within 1 year. Therefore, in this study, we aimed to investigate whether there are differences in curve progression and complication rates between patients undergoing growing rod lengthening within 1 year and those exceeding 1 year without lengthening.

EOS refers to scoliosis that occurs for various reasons before the age of 10 years [13]. Given the patients’ young age and ongoing growth and development, careful consideration of treatment options is essential [14]. Bracing is currently the only nonsurgical treatment proven to be effective, whereas other conservative approaches do not effectively control scoliosis progression. However, bracing is applicable only for patients with a Cobb angle of 20°–40° who are still in the developmental stage, and adherence to prolonged wear times can be poor [15]. Although braces can limit the progression of spinal deformity, they do not provide corrective benefits. Thus, patients who have more severe curvature and poor outcomes from conservative bracing may still require surgical intervention [16].

EOS typically affects younger patients, and direct surgical fusion can severely limit their growth potential. Postoperative complications, such as spinal shortening and crankshaft phenomenon, may arise, potentially affecting the cardiopulmonary function of these children [17]. To address these challenges, Harrington [6] introduced the single growing rod technique in the 1960s. This technique has since evolved into the currently used growing rod technique, specifically designed for the treatment of EOS.

The growing rod technique offers several advantages, including partial deformity correction, delayed progression of scoliosis, and preservation of the patient’s growth potential [18,19]. A series of distraction procedures are necessary as the patient’s spine and thorax continue to develop. These procedures are characterized by small incisions and shorter operative times, ultimately culminating in a final fusion and fixation surgery when growth ceases, a process colloquially referred to as the “graduation surgery” [9].

In growing rod surgery, most scholars generally recommend an interval between distraction procedures of every 6 to 12 months; however, a definitive interval has yet to be established. Some studies suggest that excessive distraction procedures can damage the cortical bone of the spine, increase the incidence of spontaneous fusion, enhance spinal rigidity, restrict growth potential, and diminish the overall effectiveness of the surgical correction [11]. Furthermore, each distraction procedure requires general anesthesia, which poses inherent risks and trauma to the child, and multiple surgeries also result in increased financial burden. Thus, some researchers have advocated for minimizing the number of procedures performed before fusion surgery, suggesting an interval of approximately 1 year between distractions [10,12].

Previous studies have examined the outcomes of annual distraction procedures, reporting that after a minimum of 5 years, the Cobb angle of scoliosis improved from a preoperative value of 73.8° to a final fusion angle of 42.7° [20]. In addition, another study demonstrated that a yearly distraction interval resulted in favorable corrective outcomes, with the Cobb angle improving from 73.3° preoperatively to 41.5° post-fusion [21]. These findings indicate that a 1-year interval for growing rod distractions is acceptable and not strictly limited to a 6-month interval.

Our research center has observed that many patients with EOS come from the Qinghai-Tibet Plateau region in China, where transportation is not easily accessible and travel costs can be a significant burden. In addition, language barriers and differing cultural practices contribute to a subset of patients being unable to return to our hospital for distraction procedures at the recommended intervals of every 6 months or annually. As a result, many require longer intervals between procedures. To the best of our knowledge, there is currently no relevant research on this topic; thus, in an attempt to fill this gap in the literature, this study aims to evaluate the effects of distraction surgery performed after an interval of more than 1 year.

Our findings indicate that patients in the group with intervals exceeding 1 year exhibited more significant scoliosis progression. Among those who underwent distraction surgery after more than 1 year, both the progression of the curvature and the incidence of imbalance were higher than in the group with shorter intervals. This is attributable to the fact that patients with EOS are in a critical growth phase, presenting a greater potential for growth and a higher risk of curvature progression; consequently, longer delays increase the likelihood of both progression and imbalance. However, we also noted that, despite the extended duration of growth and development, patients with intervals of >1 year had reduced height and spinal length of the intermediate segment of the growing rods as compared with those with intervals of ≤1 year. This discrepancy might be due to the lateral progression of the curvature overshadowing the vertical growth, resulting in height deficits. Previous studies have suggested that repeated distraction leads to gradual spinal rigidity and spontaneous fusion, which can interfere with spinal growth potential [11]. Noordeen et al. [22] measured the distraction force and length during extension surgeries in 26 patients with EOS and found that the force required for distraction increased with spinal growth, whereas the distance achieved with each distraction decreased over time.

Furthermore, patients who underwent distraction surgery after an interval of more than 1 year were more likely to experience complications related to instrumentation, spinal sequence, and general complications as compared with those in the other group, with a statistically significant difference in the overall complication rates between the two groups (p<0.05).

In this study, the complications we observed in patients with EOS primarily included hardware-related issues such as broken rods, broken screws, and screw loosening, as well as some cases of PJK. We believe that the primary reasons for these complications include increased stress on the instrumentation due to spinal growth and curvature progression, along with factors such as vigorous postoperative activities and trauma resulting in hardware displacement or fracture. In addition, improper placement of the instrumentation may contribute to subsequent hardware failure and the occurrence of PJK [11,23,24].

Previous studies have shown that the risk of complications associated with growing rods is negatively correlated with patient age and positively correlated with the number of surgeries performed, with each additional surgery associated with a 24% increase in complication risk [25].

Moreover, our results indicate that an interval that exceeds 1 year is also a risk factor for increased complication rates, which highlights the necessity of timely release of the stress generated by spinal growth. Thus, determining the interval for distraction surgery in patients is a multifaceted issue that requires considering factors such as corrective outcomes, spontaneous spinal fusion, patient growth potential, complication rates, and even patient costs. It is unwise to blindly extend the distraction intervals to reduce the frequency of procedures prior to fusion surgery.

The use of growth rods beyond 1 year and its potential consequences (such as accelerated progression of deformity, complications related to internal fixation, etc.) have been scarcely addressed in targeted international studies. This research not only provides important reference data for clinical practice but also offers optimized directions for surgical intervals, follow-up duration, and follow-up methods for such patients. This study aims to help the global medical community focus on the unique needs of these marginalized patients.

This study also has several limitations. Due to ethical constraints, we were able to conduct only a retrospective cohort study, which might have resulted in other factors influencing our findings. In addition, the limited number of included patients hindered our ability to perform subgroup analyses on different types of EOS. Future studies should incorporate a larger patient population to obtain more convincing results. Furthermore, most patients in the group with distraction intervals exceeding 1 year were from the Tibetan Plateau region, which may have introduced a degree of selection bias.

Despite these limitations, this study is the first to elucidate the impact of distraction intervals of longer than 1 year on surgical outcomes and complication rates. Our findings demonstrate that blindly extending the interval between surgeries to reduce the number of procedures prior to definitive fusion in patients with EOS is unwise, providing important clinical evidence for exploring the optimal distraction intervals.

When growing rod technology is used to treat patients with EOS, efforts should be made to minimize the trauma associated with regular distraction surgeries. However, extending the interval between the two distraction procedures beyond 1 year increases the risk of curve progression and spinal imbalance. In addition, a prolonged interval is correlated with a higher incidence of complications, potentially leading to an increase in unnecessary surgical procedures and greater patient suffering and costs. Thus, extending distraction intervals in an attempt to reduce the number of surgeries prior to definitive fusion is imprudent; currently, an interval of 1 year appears to be the most reasonable approach.