Our meta-analysis included 13 cohort studies covering 8424 individuals to provide a comprehensive evaluation of the long-term motor function recovery, complication, and mortality rates after early and delayed surgery in CCS patients. The results suggested that early surgical decompression was associated with improved motor recovery and fewer complications; however, no significant difference in mortality was reported.

CCS is usually caused by hyperextension of the cervical spine and may result in reduced diameter of the spinal canal. The cervical disc, posterior longitudinal ligament, and ligamentum flavum compress the cervical spinal cord anteriorly and posteriorly, causing severe damage to the central portion [30,31,32,33]. The management of CCS remains one of the most debatable topics due to the highly variable clinical presentation (mild sensory impairment to significant loss of function) and divergent periods to achieve neurological functional recovery (hours to months) [28, 34, 35]. Although the recommended treatment for CCS is surgical intervention, especially for patients with spinal instability, neurological deterioration, and severe spinal stenosis, decompression and widening of the spinal canal can significantly reduce the risk of posterior spinal cord contusion, edema, bleeding, or ischemic injury. However, due to variations in clinical presentation and postoperative recovery of CCS, the precise timing of surgery remains unclear [19, 36].

Some studies reported that early surgical decompression improved the long-term motor function in CCS patients more than delayed surgery; therefore, should be used as a neuroprotective treatment [16, 17, 23]. In addition, early surgery reduces the incidence of postoperative complications, including cardiac function and infections [5, 15]. Additionally, early surgery demonstrated good Japanese Orthopaedic Association (JOA) scores [37] and ASIA grading [38], while it lowered neuropathic pain [16], postoperative hospital stays [24], and total hospital costs [5]. However, studies on these outcome indicators are limiting; therefore, further studies are needed to support these findings.

Conversely, some studies demonstrated no significant difference in motor function recovery between early and delayed surgery [18, 22, 28]. Nevertheless, delaying surgery, if possible, can optimize the health status of patients and reduce surgical mortality in CCS, thereby maximizing the benefits for patients [19].

Further, we analyzed the comparative studies on AMS, complication rates, and mortality in early and delayed surgeries. While two studies defined early surgery as the one performed on the admission day [5, 15], those performed within 24 h were early according to other studies [17, 26, 27, 29]. Similarly, the surgery was considered early if performed within 2 days [24], 3 days [22], 4 days [18, 28], or 2 weeks [16, 23, 25]. Therefore, our study can better reflect the general trend of the effect of operation timing on CCS, and the results support the view that early surgery is more advantageous. Moreover, it can provide a future reference for the clinical diagnosis and treatment of CCS by spinal cord surgeons (if the patient's physical condition allows, early surgery may be preferable to delayed surgery).

Next, our results showed that early surgery more effectively improved AMS. AMS is a good indicator of the motor scoring system which helps to quantify early neurological deficit and motor recovery. Due to its reliability, AMS is widely used in the assessment of motor ability in SCI patients [39]. The improvement in AMS scores after early surgery may be attributed to early spinal stability and decompression, thereby reducing the possibility of irreversibly damaged spinal cord and nerve roots. Additionally, considering the advances in medical technology, surgery at an earlier stage can optimize patients' physical condition to rebuild the steady state of the spine at the earliest, thereby reducing mortality. In addition, early surgery can reduce the incidence of further complications and improve the postoperative state compared with delayed surgery.

In addition to the surgical treatment, studies have reported conservative therapy as an acceptable approach for CCS patients due to the spontaneous recovery of neurological function. Shrosbree reported that conservative therapy in CCS with extension SCI alone may lead to favorable clinical outcomes [40]. Ishida and Tominaga studied CCS patients (n = 22) without cervical spine fractures treated by conservation therapy, and reportedly, nearly all patients showed significantly improved neurological function within 6 weeks after the injury [41]. Similarly, Pollard and Apple evaluated the outcomes of conservative and surgical treatments in CCS patients, including those without cervical spine fractures or dislocations. Both treatments demonstrated improved neurological function without any significant differences [42]. Collectively, it is evident that some CCS patients have intrinsic recovery potential without undergoing surgical intervention. Therefore, conservative therapy should be considered in the decision-making process by surgeons and treating teams. Despite the acceptance of conservative treatment in many studies, it is crucial to understand that conservative therapy should only be considered for patients with spinal stability.

For CCS patients with associated fractures or dislocations, early surgery can relieve spinal cord compression while reconstructing spinal stability, which may lead to early recovery of neurological function. Thus, the severity of bony or structural or "mechanical" integrity plays an important role in the indication for surgical intervention. Our analysis included all the studies reporting the timing of surgical decompression in CCS. Only a few studies studies excluded CCS patients with associated fractures or dislocations [18, 22], while most others included such cases [5, 15,16,17, 23,24,25,26,27,28,29]. Due to insufficient literature, the subgroup analysis was not feasible for CCS caused by different mechanisms. Therefore, further research is needed to differentiate between the various etiologies of CCS (CCS with or without cervical spine fractures or dislocations) to determine the therapeutic efficacy of early surgery for CCS caused by different mechanisms.

A few limitations of this study should be acknowledged. Firstly, we included all the studies reporting the timing of surgical treatment of CCS. However, several inconsistencies were reported in defining "early surgery" in these studies. Two defined it as "admission day," four as "within 24 h," one as "within 2 days," one as "within 3 days," two as "within 4 days," and 3 as "within 2 weeks." Due to the limited number of studies, subgroup analyses were not feasible. Therefore, this phenomenon introduced bias and allowed us to conclude that early surgery significantly affected functional recovery and reduced complications; however, the optimal timing for surgery could not be defined to establish that early surgery was better. Secondly, the quality of the observed studies needs further assessment. The 13 cohort studies did not adequately eliminate the confounding factors; therefore, the observed differences in functional recovery and complications may have resulted from confounding effects of early surgical decompression indications. Thirdly, various mechanisms underlying CCS may also influence our results. CCS patients are often elderly, where mild trauma causes spinal canal stenosis without notable complications, but some patients may have fractures or dislocations, leading to potential differences in neurological recovery after early surgery [30]. Some studies excluded CCS patients with concurrent fractures or dislocations, while others included such cases, thereby showing biased results. Future studies should grade CCS patients to assess the impact of early and delayed surgery on neurological recovery, complications, and other outcome indicators.

Due to these study limitations, it is recommended that surgeons should use their own clinical experience and judgment rather than relying on the results of meta-analysis for making surgical decisions. Furthermore, randomized controlled trials (RCTs) on early and delayed surgical decompression for CCS patients may face ethical challenges; therefore, conducting high-quality prospective cohort studies is crucial, with subgroup analyses of different underlying mechanisms and early timing, to address the following two issues: (1) whether early surgery is more effective and safer than delayed surgery for CCS patients with or without fractures and dislocations and (2) optimal period for early decompression of CCS.

Despite the above-mentioned limitations, our study is the first meta-analysis to evaluate the effectiveness and safety of surgery timing. Previously, the reviews of similar studies were available without meta-analyses, due to the small number and low quality of studies [43,44,45]. Our study included reports published till February 2023 and approximately 69% (9/13) of these were published after 2020. The increased number of available evidence allowed us to exclude some low-quality cases. Our meta-analysis included eight studies (62%) that only included patients who underwent decompression surgery after 2011 by utilizing the latest surgical techniques and therefore were more applicable in developing current guidelines for early surgical decompression of CCS. In addition, we demonstrated the crucial role of early surgical decompression for CCS and provided suggestions for defining time thresholds and selecting outcome indicators for future studies, as well as guided spinal clinicians in determining the timing of surgery up to some extent.