Spinal cord injury (SCI) is a catastrophic event caused by trauma that mechanically disrupts the spinal cord. SCI may result in a significant reduction in neurological function, creating considerable physical, mental, and economic burdens to patients, their families, and society [1]. Due to the disproportionately aging general population, a nationwide Japanese survey has previously reported marked changes in the characteristics of SCI [2]. The study showed that the most common neurological location of traumatic SCI was the cervical level (88.1%). Among cervical SCI (CSCI) cases, 70.7% have CSCI without bone injury; this combination most often occurs in the elderly after minimal trauma such as falling on a level surface [2]. For this study, we defined CSCI without bone injury as CSCI with no evidence of spinal fracture or dislocation on plain radiography or computed tomography, as was reported in a previous study [3].

Therapeutic strategies for CSCI without bone injury have been inconsistent among spine surgeons as surgical reduction and fixation of the spinal column are not required for this injury. Recently, Nori et al. reported that neurological outcomes are comparable between surgery and conservative treatment for CSCI without bone injury [4]. However, the potential influence of the timing of surgical treatment was not investigated in their study [4]. Other previous studies have demonstrated that early surgical treatment of traumatic SCI affords an opportunity to restore blood flow to the spinal cord and prevent secondary injury [5,6]. Further, there has been a growing acknowledgement among spine surgeons that early surgery for SCI is a judicious and safe treatment choice [[7], [8], [9]]. According to a multicenter international prospective cohort study, early surgery within 24 h of CSCI was 2.8 times as likely to show improvement by two or more grades on the American Spinal Injury Association (ASIA) impairment scale (AIS) 6 months after CSCI as compared with late surgery [10]. Moreover, in a pooled analysis of 1548 cases derived from four independent, prospective, multicenter traumatic SCI data sources, Badhiwala et al. showed greater neurological recovery and improved AIS grades at 1 year following surgery in patients who had undergone early surgery within 24 h of SCI than did those who had undergone late surgery [11]. Although studies have previously revealed the clinical advantages of early surgery for traumatic SCI, the therapeutic effectiveness of early surgery for CSCI without bone injury in the elderly has not been extensively investigated, and the results that do exist are controversial [[12], [13], [14]].

Many studies have advocated a cutoff for early surgery at 24 h after SCI [10,11,14,15]; however, surgery within 24 h of SCI can only be performed at dedicated hospitals and institutions where resources for accommodating complicated patients are available. A survey of 971 spine surgeons worldwide previously demonstrated that 80% of respondents preferred to perform early surgery; however, surgery within 24 h of admission was only feasible for 48.3% of the respondents [7]. Therefore, for this study we defined relatively early surgery as that conducted within 48 h of SCI, which was considered to be feasible for most spine surgeons. Further, surgery within 48 h was shown to have advantages for neurological recovery in a previous study [16]. Thus, this study aimed to investigate the influence of relatively early surgery on neurological recovery in elderly patients with CSCI without bone injury.