Is it true that treatment in patients with Subaxial Cervical Spine Injury Classification System (SLICS) 4 is the surgeon’s choice?

1. Introduction

The overall annual incidence of spinal cord injury was estimated at 13.0–163.4 per million [1]. A study from the US National Spinal Cord Injury Database reports that 56% of all Spinal cord injury cases occur in the cervical spine [2]. The subaxial cervical spine is a common site of cervical injury, with more than 50% of injuries being located between the C5 and C7 region [3, 4]. Despite the high number of patients with subaxial cervical spine injuries, there was a few of standardized algorithm for deciding whether to perform surgery or non-surgical treatment, and if surgery is necessary, what type of surgery is best. Many of these decisions are made based on the physician’s experience, patients’ condition, and the facility of each hospital [5, 6, 7, 8, 9]. A Consistent and proven algorithm for diagnosis and management is necessary to avoid devastating complications such as progression of neurological deficit, functional loss, and permanent disability.

In the context of trauma patients, the foremost consideration is whether or not surgical treatment is necessary. The assessment of these critical factors is multifactorial, requiring a careful assessment of several key factors including the extent of spinal cord injury, the presence of fractures, the overall health status of the patient, and the potential effectiveness of surgery. Given the importance of these considerations, various efforts have been made to systematize the evaluation process. Notably, the Subaxial Injury Classification System (SLICS), proposed by the Spinal Trauma Study Group, has become a widely utilized tool for evaluating the need for surgery in these cases [10].

The SLICS provides a standardized approach for classifying subaxial cervical spine injuries based on three key components: morphology, integrity of the discoligamentous complex (DLC), and neurologic status (Table 1). The morphology of subaxial cervical spine trauma was divided into 3 categories: compressive, distraction, translation/rotation. Simple compression is awarded one point, while a burst facture receives two points. Distraction injuries receive three points. Rotation/translation injuries receive four points. The components of the DLC include the intervertebral disc, anterior and posterior longitudinal ligament, ligamentum flavum, interspinous and supraspinous ligament, and facet capsules. An Intact DLC receives zero points. A disrupted DLC such as dislocation or separation of facet joints, subluxation of vertebral bodies or abnormal widening of a disc space is received two points. An Indetermined DLC such as MRI signal change only, assigned one point. Normal neurologic function is given zero points. A root injury receives one-point, complete cord injury receives two points and incomplete cord injury is assigned three points. If there is continuous cord compression in the setting of neurologic deficit, an additional one point is assigned. Non-surgical treatment is indicated for SLIC score 3 or less, while a score 5 or greater indicates surgical treatment. This classification system has been a valuable tool for surgeon in making decisions for subaxial cervical spine injuries. However, a SLIC score 4 is left as a gray area where a surgeon’s experience and other patient comorbidities may drive a decision on either surgery or non-surgical management.

Thus, further research is needed to clarify the optimal management approach for patients with an SLIC score of 4, and to refine the SLIC classification system to provide more definitive guidance. The treatment outcomes of the non-surgical treatment group were compared with those of the surgical treatment group in patients with SLIC score 4 in this study. Furthermore, an analysis was conducted to determine additional factors to consider when making decisions between surgery and non-surgical treatment.

3. Results

A total of 41 trauma patients were included in the study. Table 2 summarizes descriptive statistics of patients’ demographics. Twenty-two patients were treated non-surgically and classified as a group 1. Nineteen patients were surgically treated and classified as group 2. When comparing the two groups, there were statistically significant differences in the age and duration of admission between two groups. The mean age in the group 1 is younger than group 2, at 50.41 years versus 59.21 years ( p = 0.045). The duration of admission is 21.91 days in group 1 and 35.21 days in group 2 ( p = 0.011). Other characteristics such as trauma range of cervical spine, OPLL, ALL rupture, neck muscle contusion, cervical bone fracture, and use of steroid did not exhibit any statistically significant differences between the two groups. Essentially, the results of the two groups with similar characteristics who received different treatments were compared.

Table 3 summarizes the neurologic status of the two groups. There was no neurological deterioration in both groups. No statistically significant differences were observed between the two groups with respect to ASIA and Nurick grade at the last follow-up, with p -values of 0.926 and 0.919, respectively. When comparing the number of patients with improvement in the initial and last follow-up neurological status between the two groups, no statistically significant differences were observed, with p -values of 0.613 and 0.233, respectively. There were no differences in clinical neurologic outcomes based on the treatment method used.

Univariate logistic regression analysis was carried out for all follow-up data (Table 4). The result showed that high energy injury was associated with improvement in Nurick grade (OR = 4.900, p = 0.044). No significant differences were detected in age, sex, surgery, injury energy, duration of admission, trauma range, OPLL, ALL rupture, neck muscle contusion, cervical bone fracture, and use of steroids ( $p>$ 0.05). Especially, it can be confirmed once again here that there is no correlation between the surgical treatment and improvement in neurological status.

4. Discussion

Several papers prove the validity of the SLICS [6, 14, 15]. Samuel et al. [16] presented results of 185 patients with subaxial cervical spine trauma. Sixty-six patients had a SLIC score of 3 or less and 94% of them were non-surgically treated. One hundred two patients had a SLIC score of 5 or more, and 95% of them were surgically treated. Seventeen patients had SLIC score of 4, and 65% were non-surgically treated. Joaquim et al. [17] demonstrated a clinical study of 38 patients treated for subaxial cervical spine trauma. Fourteen patients were treated non-surgically, and just one patient had a SLIC score greater than 2 points. Twenty-four patients were treated surgically, and 22 patients had a SLIC of 4 or more. Da Cruz et al. [18] compared a cohort of surgically treated patients who underwent surgery on the surgeon’s preference and those based on the SLIC score. The first group included 12 patients, and SLIC scores ranged from 2 to 9 points. Two patients had an SLIC score of less than 4. The second group included 28 patients, and SLIC scores ranged from 4 to 9 points. As a result of these studies, the SLICS and treatment choice claimed by Vaccaro et al. [19] in 2007 was widely accepted. Despite all this research, the definitive recommendation for SLIC score 4 was not made, and SLIC score 4 remains an ambiguous domain. The neurological prognosis was compared between the group of patients with SLIC score 4 who underwent surgical treatment and the group who received non-surgical treatment. There is no statistically significant difference in the last follow-up ASIA and Nurick grade between the two groups ( p = 0.926, 0.919 each). There was no statistically significant difference observed when comparing the number of patients showing improvement in neurological status between the two groups, based on the comparison of initial neurological status and final follow-up neurological status. Neither AISA grade nor Nurick grade showed a statistically significant difference ( p = 0.613, 0.233 each). There was no neurological deterioration in both groups in ASIA and Nurick grade. SLIC score 4 showed a relatively good prognosis regardless of the treatment method.

In recent years, the ambiguity of SLICS score of 4 has been criticized as a structural limitation of the SLICS classification system [14]. The morphologic characteristic category was designed to simplify the classification system and allow for more intuitive interpretation and easy memorization. However, this has led to an over-simplification of injury patterns and a decrease in overall score reliability. There are certain injury patterns that often require surgery in clinical practice but may still result in a SLICS score of 4. For example, a burst fracture (2) with a nerve root injury (1) with continuous cord compression ( + 1) falls into this category. Another example is central cord syndrome in the context of cervical spondylosis (no abnormality 0 + DLC intact 0 + incomplete cord injury 3 + continuous cord compression 1), where patients typically present with severe neurological deficits, but no mechanical instability is observed on imaging studies such as CT or MRI. Whether to perform surgery in such cases has been a subject of ongoing debate [20, 21].

Various studies have been conducted to overcome these limitations. Dvorak et al. [5] performed a systematic review of the literature and proposed algorithms based on SLICS to guide the choice of surgery. Hitti et al. [22] assessed the predictors of failure on nonoperative management. Patients who were stabilized within 8 hours after injury had a decreased incidence of failure on nonoperative management. They found stabilization 24 hours after the injury results in increased failure of nonoperative management. They suggest a modified SLIC score that includes time to stabilization and osteoporosis. Song et al. [23] pointed SLICS cannot classify extension injury and suggested modified SLICS. The objective of this study was to determine the specific characteristics in which surgery would provide greater benefits for patients with an SLIC score of 4. To achieve this, a comparison was made between the surgical and non-surgical groups across various patient characteristics. In the surgical group, the mean age is significantly higher than in the non-surgical group (59.21 $>$ 50.31, p = 0.045) and the admission duration is also significantly longer (35.2 $>$ 21.9 days, p = 0.011). In our study, there are more cases of surgery in old age. If older patients have operation, the admission duration will be longer. Age difference between the two groups can be a factor that influences the results. Generally, older age is associated with poor prognosis, so if the age is matched similarly between the two groups, surgery may show better results than non-surgical treatment. This aspect requires further investigation in the future.

The result of the univariate analysis showed that high energy injury is related to the improvement of Nurick grade. In general, when receiving low energy injury, spinal cord injury is small and prognosis is good, and when receiving high energy injury, severe spinal nerve injury and poor prognosis are expected. Generally, accidental fall, which is one of the low energy injuries, is the most common cause of spinal cord injury without radiographic abnormality [24]. Even though if the injured patient’s SLIC score is 4 and it is injured by low energy, that patient may be already accompanied by spinal cord compressive lesion such as spinal spondylosis and stenosis. Therefore, cervical degenerations play a critical role in spinal cord injury and are associated with poor prognosis [25, 26]. This consideration may help explain the association between high-energy injuries and improved prognoses.

This study has limitations, such as a relatively small sample size, single-center study, and retrospective nature. The SLIC was scored by all authors together, and inter-rater reliability between observers was not conducted.

5. Conclusion

Regardless of the treatment method, spinal cord injury patients with an SLICS point of 4 showed a relatively good prognosis. When deciding on the treatment of SLIC 4 patients, it is necessary to consider the patient’s injury type and mechanism, as well as any pre-existing conditions such as cervical spondylosis. Additionally, it would be beneficial to consider the fact that older patients tend to have longer hospital stays if they undergo surgery. Therefore, multiple factors should be taken into consideration when deciding between surgical and non-surgical treatment for SLICS 4 patients.