Objective:To propose a new grading system-the posterior ligament-bone injury classification and severity (PLICS) score for subaxial cervical spine injury, and evaluate its value in guiding the approach selection for subaxial cervical fracture and dislocation.Methods:All of 394 cases of subaxial cervical fracture and dislocation who received single anterior reduction and fixation in our hospital from January 2002 to December 2015 were retrospectively analyzed. According to the inclusion and exclusion criteria, 354 cases were finally included in this study. The Patients experienced internal fixation failure, postoperative kyphosis or interspinal process space dilation during follow-up were included into the failure group. Other patients were included into the successful group. The difference of visual analogue scale (VAS), neck disability index (NDI), ASIA score and PLICS score before and after surgery between the two groups was compared respectively. The PLICS score is composed of left, right and posterior columns. The injury of the posterior column was classified into mild, moderate and severe degrees, with 1-3 points respectively. The evaluation of lateral column injury included ligament and bone structure. The evaluation of ligament injury included: 1 point for the subluxation of the facet joint, 2 points for the dislocation or the facet joint; Fractures of the lateral column was classified into mild, moderate and severe degrees, with 1-3 points respectively. For the evaluation of the lateral column, the highest score of ligament or bone structure injury was reflected as the score of posterior column injury and was taken into the calculation of the final PLICS score.Results:All 354 patients had complete follow-up data, and the average follow-up time was 18.0±4.0 months, including 339 patients of successful group and 15 patients of failure group. At the 12 month follow-up, the average VAS score of the patients in the successful group decreased from 6.9±0.6 before the operation to 1.9±0.6 ( t=22.481, P<0.0001), and the average VAS score of the patients in the failure group decreased from 5.6±1.0 to 1.1±0.3 ( t=77.252, P<0.0001). The difference between the two groups was statistically significant. The NDI score of the successful group was significantly lower than that of the failure group (7.1%±1.2% vs 15.7%±2.7%, t=24.993, P<0.0001). PLICS score in two groups of patients were analyzed. There was a significant difference in PLICS scores between the two groups ( t=8.777, P<0.0001). According to the PLICS score, the ROC operating curve of the failure of internal fixation after anterior-only surgery was determined. The area under the curve was 0.981, and the 95% confidence interval was 0.943, 1.000. When the PLICS score was 6.5, the maximum value of the Jordan index was 0.927, the sensitivity was 0.994, and the specificity was 0.067. Considering the clinical practicality of PLICS score and the different clinical outcomes of the sub-classification groups of the PLICS score=7, we finally set the threshold as PLICS score=7 with the unilateral severe lateral mass fracture. Conclusion:The PLICS score is based on the anatomy of the posterior three-column structure of the subaxial cervical spine. It gives consideration to the bony structures, including bilateral lateral mass, spinous process, lamina, and the ligament structures. What's more, the overall damage severity of the posterior three columns of the subaxial cervical spine was quantified according to the evaluation of the injury characteristics of each column of ligament-bone structure. In this study, PLICS score and clinical efficacy were compared between two groups of patients, and it was finally determined that when PLICS score ≥7 with the unilateral severe lateral mass fracture, the risk of internal fixation failure is higher for anterior-only approach surgery alone. For these patients, anterior and posterior approach surgery may be considered.