As the population ages, the incidence of degenerative cervical disease is continuously increasing, which is the foremost cause of neurological deficit among adults worldwide.[6, 7] There is a paradigm shift in the treatment of degenerative cervical disease from posterior to anterior decompression, due to the direct removal of spinal cord compressions, such as disc herniation, osteophytes, and OPLL.[8-10] However, the anterior approach is associated with potential risks that can cause life-threatening complications in vulnerable organs anterior to the vertebral body, such as trachea, esophagus and blood vessels. Therefore, cervical spine surgery is associated with higher surgical difficulty than lumbar surgery hence the need to evaluate surgical difficulty and the associated risk factors for optimal performance in ACSS. From the perspective of developing surgical protocols, assessment of surgical procedure and surgical skill training, a classification system determining the difficulty level is extremely important. Moreover, adequate physician-patient communication is necessary for patients with high surgical difficulty.
Researchers have established several scoring systems for assessing the surgical difficulty. Natkaniec et al demonstrated that gender, tumor size, and localization are some of the parameters associated with the level of the surgical difficulty of the laparoscopic lateral transperitoneal adrenalectomy. Hasegawa et al established a novel model for the prediction of surgical difficulty in laparoscopic liver resection and included factors such as the extension of resection, location of tumor, obesity and platelet count. However, a preoperative scoring system evaluating the surgical difficulty of ACSS has not been reported. Therefore, due to lack of a gold standard to estimate for surgical difficulty, surrogate indicators are often used to indirectly reflect the difficulty and these include operative time, intraoperative blood loss and incidence of complication.[11-14] High-difficulty ACSS has been correlated with longer operative time and more intraoperative bleeding.
In this study, a number of parameters such as age, sex, BMI, number of operation levels, high signal intensity of spinal cord on T2-weighted images, OPLL, sagittal cervical circumference, coronal cervical circumference, cervical length, spinal canal occupational ratio, and coagulation function index were evaluated to identify risk factors for high-difficulty ACSS. Previous studies confirm that the elderly, obese patients and male gender are associated with longer operative time.[11, 12, 15] However, this study reported that there is no significant difference in terms of age, sex, and BMI between low-difficulty and high-difficulty groups of ACSS. Coagulation function index and platelet count are associated with intraoperative hemorrhage, however, no statistical significance in these factors was reported in our study. To our knowledge, thickness of neck might influence the operative time due to the difficulty of surgical exposure. Although surgical time tend to be longer in patients with thick neck, this trend did not reach statistical significance in our study.
Operational level was a vital factor affecting the difficulty of ACSS. In our study, as operational segments increased, prolonged operative time and more intraoperative blood loss were reported and these findings were consistent with previous research. Moreover, the incidence of complications associated with the surgical procedure increased when more segments were decompressed and fused. Kou et al reported that multilevel procedures had a significantly higher risk for epidural hematoma. Sagi et al also reported that the number of vertebral bodies exposed more than 3 levels and operative time longer than 5 hours were statistically associated with increased risk for airway complications with potentially catastrophic consequences. The selection of operational levels is mainly based on detailed clinical evaluation including extent of compression, chief complaint and the patient’s general condition. Adequate neurological decompression is essential for optimal clinical outcomes but caution should be made to reduce the affected segments to minimize surgical trauma and risk of potential complications.
The study demonstrated that OPLL was another predictive factor for high-difficulty surgery. The technical challenges faced when treating OPLL depend on the decompression procedure including less injury to the spinal cord and better protection of the venous plexus especially when combining dural ossification. Furthermore, OPLL is associated with high risks of perioperative complications, such as cerebrospinal ﬂuid leakage, dysphonia, dysphagia and neurological impairment. Spinal canal occupational ratio was used to represent the degree of compression and high signal intensity of spinal cord on T2-weighted images closely correlated with severe spinal cord compression. This study confirmed that the spinal canal occupational ratio and high signal intensity were risk factors for surgical difficulty. Therefore, surgeons should be cautious when severe compression and high signal intensity are observed on MR images.
For the clinical use of the established nomogram, a 0.906 C-index was reported for the model in addition to a good calibration curve for use in predicting the probability of high-difficulty surgery.
There are several limitations of this study that need to be addressed. First, this is a retrospective study. Second, this study was conducted in a single institution and the limited number of cases might restrict the value of its clinical use. Due to these limitations, prospective multi-center studies with a large sample size are needed to validate our results.