Safe placement of lateral mass screw in the subaxial cervical spine: a case series.

PURPOSE: Laminectomy with lateral mass screw fixation has been proven to be an effective method to treat the multilevel cervical degenerative myelopathy and severe cervical spondylosis. However, accurate and safe insertion of the lateral mass screw is technically demanding due to the individual variations of the anatomy of the lateral mass of the subaxial cervical spine. Misplaced lateral mass screw is not uncommon, and operation-related complications still beset the surgeons, which may impair the clinical outcomes. This study aimed to introduce a novel strategy for safe and accurate insertion of lateral mass screw in the subaxial cervical spine.

METHODS: From July 2014 to March 2015, 24 patients with multilevel cervical degenerative myelopathy at C3-C6 levels received laminectomy. Before the operation, the screw insertion technique depended on the pre-operative imaging and operative exploration. Following this strategy, the lateral mass screws were inserted into the subaxial cervical spines. Post-operative radiograph was performed to observe the locations of the lateral mass screws and the cervical curvature. Patients were followed up, and the functional neurological recovery was evaluated by the modified Japanese Orthopedic Association (JOA) disability scale, the Neck Disability Index (NDI) and NDI ranking system.

RESULTS: All screws were inserted into the lateral mass of C3-C6 cervical vertebrae following the current technique. Post-operative CT scans confirmed all screws inserted into the safe zone and relative safe zone of the lateral mass without any screw placed into the transverse foramen. The angle between the lateral mass screw and the vertical line was 40.49 ± 5.44 degrees on the axial CT images. Twenty-four patients were followed up for an average of 25.79 months (range, 20-30 months), and 22 cases evaluated as no or mild disability. According to the JOA score, NDI score and NDI ranking system, the postoperative function of the patients was significantly better when compared with their preoperative corresponding data (all p < 0.001) CONCLUSION: Inserting lateral mass screw following this new strategy is safe and easy to perform without any screw-related neurovascular complications, which contribute to the rigid fixation of the subaxial cervical spine and the satisfactory functional recovery.