Segmentation failure of the posterior elements at the cervical spine and cervicothoracic junction: report of three cases.

PURPOSE: Vertebral segmentation and fusion failures are quite common and often occur as incidental findings. These anatomical variants may be associated with deformity and lead to pain and other neurological signs. They are less frequent in the cervical spine. We report three cases of rare posterior arch segmentation failure at the cervical spine and cervicothoracic junction, with an interesting pattern of laminar arrangement. METHODS: The clinical and radiological findings of three patients with unusual anatomical variants of the posterior elements of the subaxial cervical spine and cervicothoracic junction are reported. RESULTS: We found various association of scoliosis, partial butterfly vertebra, absent pedicle, transverse process and lateral mass anomalies. Interestingly, we report two different and unusual laminar morphologies. CONCLUSION: Congenital morphological disorders may occur at the lower cervical spine and cervicothoracic junction, and they can involve the vertebral body as well as the posterior arch. We reported three cases of uncommon malformations, with a unique Y- and S-shaped laminar pattern.

Risk Factor Analysis of Facet Fusion Following Cervical Lateral Mass Screw Fixation with a Minimum 1-Year Follow-up: Assessment of Maximal Insertional Screw Torque and Incidence of Loosening.

Posterior stabilization is a common surgical procedure, which aims for rigid stabilization by facet fusion. Facet non-union has a potential risk of the screw loosening and malalignment. Although some authors have reported the influencing factors about screw loosening in the lumbar spine, there are few reports about the risk factor contributing to the facet non-union in the cervical spine. In all, 22 patients (78 facets and 122 screws) with degenerative cervical kyphosis or spondylolisthesis who underwent decompression and lateral mass screw (LMS) fixation were analyzed. Age, gender, smoking, bone mineral density (BMD), the degree of facet decortication with bone packing, and screw loosening were investigated as risk factors contributing to the facet non-union at each segmental fused level. Facet fusion rate was 85.9% (67/78 facets) and the incidence of loosening was 4.9% (6/122 screws, 4 patients). Insufficient facet decortication with bone packing is a significant risk factor of facet non-union (p <0.05, odds ratio: 26.5). All six loosened screws were associated with bony non-union of the facet and were located in the uppermost or lowermost vertebrae. Comparing loosened screws and stable screws, the average maximal insertional screw torque (MIT) was 9.8 cNm and 39.5 cNm, respectively (p <0.05). Additionally, the length of the stable screws was significantly longer versus the loosened screws (p <0.05). Lower MIT and shorter screw length located near the ends of the lateral mass may predict loosening, which can lead to facet non-union. Sufficient facet decortication with bone packing is one of the important factors contributing to the facet fusion.

3-Dimensional printing templates guiding versus free hand technique for cervical lateral mass screw fixation: A prospective study.

OBJECTIVE: In this randomized, single blind and controlled study, the feasibility and precision of 3-dimensional printing templates for cervical lateral mass screw insertion was evaluated. METHODS: A total of 6 patients (72 screws), who were diagnosed with cervical spondylotic myelopathy (CSM) and developmental cervical spinal stenosis, were randomly divided into A and B two groups. All subjects underwent modified posterior surgery with using cervical lateral mass screws insertion (C4-C6). Group A underwent surgeries with screw insertion assisted by the guidance of 3-dimensional printing templates and Group B underwent surgeries with screw insertion by freehand. The criteria of the accuracy of screw placement were set as the main evaluation indicators. RESULTS: There was no significant difference between the 2 groups in age, improvement rate of JOA, operation time and blood loss. According to Bayard's criteria, 32 screws (88.9%) were described as "acceptable" in group A and 22 screws (61.1%) were described as "acceptable" in Group B (P < 0.05). Based on our criteria, the "excellent and good" rate of screws was 83.3% in group A and 47.2% in Group B, respectively (P < 0.05). The precision of screws' location in Group A was superior to that in Group B. CONCLUSIONS: 3-Dimensional printing screw insertion templates may achieve (1) comprehensive visualization of the cervical vertebrae and lateral mass and the individual surgical planning using the 3-dimensional model preoperatively. (2) increasing the accuracy of cervical lateral mass screw insertion.

Surgical training using three-dimensional simulation in placement of cervical lateral mass screws: a blinded randomized control trial.

BACKGROUND CONTEXT: The skills and knowledge that residents have to master has increased, yet the amount of hours that the residents are allowed to work has been reduced. There is a strong need to improve training techniques to compensate for these changes. One approach is to use simulation-training methods to shorten the learning curve for surgeons in training. PURPOSE: To analyze the effect of surgical training using three-dimensional (3D) simulation on the placement of lateral mass screws in the cervical spine on either cadavers or sawbones. STUDY DESIGN: A blinded randomized control study. METHODS: Fifteen orthopedic residents, postgraduate year (PGY) 1 to 6, were asked to simulate Magerl lateral mass screw trajectories from C3-C7 on cadavers using a navigated drill guide, but with no feedback as to the actual trajectory within the bone (Baseline 1). This was repeated to determine baseline accuracy (Baseline 2). They were then randomized into three groups: Group 1, control, did not receive any training, whereas Groups 2 and 3 received 3D navigational feedback as to the intended drill trajectory on sawbones and cadavers, respectively. All three groups then performed final simulated drilling (final test). All 3D images were deidentified and reviewed by a blinded single fellowship-trained orthopedic spine surgeon. Each image/screw was measured for the starting site, caudad/cephalad angle, and medial/lateral angle to determine trajectory accuracy. RESULTS: The aggregate mean difference from a perfect screw was compiled for each session for each group. A negative difference shows improvement, whereas a positive difference shows regression. The difference between final test and Baseline 1 in the control group was 2.4°, suggesting regression. In contrast, the differences for groups sawbone and cadaver were -8.2° and -7.2°, respectively, suggesting improvement. When comparing the difference in aggregate sum angle for the sawbones and cadaver groups with the control group, the difference was statistically significant (p<.0001). CONCLUSIONS: Training with 3D navigation significantly improved the ability of orthopedic residents to properly drill simulated lateral mass screws. As such, training with 3D navigation may be a useful adjunct in resident surgical education.