Biomechanical Evaluation of a Novel Integrated C1 Laminar Hook Combined with C1-C2 Transarticular Screws for Atlantoaxial Fusion: An In Vitro Human Cadaveric Study

The Comparison Between Transarticular Screw Fixation and Segmental Screw-Rod Fixation for Posterior Fusion of the C1-2 Segment: A Systematic Review and Meta-Analysis

OBJECTIVE

Both transarticular screw fixation (TAS) and segmental screw-rod fixation (SF) have been widely performed for C1-2 fusion; however, just only small clinical studies and a few meta-analyses comparing the 2 surgical techniques for C1-2 posterior fusion have been reported.

METHODS

We searched the Cochrane, Embase, and Medline databases for articles comparing the intraoperative and postoperative outcomes of TAS and SF for C1-2 posterior fusion with April 14, 2022, as the publication cutoff date. The odds ratio (OR) and standardized mean difference were used to analyze differences in outcomes between the 2 abovementioned surgical techniques. A P value < 0.05 was considered statistically significant.

RESULTS

A total of 5101 publications were assessed, and 6 studies were finally included in the study. In terms of the fusion rate, SF produced significantly better outcomes than TAS did (OR = 2.96, P = 0.02). With respect to surgical outcomes, blood loss and operation times were significantly lower in the TAS group than those in the SF group (P = 0.008 and P < 0.00001, respectively). The rate of vertebral artery injury was significantly lower in the SF group than that in the TAS group (OR = 3.95, P = 0.04). However, other complications, such as screw malposition, infection, hardware failure, and nonunion, were not significantly different between the 2 groups.

CONCLUSIONS

SF showed a greater fusion rate and lower risk of vertebral artery injury than TAS did, but TAS showed less blood loss and lower operation times than SF.

Posterior atlantoaxial fusion: a comprehensive review of surgical techniques and relevant vascular anomalies

Posterior atlantoaxial fusion is an important surgical technique frequently used to treat various pathologies involving the cervical 1-2 joint. Since the beginning of the 20th century, various fusion techniques have been developed with improved safety profile, higher fusion rates, and superior clinical outcome. Despite the advancement of technology and surgical techniques, posterior C1-2 fusion is still a technically challenging procedure given the complex bony and neurovascular anatomy in the craniovertebral junction (CVJ). In addition, vascular anomalies in this region are not uncommon and can lead to devastating neurovascular complications if unrecognized. Thus, it is important for spine surgeons to be familiar with various posterior atlantoaxial fusion techniques along with a thorough knowledge of various vascular anomalies in the CVJ. Intimate knowledge of the various surgical techniques in combination with an appreciation for anatomical variances, allows the surgeon develop a customized surgical plan tailored to each patient's particular pathology and individual anatomy. In this article, we aim to provide a comprehensive review of existing posterior C1-2 fusion techniques along with a review of common vascular anomalies in the CVJ.

C2 Pedicle Screws Combined With C1 Laminar Hooks for Reducible Atlantoaxial Dislocation: An Ideal Salvage Technique for C1-C2 Pedicle Screws

BACKGROUND

A C1 laminar hook can theoretically avoid vertebral artery injury and is less technically demanding. However, only few studies with small samples analyzed the short-term outcomes of C2 pedicle screws combined with C1 laminar hooks (C2PS-C1LH) technique in the treatment of atlantoaxial dislocation. Furthermore, it is not confirmed whether similar clinical outcomes can be achieved with C1-C2 pedicle screw and rod construct (PSRC).

OBJECTIVE

To evaluate the outcomes of C2PS-C1LH and C1-C2 PSRC fixation techniques for treating atlantoaxial dislocation.

METHODS

Data of 52 patients with atlantoaxial dislocation treated by C1-C2 PSRC or C2PS-C1LH fixation were retrospectively reviewed. Outcomes evaluated by visual analog scale score for neck pain (VASSNP), Neck Disability Index (NDI), atlantodental interval (ADI), and the perioperative parameters including blood loss and operation time were analyzed and compared between 2 techniques. Patient satisfaction at final follow-up was also investigated.

RESULTS

There were no complications related to the surgical approach and instrumentation in either group. The mean bone fusion time was 5.06 ± 1.65 mo for the C2PS-C1LH group and 3.93 ± 0.99 mo for the C1-C2 PSRC group (P &gt; .05). Hundred percent of fusion rates were achieved in both groups at month 12 after operation. The ADI, VAS scores, the NDI scores, and the JOA scores were greatly improved in both the groups (P &lt; .05), but there were no significant differences between the 2 groups.

CONCLUSION

C2PS-C1LH fixation technique was comparable to C1-C2 PSRC in the treatment of reducible atlantoaxial dislocation. C2PS-C1LH fixation was an ideal alternative strategy to C1-C2 PSRC fixation.

Biomechanical Evaluation of an Anterior Upper Thoracic Plate Fixation System: An In Vitro Human Cadaveric Study

OBJECTIVE

This study aimed to evaluate the biomechanical characteristics of the anterior upper thoracic plate fixation system (AUTP).

METHODS

Twelve specimens were divided into 2 groups: the AUTP group and the anterior cervical locking plate (ACLP) group. Bone mineral density was assessed in all specimens. The specimens were loaded with pure bending moments of ±4 Nm to move toward extension/flexion, right/left lateral tilt, and right/left axial rotation. Each specimen was tested in 3 load cycles under 3 conditions (native, destabilized, and torsion). The tightening moments were assessed in every screw using a torsion meter.

RESULTS

The tightening moment of the AUTP screws was more pronounced than the ACLP (P < 0.05). Significant decreases after stabilization with the AUTP compared with the native situation were observed in the AUTP group (P < 0.05). In terms of the direction of lateral tilt and torsion, the neutral zone increased significantly after stabilization with the AUTP compared with the native situation (P < 0.05).

CONCLUSIONS

The AUTP was shown to provide more rigidity to the destabilized spine than the ACLP.

Comparison of Outcomes Between C1-C2 Screw-Hook Fixation and C1-C2 Screw-Rod Fixation for Treating Reducible Atlantoaxial Dislocation

STUDY DESIGN

Retrospective comparative study.

OBJECTIVE

To compare the outcomes of C1-C2 transarticular screw with C1 laminar hook (TAS + C1H) fixation and C1 trans-arch lateral mass screw with C2 pedicle screw (C1TLMS + C2PS) fixation in the treatment of reducible atlantoaxial dislocation (AAD).

SUMMARY OF BACKGROUND DATA

TAS + C1H is comparable to TAS with posterior wiring techniques and superior to C1 lateral mass screw combined with C2 pedicle screw (C1LMS + C2PS) in biomechanics. There were, however, few studies analyzing the differences in outcomes between TAS + C1H technique and modified C1LMS + C2PS technique (C1TLMS + C2PS) for treating AAD.

METHODS

Data of 30 patients with reducible AAD treated by TAS + C1H fixation and another 30 cases treated by C1TLMS + C2PS fixation were retrospectively analyzed. Bone fusion time was recorded. The outcomes evaluated by American Spinal Injury Association impairment scale, visual analog scale score for neck pain, neck stiffness (none/mild/severe), patient satisfaction, and Neck Disability Index (NDI) were compared between two groups.

RESULTS

There were no complications related to the surgical approach and instrumentation in either group. At the final follow-up, bone graft fusion rates were 100% in both the TAS + C1H fixation group and the C1TLMS + C2PS fixation group (P > 0.05). The neurological status evaluated by American Spinal Injury Association impairment scale were greatly improved in both screw-hook group (P < 0.001) and screw-rod group (P < 0.001), but with no significant differences between groups (P > 0.05). There were no significant differences between two groups in visual analog scale score for neck pain, neck stiffness, patient satisfaction, or Neck Disability Index (all P > 0.05).

CONCLUSION

C1TLMS + C2PS fixation was comparable to TAS + C1H fixation in fusion rate and functional outcomes for treating reducible AAD. To reduce the risk of vertebral artery injury, computed tomography scan, and reconstruction should be done to analyze vertebral artery course and C1-C2 anatomic structures before operation.

LEVEL OF EVIDENCE

3.