Computed tomography–based determination of a safe trajectory for placement of transarticular facet screws in the subaxial cervical spine

Spinous Process Screw Fixation: A Salvage Technique in Subaxial Cervical Spinal Instrumentation

OBJECTIVE

We sought to evaluate the feasibility and efficacy of spinous process screws in subaxial cervical fixation.

METHODS

A retrospective study was conducted on 7 patients receiving posterior cervical instrumentation for subaxial fracture dislocation or atlantoaxial dislocation from 2014 to 2015. In addition, a biomechanical test was performed on 7 fresh-frozen cadaveric spine samples (from the occiput to C7) from healthy human subjects with no history of spinal trauma. And lastly, the potential trajectories of cervical spinous process screws of 100 adults were measured through axial computed tomography in order to establish the general rule for applicability of this technique.

RESULTS

Rigid fixation and solid fusion were achieved in all 7 patients included in the study. Biomechanical test results revealed no significant difference between bilateral lateral mass screw fixation and the hybrid lateral mass and spinous process screw fixation constructs. Measurement of the potential trajectory suggested that spinous process screw fixation was a viable technique in the subaxial cervical spine in the general population.

CONCLUSIONS

The spinous process screw fixation technique in the subaxial cervical spine is a viable and effective salvage option for patients in whom conventional posterior fixations were not sufficient and salvage, supplementary techniques were required.

Lateral mass screw fixation in cervical spine injury

Objective:

To determine clinical outcome in patients with cervical injury after lateral mass screws fixation in a tertiary care hospital.

Methods:

This study included 88 patients, with cervical injury confirmed radiologically. Patients <12 or >70 years, with traumatic discs, cord compression without subluxation and previously operated on cervical spine were excluded from this study. All patients underwent fixation with lateral mass screws through posterior approach under fluoroscopic guidance. Frankel grading was used to assess the clinical status of these patients pre-operatively & post-operatively.

Results:

There were 60(68.18%) males and 28(31.8%) females. The ages varied from 18 to 55 years with a mean of 32 yrs ± 8 yrs. The most common level of injury was C5-C6 in 46(52%) patients. According to Frankel grading system, 35 (39.8%) patients were placed in Grade A, 15(17.05%) in Grade B, 22(25%) in Grade C, 12 (13.6%) in Grade D, four (4.5%) in Grade E on admission. Postoperatively, 16 (18.2%) patients were placed in Grade A, 23 (26.1%) in Grade B, eight (9.1%) in Grade C, nine (10.2%) in Grade D and 26(29.6%) patients in Grade E with an overall improvement in neurological function in 51(58%) and power in 37(42%) patients. The major complications encountered were respiratory infections in 10(11.36%) and wound infection in four (4.5%) while eight (9.1%) patients expired.

Conclusion:

Lateral mass screws technique is a safe and effective method for cervical fixation after proper reduction.

Biomechanical comparison of transfacet screws to lateral mass screw-rod constructs in the lower cervical spine

PURPOSE

Transfacet screws have been used as an alternative posterior fixation in the cervical spine. There is lack of spinal stability of the transfacet screws either as stand-along constructs or combined with anterior plate. This study was designed to evaluate spinal stability of transfacet screws following posterior ligamentous injury and combined with anterior plate, respectively, and compare transfacet screws to lateral mass screw-rod constructs.

METHODS

Flexibility tests were conducted on eight cadaveric specimens in an intact and injury, and instrumented with the transfacet screw fixation and lateral mass screw-rod construct at C5-C7 levels either after section of the posterior ligamentous complex or combined with an anterior plate and a mesh cage for C6 corpectomy reconstruction. A pure moment of ±2.0 Nm was applied to the specimen in flexion-extension, lateral bending, and axial rotation. Ranges of motion (ROM) were calculated for the C5-C7 segment.

RESULTS

ROM with the transfacet screws was 22 % of intact in flexion-extension, 9 % in lateral bending and 11 % in axial rotation, while ROM with the lateral mass screw-rod construct was 9 % in flexion-extension, 8 % in lateral bending and 22 % in axial rotation. The only significant difference between two constructs was seen in flexion-extension (5.8 ± 4.2° vs. 2.4 ± 1.2°, P = 0.002). When combined with an anterior plate and mesh cage, the transfacet screw fixation reduced ROM to 3.0° in flexion-extension, 1.2° in lateral bending, and 1.1° in axial rotation, which was similar to the lateral mass screw-rod construct.

CONCLUSIONS

This study identified the transfacet screw fixation, as stand-alone posterior fixation, was equivalent to the lateral mass screw-rod constructs in axial rotation and lateral bending except in flexion-extension. When combined with an anterior plate, the transfacet screw fixation was similar to the lateral mass screw-rod construct in motion constraint. The results suggested the transfacet screw fixation a biomechanically effective way as supplementation of anterior fixation.

Age-related morphologic changes of the vertebral artery in the transverse process. Analysis by multidetector computed tomography angiography

BACKGROUND CONTEXT

The V2 segment of the vertebral artery (VA) ascends and passes through the transverse foramen (TF) of the C6-C1 vertebrae. Atherosclerosis of the VA and degenerative changes in the cervical spine are likely to occur with aging, and subsequent morphologic changes may alter the normal anatomy.

PURPOSE

The aim was to determine the morphologic changes of TF and VA in relation to aging.

STUDY DESIGN/SETTING

This was a retrospective cross-sectional study.

PATIENT SAMPLE

One hundred ten consecutive patients who had undergone computed tomography angiography were included.

METHODS

The subjects were then divided into three groups according to age: Group A, less than 45 years; Group B, from 45 to 65 years; and Group C, older than 65 years. Cases with stenosis and dissection of the VA were excluded from the quantitative analysis. The areas of the VA and TF were measured, and the VA/TF occupation ratio (OR) was calculated accordingly. The presence of VAs tortuosity within the TF was also noted.

RESULTS

The TF was larger in the oldest group, but the difference was not statistically significant. There was also no significant statistical difference among the age groups in terms of the VA and VA/TF ORs (p>.05). In the Group C, the rate of overall tortuosity of the VA was 73%, and arterial tortuosity in the TF was 28.6%. In cases with tortuous VA, C6 and C4 TFs were found to be significantly larger.

CONCLUSIONS

Tortuous VAs tend to be associated with enlargement of C6 and C4 TFs. Knowledge of such changes in the anatomy is crucial during instrumentation used for cervical spine surgeries, to prevent serious complications in patients aged older than 65 years.