Instrumentation of the posterior thoracolumbar spine: from wires to pedicle screws

Xu D. A novel technique for decortication of the lumbar facet joints for posterolateral fusion with percutaneous exposure: A cadaveric feasibility study

Background

Percutaneous approaches to the spine have been explored recently for various procedures, including transforaminal lumbar interbody fusion. It is known that facet decortication leads to higher rates of fusion, but effective percutaneous approaches have not been well documented. There are a set of instruments used in the cervical spine for percutaneous decortication, the CORUS™ Spinal System-X (DI# 00852776006508), which may be useful in this setting. Our aim was to investigate the feasibility of decorticating the lumbar facet joints with these instruments in cadavers to aid in minimally invasive lumbar fusion.

Methods

We performed percutaneous facet joint decortication at each facet joint in the lumbar spine in two adult cadavers. We tested varying degrees of laterality for entry points and angulation for access at each level to optimize the innovative procedure.

Results

When using the CORUS™ Spinal System-X to obtain percutaneous access for facet decortication in the lumbar spine, we successfully dissected down to the facet joint without neurovascular injury. At the L1-L2 and L2-L3 levels, access was best obtained at 4 cm from midline with an angulation of 10°. At the L3-L4 and L4-L5 level, access was best obtained at 4 cm from midline with an angulation of 20°.

Conclusions

This study demonstrates that percutaneous lumbar facet joint decortication is feasible with the CORUS™ Spinal System-X instruments, and warrants further, comparative study in the clinical setting.

A Novel Plate-Based System (UNIMAX) for Posterior Instrumented Spinal Fusion

Introduction

The polyaxial head pedicle screw-rod system is a commonly used spinal instrumentation technique to achieve stabilization, deformity correction, and bony fusion. We present a novel plate-based pedicle screw system (UNIMAX^TM) that can be used for multi-level instrumentation with potential advantages for selected applications.

Methods

Bilateral titanium monoaxial pedicle screws are linked at each level by robust transversely oriented cross plates forming ring constructs capable of rigid triangulation at each level. The cross plates are then interconnected by sagittally oriented rigid plates situated medial to the screw heads. Biomechanically, the construct was tested for quasi-static torsion and fatigue in axial compression. The system is approved by the Food and Drug Administration (FDA). The system and case examples are presented showing its potential advantages.

Results

The quasi-static torsion, the mean for the angular displacement, torsional stiffness, and torsional ultimate strength was 2.5 degrees (SD ± 0.8), 5.3 N-m/mm (SD ± 0.7), and 21.6 N-m (SD ± 4.4). For the fatigue in axial compression, the closed ring construct failed when the applied load and bending moment were ≥ 1500 N and ≥ 60 N.m. This system maximizes the construct rigidity, allows easy extension to adjacent levels, and can be incorporated intuitively into practice. The ring construct with triangulation at each level, together with its biomechanical robustness, predicts a high pullout resistance. It requires an open posterior approach incompatible with minimally invasive techniques.

Conclusion

This system may have advantages over the screw-rod systems in carefully selected situations requiring extra rigidity and high pull-out strength for complex reconstructions, sagittal and/or coronal correction, patients with poor bone quality, revisions, and/or extension to adjacent levels.

Accuracy of robot-assisted versus conventional freehand pedicle screw placement in spine surgery: a systematic review and meta-analysis of randomized controlled trials

This systematic review and meta-analysis investigated differences in accuracy, operation time, and radiation exposure time between robot-assisted and freehand techniques for pedicle screw insertion. Two investigators independently searched for articles on randomized controlled trials (RCTs) published from 2012 to 2019. The final meta-analysis included seven RCTs. We compared the accuracy of pedicle screw placement, operation time, and radiation exposure time between robot-assisted and conventional freehand groups. Seven RCTs included 540 patients and placement of 2,476 pedicle screws, of which 1,220 were inserted using the robot-assisted technique and 1,256 were inserted using the conventional freehand technique. The pedicle screw positions were classified using the Gertzbein and Robbins classification (grade A-E). The combined results of Grade A [odds ratio (OR) =1.68; 95% confidence intervals (CI): 0.82-3.44; P=0.16), Grade A+B (OR =1.70; 95% CI: 0.47-6.13; P=0.42), and Grade C+D+E (OR =0.59; 95% CI: 0.16-2.12; P=0.42) for the accuracy rate revealed no significant difference between the two groups. Subgroup analysis results revealed that the TiRobot-assisted technique presented a significantly improved pedicle screw insertion accuracy rate compared with that of the conventional freehand technique, based on Grade A, Grade A+B, and Grade C+D+E classifications. The SpineAssist-assisted technique presented an inferior pedicle screw insertion accuracy rate compared with that of the conventional freehand technique, based on Grade A, Grade A+B, and Grade C+D+E classifications. No difference between the Renaissance-assisted and conventional freehand techniques was noted for pedicle screw insertion accuracy rates, based on both Grade A (OR =1.58; 95% CI: 0.85-2.96; P=0.15), Grade A+B (OR =2.20; 95% CI: 0.39-12.43; P=0.37), and Grade C+D+E (OR =0.45; 95% CI: 0.08-2.56; P=0.37) classifications. Regarding operation time, robot-assisted surgery had significantly longer operation time than conventional freehand surgery. The robot-assisted group had significantly shorter radiation exposure time. Regarding the pedicle screw insertion accuracy rate, the TiRobot-assisted technique was superior, the SpineAssist-assisted technique was inferior, and Renaissance was similar to the conventional freehand technique.

History of Spinal Fusion: Where We Came from and Where We Are Going

Spinal fusion surgery is performed all over the world to help patients with cervical and thoracolumbar pathology. As outcomes continue to improve in patients with spine-related pathology, it is important to understand how we got to modern day spinal fusion surgery. Scientific innovations have ranged from the first spinal fusions performed with basic instrumentation in the late nineteenth century to contemporary tools such as pedicle screws, bone grafts, and interbody devices. This article tracks this technological growth so that surgeons may better serve their patients in treating spine-related pain and disability.

Accuracy of Current Techniques for Placement of Pedicle Screws in the Spine: A Comprehensive Systematic Review and Meta-Analysis of 51,161 Screws

BACKGROUND

Pedicle screws (PSs) are routinely used for stabilization to enhance fusion in a variety of spinal diseases. Although the accuracy of different PS placement methods has been previously reported, most of these studies have been limited to 1 or 2 techniques. The purpose was to determine the current accuracy of PS placement among 4 modalities of PS insertion (freehand [FH], fluoroscopy-assisted [FA], computed tomography navigation-guided [CTNav], and robot-assisted [RA]) and analyze variables associated with screw misplacement.

METHODS

A systematic review was performed of peer-reviewed articles reporting PS accuracy of 1 technique from January 1990 to June 2018. Accuracy of PS placement, PS insertion technique, and pedicle breach (PB) data were collected. A meta-analysis was performed to estimate the overall pooled (OP) rates of PS accuracy as a primary outcome, stratified by screw insertion techniques. Potential determinants were analyzed via meta-regression analyses.

RESULTS

Seventy-eight studies with 7858 patients, 51,161 PSs, and 3614 cortical PBs were included. CTNav showed the highest PS placement accuracy compared with other techniques: OP accuracy rates were 95.5%, 93.1%, 91.5%, and 90.5%, via CTNav, FH, FA, and RA techniques, respectively. RA and CTNav were associated with the highest PS accuracy in the thoracic spine, compared with FH.

CONCLUSIONS

The OP data show that CTNav has the highest PS accuracy rates. Thoracic PSs were associated with lower accuracy rates; however, RA showed fewer breaches in the thoracic spine compared with FH and FA. Given the heterogeneity among studies, further standardized and comparative investigations are required to confirm our findings.