The FDA Reclassification of Cervical Pedicle and Lateral Mass Screws: A Case Study in Regulatory History

The classification of medical devices by the Food and Drug Administration (FDA) involves rigorous scrutiny from specialized panels that designate devices as Class I, II, or III depending on their levels of relative risk to patient health. Posterior rigid pedicle screw systems were first classified by the FDA in 1984 and have since revolutionized the treatment of many spine pathologies. Despite this early classification by the FDA, posterior cervical pedicle and lateral mass screws were not reclassified from unclassified to Class III and then to Class II until 2019, nearly 35 years after their initial classification. This reclassification process involved a decades-long interplay between the FDA, formal panels, manufacturers, academic leaders, practicing physicians, and patients. It was delayed by lawsuits and a paucity of data demonstrating the ability to improve outcomes for cervical spinal pathologies. The off-label use of thoracolumbar pedicle screw rigid fixation systems by early adopters assisted manufacturers and professional organizations in providing the necessary data for the reclassification process. This case study highlights the collaboration between physicians and professional organizations in facilitating FDA reclassification and underscores changes to the current classification process that could avoid the prolonged dichotomy between common medical practice and FDA guidelines.

Complications associated with subaxial placement of pedicle screws versus lateral mass screws in the cervical spine (C2-T1): systematic review and meta-analysis comprising 4,165 patients and 16,669 screws

Lateral mass screw (LMS) and cervical pedicle screw (CPS) fixation are among the most popular techniques for posterior fusion of the cervical spine. Early research prioritized the LMS approach as the trajectory resulted in fewer neurovascular complications; however, with the incorporation of navigation assistance, the CPS approach should be re-evaluated. Our objective was to report the findings of a meta-analysis focused on comparing the LMS and CPS techniques in terms of rate of various complications with inclusion of all levels from C2 to T1. We conducted a systematic review of PubMed and EMBASE databases with final inclusion criteria focused on identifying studies that reported outcomes and complications for either the CPS or LMS technique. These studies were then pooled, and statistical analyses were performed from the cumulative data. A total of 60 studies comprising 4165 participants and 16,669 screws placed within the C2-T1 levels were identified. Within these studies, the LMS group had a significantly increased odds for lateral mass fractures (odds ratio [OR] = 43.2, 95% confidence interval [CI] = 2.62-711.42), additional cervical surgeries (OR = 5.56, 95%CI = 2.95-10.48), and surgical site infections (SSI) (OR = 5.47, 95%CI = 1.65-18.16). No other significant differences between groups in terms of complications were identified. Within the subgroup analysis of navigation versus non-navigation-guided CPS placement, no significant differences were identified for individual complications, although collectively significantly fewer complications occurred with navigation (OR = 5.29, 95%CI = 2.03-13.78). The CPS group had significantly fewer lateral mass fractures, cervical revision surgeries, and SSIs. Furthermore, navigation-assisted CPS placement was associated with a significant reduction in complications overall.

Minimally Invasive Posterior Cervical Fusion: A Handsome Option

Cervical spondylosis is the leading cause of cervical myelopathy. When surgery is indicated, it is commonly addressed through an anterior or posterior cervical approach, such as cervical discectomy and fusion (ACDF) or laminectomy and fusion (LMF). Besides their own merits, each one has specific approach- or device-related complications, such as dysphagia, significant postoperative pain, wound infection, adjacent segment degeneration (ASD), and pseudoarthrosis. Through a tissue-sparing minimally invasive technique, posterior cervical fusion (PCF) has shown unfolding compelling evidence of biomechanical stability, good clinical outcomes, and high fusion rates, with fewer complications and better econometrics. On the basis of our own experience, we discuss here the indications, advantages, and drawbacks of minimally invasive PCF.

Complications associated with subaxial placement of pedicle screws versus lateral mass screws in the cervical spine: systematic review and meta-analysis comprising 1768 patients and 8636 screws

Lateral mass screw (LMS) fixation for the treatment of subaxial cervical spine instability or deformity has been traditionally associated with few neurovascular complications. However, cervical pedicle screw (CPS) fixation has recently increased in popularity, especially with navigation assistance, because of the higher pullout strength of the pedicle screws. To their knowledge, the authors conducted the first meta-analysis comparing the complication rates during and/or after CPS and LMS placement for different pathologies causing cervical spine instability. A systematic literature search of PubMed and Embase from inception to January 12, 2021 was performed to identify studies reporting CPS and/or LMS-related complications. Complications were categorized into intraoperative and early postoperative (within 30 days of surgery) and late postoperative (after 30 days from surgery) complications. All studies that met the prespecified inclusion criteria were pooled and cumulatively analyzed. A total of 24 studies were conducted during the time frame of the search and comprising 1768 participants and 8636 subaxially placed screws met the inclusion criteria. The CPS group experienced significantly more postoperative C5 palsy (odds ratio [OR] = 3.48, 95% confidence interval [CI] = 1.27-9.53, p < 0.05). Otherwise, there were no significant differences between the LMS and CPS groups. There were no significant differences between the CPS and LMS groups in terms of neurovascular procedure-related complications other than significantly more C5 palsy in the CPS group.

Intraoperative Computed Tomography-Assisted Spinal Navigation in Dorsal Cervical Instrumentation: A Prospective Study on Accuracy Regarding Different Pathologies and Screw Types

BACKGROUND

Intraoperative computed tomography (iCT) navigated dorsal instrumentation has been successfully introduced as a new clinical standard. The proximity of vital anatomic structures makes cervical spine instrumentation an especially delicate task. Therefore, navigated approaches might prove to be beneficial. In this study, the accuracy of conventional instrumentation was compared with iCT navigated dorsal cervical spine instrumentation with focus on cervical pedicle screws (CPSs) versus lateral mass screws (LMSs) and pathologies.

METHODS

We analyzed a prospective consecutive series of patients undergoing cervical dorsal instrumentation with iCT and spinal navigation and retrospectively analyzed a cohort that received conventional cervical instrumentation with C-arm fluoroscopy (control group). Accuracy was assessed with a modified Gertzbein-Robbins classification. Underlying pathologies were taken into account regarding accuracy in different entities.

RESULTS

Fifty-nine patients were treated using iCT (357 screws: 238 CPSs, 119 LMSs), and 98 patients underwent conventional instrumentation (632 screws: 69 CPSs, 563 LMSs). We achieved an initial accuracy of 93.28% (n = 220 screws) in the iCT group and 80.9% (n = 511 screws) in the control group (P < 0.001). Significant differences were found regarding the accuracy of CPS placement in cases of degenerative disorders (iCT vs. control; 94% vs. 63%; P < 0.001) and trauma (iCT vs. control; 88% vs. 72%; P < 0.05). iCT yielded favorable precision rates in regard to LMS placement (iCT vs. control; 94.2% vs. 82%; P < 0.05).

CONCLUSIONS

Accuracy of iCT navigated instrumentation was significantly higher than conventional instrumentation. An overall tendency toward the use of CPSs with iCT navigation is evident, increasing the mechanical properties of the construct. iCT appears to be especially beneficial in elective surgery cases of degenerative spinal disorders.

Accuracy of freehand pedicle screws versus lateral mass screws in the subaxial cervical spine

STUDY DESIGN

Radiographic comparative study with prospectively collected data.

OBJECTIVES

To assess the accuracy of subaxial cervical pedicle screw (CPS) placement with freehand technique compared to lateral mass screws (LMS). The freehand cervical pedicle screw insertion technique guided by intraoperative lateral C-arm imaging has been shown to be both safe and effective. However, no study has performed a 100% audit of this technique using pre- and postoperative computed tomography (CT) to determine its true accuracy, as well as its reduction capability of CPS and LMS instrumentation.

METHODS

36 consecutive patients treated surgically by a single surgeon with the exclusive practice of LMS and subsequently CPS over 2 years were included. CT and EOS slot scanner were performed pre- and post-operatively to determine the extent of pedicle screw breach and to assess sagittal alignment reduction between CPS and LMS groups. Predictors of pedicle screw breaches were also identified using multivariate analysis.

RESULTS

CPS fixation was more effective in restoring global cervical angle and had superior reduction capability of cervical lordosis at the levels of C3/4 (5.00 ± 3.92, p = 0.008), C4/5 (6.63 ± 5.5, p = 0.010) and C5/6 (7.22 ± 6.19, p = 0.004) compared to LMS fixation. Pedicle screw breaches occurred most commonly at C4 (p = 0.003), and most commonly involved the lateral pedicle wall (p < 0.001). Placement of freehand pedicles screws on the concavity of rotated vertebrae was predictive of pedicle screw breach (OR 2.567, 95% CI 1.058-6.228, p = 0.037). There was no significant difference in the complication rate.

CONCLUSIONS

Although freehand cervical pedicle screw fixation is technically more demanding, it is generally safe and effective. However, the increased risk of screw breaches in the context of a rotated spine should be taken into consideration. Lateral mass screw fixation is advised if spinal realignment is not necessary.

Computed Tomography Scan-Based Morphometric Analysis of Lateral Masses of Atlas Vertebrae in Normal Indian Population

Study Design

A cross-sectional observational study involved the analysis of computed tomography (CT) scan data from 125 Indian subjects of 18 years or older with normal imaging findings. Scans were obtained from patients with head injuries as a part of the screening process along with brain CT scans.

Purpose

To establish the dimensions of lateral masses of the atlas vertebrae in normal disease-free Indian individuals.

Overview of Literature

Lateral mass fixation has become the standard of care in fixation of the supra-axial cervical spine. Many studies have investigated the dimensions of lateral masses in cadaveric specimens; however, studies involving the radiological morphometric analysis of the lateral masses of the atlas vertebra in living patients are lacking.

Methods

Subjects underwent craniovertebral junction CT scans during evaluations of head injury. All had normal radiology reports. The CT scans were obtained using a CT Philips Brilliance 64 machine (Philips, Amsterdam, Netherlands) with a slice thickness of 1 mm and then analyzed using Horos software ver. 2.0.2 (Horos Project, Annapolis, MD, USA) on a MacBook.

Results

Lateral masses of the atlas vertebrae were found to be larger in males than females and larger on the right than the left side. The angle of permissible medialization was found to be larger on the right side. The analysis of the average dimensions indicated the conventionally described screw positions to be safe.

Conclusions

The present study provides information that may help to establish standard dimensions of lateral masses of the atlas vertebrae among the normal Indian population. We demonstrate that there is no significant difference when compared with the Western population. The results presented here will be of use to clinicians as they may inform preoperative planning for lateral mass fixation surgeries.

Posterior Rigid Instrumentation of C7: Surgical Considerations and Biomechanics at the Cervicothoracic Junction. A Review of the Literature

BACKGROUND

The cervicothoracic junction is a challenging anatomic transition in spine surgery. It is commonly affected by different types of diseases that may significantly impair stability in this region. The seventh cervical vertebra (C7) is an atypical cervical vertebra with unique anatomic features compared to subaxial cervical spine (C3 to C6). C7 has relatively broader laminae, larger pedicles, smaller lateral masses, and a long nonbifid spinous process. These features allow a variety of surgical methods for performing posterior rigid instrumentation in the form of different types of screws, such as lateral mass screws, pedicle screws, transfacet screws, and intralaminar screws. Many biomechanical studies on cadavers have evaluated and compared different types of implants at C7.

METHODS

We reviewed PubMed/Medline by using specific combinations of keywords to summarize previously published articles that examined C7 posterior rigid instrumentation thoroughly in an experimental fashion on patients or cadavers with additional descriptive radiologic parameters for evaluation of the optimum surgical technique for each type.

RESULTS

A total of 44 articles were reported, including 22 articles that discussed anatomic considerations (entry points, sagittal and axial trajectories, and features of screws) and another 22 articles that discussed the relevant biomechanical testing at this transitional region if C7 was directly involved in terms of receiving posterior rigid implants.

CONCLUSIONS

C7 can accommodate different types of screws, which can provide additional benefits and risks based on availability of bony purchase, awareness of surgical technique, biomechanics, and anatomic considerations.

Reduction and ring fixation of instable C1 fractures with monoaxial pedicle screws

INTRODUCTION

Ring fixation of C1 can be performed using pedicle screws and a rod in case of unstable Jefferson or lateral mass fractures of C1.

MATERIALS AND METHODS

In a case series of three patients, we stabilized C1 fractures surgically using a modified technique of C1 ring fixation by using monoaxial instead of polyaxial screws. Functional outcome and pain was recorded postoperatively.

RESULTS

In this very small case series, we observed good results concerning pain and functional outcome. All fractures were bony healed within 13 weeks. In one case, a screw penetrated the spinal canal and had to be repositioned. A mild irritation of C2 nerve root occurred in two cases postoperatively.

CONCLUSION

C1 Ring fusion with monoaxial screws provides a good ability to reduce the fracture indirectly by the screws and the rod itself.

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.

Safe, Effective and Easily Reproducible Fusion Technique for CV Junction Instability

INTRODUCTION

The Craniovertebral junction (CVJ) refers to a bony enclosure where the occipital bone surrounds the foramen magnum, the atlas and the axis vertebrae. Because of the complexity of structures, CVJ instability is associated with diagnostic and therapeutic problems. Posterior CV fusion procedures have evolved a lot over the last couple of decades. There has been a lookout for one such surgical procedure which is inherently safe, simple, easily reproducible and biomechanically sound. In our study, we present the initial experience the cases of CV junction instrumentation using O-C1-C2 screw & rod construct operated by the author.

AIMS AND OBJECTIVES

The current study is a descriptive analysis of the cases of CVJ instability treated by us with instrumentation using O-C1-C2 screw and rod construct fusion technique.

MATERIALS AND METHODS

It is a retrospective, analytical study in which cases of CV junction instability operated by the author between January 2010 to March 2014 were analysed using various clinical, radiological and outcome parameters.

CONCLUSION

CV junction instrumentation using O-C1-C2 screw and rod construct fusion technique proved to be safe, effective, easily reproducible and biomechanically sound technique which can be adopted by all surgeons who may be at any stage of their learning curve.