A biomechanical analysis of anterior cervical discectomy and fusion alone or combined cervical fixations in treating compression-extension injury with unilateral facet joint fracture: a finite element study

Does Screw Number of Zero-profile Implants in Fusion Segment Influence Intervertebral Stability?

OBJECTIVE

The unclear clinical outcomes of two different zero-profile implants with different number of screws in hybrid surgery restricts the choice of patient-specific implants. This study aims to compare two different implants on its postoperative subsidence, motion stabilization and clinical outcomes. It also provides references to the most reasonable implant choice in fusion surgery.

METHODS

This was a retrospective study. From February 2014 to March 2022, 173 patients who underwent hybrid surgery were included. Among them, 122 received surgery with a four screw implant, while 51 received a two screw implant. We analyzed the significance of patient-specific factors, radiographic factors and clinical outcomes. The Wilcoxon rank sum test, t tests/analysis of variance (ANOVA) test and stepwise multivariate logistic regression were adopted for statistical analysis.

RESULTS

No statistically significant difference was observed between the two screw and four screw groups in terms of immediate, middle, and long-term stability and fusion rate (p > 0.05). However, the two screws group had higher FSU height subsidence at 3, 6, and 12 months postoperatively and higher rates of significant subsidence at three and 6 months postoperatively (p < 0.05). Both groups showed significant clinical improvements at the final follow-up.

CONCLUSION

Two screw and four screw implants provide comparable stability, fusion rates and clinical outcomes. However, the two screw implant was inferior to the four screw implant in subsidence prevention. Therefore, the two-screw implant is non-inferior to the four-screw implant in most patients. It can be used as the priority choice in the fusion segment by its easy manageability. However, the patients with a high risk of subsidence such as multilevel surgery, the elderly, lower BMD, bad cervical alignment should receive a four screw implant rather than a two screw implant.

Biomedical analysis of four fixation systems in treatment of type II traumatic spondylolisthesis of the axis: a finite element analysis

This study aimed to compare the properties and safety of self-designed plates in type II traumatic spondylolisthesis of the axis with those of traditional devices via finite element (FE) analysis. We constructed a hangman's fracture FE model from the occipital bone (C0) level to the C3 level. Then, FE models were constructed for the following four fixation systems: an anterior cervical L-shaped plate with four vertebral screws (4-ACLP), or six screws (6-ACLP), an anterior cervical orion plate (ACOP), and a posterior fixation system. A preloaded compressive force of 50 N and a moment of 1.5 N·m were applied to each model under six working conditions. The mobility of the C2/3 segment decreased significantly in four fixation models. In the Mises stress cloud diagram, 4-ACLP showed a better stress distribution in both the bone graft and fixation system than 6-ACLP and ACOP. The resultant force of 4-ACLP was lower but higher than ACOP in axial force. Additionally, the cage in the 4-ACLP configuration experienced the highest stress in the six working conditions. Hence, this novel self-designed plate has the potential to mitigate the operational difficulties, provide sufficient stability, reduce the risk of plate or screw fractures, and improve bone fusion.

The Effect of Anterior-Only, Posterior-Only, and Combined Anterior Posterior Fixation for Cervical Spine Injury with Soft Tissue Injury: A Finite Element Analysis

OBJECTIVE

This finite element analysis aimed to investigate the effects of surgical procedures for cervical spine injury.

METHODS

A three-dimensional finite element model of the cervical spine (C2-C7) was created from computed tomography. This model contained vertebrae, intervertebral discs, anterior longitudinal ligament, and posterior ligament complex. To create the cervical spine injury model, posterior ligament complex and anterior longitudinal ligament at C3-C4 were resected and the center of the intervertebral disc was resected. We created posterior-only fixation (PF), anterior-only fixation (AF), and combined anterior-posterior fixation (APF) models. A pure moment with a compressive follower load was applied, and range of motion, annular/nucleus stress, instrument stress, and facet forces were analyzed.

RESULTS

In all motion except for flexion, range of motion of PF, AF, and APF models decreased by 80%-95%, 85%-93%, and 97%-99% compared with the intact model. C3-C4 annulus stress of PF, AF, and APF models decreased by 28%-72%, 96%-100%, and 99%-100% compared with the intact model. Facet contact forces of PF, AF, and APF models decreased by 77%-79%, 97%-99%, and 77%-86% at C3-C4 compared with the intact model. Screw stress in the PF model was higher than in the APF model, and plate stress in the AF model was lower than in the APF model, but bone graft stress in the AF model was higher than in the APF model.

CONCLUSIONS

Cervical stabilization was preserved by the APF model. Regarding range of motion, the PF model had an advantage compared with the AF model except for flexion. An understanding of biomechanics provides useful information for the clinician.

Clinical and Radiographic Outcomes of Combined Posterior Transfacet Screw Fixation and Anterior Cervical Discectomy and Fusion Surgery for Unilateral Cervical Facet Fracture with Traumatic Disc Herniation: A Retrospective Cohort Study

Introduction

Combined lateral mass screw-rod (LMSR) fixation and anterior cervical discectomy and fusion (ACDF) surgery is currently the most widely described and accepted procedure for subaxial cervical facet fracture with traumatic disc herniation. Recent biomechanical studies have demonstrated that the use of transfacet screw (TFS) can be considered as a simple alternative method to LMSR. However, to date, little is known about the feasibility and effectiveness of TFS in the combined approach. The aim of this study was to compare the clinical and radiographic results of TFS + ACDF surgery and LMSR + ACDF surgery, and to provide a less invasive alternative technique for spine surgeons.

Method

We retrospectively reviewed patients with unilateral cervical facet fracture with traumatic disc herniation who had undergone TFS + ACDF (N = 36) or LMSR + ACDF (N = 34) with a minimum 2-year follow-up. Clinical assessments, which included American Spinal Injury Association impairment scale (AIS), visual analog scale for neck pain (VASSNP) score and patient satisfaction, were made before surgery and at follow-up. For the radiographic outcomes, the instability parameters of segmental kyphosis and sagittal translation were measured.

Results

The demographic characteristics of the two groups of patients were similar. In terms of clinical outcomes, both two groups were associated with significant improvements at the final follow-up. There were no significant between-group differences in VASSNP score or patient satisfaction (both P > 0.05). The LMSR + ACDF group suffered more blood loss and had longer operative time (mean 206.0 ml; mean 274.4 min, respectively) than in the TFS + ACDF group (mean 110.0 ml; mean 142.8 min, respectively) (P < 0.001 for both comparisons). For the radiographic results, the segmental kyphosis and sagittal translation were significantly corrected after surgery in both groups (P < 0.001 for both groups), and no significant differences were found between groups at the last follow-up (P > 0.05).

Conclusion

In the absence of any self-evident clinical and radiographic benefits of one technique over the other (TFS + ACDF vs. LMSR + ACDF), we recommend combined TFS + ACDF surgery as a safe and less invasive alternative treatment for unilateral cervical facet fractures with traumatic disc herniation, as it was associated with a shorter duration of surgery and lower estimated blood loss than LMSR + ACDF surgery.