Preliminary results in anterior cervical discectomy and fusion with the uncovertebral joint fusion cage in a goat model

Anatomical Brushite-Coated Mg-Nd-Zn-Zr Alloy Cage Promotes Cervical Fusion: One-Year Results in Goats

In this study, an anatomical brushite-coated Mg-Nd-Zn-Zr alloy cage was fabricated for cervical fusion in goats. The purpose of this study was to investigate the cervical fusion effect and degradation characteristics of this cage in goats. The Mg-Nd-Zn-Zr alloy cage was fabricated based on anatomical studies, and brushite coating was prepared. Forty-five goats were divided into three groups, 15 in each group, and subjected to C2/3 anterior cervical decompression and fusion with tricortical bone graft, Mg-Nd-Zn-Zr alloy cage, or brushite-coated Mg-Nd-Zn-Zr alloy cage, respectively. Cervical radiographs and computed tomography (CT) were performed 3, 6, and 12 months postoperatively. Blood was collected for biocompatibility analysis and Mg2+ concentration tests. The cervical spine specimens were obtained at 3, 6, and 12 months postoperatively for biomechanical, micro-CT, scanning electron microscopy coupled with energy dispersive spectroscopy, laser ablation-inductively coupled plasma-time-of-flight mass spectrometry, and histological analysis. The liver and kidney tissues were obtained for hematoxylin and eosin staining 12 months after surgery for biosafety analysis. Imaging and histological analysis showed a gradual improvement in interbody fusion over time; the fusion effect of the brushite-coated Mg-Nd-Zn-Zr alloy cage was comparable to that of the tricortical bone graft, and both were superior to that of the Mg-Nd-Zn-Zr alloy cage. Biomechanical testing showed that the brushite-coated Mg-Nd-Zn-Zr alloy cage achieved better stability than the tricortical bone graft at 12 months postoperatively. Micro-CT showed that the brushite coating significantly decreases the corrosion rate of the Mg-Nd-Zn-Zr alloy cage. In vivo degradation analysis showed higher Ca and P deposition in the degradation products of the brushite-coated Mg-Nd-Zn-Zr alloy cage, and no hyperconcentration of Mg was detected. Biocompatibility analysis showed that both cages were safe for cervical fusion surgery in goats. To conclude, the anatomical brushite-coated Mg-Nd-Zn-Zr alloy cage can promote cervical fusion in goats, and the brushite-coated Mg-Nd-Zn-Zr alloy is a potential material for developing absorbable fusion cages.

Uncovertebral Joint Fusion Versus End Plate Space Fusion in Anterior Cervical Spine Surgery: A Prospective Randomized Controlled Trial

BACKGROUND

The uncovertebral joint is a potential region for anterior cervical fusion. Currently, we are aware of no clinical trials on human uncovertebral joint fusion (UJF). The purpose of this study was to compare the time it took to achieve osseous union/fusion and the clinical efficacy of UJF to end plate space fusion (ESF)-i.e., traditional anterior cervical discectomy and fusion (ACDF)-in anterior cervical surgery.

METHODS

Patients with single-level cervical spondylosis were recruited from April 2021 through October 2022 and randomly divided into the UJF and ESF groups, with 40 patients in each group. Autologous iliac bone was used for bone grafting in both groups. The primary outcome was the early fusion rate at 3 months postoperatively. Secondary outcomes included the prevalence of complications and patient-reported outcome measures (PROMs), including the Japanese Orthopaedic Association (JOA) score, Neck Disability Index (NDI), and visual analog scale (VAS) scores for arm and neck pain.

RESULTS

A total of 74 patients (92.5%) with an average age of 49.8 years (range, 26 to 65 years) completed the trial and were included in the analysis. There was no significant difference between the 2 groups at baseline. The operative duration and intraoperative blood loss were also comparable between the 2 groups. The fusion rate in the UJF group was significantly higher than that in the ESF group at 3 months (66.7% compared with 13.2%, p < 0.0001) and 6 months (94.1% compared with 66.7%, p = 0.006) after the operation. No significant difference was found in the fusion rate between the 2 groups 12 months postoperatively. Overall, the PROMs significantly improved after surgery in both groups and did not differ significantly between the groups at any follow-up time point. The prevalence of complications was not significantly different between the 2 groups.

CONCLUSIONS

In our study of anterior cervical fusion surgery, we found that the early fusion rate after UJF was significantly higher than that after ESF.

LEVEL OF EVIDENCE

Therapeutic Level I . See Instructions for Authors for a complete description of levels of evidence.

Biomechanical performance of the novel assembled uncovertebral joint fusion cage in single-level anterior cervical discectomy and fusion: A finite element analysis

Introduction: Anterior cervical discectomy and fusion (ACDF) is widely accepted as the gold standard surgical procedure for treating cervical radiculopathy and myelopathy. However, there is concern about the low fusion rate in the early period after ACDF surgery using the Zero-P fusion cage. We creatively designed an assembled uncoupled joint fusion device to improve the fusion rate and solve the implantation difficulties. This study aimed to assess the biomechanical performance of the assembled uncovertebral joint fusion cage in single-level ACDF and compare it with the Zero-P device.

Methods: A three-dimensional finite element (FE) of a healthy cervical spine (C2−C7) was constructed and validated. In the one-level surgery model, either an assembled uncovertebral joint fusion cage or a zero-profile device was implanted at the C5–C6 segment of the model. A pure moment of 1.0 Nm combined with a follower load of 75 N was imposed at C2 to determine flexion, extension, lateral bending, and axial rotation. The segmental range of motion (ROM), facet contact force (FCF), maximum intradiscal pressure (IDP), and screw−bone stress were determined and compared with those of the zero-profile device.

Results: The results showed that the ROMs of the fused levels in both models were nearly zero, while the motions of the unfused segments were unevenly increased. The FCF at adjacent segments in the assembled uncovertebral joint fusion cage group was less than that that of the Zero-P group. The IDP at the adjacent segments and screw–bone stress were slightly higher in the assembled uncovertebral joint fusion cage group than in those of the Zero-P group. Stress on the cage was mainly concentrated on both sides of the wings, reaching 13.4–20.4 Mpa in the assembled uncovertebral joint fusion cage group.

Conclusion: The assembled uncovertebral joint fusion cage provided strong immobilization, similar to the Zero-P device. When compared with the Zero-P group, the assembled uncovertebral joint fusion cage achieved similar resultant values regarding FCF, IDP, and screw–bone stress. Moreover, the assembled uncovertebral joint fusion cage effectively achieved early bone formation and fusion, probably due to proper stress distributions in the wings of both sides.

Technical Notes for Establishing a Cervical Fusion Model in Goats Based on Distinctive Anatomy

Goat is an adequate experimental model for cervical spine testing. However, studies on the anatomy of the cervical spine in goats are limited, and there is no uniform standard for establishing a single-segment anterior cervical discectomy and fusion (ACDF) model in goats. To address this issue, we investigated the cervical spine anatomy of goats and provided a technical basis for establishing a single-segment ACDF model in goats. We measured the imaging anatomical parameters using Mimics Medical 20.0 software. We then performed histological analysis of the cervical spine segment 2-3 (C2-3) segment of six goat cervical spine specimens. Based on the measurements and histological analysis, the fusion cage was designed to be wedge-shaped, the length of the plate was 25 mm, and the length of the screw was 15 mm. Based on the anatomical characteristics of goats, we believed that the C2-3 segment of goats was most suitable for a single-segment ACDF model in goats, and the decompression should be performed medial to the pterygoid joint on both sides, the thickness of the removed endplate was ∼0.6 mm, the cage implanted in the anterior two-thirds of the intervertebral space could maximize the contact area of the cage-endplate interface, and the location of the midline spur could position the implantation of the internal fixtures. Radiological examination at 12 weeks postoperatively suggested that the internal fixtures were in place and new bone formation was visible. These results demonstrated that these technical notes based on anatomical features were practical and could minimize damage to animals.