Effect of Dome-Shaped Titanium Mesh Cages on Cervical Endplate Under Cyclic Loading: An In Vitro Biomechanics Study

Early radiographic outcomes after anterior cervical discectomy and fusion with anatomic versus lordotic cages

Background

Anterior cervical discectomy and fusion (ACDF) interbody implants are shaped anatomically, with a convex superior aspect, or lordotically, with an angle and flat surfaces. However, the effect of implant shape on cervical sagittal balance (CSB) is not well described.

Methods

Of the 192 cases reviewed from 2018 to 2019, 118 were included with matching pre- and postoperative imaging. Cases were categorized by interbody implant type (anatomic or lordotic) and number of levels fused (1-level, 2-level, etc.). SurgiMap was used to measure cervical lordosis (CL), C2-C7 sagittal vertical axis (cSVA), T1 slope (T1S), and T1S minus CL (T1S-CL) on pre- and postoperative imaging. Pre- and postoperative parameters were compared within and between each cohort. Change in CL (ΔCL), cSVA (ΔcSVA), and T1S-CL (ΔT1S-CL) were calculated as the difference between pre- and postoperative values and were compared accordingly (1) anatomic versus lordotic and (2) 1-level versus 2-level versus 3-level fusion.

Results

Thirty-nine (33.1%), 57 (48.3%), and 22 (18.6%) cases comprised the anatomic, lordotic, and mixed (anatomic and lordotic) groups, respectively. ACDFs improved CL and T1S-CL by 5.71° (p<.001) and 3.32° (p<.01), respectively. CL was improved in the lordotic (5.27°; p<.01) and anatomic (4.57°; p<.01) groups, while only the lordotic group demonstrated improvement in T1S-CL (3.4°; p=.02). There were no differences in ΔCL (p=.70), ΔcSVA (p=.89), or ΔT1S-CL (p=.1) between the groups. Two- and 3-level fusions improved CL by 7.48° (p<.01) and 9.62° (p<.01), and T1S-CL by 4.43° (p<.01) and 5.96° (p<.01), respectively.

Conclusions

Overall, ACDFs significantly improved CL and T1S-CL however, there were no differences in CSB correction between the anatomic and lordotic groups. Two- and 3-level fusions more effectively improved CL (vs. single-level) and T1S-CL (vs. 3-level). These results suggest that implants should continue to be personalized to the patient's anatomy, however, future research is needed to validate these findings and incorporate the effects of preoperative deformities.

Efficacy of a newly designed helical-shaped 3D-printed titanium cage for cervical vertebral defect healing in rabbits

Three-dimensional (3D) printed titanium (Ti-6Al-4V alloy) cages are widely used for spinal fusion applications. However, the structural design and shape of the cages are a major determinant of the optimal clinical outcome. In this study, we constructed a newly designed 3D-printed helical-shaped titanium cage (HTC) with a flexible body, and compared its healing and fusion efficacy in cervical vertebral defects after corpectomy in rabbits to that of a 3D-printed traditional titanium cage (TTC). We performed radiological examinations 1 and 16 weeks after TTC and HTC implantation. We assessed bone ingrowth in TTC and HTC using micro-computed tomography (micro-CT) and histological staining of tissue sections at 16 weeks. The radiographic data showed that the HTC-implanted group had better restoration of vertebral height than the TTC group, indicating a lower risk of cage subsidence. The micro-CT and histological observations showed that HTC promoted bone regeneration and osseointegration more effectively than TTC. Histomorphometry further revealed significant new bone formation in the HTC group compared to the TTC group. These findings demonstrate that HTC has better healing and bone fusion effects than TTC in cervical vertebral defects in rabbits, indicating its potential clinical value.

Evaluation of the contact surface between vertebral endplate and 3D printed patient-specific cage vs commercial cage

Biomechanical study. To evaluate the performance of the contact surface for 3D printed patient-specific cages using CT-scan 3D endplate reconstructions in comparison to the contact surface of commercial cages. Previous strategies to improve the surface of contact between the device and the endplate have been employed to attenuate the risk of cage subsidence. Patient-specific cages have been used to help, but only finite-element studies have evaluated the effectiveness of this approach. There is a possible mismatch between the CT-scan endplate image used to generate the cage and the real bony endplate anatomy that could limit the performance of the cages. A cadaveric model is used to investigate the possible mismatch between 3D printed patient-specific cages and the endplate and compare them to commercially available cages (Medtronic Fuse and Capstone). Contact area and contact stress were used as outcomes. When PS cage was compared to the Capstone cage, the mean contact area obtained was 100 ± 23.6 mm² and 57.5 ± 13.7 mm², respectively (p < 0.001). When compared to the Fuse cage, the mean contact area was 104.8 ± 39.6 mm² and 55.2 ± 35.1 mm², respectively(p < 0.001). Patient-specific cages improve the contact area between the implant and the endplate surface, reducing the contact stress and the risk of implant subsidence during LIF surgeries.

Choice of Spinal Interbody Fusion Cage Material and Design Influences Subsidence and Osseointegration Performance

OBJECTIVE

The objective of the study was to quantify the effect of cage material (titanium-alloy vs. polyetheretherketone or PEEK) and design (porous vs. solid) on subsidence and osseointegration.

METHODS

Three lateral cages (solid PEEK, solid titanium, and 3-dimension-printed porous titanium cages) were evaluated for cage stiffness, subsidence compression stiffness, and dynamic subsidence displacement under simulated postoperative spine loading. Dowel-shaped implants made of grit-blasted solid titanium alloy (solid titanium) and porous titanium were fabricated using commercially available processes. Samples were processed for mechanical push-out testing and polymethylmethacrylate histology following an established ovine bone implantation model.

RESULTS

The solid titanium cage exhibited the greatest stiffness (57.1 ± 0.6 kN/mm), followed by the porous titanium cage (40.4 ± 0.3 kN/mm) and the solid PEEK cage (37.1 ± 1.2 kN/mm). In the clinically relevant dynamic subsidence, the porous titanium cage showed the least amount of subsidence displacement (0.195 ± 0.012 mm), significantly less than that of the solid PEEK cage (0.328 ± 0.020 mm) and the solid titanium cage (0.538 ± 0.027 mm). Bony on-growth was noted histologically on all implant materials; however, only the porous titanium supported bony ingrowth with marked quantities of bone formed within the interconnected pores through 12 weeks. Functional differences in osseointegration were noted between groups during push-out testing. The porous titanium showed the highest maximum shear stress at 12 weeks and was the only group that demonstrated significant improvement (4-12 weeks).

CONCLUSIONS

The choice of material and design is critical to cage mechanical and biological performances. A porous titanium cage can reduce subsidence risk and generate biological stability through bone on-growth and ingrowth.

Cervical non-fusion using biomimetic artificial disc and vertebra complex: technical innovation and biomechanics analysis

Background

Changes in spinal mobility after vertebral fusion are important factors contributing to adjacent vertebral disease (ASD). As an implant for spinal non-fusion, the motion-preserving prosthesis is an effective method to reduce the incidence of ASD, but its deficiencies hamper the application in clinical. This study designs a novel motion-preserving artificial cervical disc and vertebra complex with an anti-dislocation mechanism (MACDVC-AM) and verifies its effect on the cervical spine.

Methods

The MACDVC-AM was designed on the data of healthy volunteers. The finite element intact model, fusion model, and MACDVC-AM model were constructed, and the range of motion (ROM) and stress of adjacent discs were compared. The biomechanical tests were performed on fifteen cervical specimens, and the stability index ROM (SI-ROM) were calculated.

Results

Compared with the intervertebral ROMs of the intact model, the MACDVC-AM model reduced by 28–70% in adjacent segments and increased by 26–54% in operated segments, but the fusion model showed the opposite result. In contrast to the fusion model, the MACDVC-AM model diminished the stress of adjacent intervertebral discs. In biomechanical tests, the MACDVC-AM group showed no significant difference with the ROMs of the intact group (p > 0.05). The SI-ROM of the MACDVC-AM group is negative but close to zero and showed no significant difference with the intact group (p > 0.05).

Conclusions

The MACDVC-AM was successfully designed. The results indicate that the MACDVC-AM can provide physiological mobility and stability, reduce adjacent intervertebral compensatory motion, and alleviate the stress change of adjacent discs, which contributes to protect adjacent discs and reduce the occurrence of ASD.

Comparative Analysis of 3D-Printed Artificial Vertebral Body Versus Titanium Mesh Cage in Repairing Bone Defects Following Single-Level Anterior Cervical Corpectomy and Fusion

Background

The aim of this study was to compare the clinical and radiological outcomes of the 3D-printed artificial vertebral body vs the titanium mesh cage in repairing bone defects for single-level anterior cervical corpectomy and fusion (ACCF).

Material/Methods

A total of 51 consecutive patients who underwent single-level ACCF in Huai’an Second People’s Hospital from July 2017 to August 2020 were retrospectively reviewed. According to the implant materials used, patients were divided into a 3D-printed artificial vertebral body group (3D-printed group) (n=20; 12 males, 8 females) and a titanium mesh cage group (TMC group) (n=31; 15 males, 16 females). General data, radiological parameters, and clinical outcomes were recorded.

Results

The rate of subsidence in the 3D-printed group (0.01, 2/20) was lower than in the TMC group (0.29, 9/31) (P<0.05). HAE and HPE of the patients in the 3D-printed group were significantly higher than those in the TMC group (P<0.05). C2–C7 Cobb angle and SA of the patients in the 3D-printed group were significantly larger than those in the TMC group (P<0.05). All patients in the 2 groups showed significant improvement in VAS, JOA, and NDI scores at 3 months and 1 year after surgery.

Conclusions

3D-printed artificial vertebral body helps maintain intervertebral height and cervical physiological curvature and is a good candidate for ACCF.