The Significance of Extra-Cage Bridging Bone via Radiographic Lumbar Interbody Fusion Criterion

Feasibility of the Non-Window-Type 3D-Printed Porous Titanium Cage in Posterior Lumbar Interbody Fusion: A Randomized Controlled Multicenter Trial

BACKGROUND

Three-dimensionally printed titanium (3D-Ti) cages can be divided into 2 types: window-type cages, which have a void for bone graft, and non-window-type cages without a void. Few studies have investigated the necessity of a void for bone graft in fusion surgery. Therefore, the present study assessed the clinical and radiographic outcomes of window and non-window-type 3D-Ti cages in single-level posterior lumbar interbody fusion.

METHODS

A total of 70 patients were randomly assigned to receive either a window or non-window cage; 61 patients (87%) completed final follow-up (32 from the window cage group, 29 from the non-window cage group). Radiographic outcomes, including fusion rates, subsidence, and intra-cage osseointegration patterns, were assessed. Intra-cage osseointegration was measured using the intra-cage bridging bone score for the window cage group and the surface osseointegration ratio score for the non-window cage group. Additionally, we looked for the presence of the trabecular bone remodeling (TBR) sign on computed tomography (CT) images.

RESULTS

Of the 61 patients, 58 achieved interbody fusion, resulting in a 95.1% fusion rate. The fusion rate in the non-window cage group was comparable to, and not significantly different from, that in the window cage group (96.6% and 93.8%, p > 0.99). The subsidence rate showed no significant difference between the window and non-window cage groups (15.6% and 3.4%, respectively; p = 0.262). The intra-cage osseointegration scores showed a significant difference between the groups (p = 0.007), with the non-window cage group having a higher proportion of cases with a score of 4 compared with the window cage group. The TBR sign was observed in 87.9% of patients who achieved interbody fusion, with a higher rate in the non-window cage group across the entire cohort although the difference was not significant (89.7% versus 78.1%, p = 0.385).

CONCLUSIONS

Non-window-type 3D-Ti cages showed equivalent clinical outcomes compared with window-type cages and comparable interbody fusion rates. These results suggest that the potential advantages of 3D-Ti cages could be optimized in the absence of a void for bone graft by providing a larger contact surface for osseointegration.

LEVEL OF EVIDENCE

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

Mechano-driven intervertebral bone bridging via oriented mechanical stimulus in a twist metamaterial cage: An in silico study

Stiffer cages provide sufficient mechanical support but fail to promote bone ingrowth due to stress shielding. It remains challenging for fusion cage to satisfy both bone bridging and mechanical stability. Here we designed a fusion cage based on twist metamaterial for improved bone ingrowth, and proved its superiority to the conventional diagonal-based cage in silico. The fusion process was numerically reproduced via an injury-induced osteogenesis model and the mechano-driven bone remodeling algorithm, and the outcomes fusion effects were evaluated by the morphological features of the newly-formed bone and the biomechanical behaviors of the bone-cage composite. The twist-based cages exhibited oriented bone formation in the depth direction, in comparison to the diagonal-based cages. The axial stiffness of the bone-cage composites with twist-based cages was notably higher than that with diagonal-based cages; meanwhile, the ranges of motion of the twist-based fusion segment were lower. It was concluded that the twist metamaterial cages led to oriented bone ingrowth, superior mechanical stability of the bone-cage composite, and less detrimental impacts on the adjacent bones. More generally, metamaterials with a tunable displacement mode of struts might provide more design freedom in implant designs to offer customized mechanical stimulus for osseointegration.

Feasibility of Non-window Three-Dimensional-Printed Porous Titanium Cage in Posterior Lumbar Interbody Fusion: A Pilot Trial

Background

The commercially available design of a three-dimensional (3D)-printed titanium (3D-Ti) cage can be divided into two types according to the presence of a window: a cage with a window that allows filling of bone graft materials and a non-window cage for stand-alone use. This prospective observational case series study aimed to explore the clinical feasibility of using a non-window type 3D-Ti cage in cases of combined window and non-window cage implantation. Furthermore, we evaluated the bone in growth patterns of non-window cages and their correlation with published fusion grading systems.

Methods

A total of 31 consecutive patients who underwent single-level posterior lumbar interbody fusion surgery were included. Two 3D-Ti cages with different designs were inserted: a non-window cage on the left side and a window cage on the right side. Radiographic fusion was defined by the segmental angle between flexion and extension radiographs (F-E angle) and cage bridging bone (CBB) scores on computed tomography. The association between the F-E angle and osteointegration scoring system including the surface osteointegration ratio (SOR) score was analyzed.

Results

Radiographic fusion was achieved in 27 of 31 patients (87%) at 12 months postoperatively. Among the non-window cages, 23 of 31 (74.2%) had fair SOR scores, while 19 of 31 (61.3%) window cages had fair intra-cage CBB scores. The higher the SOR score was, the smaller the flexion-extension angle (SOR 0 vs. SOR 1: 6.30° ± 2.43° vs. 1.95° ± 0.99°, p < 0.001; SOR 0 vs. SOR 2: 6.03° ± 2.43° vs. 0.99°± 0.74°, p < 0.001).

Conclusions

The clinical feasibility of using a non-window 3D-Ti cage during lumbar interbody fusion might be acceptable. Furthermore, a newly suggested fusion criterion for the use of the non-window cage, the SOR score, showed a significant association with the published fusion grading systems, demonstrating its feasibility in determining interbody fusion in lumbar spinal surgery.

Biportal Endoscopic Transforaminal Lumbar Interbody Fusion Using Double Cages: Surgical Techniques and Treatment Outcomes

Objective: To describe the surgical techniques and the treatment outcomes of biportal endoscopic transforaminal lumbar interbody fusion (BETLIF) using double cages.Methods: This study included 89 patients with 114 fusion segments between July 2019 and May 2021. One pure polyetheretherketone (PEEK) cage and 1 composite titanium-PEEK cage were used for interbody fusion. Clinical outcomes measures included visual analogue scale (VAS) scores for lower back pain and leg pain, Oswestry Disability Index (ODI), and Japanese Orthopedic Association (JOA) scores. Computed tomography (CT) of the lumbar spine 1 year postoperatively was used to evaluate the Bridwell interbody fusion grades.Results: There were significant improvement in VAS for lower back pain from 5.2 ± 3.1 to 1.7 ± 2.1, VAS for leg pain from 6.3 ± 2.5 to 1.7 ± 2.0, ODI from 46.7 ± 17.0 to 12.7 ± 16.1, and JOA score from 15.6 ± 6.3 to 26.4 ± 3.2. The p-values were all < 0.001. The average hospital stay was 5.7 ± 1.1 days. The CT studies available for 60 fusion segments showed successful fusion (Bridwell grade I or grade II) in 56 segments (93.3%). Significant cage subsidence of more than 2 mm was only noted in 3 segments (5.0%). Complications included 1 dural tear, 2 pedicle screws malposition, and 2 epidural hematomas, in which 2 patients required reoperations.Conclusion: BETLIF with double cages provided good neural decompression and a sound environment for interbody fusion with a big cage footprint, a large amount of bone graft, endplate preservation, and segmental stability.

Characteristics of interbody bone graft fusion after transforaminal lumbar interbody fusion according to intervertebral space division

BACKGROUND

According to intervertebral space division, the characteristics of interbody bone graft fusion after transforaminal lumbar interbody fusion (TLIF) were assessed via computed tomography (CT) scan to provide a theoretical basis for selecting the bone grafting site of interbody fusion.

METHODS

The medical records of 57 patients with lumbar spinal stenosis and disc herniation treated with TLIF were analysed retrospectively. In total, 57 segments received lumbar interbody fusion. A thin-layer CT scan was performed to evaluate fusion in each zone of the fusion space.

RESULTS

The fusion rates were 57.89% (n = 33) in the anterior cage zone, 73.68% (n = 42) in the posterior cage zone, 66.67% (n = 38) in the decompression zone, 26.32% (n = 15) in the contralateral decompression zone and 94.74% (n = 54) in the inner cage zone. There were significant differences among the fusion rates of the five zones (P < 0.001). Further pairwise comparison revealed that the fusion rates in the inner cage significantly differed from the anterior and posterior cages and decompression and contralateral decompression zones (P = 0.001, 0.002, 0.001 and 0.001, respectively).

CONCLUSION

We think the central cage zone (i.e., inner cage) should be the focus of bone grafting. Although there is small volume of bone graft on the posterior cage zone, the fusion rate is relatively high, only secondary to the inner cage zone. The fusion rate is of the contralateral decompression zone is lower although there is a bone graft.