Expandable titanium interbody cage with adjustable height and lordosis for anterior cervical discectomy and fusion: a clinical and radiological study

Introduction

Anterior cervical discectomy and fusion (ACDF) is a long-standing, safe, and effective procedure for treating degenerative disc disease of the cervical spine (1,2). It is a commonly accepted surgical treatment for cervical myelopathy and cervical spondylosis. In the United States, more than 130,000 ACDF procedures are performed each year, and this number has been increasing by over 5% annually (3). Studies have shown that patients experience significant improvements in pain relief, functional outcomes, and overall satisfaction following the surgery (4).

The primary goal of ACDF in cervical myelopathy cases is to achieve adequate neural decompression, relieving pressure on both the spinal cord and nerve roots (5). Multiple studies have also demonstrated that restoring proper cervical and segmental lordosis (SL) is essential for optimal long-term outcomes (6,7).

However, achieving ideal cervical alignment during ACDF remains challenging. Static interbody cages prolong operative time and heavily depend on bone quality. Their insertion may compromise endplates due to impaction. In cases of severe fixed kyphosis, a more complex 360-degree surgical approach may be necessary, though this carries three times the morbidity risk compared to an anterior-only procedure (8).

Recent advancements have introduced expandable interbody cages, allowing surgeons to provide patient-specific interventions and achieve optimal angular corrections. These expandable cages offer reduced size during insertion, minimizing endplate violation while restoring intervertebral height, and they allow for adjustable lordosis, enhancing sagittal balance correction. The VariLift-C^® cervical interbody fusion device was among the first expandable cages available in the cervical spine (9). The HIJAK AC Spacer System^® is the first expandable titanium cage (ETC) with adjustable height and lordosis (Figure 1). In addition to reducing the potential for end plate violation with a smaller insertion size, this ETC allows up to 20° of lordotic correction, potentially enabling the surgeon to achieve superior restoration of sagittal balance.

Figure 1 Expandable titanium cage for ACDF procedures. The left image shows the cage in its unexpanded state, while the right image illustrates the fully expanded configuration. This design allows for adjustable height and lordosis, enabling precise corrections in cervical alignment during ACDF. ACDF, anterior cervical discectomy and fusion.

Despite these advancements, there is a lack of published data on the clinical benefits of these cages. Thus, this study aimed to investigate the outcomes of ACDF using cages with adjustable height and lordosis, specifically assessing clinical outcomes regarding pain and disability, evaluating the restoration of sagittal alignment from the early postoperative stage to 1-year follow-up, determining the incidence of subsidence, assessing fusion rates, and recording associated complications. We present this article in accordance with the STROBE reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-25-44/rc).

Methods

Study design and clinical setting

The study population comprises consecutive patients who underwent ACDF with the HIJAK AC Spacer System^® at Weill Cornell Medicine, Department of Neurosurgery, New York-Presbyterian Hospital between September 2019 and July 2023. Surgical indications included radiculopathy, myelopathy, and mechanical neck pain, which was unresponsive to conservative treatment. Unless contraindicated, patients underwent at least 6 weeks of conservative management, which included physical therapy, non-steroidal anti-inflammatory drugs (NSAIDs) or muscle relaxants, activity modification, and, in some cases, epidural steroid injections. Surgery was indicated for persistent symptoms despite treatment, progressive neurological deficits, or severe mechanical neck pain with radiographic evidence of instability or degenerative disc disease. Patients who underwent revision surgery at the same level for pseudarthrosis, had non-degenerative pathologies such as spinal tumors, or had incomplete data were excluded from the study. A single senior surgeon performed all surgeries, and all patients received the same postoperative protocol.

This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. It was approved by the Weill Cornell Medicine Institutional Review Board (IRB) (approval No. 2405027424), and individual consent for this retrospective analysis was waived.

Outcome measures

Demographics including age, gender, body mass index (BMI), American Society of Anesthesiologists (ASA) score, diagnosis, operation level, baseline pain and disability, and length of hospitalization were collected. Clinical and radiographic outcomes following ACDF were recorded preoperatively, immediate post-op, and at follow-up. Patient-reported outcomes, including Neck Disability Index (NDI) and Numeric Rating Scale for neck (NRS-N) and arm pain (NRS-A) (10), were collected. Radiographic variables were:

• Anterior and posterior disc height (PDH) at the level of the hardware;
• Cervical lordosis (CL): defined as the angle between the inferior endplate of C2 and the inferior endplate of C7;
• SL: defined as the angle between the superior endplate of the vertebral body above the hardware and the inferior endplate of the vertebral body below the hardware;

Cage subsidence: a decrease in the total intervertebral height (TIH) at the level where the cage was placed by more than 2 mm between the immediate post-operative and follow-up radiographs. The TIH was measured as the distance between the midpoints of the upper and lower endplates of the vertebrae surrounding the cage, with measurements taken from the immediate postoperative period to the follow-up (11);

Fusion: using dynamic radiographs magnified by 150%, an anterior cervical fusion is defined as interspinous motion of less than 1 mm, with adequate validation requiring superjacent interspinous motion of at least 4 mm (12).

Clinical outcome measures and complications were documented during each follow-up evaluation.

Surgical procedure

After informed consent was obtained, all patients were scheduled for navigated ACDF. We utilized a Smith-Robison approach to reach the diseased levels (13-15). The surgery was performed under general anesthesia, with the patient’s head immobilized in a Mayfield head holder. Total navigation (Brainlab AG, Feldkirchen, Germany) guidance was utilized throughout the procedure, and the reference array was attached to the Mayfield head holder.

The anterior cervical area was prepped and draped in a regular sterile fashion. A low-dose intraoperative computed tomography (CT) scan is obtained for navigation. The skin incision was determined with navigation. A small skin incision was made, and the platysma was divided sharply. A combination of sharp and blunt dissection was used to gain access to the anterior longitudinal ligament. The longus colli muscle is mobilized on both sides, and the correct levels were confirmed with navigation.

The disc space of the correct level was confirmed with navigation and then incised, and a self-retaining retractor was placed. Distraction pins were placed into the bone above and below using navigation. The microscope was brought in. Under the microscope, a discectomy was performed, and the endplates were carefully prepared for the fusion. The posterior longitudinal ligament was removed, and generous bilateral foraminotomies were performed. Using navigation guidance, an expandable titanium lordotic cage filled with ViviGen material and demineralized bone matrix (DBM) for the fusion was placed. Although not mandatory, navigation was used to enhance level localization, implant positioning, and reduce radiation exposure, consistent with findings from previous reports (16) (Figure 2). This provided lordosis to the level. Any anterior osteophytes were then removed.

Figure 2 Illustration of the expandable titanium cage application in ACDF. (A) Preoperative depiction of cervical pathology. (B) Initial insertion of the expandable cage with the cage applicator. (C) Cage positioned in its unexpanded state within the IVD space. (D) Cage expanded to the desired height and lordosis. (E) Final configuration with plate and screws secured in position. ACDF, anterior cervical discectomy and fusion; IVD, intervertebral disc.

The degree of expansion was determined intraoperatively based on tactile feedback, using the senior surgeon’s ‘two-finger feel’ technique—a manual assessment of resistance during expansion to optimize stability while avoiding over-distraction and endplate damage. Expansion was completed under the microscope to allow precise visual control.

The appropriate size anterior cervical locking plate was chosen and bent into gentle lordosis. Two screws were then placed into each of the vertebral bodies. Intraoperative neurophysiological monitoring was used throughout the procedure. An intraoperative CT scan was obtained to confirm the accurate placement of all instrumentation. Any bleeding was carefully inspected and controlled. Subsequently, the surgical wound was closed layer by layer. Postoperative images were obtained to measure radiographic variables (Figure 3).

Figure 3 Clinical case of ACDF with an ETC. A 30-year-old patient was admitted for lower limb numbness, bilateral upper extremity tingling, and right upper extremity weakness. (A) Sagittal and (B) axial C-spine MRI showing a disc bulge at C6–7 with associated mass effect and intramedullary edema. (C) Preoperative radiograph showing degenerative cervical spine changes. (D) Day-1 postoperative radiograph showing placement of the ETC with secured plate and screws. Cervical lordosis improved from 2.85° preoperatively to 8.03° postoperatively, and segmental lordosis increased from 10.17° to 18.67°. ACDF, anterior cervical discectomy and fusion; ETC, expandable titanium cage; MRI, magnetic resonance imaging.

Statistical analysis

Continuous data were described using either mean (standard deviation) or median with interquartile range (IQR), while count data were presented as counts and percentages (%). We assessed the normality of the data using the Shapiro-Wilk test. To compare measurements at different time points, we employed either the Wilcoxon Signed Rank Test or, when applicable, the paired t-test. We performed simple logistic regression to analyze the association between subsidence and year of surgery. Statistical Significance was set at 0.05, and all statistical analyses were conducted using R studio version 4.1.2 (Vienna, Austria), and visualization was done using GraphPad Prism version 10.4.1 (San Diego, CA, USA).

Results

Demographics

Between September 2019 and July 2023, 86 patients underwent ACDF with the ETC. Of these, 44 patients who had complete imaging at pre-operative, post-operative, and follow-up were included in the study.

The mean age was 53±13 years, with a gender distribution [of 21 males (47.7%) and 23 females (52.3%)] (Table 1). The median follow-up duration for the study cohort was 12 months (IQR, 11–13 months), ensuring adequate postoperative observation for clinical and radiological outcomes.

The median BMI was 25.9 kg/m² (IQR, 22.4–29.9 kg/m²). Eight patients (18.2%) were smokers, and most had an ASA score of II (72.7%). Radiculopathy was the most common diagnosis in 30 patients (68.2%), followed by a combination of myelopathy and radiculopathy in 9 patients (20.5%). Preoperative assessments showed a median NDI of 35 (IQR, 28–50), an NRS-A of 2 (IQR, 0–4), and an NRS-N of 6 (IQR, 3–8). Detailed demographic and clinical characteristics are provided in Table 1.

Surgical outcomes

Seventy-seven levels were treated with the ETC, with the most treated level being C5–6 (39.0%), followed by C4–5 (26.0%) (Table 2). Most surgeries involved a two-level fusion (61.4%). The median duration of surgery was 127 minutes (IQR, 107.2–153 minutes), and the median hospital stay was 31 hours (IQR, 24–48 hours). Notably, there were no complications such as cerebrospinal fluid (CSF) leak, wound infection, hematoma, neurological deterioration, or reoperations.

Clinical outcomes

The NRS-A score significantly decreased from the preoperative median of 2 (IQR, 0–4) to a postoperative median of 0 (IQR, 0–1.5) (P=0.006). This improvement was sustained at follow-up, with a median NRS-A score of 0 (IQR, 0–2.2), significantly lower than the preoperative score (P=0.03). However, no statistically significant difference was observed between the immediate postoperative and follow-up scores (P=0.54) (Figure 4A).

Figure 4 Changes in clinical outcomes over time. Line plots with error bars showing changes in clinical outcomes over time. (A) NRS-Arm: significant postoperative improvement was sustained at follow-up. (B) NRS-Neck: progressive decreases across all time points. (C) NDI: no immediate postoperative change, but significant improvement at follow-up compared to preoperative values. Points represent median values, and error bars represent the IQR with statistical significance annotated for preoperative to follow-up. Postoperative refers to the first assessment after surgery at 2 weeks. ‘Final follow-up’ represents the last available assessment, which varied from patient to patient. *, P≤0.05; **, P≤0.01; ***, P≤0.001. IQR, interquartile range; NDI, Neck Disability Index; NRS, Numeric Rating Scale; post-op, post-operative; pre-op, pre-operative.

The NRS-N score significantly decreased from the preoperative median of 6 (IQR, 3–8) to a postoperative median of 3 (IQR, 1–5) (P=0.002). At follow-up, the median NRS-N score decreased to 2 (IQR, 0.1–4), which was significantly lower than both the preoperative (P<0.001) and immediate postoperative scores (P=0.003) (Figure 4B).

There was no statistically significant change in the NDI from the preoperative median of 35 (IQR, 28–50) to the immediate postoperative median of 46 (IQR, 18–53.5) (P=0.62). However, significant improvements were observed at follow-up, with the NDI decreasing to a median of 9 (IQR, 3–23.2), which was significantly lower than both the preoperative (P=0.03) and immediate postoperative scores (P=0.03) (Figure 4C).

Radiological parameters

The CL increased from the preoperative median of 4.4° (IQR, 0.1°–13°) to the postoperative median of 9.0° (IQR, 4.5°–13.0°) (P<0.001). This was sustained at follow-up, with a median CL of 8.3° (IQR, 4.9°–14.2°), which remained significantly higher than the preoperative values (P<0.001). However, there was no statistically significant difference between the postoperative and follow-up values (P=0.13), suggesting that the cervical alignment was maintained over time (Figure 5A).

Figure 5 Changes in radiological parameters over time. Line plots with error bars showing changes in radiological parameters over time. (A) Cervical lordosis: significant postoperative improvement, maintained at follow-up. (B) Segmental lordosis: significant postoperative improvement, stable at follow-up. (C) Anterior disc height: significant postoperative increase, with slight reduction at follow-up while remaining above preoperative values. (D) Posterior disc height: significant postoperative increase, with slight reduction at follow-up while remaining above preoperative values. Points represent median values with error bars indicating the IQR, except for posterior disc height, which is expressed as mean ± SD. Statistical significance is annotated for preoperative to follow-up comparisons. Postoperative refers to the first assessment after surgery, day 1 post-op. ‘Final follow-up’ represents the last available assessment, which varied from patient to patient. **, P≤0.01; ***, P≤0.001. IQR, interquartile range; mm, millimeters; post-op, post-operative; pre-op, pre-operative; SD, standard deviation.

The SL significantly increased from a preoperative median of −0.9° (IQR, −10.7° to 3.4°) to an immediate postoperative median of 2.4° (IQR, 0.3° to 5.1°) (P<0.001). This was maintained at follow-up, with a median SL of 2.5° (IQR, 0.4° to 5.2°), which remained significantly higher than the preoperative values (P<0.001). However, no statistically significant difference was observed between the immediate postoperative and follow-up values (P=0.54), indicating stability in segmental alignment after surgery (Figure 5B).

The anterior disc height (ADH) significantly increased from a preoperative median of 4.0 mm (IQR, 3.1–4.6 mm) to an immediate postoperative median of 8.5 mm (IQR, 7.9–9.3 mm) (P<0.001). At follow-up, the ADH slightly decreased to a median of 7.8 mm (IQR, 7.1–8.5 mm), but it remained significantly higher than both the preoperative (P<0.001) and postoperative measurements (P<0.001) (Figure 5C).

The PDH increased from a preoperative mean of 3.4±1.33 to 4.7±1.31 mm postoperatively (P<0.001). At follow-up, PDH decreased slightly to 4.1±1.32 mm but remained significantly higher than preoperative values (P=0.002). However, the decrease from postoperative to follow-up was also statistically significant (P<0.001) (Figure 5D).

Fusion and subsidence rates

Of the 77 levels treated, fusion occurred in 69 with a fusion rate of 89.6%. Twenty-nine (65.9%) patients had approximately 12 months of follow-up (range, 11.6–41.2 months), and a total of 53 levels treated, among these levels fusion occurred in 51 levels with a fusion rate of 96.2%. With respect to subsidence, in the whole cohort of the 16 of the 77 treated segments subsidence was observed in 16 levels given a subsidence rate of 20.8%. In the cohort who completed at least 12 months of follow-up subsidence was observed in 10/53 segments with a subsidence rate of 18.9%.

Figure 6 depicts a significant decline in the rate of new subsidence per year, starting at 40% in 2019 and dropping to 0% by 2023. A simple logistic regression analysis was used to assess the trend in subsidence over time. For each additional year, the odds of subsidence decreased by approximately 41.2% (odds ratio =0.5877, 95% confidence interval: 0.3366, 0.9634, P=0.04). Figure 7 shows a sample subsidence case.

Figure 6 Subsidence rate over time. Bar graph showing the subsidence rates (%) in patients undergoing ACDF with an expandable titanium cage from 2019 to 2023. ACDF, anterior cervical discectomy and fusion.

Figure 7 Sample subsidence case. (A) Day-1 postoperative radiograph. (B) Radiograph at final follow-up. The total intervertebral height decreased from 33.74 mm on the day 1 postoperative image to 28.94 mm at the final follow-up, indicating a subsidence of 4.8 mm.

Discussion

ACDF is a common and effective surgical method for treating cervical pathologies (1,2). One key advantage of ACDF over other approaches is its ability to successfully correct the lordotic angle at both the segmental and cervical levels (17). Various studies have highlighted the importance of restoring cervical and SL after ACDF. In a series of 104 patients, Hu et al. reported that patients with restored lordosis after 1- and 2-level ACDF had greater improvements in NDI score than those with unchanged alignment or residual cervical kyphosis, along with a lower incidence of adjacent segment degeneration (ASD) (18).

Furthermore, Liu et al. highlighted that inadequate lordosis restoration strongly predicted radiographic ASD (19). Despite this evidence, current ACDF solutions have limitations. Due to their rigid, pre-contoured design, conventional plating systems with fixed lordosis may not adequately restore segmental alignment in multilevel fusions (20,21). Additionally, stand-alone interbody spacers are susceptible to subsidence, which can lead to postoperative loss of lordosis and potentially affect clinical outcomes (22).

To address these limitations, expandable cages might offer a viable solution. This study is the first to describe the clinical, surgical, and radiological outcomes of a non-cylindrical expandable cervical cage for ACDF that can be adjusted in height and lordosis. Our findings indicate that ACDF using this expandable cervical cage is a safe surgical intervention for various cervical spine conditions. The ETC restored anterior and PDH while significantly improving sagittal alignment, with these improvements being sustained up to a year postoperatively. Moreover, the absence of intraoperative and postoperative complications, along with no revision surgery secondary to pseudoarthrosis or ASD, points to the safety profile of using these cages. These findings suggest that using an ETC in ACDF effectively improves sagittal alignment and maintains a favorable safety profile. Additionally, patients experienced significant reductions in neck and arm pain, as reflected by lower NRS scores, and notable improvements in functional outcomes, as indicated by the NDI.

In a retrospective series of 78 patients with degenerative cervical stenosis, Byvaltsev et al. reported a significant increase in C2–C7 lordosis from −9.3 to −15.1 at long-term follow-up without significant loss of alignment throughout the follow-up period (23). Similarly, Waschke et al. reported a significant increase in SL of 7.6 degrees at 2-year follow-up compared to pre-surgery values, with no difference between immediate post-surgery values and at follow-up in a series of 48 patients (24). In both studies, an anterior cervical corpectomy and fusion (ACCF) was performed. While this differs from our approach, parallels can be drawn. Our study demonstrated significant improvement in segmental and CL using an interbody ETC. The SL improved from a median of −0.9° preoperatively to 2.4° postoperatively, maintaining at 2.5° at follow-up. Similarly, global CL increased from 4.4° to 10.6° postoperatively and remained at 10.3° at follow-up. Furthermore, our results demonstrate a more substantial improvement in both cervical and SL compared to static cages. For example, using static cages, Altorfer et al. reported an increase in CL of 2.3° and SL of 1.4° (25). In contrast, our study achieved a median increase of 4.6° in CL and 3.3° in SL, maintained through follow-up. These findings suggest that ETC may offer superior lordosis restoration, particularly in cases requiring greater sagittal alignment correction than static interbody devices. However, further comparative studies are needed to confirm these advantages.

We found an 89.6% fusion rate, slightly lower than the rate reported in the literature for titanium interbody cages. A recent systematic review by Goldberg et al. reported that the average fusion rate for titanium interbody cages was 92.9% (84–100%) (26). Their final analysis included six studies with 279 patients, but our fusion criteria differed (27-32). The criteria included in the studies were the assessment of osseous bridging in or around the cage, the absence of motion between spinous processes on flexion-extension radiographs, and the lack of radiolucent halos around the cage or graft. However, our criteria for fusion involved plain flexion-extension radiographic evaluation with <1 mm of interspinous process motion on a >150% magnified image with >4 mm of motion at an adjacent, unoperated level. A modern and rigorous criteria endorsed by the Cervical Spine Research Society (CSRS) (33).

Furthermore, despite our cohort’s slightly lower fusion rate, there were no reoperations due to pseudoarthrosis. This may, however, be due to the relatively short-term radiographic follow-up in our study. In contrast, a study on expandable cervical corpectomy cages with an average follow-up of 60 months (5 years) reported fusion rates of 50% on X-ray and 47.4% on CT (23). The authors suggested that the bulky design of corpectomy cages may limit bone graft volume and distribution, potentially affecting osseous integration. However, sagittal alignment remained stable, and ASD did not significantly progress over time. Although corpectomy cages differ from expandable interbody cages, this study highlights the influence of implant design on long-term fusion success. Unlike corpectomy cages, expandable interbody cages are designed for placement within the disc space, allowing for greater endplate contact and better graft packing, which may enhance fusion rates. However, long-term data on expandable interbody cages remain limited, and further studies with extended follow-up are needed to determine whether similar concerns apply to these implants.

Our subsidence rate of 20.8% is comparable to that reported in the literature on interbody titanium cages. For instance, Goldberg et al., in their systematic review, reported an average subsidence rate of 27.5% (26). Several factors have been identified as risk factors for cage subsidence, including smoking, treatment of lower-level discs, multilevel fusion, malalignment of the cervical spine, hypermobility at the operated level, suboptimal surgical techniques (e.g., inadequate preparation of the adjacent endplates or excessive intraoperative distraction), and inappropriate cage selection (29,31,34-36).

With static interbody cages, including hyper-lordotic version, subsidence is partly due to the violation of endplates necessary for implantation (37). A biomechanical study by Truumees et al. found that larger interbody grafts required significantly higher distractive forces for insertion, potentially harming the endplates (38). Smaller grafts were recommended since they need less distractive force. However, complications associated with using smaller grafts include micromotion, delayed fusion, and a higher risk of extrusion (31).

Expandable cages demonstrate a benefit in this context. These cages have a reduced size during insertion, minimizing endplate violation while maintaining the ability to achieve sufficient restoration of intervertebral height. Nevertheless, caution is needed when using these cages, as over-distraction can lead to higher subsidence rates. We observed this in our cohort, finding that for each additional year of experience, the odds of subsidence decreased by approximately 41.2%. This suggests that the surgeon’s experience and learning curve with the expandable cage are necessary to attain the optimal lordotic angle and minimize subsidence risks associated with overextending disc height and lordotic angle.

The risks of over-distraction extend beyond subsidence alone. The expansion mechanism of these cages may influence biomechanical loading at adjacent levels, potentially contributing to altered load distribution, increased facet joint stress, or ASD. However, further studies are needed to quantify these effects and determine optimal expansion parameters to balance alignment benefits with mechanical stability.

While ETCs offer advantages such as improved sagittal alignment, greater disc height restoration, and reduced risk of endplate violation, their higher cost compared to static cages remains a significant concern in value-based healthcare. Studies have highlighted that ETCs can cost as much as $5,000 per implant, prompting questions regarding their cost-benefit ratio in modern surgical decision-making (39). Elder et al. previously noted that, in the cervical spine, while expandable vertebral body replacement cages may facilitate height restoration, their routine use is difficult to justify, given the lack of significant outcome differences compared to static alternatives (40). These findings suggest that ETCs may provide specific advantages, but their widespread use remains controversial due to the absence of clear long-term benefits and increased costs. Further cost-effectiveness studies evaluating surgical outcomes, reoperation rates, and overall healthcare expenditures are necessary to define their role in spine surgery better.

This study has its limitations. First, this is a retrospective study, which carries inherent biases and constraints associated with this design. Second, we utilized only one implant, which may limit the generalizability of the results to other implants. However, to our knowledge, no other non-cylindrical titanium or polyetheretherketone (PEEK) cages can expand in height and lordosis. Third, we conducted this study at a single institution by a single surgeon to ensure consistency in technique and perioperative care. This may, however, limit the generalizability of the findings, as the surgeon’s experience significantly influenced the surgical outcomes when using expandable cages. Fourth, although we included cases with at least nine months of follow-up and a median follow-up of 12 months, longer follow-up may be necessary to fully assess the long-term durability of the device, fusion integrity, and potential late-onset complications. Fifth, we had no control group, so we cannot directly compare our results with those of static interbody cages; this should be a focus for future prospective studies. Sixth, we did not have data on preoperative bone quality, including osteoporosis rates or Hounsfield unit (HU) measurements at the operative levels. Given the potential impact of bone density on implant subsidence and fusion outcomes, future studies incorporating HU assessment or formal osteoporosis screening would be valuable in further refining patient selection and surgical decision-making.

Conclusions

This study showed that ETC with adjustable height and lordosis restored and maintained cervical alignment and increased disc height. Patients also experienced a significant reduction in pain outcomes and improvement in function with no neurological complications. There was also a decrease in rates of new subsidence over time. However, future prospective studies are necessary to compare this cage to traditional static implants and evaluate how they perform in the long term.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-25-44/rc

Data Sharing Statement: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-44/dss

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-44/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-25-44/coif). O.N.K. reports serving as an instructor for Joimax and Arthrex. R.H. reports consultancy relationships with DePuy Synthes, Brainlab, and Aclarion, and financial interests with Real Spine and OnPoint. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. It was approved by the Weill Cornell Medicine Institutional Review Board (IRB) (Approval No. 2405027424), and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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