Self-stabilizing zero-profile 3D-printed vertebral body versus traditional titanium mesh-cage with plate in anterior cervical corpectomy and fusion: an open-label randomized controlled trial on efficacy and complications for cervical spondylotic myelopathy

Abstract

Objective

This study aimed to compare the perioperative and postoperative outcomes between self-stabilizing zero-profile 3D-printed vertebral body (Ss-Zp 3D-VB) and traditional titanium mesh-cage with plate (TMC-plate) in anterior cervical corpectomy and fusion (ACCF) for cervical spondylotic myelopathy (CSM).

Methods

Between January 2022 and March 2024, 74 patients diagnosed with CSM and scheduled to undergo ACCF were prospectively enrolled. Participants were randomly assigned to receive either the Ss-Zp 3D-VB or a TMC-plate. The Ss-Zp 3D-VB implant incorporates anatomically contoured endplates, a modulus-adapted porous structure, and a self-locking multidirectional screw trajectory, obviating the need for supplemental anterior plating. Outcome measures included surgical parameters (operative time, blood loss), length of hospitalization, clinical scores (JOA, NDI, VAS), radiographic assessments (intervertebral height, implant subsidence, C2–C7 Cobb angle, fusion rate), and incidence of dysphagia.

Results

A total of 62 participants (30 in the Ss-Zp 3D-VB group and 32 in the TMC-plate group) were analyzed, with a follow-up rate of 83.8%. The Ss-Zp 3D-VB group demonstrated significantly shorter operation time compared to the TMC-plate group (71.63 ± 8.79 vs. 102.06 ± 13.09, mean difference= − 30.43, 95% CI=[− 35.48,-24.77], P < 0.001), with no intergroup differences in intraoperative blood loss or hospitalization duration (P > 0.05). Both groups exhibited comparable improvements in JOA and NDI scores through 12-month follow-up (JOA improvement: 5.07 ± 1.39 vs. 5.13 ± 1.79, P = 0.887; NDI improvement: 17.37 ± 2.53 vs. 17.66 ± 2.55, P = 0.655). While VAS scores favored the 3D-VB group at 3 months (2.87 ± 0.82 vs. 3.62 ± 0.91, mean difference=− 0.76, 95% CI=[− 1.21,− 0.34], P = 0.001), this difference diminished by 12 months (P > 0.05). Radiologically, the 3D-VB group showed less intervertebral height loss at both 3 months (0.75 ± 0.40 vs. 2.51 ± 0.56 mm, mean difference=− 1.75, 95% CI=[− 2.00,− 1.54], P < 0.001) and 12 months (2.07 ± 1.14 vs. 3.14 ± 0.85 mm, mean difference=− 1.07, 95% CI=[− 1.52,− 0.53], P < 0.001). The implant subsidence rate was markedly lower in the Ss-Zp 3D-VB group at 12 months (6.7% vs. 43.8%, RR = 0.15, 95% CI=[0.04,0.62], P < 0.001). Dysphagia incidence was significantly reduced in the Ss-Zp 3D-VB group at 3 months (3.3% vs. 28.1%, RR = 0.12, 95% CI=[0.02,0.88], P = 0.013), though this difference attenuated by final follow-up (P > 0.05). Both groups achieved similar fusion rates (100% vs. 90.6%, P > 0.05) and maintained equivalent cervical alignment (P > 0.05).

Conclusion

The Ss-Zp 3D-VB significantly reduces operative time, implant subsidence, and dysphagia risk compared to traditional TMC-plate constructs, while achieving equivalent fusion rates and neurological recovery, supporting its potential as a biomechanically optimized option for cervical reconstruction in CSM.

Trial registration

Chinese Clinical Trial Registry, ChiCTR2000040313. Registered 27 November 2020, https://www.chictr.org.cn/bin/project/edit?pid=64762.

Introduction

Cervical spondylotic myelopathy (CSM), a progressive neurological disorder resulting from cervical spine degeneration, presents with characteristic symptoms including upper and lower extremity paresthesia, motor weakness, and functional impairment that significantly diminishes patients’ quality of life [1–3]. As a well-established surgical intervention, anterior cervical corpectomy and fusion (ACCF) provides effective neural decompression while restoring spinal stability [4, 5]. The conventional approach employing tricortical iliac crest autografts with anterior plating, while historically considered the gold standard, carries substantial drawbacks, including graft-related complications (resorption, collapse) and donor site morbidity (chronic pain, infection rates up to 20.6%), prompting the search for improved alternatives [6–8].

Titanium mesh cage (TMC) constructs, when combined with autologous bone or synthetic hydroxyapatite grafts, have emerged as viable substitutes for traditional iliac crest harvesting [9]. However, these implants present several biomechanical challenges: suboptimal osseointegration at the bone-implant interface, significant subsidence rates (reported 9-79.7% in literature), and potential migration [9, 10]. The underlying mechanisms of TMC failure involve both material properties and design limitations.

Recent advances in additive manufacturing have enabled the development of three-dimensionally printed vertebral body (3D-VB) implants with superior biomechanical characteristics [11, 12]. Utilizing preoperative CT/MRI data, these patient-specific prostheses are fabricated from medical-grade Ti6Al4V alloy with precise anatomical matching [13, 14]. The microarchitecture of 3D-VBs demonstrates several advantageous features: optimized surface contact area, controlled porosity with interconnected pores facilitating osteoconduction, and elastic modulus approaching that of native bone [13–15]. While representing a significant advancement, conventional 3D-VBs still require supplemental anterior plating, which prolongs operative time and may contribute to postoperative dysphagia [16–18].

The self-stabilizing zero-profile 3D-printed vertebral body (Ss-Zp 3D-VB) represents a significant evolution of this technology, featuring intrinsic stabilization mechanisms achieved through anatomically contoured endplates. Recent systematic reviews and biomechanical studies confirm that 3D-printed vertebral bodies offer superior biomechanic performance compared to conventional cages [9, 19, 20]. These collective findings underscore the potential of 3D-printed technology to address longstanding limitations of traditional implants. Specifically, the superior endplate of the Ss-Zp 3D-VB is concave and the inferior endplate convex, mirroring the native anatomy of the cervical vertebrae. This design ensures optimal congruency with the adjacent vertebral endplates upon implantation, enhancing stability and minimizing micromotion. Furthermore, the Ss-Zp 3D-VB incorporates a dual-plane screw trajectory design that optimizes biomechanical stability, thereby obviating the need for supplemental plate fixation. A pivotal biomechanical innovation resides in its multidirectional screw angulation design: cephalad screws are oriented at 35° cranial and 5° medial inclination, while caudal screws are angled at 35° caudal and 5° medial inclination. This dual-plane convergent screw alignment establishes a self-locking “V-shaped” configuration in both sagittal and coronal dimensions, effectively resisting axial pullout forces and minimizing postoperative screw loosening risks. To further enhance safety, the anterior margin of the implant features an integrated stop plate, which prevents inadvertent over-insertion into the spinal canal. The porosity of Ss-Zp 3D-VB was 68.0% ± 5.3%, the pore size was (800 ± 200) µm, the elastic modulus was (2.5 ± 0.2) GPa, and the compressive strength was (63.0 ± 4.7) MPa [21].

Following successful application in ossification of posterior longitudinal ligament (OPLL) cases [21], our institution has employed Ss-Zp 3D-VBs for other CSM patients since 2022. This open-label randomized controlled trial systematically compares clinical and radiographic outcomes between Ss-Zp 3D-VB and traditional titanium mesh-cage with plate (TMC-plate) constructs in ACCF procedures, with particular focus on implant performance and potential for widespread clinical implementation.

This work has been reported in line with the TITAN criteria [22].

Methods

Study design

Given the inherent differences in the interventions—including distinct implant designs, surgical procedures, and the use of postoperative imaging that could reveal treatment allocation—blinding was not feasible. Therefore, a prospective, open-label, randomized controlled trial design was adopted. The study protocol received approval from the institutional review board and was registered with the Chinese Clinical Trial Registry. This manuscript was prepared in accordance with the CONSORT guidelines for reporting randomized trials [23].

Primary hypothesis

We hypothesized that the Ss-Zp 3D-VB group would exhibit significantly lower rates of postoperative dysphagia and implant subsidence compared to the TMC-plate group, while demonstrating comparable fusion rates and neurological recovery.

Participant recruitment

The sample size was determined based on an anticipated 40% absolute reduction in implant subsidence rates (50% in the TMC-plate group vs. 10% in the 3D-VB group), with α = 0.05 and 80% power, yielding 20 patients per group. Accounting for an estimated 15% dropout rate, a minimum of 46 participants were required.

This open-label randomized controlled trial enrolled 74 consecutive patients diagnosed with CSM between January 2022 and March 2024 at our institution. Following institutional review board approval, all participants provided informed written consent. Preoperative diagnostic evaluation involved comprehensive cervical spine imaging, including both CT and MRI scans performed by board-certified radiologists to confirm spinal cord compression levels and establish baseline morphological parameters.

Patient selection followed stringent inclusion criteria: (1) adults aged 18–80 years; (2) clinically confirmed CSM meeting international diagnostic standards; (3) radiographic evidence of cervical degeneration with spinal cord compression; (4) minimum 6 months of unsuccessful conservative management; and (5) planned single-level corpectomy. Exclusion criteria encompassed: (1) untreated osteoporosis (T-score ≤-2.5); (2) multilevel cervical stenosis (> 2 segments); (3) significant cervical deformity; (4) previous cervical spine operations; (5) non-degenerative pathologies (neoplasms, infections, trauma); (6) active psychiatric conditions; and (7) anticipated follow-up difficulties.

Participants were allocated via covariate-adaptive randomization—stratified by enrollment time, age, and sex—to either the Ss-Zp 3D-VB group or the conventional TMC-plate group. After excluding 12 patients lost to follow-up, the final analysis included 62 participants, representing an 83.8% retention rate (Fig. 1).

Fig. 1.

Flow chart for the study

Surgical technique and postoperative rehabilitation

The study utilized two distinct implant systems: TMC-plates (Fig. 2) manufactured by Beijing Fule Science & Technology Development Co., Ltd (Beijing, China) and standardized version Ss-Zp 3D-VBs (Fig. 3) produced by AK Medical Holdings Limited (Beijing, China). The assigned implant was selected intraoperatively based on preoperative randomization. All surgical procedures were performed by a single senior spine surgeon with over 15 years of specialized experience in anterior cervical surgery to maximize technical consistency. A standardized surgical protocol was strictly followed throughout the study.

Fig. 2.

Titanium mesh cage and anterior cervical plate in the TMC group: A Titanium mesh cage with a thickness of 1.0 mm, diameter specifications: 8 mm, 10 mm, and 12 mm, featuring sidewall perforations (3 mm diameter), B Anterior cervical plate with a thickness of 2.0 mm and variable length options ranging from 30 mm to 42 mm, incremented in 2.0 mm steps

Fig. 3.

Self-stabilizing zero-profile 3D-Printed microporous titanium alloy vertebral body prosthesis in the Ss-Zp 3D-VB Group: A Lateral and anterior views of the Ss-Zp 3D-VB. The height of the patient-specific implant was determined using the formula: [(superior vertebral height + inferior vertebral height)/2 + 2 × disc height]. Based on accumulated clinical data and anatomical studies of the Chinese population, a standardized (off-the-shelf) version was subsequently developed, with heights ranging from 20 to 50 mm in 2 mm increments. Prosthesis diameter specifications (width × depth): 10 mm × 12 mm, 12 mm × 14 mm, and 14 mm × 16 mm. B Schematic illustration of the Ss-Zp 3D-VB superior and inferior surfaces; the superior surface features a concave curvature and the inferior surface a convex slope, which closely conform to the adjacent vertebral endplates. C Microporous architecture showing a mean pore size of 800 ± 200 μm

All patients were placed in the standard supine position for surgery. The anterior cervical spine was accessed through the classical Smith-Robinson approach [13]. Following exposure, the anterior longitudinal ligament was carefully dissected, and intervertebral disc material was meticulously removed using sharp dissection instruments and curettes. The targeted vertebral body was then resected using a combination of ultrasonic bone scalpel and high-speed drill techniques. Adjacent vertebral endplates were prepared with precision using high-speed burrs and curettes to create optimal fusion surfaces. At this stage, it is essential to thoroughly remove any osteophytes from the anterior edge of the vertebral body at the operative site using a rongeur. This critical step ensures an optimal bone-implant interface and allows for proper seating of the reconstructive hardware.

In the TMC-plate group, the titanium mesh cages were carefully contoured intraoperatively to match the anatomical angles of the proximal and distal vertebral endplates. The cages were packed with morselized autologous bone harvested from the resected vertebral body before being positioned in the intervertebral space. Final stabilization was achieved using a standard anterior cervical plating system.

For patients receiving Ss-Zp 3D-VB implants, the prostheses were preoperatively customized based on detailed CT measurements. Following vertebral body resection, trial implants were used to assess the appropriate height and depth of the intervertebral space. A standard-sized Ss-Zp 3D-VB prosthesis (typically 12 × 14 × 24 mm) was selected, with height being the primary determinant. The implant was then precisely inserted and secured using its integrated self-locking screw mechanism. Unlike the TMC-plate procedure, the Ss-Zp 3D-VB does not require additional autologous bone grafting, as its porous architecture is specifically designed to facilitate direct osseointegration and bone ingrowth without filler material.

Both groups underwent identical surgical closure procedures, including the placement of negative-pressure drainage systems and layered wound closure. Postoperative care was standardized: drains were generally removed within 48–72 h. Patients in the Ss-Zp 3D-VB group did not require a cervical collar but were advised to avoid excessive cervical rotation for one month. Those in the TMC-plate group were instructed to wear a cervical orthosis continuously for one month. All patients were encouraged to mobilize early, beginning ambulation and supervised rehabilitation exercises on postoperative day two [21].

Outcome assessment

Patients underwent standardized postoperative evaluations at 3-month and 12-month intervals following surgery. All clinical and radiographic assessments were conducted independently by two fellowship-trained spine surgeons to ensure objective data collection. Key perioperative parameters, including operative duration, estimated blood loss, and length of hospital stay, were systematically documented.

Comprehensive cervical spine imaging was systematically performed at each follow-up visit, incorporating the following parameters: (1) intervertebral height analysis, quantified as the mean distance between the anterior and posterior margins of adjacent vertebral endplates within the fused segment; (2) subsidence assessment, defined as a reduction in intervertebral height exceeding 3 mm compared to immediate postoperative measurements; (3) sagittal alignment measurement, calculated via the C2-C7 Cobb angle (Fig. 4, with positive values denoting lordosis and negative values indicating kyphosis); and (4) fusion evaluation, utilizing thin-slice CT (0.5–1.0 mm) with multiplanar reconstruction (MPR) at 3 and 12 months postoperatively. Fusion was rigorously defined as the presence of continuous bridging trabecular bone across the implant–vertebra interface on both sagittal and coronal views, absent radiolucent lines exceeding 50% of the interface circumference. Quantitative analysis of interspinous process motion (ISPM) was performed using flexion–extension radiographs, with fusion confirmed if translational motion measured less than 1 mm [24]. To ensure objectivity, all radiographic assessments were conducted independently by two fellowship-trained spine surgeons, with a third senior surgeon resolving any discrepancies.

Fig. 4.

Schematic illustration of the C2-C7 cobb angle measurement method: The angle is measured between the inferior endplate of C2 and the inferior endplate of C7 on lateral radiographs, with positive values indicating cervical lordosis and negative values denoting kyphotic alignment

Postoperative dysphagia was assessed using the Eating Assessment Tool (EAT-10) [25], a validated patient-reported outcome instrument for dysphagia evaluation, comprising ten items scored on a 5-point Likert scale (0–4) with total scores ranging from 0 to 40, where a score ≥ 3 indicates clinically significant dysphagia and demonstrates high internal consistency and test-retest reliability [26].

Validated assessment tools were systematically administered preoperatively and at each postoperative follow-up, including: (1) the Japanese Orthopedic Association (JOA) scoring system to evaluate neurological function and myelopathy severity [27]; (2) the Neck Disability Index (NDI), a patient-reported questionnaire quantifying functional limitations related to cervical spine pathology [28]; and (3) the Visual Analog Scale (VAS) for standardized assessment of neck and upper extremity pain intensity (ranging from 0 [no pain] to 10 [worst imaginable pain]) [29]. Assessments were administered preoperatively and at each postoperative follow-up visit by independent clinical staff blinded to the treatment allocation.

Statistical analysis

Statistical analyses were performed using SPSS version 27.0 (IBM Corp., Armonk, NY, USA). The normality of continuous data was assessed using the Shapiro–Wilk test., and homogeneity of variance was verified with Levene’s test. Normally distributed variables were presented as mean ± standard deviation and compared between groups using the independent samples t-test; non-normally distributed data were expressed as median (interquartile range) and analyzed with the Mann–Whitney U test. Categorical variables were summarized as frequencies (%) and compared using the chi-square test or Fisher’s exact test, as appropriate.

For statistically significant continuous outcomes, effect sizes were reported as Cohen’s d (for parametric tests) or Hedges’ g (for non-parametric tests) accompanied by 95% confidence intervals (CI) for the mean difference. For categorical outcomes, risk ratios (RR) with 95% CI were calculated. To control for Type I error inflation resulting from multiple comparisons across different follow-up time points and outcome measures, the Bonferroni correction was applied by adjusting the significance threshold α based on the number of pairwise comparisons performed.

A two-sided p value < 0.05 was considered statistically significant.

Results

Patient demographics

After excluding 12 patients lost to follow-up (7 in the Ss-Zp 3D-VB group and 5 in the TMC-plate group), the final analysis included 62 participants, representing a retention rate of 83.8%. Reasons for loss to follow-up included change of contact information (1 in the Ss-Zp 3D-VB group, 2 in the TMC-plate group), refusal to continue participation (2 in the Ss-Zp 3D-VB group), and inability to return due to intercurrent illness or trauma (4 in the Ss-Zp 3D-VB group, 3 in the TMC-plate group). The final cohort comprised 30 patients in the Ss-Zp 3D-VB group and 32 patients in the TMC-plate group. There were 38 male and 24 female patients, with a mean age of 47.53 years. There were no significant between-group differences in gender, age, BMI, BMD, and pathologic level (P > 0.05) (Table 1).

Table 1.

Patient demographics

	Ss-Zp 3D-VB (n = 30)	TMC-plate (n = 32)	t/χ² value	Cohen’s d/Cramer’s V	P value
Gender (Men/Women)	18/12	20/12	0.041	0.026	0.840
Mean age (year)	45.9 ± 8.47	49.06 ± 9.55	− 1.376	− 0.350	0.174
BMI (kg/m2)	23.42 ± 2.37	24.04 ± 2.21	− 1.073	− 0.273	0.288
BMD (T-score)	− 0.28 ± 0.51	− 0.43 ± 0.46	1.267	0.322	0.210
Pathological level
C3	2	2	1.088	0.132	0.896
C4	6	4
C5	8	9
C6	9	9
C7	5	8
Operation time (min)	71.63 ± 8.79	102.06 ± 13.09	− 10.672	− 2.712	< 0.001
Intraoperative blood loss (ml)	78.67 ± 16.18	78.75 ± 16.70	− 0.020	− 0.005	0.984
Duration of hospitalization (day)	6.70 ± 1.09	6.97 ± 1.31	− 0.877	− 0.223	0.384

BMD, bone mineral density; BMI, body mass index.

Comparison of operation time, intraoperative blood loss, and days of hospitalization

Ss-Zp 3D-VB group exhibited significantly shorter operation times compared to the TMC-plate group (71.63 ± 8.79 vs. 102.06 ± 13.09, mean difference=-30.43, 95% CI=[-35.48,-24.77], P < 0.001). No between-group differences were observed in the intraoperative blood loss and the duration of hospitalization (P > 0.05).

Patient-reported scores

Regarding patient-reported scores, the JOA, NDI, and VAS scores of patients in both groups at each preoperative and postoperative follow-up are presented in Fig. 5. There were no significant differences between the Ss-Zp 3D-VB group and TMC-plate group regarding all three clinical scores preoperatively (P > 0.05).

Fig. 5.

The JOA, NDI, and VAS scores of patients in both groups at each preoperative and postoperative time point: a JOA scores, b NDI scores, c VAS scores

At the 12-month follow-up, significant improvements were observed in all the clinical scores of both groups compared with preoperative scores. No significant between-group differences in JOA and NDI scores were noted at 3 and 12 months (P > 0.05). For the VAS, a significant difference was only observed at 3 months postoperatively: Ss-Zp 3D-VB group had lower scores than its counterpart (2.87 ± 0.82 vs. 3.62 ± 0.91, mean difference=− 0.76, 95% CI=[− 1.21,− 0.34], P = 0.001). At 12 months, there is no significant difference between groups (P > 0.05).

Radiologic parameters and complications

Table 2 shows the intervertebral height, incidence of implant subsidence, cervical alignment (C2-C7 Cobb angle), postoperative dysphagia, and fusion rate between the two groups.

Table 2.

Radiologic parameters and complications

Variable measure	Ss-Zp 3D-VB (n = 30)	TMC-plate (n = 32)	Mean difference/Risk ratio [95% CI]	t/χ² value	Cohen’s d/Cramer’s V	P value
Intervertebral height (mm)
Preoperative	47.63 ± 8.40	47.47 ± 7.77	0.16[− 3.54,4.16]	0.075	0.019	0.940
Postoperative	57.98 ± 7.53a	57.78 ± 7.40a	0.20[− 3.19,3.62]	0.105	0.027	0.917
3 months postoperative	57.23 ± 7.55a	55.28 ± 7.25a	1.95[− 1.44,5.28]	1.038	0.264	0.303
12 months postoperative	55.91 ± 7.22a	54.64 ± 7.47a	1.27[− 2.13,4.69]	0.678	0.172	0.500
Height loss (mm)
3 months postoperative	0.75 ± 0.40	2.51 ± 0.56	− 1.75[− 2.00,− 1.54]	− 14.122	− 3.589	< 0.001
12 months postoperative	2.07 ± 1.14	3.14 ± 0.85	− 1.07[− 1.52,− 0.53]	− 4.206	− 1.069	< 0.001
C2-C7 Cobb angle (°)
Preoperative	13.91 ± 3.15	12.58 ± 4.56	1.34[− 0.57,3.31]	1.333	0.339	0.188
Postoperative	18.19 ± 3.92a	17.12 ± 4.82a	1.07[− 1.06,3.21]	0.954	0.242	0.344
3 months postoperative	16.37 ± 3.87a	14.94 ± 4.84	1.43[− 0.74,3.63]	1.276	0.324	0.207
12 months postoperative	16.10 ± 3.83ab	14.51 ± 5.04b	1.59[− 0.60,3.87]	1.393	0.354	0.169
Implant subsidence rate; n (%)
3 months postoperative	0(0)	4(12.50%)	–*	4.009	0.254	0.114
12 months postoperative	2(6.67%)	14(43.75%)	0.15[0.04,0.62]	11.121	0.424	< 0.001
Dysphagia; n (%)
3 months postoperative	1(3.33%)	9(28.13%)	0.12[0.02,0.88]	7.035	0.337	0.013
12 months postoperative	0(0)	4(12.50%)	–*	4.009	0.254	0.114
Fusion; n (%)	30(100%)	29(90.63%)	1.10[0.99,1.23]	2.956	0.218	0.238

^asignificantly different from preoperative groups (multiple pairwise within-group post hoc comparison tests);

^bsignificantly different from postoperative groups (multiple pairwise within-group post hoc comparison tests);

^csignificantly different from the 3-month postoperative groups (multiple pairwise within-group post hoc comparison tests).

^*Risk ratio and 95% confidence interval could not be calculated due to the absence of complications in the Ss-Zp 3D-VB group.

Both groups’ intervertebral height and cervical alignment at the 12-month follow-up were markedly improved compared with those at the preoperative assessment (P < 0.05). There was no significant difference in fusion rates between the two groups (100% vs. 90.63%, P > 0.05).

At the 3-month follow-up, the intervertebral height loss was statistically different between groups: 0.75 ± 0.40 mm in the Ss-Zp 3D-VB group and 2.51 ± 0.56 mm in the TMC-plate group (mean difference=− 1.75, 95% CI=[− 2.00,− 1.54], P < 0.001). Similarly, at the 12-month follow-up, the mean height loss was statistically different: 2.07 ± 1.14 mm in the Ss-Zp 3D-VB group and 3.14 ± 0.85 mm in the TMC-plate group (mean difference=− 1.07, 95% CI=[− 1.52,− 0.53], P < 0.001).

The implant subsidence rate was 0 (0/30) in the Ss-Zp 3D-VB group and 12.50% (4/32) in the TMC-plate group at 3 months postoperatively (P > 0.05); and 6.67% (2/30) in Ss-Zp 3D-VB group and 43.75% (14/32) in TMC-plate group at 12 months postoperatively (RR = 0.15, 95% CI=[0.04,0.62], P < 0.001). During the 12-month follow-up, the C2-7 Cobb angle in the Ss-Zp 3D-VB group was similar to that in the TMC-plate group (P > 0.05).

1 (3.33%) patient in the Ss-Zp 3D-VB group exhibited dysphagia 3 months after the operation, whereas 9 (28.13%) patients in the TMC-plate group exhibited dysphagia 3 months after the operation (RR = 0.12, 95% CI=[0.02,0.88], P = 0.013). At 12 months postoperatively, 0 (0) patients in the Ss-Zp 3D-VB group exhibited dysphagia, and 4 (12.50%) patients in the TMC-plate group exhibited dysphagia (P > 0.05).

Representative case presentation

Figures 6 and 7 illustrate typical preoperative and postoperative imaging comparisons for patients who underwent ACCF using the Ss-Zp 3D-VB and the conventional TMC-plate, respectively. These cases visually demonstrate key radiological outcomes discussed in the previous section, including implant positioning, maintenance of intervertebral height, subsidence behavior, and spinal cord decompression

Fig. 6.

A 72-year-old female with CSM at C4–6 undergoing C5 subtotal corpectomy, decompression, and Ss-Zp 3D-VB implantation (see Fig. 3). A, B Preoperative posterior-anterior and lateral radiographs demonstrating intervertebral space narrowing and osteophytic lipping at C4–5 and C5–6, C, D Preoperative sagittal and axial CT reconstructions showing posterior marginal osteophytes at C4–6, encroaching into the spinal canal, E Preoperative T2-weighted sagittal MRI revealing spinal cord compression at C4–5 and C5–6, with intramedullary hyperintense signal, F, G Immediate postoperative posterior-anterior and lateral radiographs confirming proper positioning of the self-stabilizing zero-profile prosthesis. H, I Sagittal and axial CT reconstructions at 1 week postoperatively, demonstrating optimal prosthesis placement and complete resection of osteophytes, J, K Lateral radiographs at 12-month follow-up, showing stable prosthesis positioning without interval change, L, M Flexion-extension lateral radiographs at 6 months, confirming prosthesis stability without positional migration, N Sagittal CT reconstruction at 12 months, verifying maintained prosthesis alignment without subsidence.

Fig. 7.

A 52-year-old male with CSM at C5–6 undergoing C6 subtotal corpectomy, decompression, and TMC-plate anterior cervical fusion. A, B Preoperative lateral radiographs demonstrating anterior/posterior osteophytic lipping at C5–6 and C6–7, C Preoperative T2-weighted sagittal MRI revealing spinal cord compression at C5–6, D Preoperative sagittal CT reconstruction showing posterior osteophytes formation at C5–6, E, F Immediate postoperative posterior-anterior and lateral radiographs confirming proper TMC positioning, G, H Coronal and sagittal CT reconstructions at 1 week postoperatively, showing slight TMC tilt without significant subsidence, I, J Lateral radiographs at 6-month follow-up, demonstrating TMC subsidence with screw contact, K, L Coronal and sagittal CT reconstructions at 6 months, confirming inferior margin subsidence and screw impingement

Discussion

In this open-label randomized controlled trial, we compared the Ss-Zp 3D-VB with TMC-plate in ACCF for CSM. The Ss-Zp 3D-VB demonstrated superior outcomes in operative time, early postoperative dysphagia, and implant subsidence rates, while achieving comparable neurological recovery, fusion rates, and cervical alignment to the TMC-plate group.

The significantly shorter operative time in the Ss-Zp 3D-VB group (mean difference: − 30.43 min, P < 0.001) aligns with the streamlined surgical workflow enabled by its integrated design, which eliminates the need for intraoperative cage contouring and additional plating. This efficiency stems from preoperative CT-based customization, ensuring anatomical fit without supplemental fixation [30, 31], as supported by biomechanical studies highlighting the self-locking screw mechanism and recent comparative studies showing reduced operative duration with self-stabilizing 3D-printed systems [32, 33]. In contrast, TMC-plate procedures require extended exposure and fixation, potentially increasing anesthesia-related risks in elderly or comorbid patients [12]. Although intraoperative blood loss and hospital stay were similar between groups, the reduced operative duration may translate to lower overall surgical costs and improved resource utilization in high-volume centers.

A notable reduction in early dysphagia was observed in the Ss-Zp 3D-VB group at 3 months (RR = 0.12, P = 0.013), likely attributable to its zero-profile configuration that minimizes esophageal irritation and prevertebral soft tissue disruption [30, 32]. Traditional plating in the TMC group, by contrast, may exacerbate postoperative edema and hardware prominence, contributing to higher incidence rates (28.1% vs. 3.3%). However, this difference attenuated by 12 months, suggesting that dysphagia in plated constructs is often transient and resolves with tissue adaptation [21, 34]. These findings corroborate systematic reviews and meta-analyses indicating significantly lower dysphagia risks with zero-profile devices compared to plated constructs in anterior cervical fusion [9, 35].

Implant subsidence emerged as a key differentiator, with the Ss-Zp 3D-VB group exhibiting lower rates at 12 months (6.7% vs. 43.8%, RR = 0.15, P < 0.001) and less intervertebral height loss (mean difference: − 1.07 mm, P < 0.001). This superiority can be explained by the implant’s modulus-adapted porous structure (elastic modulus: 2.5 ± 0.2 GPa), which approximates native bone and mitigates stress shielding, promoting osseointegration through interconnected pores (size: 800 ± 200 μm) [31]. The multidirectional screw trajectory further enhances axial stability by creating a convergent “V-shaped” configuration, reducing micromotion and pullout risks [21]. In comparison, TMC constructs are prone to endplate failure due to higher rigidity and point-loading, as evidenced by subsidence rates of 9-79.7% in prior reports and confirmed by multiple meta-analyses showing significantly lower subsidence with 3D-printed vertebral bodies (OR ≈ 0.12–0.15) [9, 10, 13]. Despite these differences, both groups maintained similar C2-C7 Cobb angles, indicating that subsidence in this cohort did not significantly impact global sagittal balance, though longer follow-up is needed to assess potential kyphotic progression [36, 37]. Fusion rates were equivalent (100% vs. 90.6%, P > 0.05), consistent with meta-analyses showing comparable osseous integration between 3D-printed and titanium implants.

Clinical improvements in JOA, NDI, and VAS scores were comparable between groups, reflecting effective neural decompression in both approaches. The transient VAS advantage in the Ss-Zp 3D-VB group at 3 months (mean difference: − 0.76, P = 0.001) may relate to reduced soft tissue trauma and early stability, but long-term equivalence suggests that implant choice does not differentially affect neurological recovery in single-level CSM.

Despite these benefits, Ss-Zp 3D-VB implementation faces barriers, including higher costs (¥30,000–40,000 RMB for customized vs. ¥10,000–15,000 RMB for standardized versions) and manufacturing lead times (3–5 days), potentially limiting accessibility in resource-constrained settings [35]. The standardized off-the-shelf variant, based on population-specific anatomical data, addresses some delays but requires intraoperative trialing [21]. Additionally, while limited exposure in Ss-Zp 3D-VB may reduce adjacent segment degeneration (ASD) risk compared to TMC-plate, our 12-month follow-up precludes definitive conclusions, necessitating extended monitoring [4].

This study has limitations. The single-center, open-label design introduces potential bias, though objective radiographic assessments mitigate this. The modest sample size (n = 62) limits power for detecting rare events, and short follow-up hinders evaluation of long-term outcomes like ASD, implant durability, or revision rates. Generalizability may be restricted to single-level CSM in non-osteoporotic patients, as per inclusion criteria.

Conclusion

The Ss-Zp 3D-VB appears to be a promising alternative to traditional TMC-plate constructs in ACCF, offering reduced operative time, lower early dysphagia rates, and diminished implant subsidence while maintaining comparable fusion and neurological outcomes. These early findings suggest its potential as a biomechanically optimized option for cervical reconstruction in CSM. However, given the preliminary nature of this trial, further validation through larger, multicenter randomized studies with longer follow-up is necessary before widespread clinical adoption can be recommended.

Author contributions

Xiuzhi Li and Haijiao Wang: conception and design of the study; Yuwei Li, Xiuzhi Li, Citing Guo, Wei Cui, and Shifeng Gu: acquisition of data; Citing Guo, Wei Cui, and Shifeng Gu: data collection and interpretation; Yuwei Li and Citing Guo: drafting of the manuscript; Xiuzhi Li, Citing Guo, and Haijiao Wang: critical revision of the manuscript for important intellectual content; Yuwei Li and Wei Cui: statistical analysis; Yuwei Li and Haijiao Wang: obtaining funding. All authors have read and approved the manuscript.

Funding

This work was supported by a medical science and technology research project of Henan province, People’s Republic of China (grant no. LHGJ20230937).

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The study protocol received approval from the Ethics Committee of Luohe Central Hospital (approval number: LH-KY-2022-001-118). Written informed consent was obtained from all participants prior to study inclusion.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.