Comparative review of anchored cage devices and standalone cages in multilevel anterior cervical discectomy and fusion surgeries

Abstract

Background:

Anterior plating has conventionally been the standard for multilevel anterior cervical discectomy and fusion (ACDF). However, concerns about complications linked to plate and screw constructs have prompted interest in alternative solutions such as standalone spacers with or without screws. This study compares clinical and radiological outcomes of standalone cages and anchored cage devices in multilevel ACDF.

Methods:

A retrospective analysis of 85 patients treated for multilevel ACDF over 5 years at a tertiary spinal center on patients receiving either standalone cages or anchored cage devices. Outcomes assessed included the Odom's Criteria, Neck Disability Index (NDI), Visual Analog Scale (VAS) scores for neck and upper limb pain, fusion rates, subsidence, cobbs angle, C2-C7 SVA, and complications. Statistical analysis utilized t-tests and Chi-square tests with statistical significance set at P < 0.05.

Results:

A total of 85 patients (46 standalone and 39 anchored cage) with an average follow-up of 3.2 years were included. Both groups exhibited comparable clinical improvements postoperatively. Anchored cage devices had higher fusion rates (91% vs. 88%) but greater subsidence (32.1% vs. 29.0%). Dysphagia incidence was marginally higher in standalone cages. No statistically significant differences in clinical or radiological outcomes were observed.

Conclusion:

Both standalone cages and anchored cage devices are effective for multilevel ACDF, with comparable short-term outcomes. Device selection should consider surgeon preference, cost, and patient-specific factors. Further long-term studies are needed to validate these findings.

INTRODUCTION

Cervical degenerative disc disease frequently leads to radiculopathy or myelopathy, which may necessitate surgical intervention when conservative treatments fail. The anterior approach to cervical spine fusion was first described by Robert Robinson and George Smith in the 1950s, with Cloward later modifying the technique by introducing the use of a bone dowel to enhance fusion.[1,2] Anterior cervical discectomy and fusion (ACDF) has since become the gold standard for treating cervical disc herniation, offering immediate decompression of the central canal and neural foramina, restoration of disc height, and load-bearing support to the anterior column, while promoting interbody fusion through cage replacement.[3,4] Despite its widespread success, drawbacks such as subsidence, pseudoarthrosis, and variable fusion rates have been reported.[5] These challenges have driven the evolution of alternative cage systems to address these limitations.

Multilevel ACDF is a common surgical procedure for managing symptoms related to multilevel cervical disc herniations. Historically, anterior plating was the standard for achieving fusion, but accumulating evidence has demonstrated that standalone cages with integrated anchoring screws can achieve comparable clinical and radiological outcomes while potentially reducing complications.[6,7]

Standalone cages have reduced the need for anterior plating, which may reduce the incidence of dysphagia and simplify the surgical procedure. On the other hand, anchored cage devices incorporate screws directly into the device, providing enhanced stability without requiring separate plate fixation in some patients, where a plate may be considered with standalone cage. This study aims to compare these two cage designs, examining their relative benefits, limitations, and overall efficacy in multilevel ACDF, and to guide surgeons in selecting the most appropriate device for their patients.

METHODS

Study design

This retrospective analysis reviewed 85 patients undergoing multilevel ACDF from 2017 to 2022. Patients were divided into two groups based on the cage used:

1. Standalone – CeSPACE cage[8]

2. Anchored cage devices – Zero-P cage.[9]

Inclusion and exclusion criteria

Inclusion

• Multilevel cervical disc degeneration with radiculopathy or myelopathy

• Failure of conservative treatment.

Exclusion

• Trauma, tumors, or infections requiring ACDF

• Single-level ACDF procedures

• Revision cases.

Outcome measures

• Clinical: Pre- and post-operative Neck Disability Index (NDI) and Visual Analog Scale (VAS) scores for neck and arm pain

• Radiological: Pre- and post-operative Cobb’s angle and postoperative fusion and subsidence rates on follow-up imaging

• Complications: Dysphagia, dysphonia, CSF leak, infection, and adjacent segment disease on immediate and long-term follow-up.

Statistical analysis

Data were analyzed using Student’s t-tests for continuous variables and Chi-square tests for categorical variables. P <0.05 was considered statistically significant.

RESULTS

Demographics

The study population comprised 85 patients and divided into two groups: 46 patients received standalone cages and 39 patients received anchored cage devices. The average age across the cohort was 57 years (range 33–83 years), with a male: female ratio of 27:12 for anchored cage devices and 28:18 for standalone cage. Comorbidities were noted to be higher in the standalone cage group (67%) compared to the anchored cage devices group (49%) [Table 1]. This difference in comorbidity was incidental as it was based on individual surgeon’s routine practice. The majority of procedures involved two-level ACDF procedures, with only 3 subjects requiring three-level fusions.

Table 1.

Demographics

Variables	Anchored cage devices	Standalone cage
Number of patients (n)	39	46
Mean age, years (range)	56.5±11.8 (33–83)	59.3±10.7 (33–80)
Male:female	27:12	28:18
2-level ACDF	38	44
3-level ACDF	1	2

ACDF - Anterior cervical discectomy and fusion

Clinical outcomes

Postoperative improvements in pain, myelopathy, Odom’s criteria, the NDI and VAS scores were observed in both study groups. [Table 2.1, 2.2, 2.3, 2.4] In the cage screw devices group, the mean preoperative NDIscore of 47.85 significantly decreased to 22.3 postoperatively (P = 0.038), marking a 53.4% reduction. Arm pain, measured by the VAS, improved from 6.0 to 3.0, representing a statistically significant 50.1% reduction (P = 0.013). However, while neck pain (VAS)scores also improved from 4.7 to 3.6, this change was not statistically significant (P = 0.099).

Table 2.1.

Clinical outcomes - Symptoms

Postoperative symptoms	Improve (%)	Persistent (%)	Worse (%)	Test type	P
Postoperative radicular pain
Anchored cage devices	80	14	6	Welch’s t-test	0.1239
Standalone cage	91	9	0
Postoperative neck pain
Anchored cage devices	67	31	2	Welch’s t-test	0.8107
Standalone cage	70	21	9
Postoperative myelopathy
Anchored cage devices	57	38	5	Welch’s t-test	0.3341
Standalone cage	67	24	9

Table 2.2.

Clinical outcomes – Odom’s criteria

Odom’s criteria	Excellent (%)	Good (%)	Fair (%)	Poor (%)	Test type	P	Significance
Type of cage
Anchored cage device	46	15	13	26	Welch’s t-test	0.1239	No
Standalone cage	59	14	5	22

Table 2.3.

Clinical outcomes – Patient-reported outcome measures

Measures	Premean	Postmean	Percentage reduction	Test type	P	Significance
Anchored cage device
NDI	47.85	22.3	53.4	Paired t-test	0.038	Yes
Neck VAS	4.72	3.55	24.7	Paired t-test	0.099	No
Arm VAS	5.95	2.97	50.1	Paired t-test	0.013	Yes
Standalone cage
NDI	47.33	27.33	42.2	Paired t-test	0.0008	Yes
Neck VAS	4.99	2.49	50.0	Paired t-test	0.0011	Yes
Arm VAS	4.54	2.07	54.4	Paired t-test	0.0042	Yes

NDI - Neck Disability Index; VAS - Visual Analog Scale

Table 2.4.

Clinical outcomes – Patient-reported outcome measures

Measure - anchored cage device versus standalone cage	Premean	Postmean	Percentage reduction	Test type	Independent t-test, P	Significance
NDI	-	-	-	Independent t-test	0.56	No
Neck VAS	-	-	-	Independent t-test	0.15	No
Arm VAS	-	-	-	Independent t-test	0.64	No

NDI - Neck Disability Index; VAS - Visual Analog Scale

In the standalone cage group, the NDI scores decreased from a mean of 47.33 preoperatively to 27.33 postoperatively, reflecting a 42.3% reduction, which was statistically significant (P = 0.0008). Statistically significant improvements were also observed in VAS scores for arm pain, which decreased from 4.54 to 2.07, a 54.4% reduction (P = 0.0042). These findings suggest that both cage designs effectively enhance NDI and arm pain outcomes, while the standalone cage group exhibited superior control of neck pain.

Radiological outcomes

Radiological assessments revealed comparable fusion rates between the groups, with the anchored cage devices group achieving a 91% fusion rate and the standalone cages group reaching 88%, a difference that was not statistically significant (p >0.66) [Table 3]. Subsidence was slightly greater in the anchored cage devices group (0.54 mm) compared to the standalone cages group (0.41 mm).

Table 3.

Radiological outcomes

Radiological parameter	Anchored cage devices	Standalone cages	P (Welch’s t-test)
Fusion rate (%)	91	88	0.66
Subsidence (mm)	0.54	0.41	0.2581
Cobb’s angel (lordosis) gained	2.7	1.8	0.6211
Postoperative C2–C7 SVA (average)	16.95	19.95	0.1222

SVA - Sagittal vertical axis

The difference in preoperative Cobb’s angle measured on magnetic resonance imaging (MRI) and postoperative Cobb’s angle measured on X-rays was reviewed, as preoperative X-rays and postoperative MRIs were not routinely performed in all patients.[10] The difference in Cobb’s angle was analyzed to assess the gain in postoperative cervical lordosis. Both groups showed comparable improvements, with mean increases of approximately 2° in cervical lordosis. Postoperative C2–C7 sagittal vertical axis values were also higher than the normal range in both groups. Statistical analysis indicated no significant differences in these radiological parameters between the two groups.

Complications

The complication profiles of the two groups were similar, highlighting the safety of both cage designs. Dysphagia was reported in 5% of patients in the anchored cage devices group and 12% in the standalone cages group. Dysphonia occurred in none of the patients in the anchored cage devices but was observed in 7% of the patients in the standalone cages, as demonstrated in Table 4. Higher percentage in of dysphonia and dysphagia in stand-alone cage group is likely due to overall higher number of cases including 3 level. Adjacent segment disease requiring intervention was noted in 5% of anchored cage device cases and 7% of standalone cages cases. None of these differences reached statistical significance, reinforcing the reliability and favorable safety profiles of both devices.

Table 4.

Complications

Symptom	Anchored cage devices (%)	Standalone cages (%)	P (Welch’s t-test)	Significance
Dysphagia	5	12	0.2776	No
Dysphonia	0	7	0.083	No
Adjacent segment disease	5%	7%	0.786	No

DISCUSSION

This study provides a unique comparison between standalone cages and anchored cage devices for multilevel ACDF surgery, addressing a gap in the existing literature. Most previous studies have focused on comparing standalone cages with plating systems rather than with screw-anchoring cage designs.[11,12,13,14] While many studies highlight the superiority of anchored cage devices in terms of radiological correction and subsidence, our findings indicate that standalone cages perform equivalently to anchored cage devices’ constructs in the short term for multilevel ACDF.

In 2021, we published a similar study focusing on complications between standalone cages and anchored cage devices constructs. That study reported no significant differences in short-term complications between the groups for both multilevel and single-level procedures.[15] Since its adoption as the gold standard for managing cervical spine degenerative diseases, including disc herniation, ACDF has been extensively studied for its efficacy and limitations.[5,6,7,16,17] However, most research compares cage systems with or without plating, and there are limited data on the direct comparison of standalone cages and screw-anchoring designs without plating.

Our analysis reveals that both anchored cage devices and standalone cages achieve comparable outcomes in terms of clinical improvement, radiological parameters, and safety. These results align with prior studies by Balakumar B et al. (2021) and Cho HJ et al. (2015), which demonstrated that newer cage designs, such as anchored cage devices and standalone systems, reduce complications commonly associated with anterior plate systems.[18,19]

Standalone cages offered similar clinical outcomes while providing distinct advantages, including better control of neck pain, slightly lower dysphagia rates, and reduced surgical complexity. The absence of screws in standalone cages eliminates stress risers at the bone–implant interface, potentially contributing to lower subsidence rates. These findings are consistent with Yang et al. (2019) who reported reduced dysphagia rates with standalone cages compared to screw-fixation systems.[16]

Anchored cage devices demonstrated slightly higher fusion rates (91% vs. 88%) compared to standalone cages, likely due to the added stability of the screw-integrated design. These fusion rates align with the literature, which reports an average range of 85%–95% for multilevel ACDF (Chong et al. 2015).[12] However, anchored cage devices exhibited marginally higher subsidence (0.54 mm vs. 0.41 mm), consistent with biomechanical analyses by Scholz et al. and Dawood O et al. (2018).[20,21] The clinical impact of subsidence remains uncertain, as Noordhoek et al. (2018) noted that subsidence does not always correlate with inferior patient-reported outcomes.[13]

Both devices demonstrated favorable safety profiles, with low complication rates overall. Dysphagia, a common postoperative complication, occurred in 5%–12% of cases across both groups. Yang et al. (2019) and Balakumar B et al. (2021) emphasized that intraoperative technique and patient anatomy significantly influence dysphagia rates, suggesting that device design alone is not solely responsible for this complication.[16,18]

Study limitations

This study’s retrospective design introduces potential selection and reporting biases. In addition, the short follow-up period limits the evaluation of long-term outcomes, such as the progression of adjacent segment disease. Future research should prioritize randomized controlled trials with longer follow-up periods to provide more robust evidence regarding the comparative efficacy and safety of these devices.

CONCLUSION

Anchored cage devices and standalone cages provide similar clinical and radiological outcomes in multilevel ACDF. Anchored cage devices may be favored for their higher fusion rates, while standalone cages are advantageous for better neck pain control, reducing surgical complexity and cost. Future studies with long-term follow-up and randomized designs are warranted to establish definitive guidelines for device selection.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.