Abstract
Objective
Based on the varying number and relative positions of cervical disc replacement (CDR) and anterior cervical discectomy and fusion (ACDF) procedures, three‐segment hybrid surgery (HS) presents a diverse structural approach. Currently, the potential differential effects of HS with different segment combinations and surgical procedures on overloaded vertebral body (OVB) occurrence remain unexplored. The purpose of this retrospective study is to compare the clinical and radiological outcomes of HS and ACDF in treating cervical degenerative disc disease (CDDD), aiming to provide further insights into OVB.
Methods
This study included patients with three‐level CDDD who underwent ACDF or HS at our institution. Eligible patients were divided into three groups: Type I (one‐level CDR and two‐level ACDF), Type II (two‐level CDR and one‐level ACDF), and ACDF (three‐level ACDF). For radiographic analysis, patients were further divided into the Replacement Segment Group and the Nonreplacement Segment Group based on the presence of replacement segments above and below the OVB. Clinical outcomes were evaluated using visual analog scale (VAS) scores for neck and arm pain, Japanese Orthopedic Association (JOA) scores, and neck disability index (NDI) scores. The cervical radiological parameters assessed included (1) vertebral cross‐sectional area (CSA), (2) wedge angle (WA), (3) anterior vertebral height (AH), (4) posterior vertebral height (PH), and (5) Hounsfield unit (HU) values. Statistical methods included paired t‐test, ANOVA test, and chi‐square test. Independent samples t‐test, Mann–Whitney U test, and Wilcoxon signed‐rank test were used to compare the differences between two groups according to the results of normal distribution test.
Results
A total of 123 patients, evenly distributed among three groups, were included and were well matched in terms of demographic characteristics. The likelihood of vertebral body collapse (VBC) was notably higher in the ACDF group (41.5%) compared with the Type I (17.9%) and Type II (8.9%) groups (p < 0.01). Following surgery, both at 3 and 6 months, the ACDF group demonstrated higher VAS neck scores and NDI scores compared with the Type I and Type II groups (p < 0.01). Additionally, the WA and AH values of the upper and lower adjacent OVB were consistently lower in the ACDF group than in the Type I and Type II groups at 6 and 12 months and at the final follow‐up (p < 0.01). Notably, in the Nonreplacement Segment Group, WA significantly decreased at 12 months postoperatively and at the final follow‐up compared with the Replacement Segment Group (p < 0.01).
Conclusions
Three levels of HS appear to reduce stress concentrations and alleviate morphological changes in OVB. The occurrence of more VBC patients with OVB was associated with the use of Zero‐P or Zero‐P VA implants.
Keywords: Clinical Outcomes, Overloaded Vertebral Body, Radiological Outcomes, Three‐Level Surgery, Vertebral Body Collapse
This study compares the clinical and radiological outcomes of hybrid surgery (HS) and anterior cervical discectomy and fusion (ACDF) for cervical degenerative disc disease (CDDD), providing new insights into the phenomenon of overloaded vertebral body (OVB) and highlighting the potential benefits of HS in reducing OVB occurrence.
Introduction
We introduced the concept of the “overloaded vertebral body” (OVB) in multilevel anterior cervical spine surgery, denoting the vertebral body situated centrally within the surgical segments where operative intervention is performed on both upper and lower segments. 1 It was hypothesized that the occurrence of OVB might be linked to biomechanical vulnerabilities in the anterior segment of the vertebral body, as well as intraoperative endplate wear and screw application.2, 3 Previous observations among patients undergoing multilevel anterior cervical discectomy and fusion (ACDF) have shown that there is a tendency for middle cervical vertebral body collapse (VBC) during the early postoperative period due to the influence of stress concentration.4, 5 Our institution was the first to report this phenomenon and offer a precise definition, thereby contributing innovatively to the field. However, whether the occurrence of OVB is exclusive to multilevel ACDF remains uncertain.
Hybrid constructs combining cervical disc replacement (CDR) and ACDF offer a viable solution for symptomatic patients with multilevel disc disease in an unsynchronized stage of degeneration.6, 7, 8, 9 Hybrid surgery (HS) presents the most suitable surgical approach for each target segment, while still considering the extent of cervical disc degeneration, potentially restoring cervical spine biomechanics.10, 11, 12 Recent investigations suggest that three‐level HS, compared with ACDF, may yield comparable or potentially superior outcomes.13, 14 In HS, compared with fusion segments, replacement segments typically have strict surgical indications,15, 16 including but not limited to the need for stability, mobility, and good bone quality. Additionally, the endplates are extensively ground to facilitate smooth insertion of the implant during surgery, and no screws are needed. The subsequent postoperative biomechanical stresses on the cervical spine may vary accordingly and significantly impact the rate of OVB occurrence.
Currently, the potential differential effects of HS with different segment combinations and surgical procedures on OVB occurrence remain unexplored. Furthermore, it remains unclear whether bone density, an important factor in implant subsidence and collapse, also affects the occurrence of OVB. As such, the purpose of this study was to (i) investigate the effect of three‐segment HS and ACDF on OVB postoperative changes, (ii) evaluate the effect of these postoperative changes on patient prognosis, and (iii) explore the alterations in bone density associated with these procedures.
Materials and Methods
Participants and Procedure Selection
This study retrospectively analyzed patients suffering from cervical degenerative disc disease (CDDD) involving three levels who received treatment with ACDF or HS using Zero‐P or Zero‐P VA implants (Synthes, Oberdorf, Switzerland) and Prestige‐LP discs (Medtronic Sofamor Danek) in our hospital between June 2012 and August 2022. The inclusion criteria consisted of (1) a diagnosis of cervical myelopathy and radiculopathy; (2) refractory to conservative treatments for at least 6 weeks; (3) lesion segment confirmed by clinical symptoms and radiographic images; (4) surgery on three levels between C3 and C7; and (5) a follow‐up period exceeding 12 months. The exclusion criteria consisted of (1) previous cervical spine surgery; (2) the presence of cervical stenosis, osteoporosis, tumor, or infection; (3) a history of trauma or deformity; and (4) incomplete follow‐up data or unclear radiographic parameters precluding measurement. For three‐level patients, the primary goals of surgery are to address anterior compressive pathologies, restore disc height, and correct cervical alignment, making anterior surgery the preferred choice. ACDF or CDR was chosen based on the degree of degeneration in each segment, with CDR indicated by prior studies for certain lesion segments and ACDF performed if radiological images showed instability, bridging osteophytes, or facet degeneration. 17 Eligible patients were divided into the following three groups: one‐level CDR and two‐level ACDF (Type I group), two‐level CDR and one‐level ACDF (Type II group) and three‐level ACDF (ACDF group). Approval from the medical ethics committee of our hospital (No. 2019‐567) was obtained, and written informed consent was provided by all patients.
Surgical Technique
Following the previously outlined procedure, an incision was made using a standard Smith‐Robinson approach to access the surgical segment. 18 Emphasis was placed on the meticulous preservation and identification of the normal anatomy in anticipation of the forthcoming fusion or replacement measures. Subsequent to the thorough discectomy decompression of all targeted segments, a suitably sized Prestige‐LP disc (Medtronic Sofamor Danek) and channel were introduced into the endplate. Subsequently, a properly sized Zero‐P or Zero‐P VA implant (Synthes, Oberdorf, Switzerland) was placed at the ACDF level and packed with β‐tricalcium phosphate. C‐arm fluoroscopy was used to ensure the implant was positioned correctly. After the drainage tube was inserted, the incision was closed.
Clinical Evaluation
The assessment of clinical results was conducted based on the visual analog scale (VAS) evaluations of pain in the neck and arm, along with the Japanese Orthopedic Association (JOA) assessments and neck disability index (NDI) evaluations. The assessment of pain intensity in the neck and arm was determined using the VAS score, while the evaluation of nerve functional recovery was based on the JOA score, and the assessment of neck function was established through the NDI score.
Radiological Evaluation
Cervical parameters were assessed using lateral radiographs and cervical CT with three‐dimensional reconstruction. Subsequently, the images underwent analysis within the picture archiving and communication system (PACS). Two researchers conducted measurements on all the data, and the resulting average value of the dual measurements was subjected to analysis. An additional specialist was consulted to verify the precision of the data.
The assessment included the following cervical parameters: vertebral cross‐sectional area (CSA), wedge angle (WA), anterior and posterior vertebral height (AH and PH), and Hounsfield unit (HU) values (Figure 1).
FIGURE 1.
Schematic diagram of the parameters. X‐rays and CT images show several parameters (A,B) and Hounsfield unit (HU) values (C–E) measured in this investigation. The CSA was described as the area bounded by the upper and lower endplates and the anterior and posterior edges of the vertebra, while the WA was defined by the angle of the tangent line connecting these endplates. Positive WA values denoted lordosis, whereas negative values indicated kyphosis. Vertebral height, measured as the linear distance from the upper to lower endplate, was categorized into AH and PH. The HU value was measured three times by selecting the elliptical region of interest on sagittal, mid‐coronal, and mid‐axial plane CT image reconstruction, and the average value was defined as the final HU.
The CSA was described as the area bounded by the upper and lower endplates and the anterior and posterior edges of the vertebra, while the WA was defined by the angle of the tangent line connecting these endplates. Positive WA values denoted lordosis, whereas negative values indicated kyphosis. Vertebral height, measured as the linear distance from the upper to lower endplate, was categorized into AH and PH. WR was computed using the formula: WR = AH/PH × 100%. 19 According to the study by Genant et al., 19 a vertebral body with a WR < 80% is considered to have VBC. The HU value was measured three times by selecting the elliptical region of interest on sagittal, mid‐coronal, and mid‐axial plane CT image reconstruction, and the average value was defined as the final HU. 20
Statistical Analysis
Statistical analysis was conducted utilizing SPSS software (version 24.0, USA), SPSS software, ChicagoIL, with a location in the United States of America, and the mean ± standard deviation (SD) serves as the representation for continuous variables. ANOVA tests were applied to compare the clinical and radiographic effects as qualitative data among the three groups. To compare cervical parameters post‐surgery, a paired t‐test was utilized. Depending on the normality of the data, either Student's t‐test or the Mann–Whitney U test was employed to analyze continuous variables. Categorical data were examined using the chi‐square test or Fisher's exact test. A p value of less than 0.01 was considered statistically significant.
Results
Demographic and Surgical Data
A total of 123 patients met the criteria for inclusion and exclusion in the study, as shown in Figure 2. VBC was significantly more likely in the ACDF group (41.5%) than in the Type I group (17.9%) and Type II group (8.9%, p < 0.01). Compared with Type II, the ACDF group had a significantly higher mean age (p < 0.01). The types of implants adjacent to the segments where VBC occurred are shown in Table 1.
FIGURE 2.
A flowchart of patients included in the study.
TABLE 1.
Summary of the patient demographic data.
| Type I | Type II | ACDF | Statistic value | p value | |
|---|---|---|---|---|---|
| N | 53 | 28 | 42 | ||
| Gender, n | |||||
| Male | 24 | 13 | 23 | 0.923 | 0.633 a |
| Female | 29 | 15 | 19 | ||
| Age, year | 50.75 ± 7.99 | 47.04 ± 7.16 | 57.07 ± 10.58 | 11.956 | <0.01 b |
| BMI | 24.16 ± 3.50 | 24.74 ± 3.76 | 24.17 ± 3.73 | 0.264 | 0.768 a |
| Levels, n | |||||
| C3‐6 | 15 | 11 | 12 | 1.196 | 0.374 b |
| C4‐7 | 38 | 17 | 30 | ||
| Operation time, min | 164.25 ± 20.32 | 164.18 ± 22.39 | 155.67 ± 24.98 | 2.005 | 0.139 a |
| Blood loss, mL | 70.19 ± 21.44 | 70.71 ± 18.44 | 63.57 ± 17.51 | 1.687 | 0.189 a |
| FU, mouths | 24.28 ± 15.87 | 23.82 ± 15.49 | 29.12 ± 19.19 | 1.201 | 0.305 a |
| VBC, n | 19 | 5 | 34 | 21.862 | <0.01 a |
| FR | 2 | / | / | ||
| RF | 11 | 2 | / | ||
| RR | / | 3 | / | ||
| FF | 6 | / | 34 | ||
Note: Bold values represents that the results have statistical significance. t the anterior edge of the superior OVB.
Abbreviations: ACDF, anterior cervical discectomy and fusion; BMI, body mass index; FF, The segments upper and below the vertebral body are both fused; FR, The upper segment of the vertebral body is fused, and the lower segment is replaced; FU, follow‐up; VBC: vertebral body collapse; RF, The upper segment of the vertebral body is replaced, and the lower segment is fused; RR, The segments upper and below the vertebral body are both replaced.
Chi‐square test for the three groups.
ANOVA test for the three groups.
Clinical Outcomes
Throughout the postoperative monitoring period, there was a significant decrease in the VAS score for both the neck and arms across all groups (p < 0.01), with continued improvement observed throughout. Additionally, notable discrepancies were observed in the VAS scores pertaining to the neck among all three groups at the 3 and 6 months postoperative timepoints. At 3 months postoperatively, the VAS score for the neck in the ACDF group (3.24 ± 0.92) was notably greater than that of either the Type I group (2.58 ± 0.84) or the Type II group (2.57 ± 0.92) (p < 0.01). Similarly, at 6 months postoperatively, the neck VAS score in the ACDF group (2.74 ± 1.06) remained significantly greater than that in the Type I group (1.94 ± 0.66) and the Type II group (2.07 ± 0.60) (p < 0.01). Nevertheless, there was an improvement in JOA scores across all three groups (p < 0.01), which continued throughout the follow‐up period, with no discernible differences among the groups at any of the follow‐up intervals (p > 0.01). All groups experienced a decrease in NDI scores postoperatively (p < 0.01). Additionally, notable discrepancies were observed in the NDI scores among the three groups at the 3 and 6 months postoperative timepoints. At 3 months postoperatively, the NDI score in the ACDF group (17.69 ± 3.91) was notably greater than that in both the Type I group (13.43 ± 4.27) and the Type II group (14.68 ± 2.83) (p < 0.01). Similarly, the NDI score at the 6 months timepoint remained significantly greater in the ACDF group (13.55 ± 4.30) than that in the Type I group (10.08 ± 4.29) and the Type II group (10.39 ± 3.60) (p < 0.01) (Figure 3).
FIGURE 3.
Clinical analysis of visual analog scale (VAS) scores of the neck and arm, Japanese Orthopedic Association (JOA) scores, and neck disability index (NDI) scores.
Radiological Outcomes
Comparing the CSA of the upper and lower OVB among the three patient groups revealed no significant differences across all follow‐up timepoints. Nonetheless, in the ACDF group, the CSA of the upper OVB significantly declined at 3 months postoperatively compared with 1 week postoperatively (p < 0.01). Similarly, the lower OVB CSA in the ACDF group showed significant decreases at 3, 6, and 12 months postoperatively compared with 1 week postoperatively (p < 0.01). The ACDF group showed significant reductions in WA at 6 and 12 months, as well as during the final follow‐up, when compared with the Type I and Type II groups (p < 0.01). No significant differences were observed during other follow‐up periods. Additionally, in the ACDF group, the WA of the upper OVB significantly decreased at 3, 6, and 12 months and at the final follow‐up (p < 0.01). Both Type I and ACDF groups also showed significant reductions in WA at 3, 6, and 12 months postoperatively compared with 1 week postoperatively (p < 0.01) (Figure 4).
FIGURE 4.
Radiological analysis of the upper and lower cross‐sectional areas (CSA) and wedge angles (WAs) in patients.
At 6 and 12 months postoperatively, as well as during the final follow‐up, significant decreases were observed in the AH of the upper and lower OVB in the ACDF group, compared with both the Type I and Type II groups (p < 0.01). No significant differences were noted during other follow‐up periods. In the Type I group, the AH of the lower OVB significantly decreased at 3 and 6 months postoperatively compared with 1 week postoperatively (p < 0.01). Additionally, in the ACDF group, significant decreases in AH were observed in both upper and lower OVB at 3 months, 6 months, and 12 months postoperatively compared with one week after surgery (p < 0.01). The posterior vertebral height (PH) of the upper and lower OVB did not show significant differences at any follow‐up timepoint among the three groups. However, at 12 months postoperatively, the PH of the upper OVB in the ACDF group significantly increased compared with 1 week postoperatively (p < 0.01). Conversely, in the Type II group, the PH of the lower OVB significantly decreased at 3 months postoperatively compared with 1 week postoperatively (p < 0.01). In the ACDF group, the PH of the lower OVB significantly increased at 3, 6, and 12 months postoperatively, as well as at the final follow‐up (p < 0.01) (Figure 5).
FIGURE 5.
Radiological analysis of the upper and lower anterior vertebral height and posterior vertebral height in patients.
The evaluation of bone mineral density in the three groups of patients involved the analysis of HU values from cervical vertebrae C3 to C7. There were no notable variations observed among the groups regarding the HU values before surgery at any of the subsequent time intervals. A gradual decline in HU values was observed from the C3 to the C7 vertebra across all cohorts (Table 2).
TABLE 2.
Summary of the Hounsfield unit (HU) values of the Type I group, Type II group, and ACDF group.
| Type I | Type II | ACDF | Statistic value | p value a | ||
|---|---|---|---|---|---|---|
| HU values | C3 | 389.02 ± 86.48 | 405.96 ± 77.52 | 374.81 ± 65.04 | 1.358 | 0.261 |
| C4 | 362.60 ± 96.11 | 359.93 ± 93.57 | 355.88 ± 76.28 | 0.067 | 0.936 | |
| C5 | 339.02 ± 104.18 | 351.14 ± 75.63 | 325.07 ± 66.44 | 0.786 | 0.327 | |
| C6 | 319.02 ± 80.27 | 332.00 ± 73.87 | 301.05 ± 61.64 | 1.602 | 0.186 | |
| C7 | 299.23 ± 79.20 | 306.43 ± 79.89 | 263.74 ± 61.81 | 3.741 | 0.039 |
Abbreviations: ACDF, anterior cervical discectomy and fusion; HU, Hounsfield Unit.
ANOVA test for the three groups.
The patients were categorized into two groups, one with replacement segments present above and below the OVB called the Replacement Segment Group, and the other without replacement segments termed as the Nonreplacement Segment Group for the purpose of radiographic examination. The WA in the Nonreplacement Segment Group significantly decreased at 12 months postoperatively and at the final follow‐up compared with that in the Replacement Segment Group (p < 0.01). In the Replacement Segment Group, the WA significantly decreased at 6 months and 12 months and at the final follow‐up compared with that at 1 week postoperatively (p < 0.01). CSA, WA, AH, and PH significantly decreased at 6 months and 12 months and at the final follow‐up compared with 1 week postoperatively in the Nonreplacement Segment Group (p < 0.01) (Table 3).
TABLE 3.
Summary of the upper and lower cross‐sectional areas, wedge angles, anterior vertebral heights, and posterior vertebral heights of the Replacement Segment Group and Nonreplacement Segment Group.
| VBC | |||||
|---|---|---|---|---|---|
| Replacement Segment Group (n = 18) | Nonreplacement Segment Group (n = 40) | Statistic value | p value a | ||
| CSA | Po‐1w | 2.59 ± 0.82 | 2.66 ± 0.42 | −0.461 | 0.646 |
| Po‐3m | 2.42 ± 0.68 | 2.44 ± 0.51* | −0.122 | 0.903 | |
| Po‐6m | 2.51 ± 0.65 | 2.37 ± 0.59* | −0.836 | 0.406 | |
| Po‐12m | 2.52 ± 0.74 | 2.35 ± 0.62* | 0.938 | 0.352 | |
| FFU | 2.60 ± 0.75 | 2.34 ± 0.59* | 1.458 | 0.150 | |
| WA | Po‐1w | −0.93 ± 2.75 | 0.56 ± 4.36 | −1.365 | 0.177 |
| Po‐3m | −2.60 ± 2.53 | −1.82 ± 5.90* | −0.553 | 0.582 | |
| Po‐6m | −3.36 ± 2.70* | −4.36 ± 5.63* | 0.732 | 0.467 | |
| Po‐12m | −3.36 ± 2.60* | −5.76 ± 4.60* | 2.586 | <0.01 | |
| FFU | −3.19 ± 2.08* | −5.74 ± 4.49* | 3.026 | <0.01 | |
| AH | Po‐1w | 1.23 ± 0.17 | 1.33 ± 0.18 | −2.056 | 0.044 |
| Po‐3m | 1.15 ± 0.14 | 1.16 ± 0.23* | −0.143 | 0.887 | |
| Po‐6m | 1.16 ± 0.16 | 1.10 ± 0.22* | 1.224 | 0.226 | |
| Po‐12m | 1.14 ± 0.21 | 1.09 ± 0.22* | 0.776 | 0.441 | |
| FFU | 1.12 ± 0.17 | 1.06 ± 0.24* | 0.948 | 0.347 | |
| PH | Po‐1w | 1.44 ± 1.19 | 1.43 ± 0.18 | 0.145 | 0.886 |
| Po‐3m | 1.42 ± 0.15 | 1.48 ± 0.23 | −1.117 | 0.269 | |
| Po‐6m | 1.45 ± 0.16 | 1.52 ± 0.23* | −1.238 | 0.221 | |
| Po‐12m | 1.41 ± 0.19 | 1.53 ± 0.25* | −1.720 | 0.091 | |
| FFU | 1.50 ± 0.20 | 1.51 ± 0.28* | −0.078 | 0.938 | |
Note: Bold values represents that the results have statistical significance.
Abbreviations: AH, anterior vertebral height; CSA, vertebral cross‐sectional area; FFU, final follow‐up; PH, posterior vertebral height; Po‐12m, 12 months postoperatively; Po‐1w, 1 week postoperatively; Po‐3m, 3 months postoperatively; Po‐6m, 6 months postoperatively; VBC, Vertebral body collapse; WA, wedge angle.
Independent samples t‐test for the Replacement Segment Group and Nonreplacement Segment Group.
Significance on parameters between Po‐1w (p < 0.01).
Discussion
Main Findings
The study investigated the clinical and radiological outcomes of three‐level HS and ACDF in the treatment of CDDD. The results indicate that three‐level HS may offer certain advantages over ACDF in terms of reducing the incidence of VBC.
Clinical Outcomes and Comparisons between HS and ACDF
CDDD is characterized by chronic, acquired degeneration of the cervical spine, leading to symptoms such as neck pain, radiculopathy, and/or myelopathy. 21 Compared with single‐level procedures, multilevel surgery provides unique advantages in reconstruction that enable multidirectional decompression and comprehensive correction of compressive factors, including intervertebral discs, osteophytes, and the posterior longitudinal ligament.22, 23 Based on the extent of degeneration across various segments, HS aims to restore cervical stability at target levels. 24 In theory, the approach provides adequate mobility at joint replacement levels while ensuring fixation at joint fusion levels.17, 25 By performing this surgery, the vertebral body is preserved structurally, and its physiological curvature is restored.
There was no significant difference between the three‐level HS and ACDF groups in terms of JOA and NDI scores, according to Xu et al. 26 Zhang et al. 16 showed that the results of a meta‐analysis revealed better recovery of NDI scores at follow‐up in the HS group than in the ACDF group. Brotzki et al. 13 showed that patients who underwent cervical total disc replacement with more replacement segments had significantly lower postoperative VAS scores than patients who underwent ACDF or HS. Jang et al. 27 found through a retrospective review of three‐level ACDF and HS groups that both groups demonstrated significant improvements in arm pain relief and functional prognosis. However, the HS group showed significantly greater improvement in the NDI score at 6 months postoperatively than did the ACDF group. Our research suggests that three‐level ACDF may have adverse effects on neck VAS and NDI scores compared with three‐level HS. For patients with significant morphological changes in vertebral bodies leading to VBC at 3 months postoperatively, we administered anti‐osteoporosis treatment to promote bone formation and increased the duration of wearing a neck brace to enhance stability.28, 29 Prolonged use of a cervical collar during treatment may result in neck pain, which could be a contributing factor to the unfavorable postoperative outcomes observed in the ACDF group in this study. 30 Similarly, biomechanical changes resulting from soft tissue reconstruction, such as overall cervical muscle and ligament reconstruction, may also contribute to differences in clinical presentation.
Stress Concentration and VBC Between HS and ACDF
The stress on OVB varies in different activity states, leading to both stress concentration and insufficient stress stimulation. For example, the anterior segment of the vertebra is in direct contact with the metal plate of the Zero‐P or Zero‐P VA during forward bending and backward extension, as the anterior segment consists of a metal plate with a higher elastic modulus than bone tissue. This leads to an increase in stress on the front edge of the vertebral body due to the absence of intervertebral disc cushioning in the OVB, resulting in a concentration of stress. This increased stress makes bone tissue prone to microinjuries or even collapse, ultimately resulting in a significant decrease in the height of the anterior edge of the vertebral body. Conversely, Prestige‐LP may preserve partial mobility of the segment during forward bending and backward extension, potentially reducing stress on the bone tissue of the anterior edge of the vertebral body. This reduced stress may lead to insufficient stress stimulation and slow bone tissue growth, ultimately resulting in bone loss. Our institution's research findings indicate that intermediate vertebral bodies exhibit a distinct pattern of morphological changes following consecutive two‐level CDA, which may be attributed to anterior bone loss (ABL). 31 In this study, the WA and AH of the upper and lower segments of the OVB in the three‐level ACDF surgery group were significantly smaller than those in the three‐level HS surgery group, while the incidence of VBC was lower in the HS surgery group. This indicates that the replacement segments offset the stress on the OVB. In the three‐level HS group, the replacement segments significantly preserved the mobility of the current segment, ensuring that stress was not overly concentrated during forward bending or backward extension, thereby protecting the relatively fragile endplates formed by postoperative grinding. Therefore, significant anterior height loss of the vertebral bodies was not prominently observed in OVB patients after three‐level HS surgery. Furthermore, in the vertebral bodies with significant VBC, we observed that the presence of replacement segments around them more effectively preserved the WA (Figure 6).
FIGURE 6.
Installation according to the severity of vertebral deformity. Yellow arrows indicate vertebrae with significant morphological changes. A middle‐aged male patient underwent C4/5 CDR and C5/6 and C6/7 ACDF (A–D). At the final follow‐up, C4/5 retained mobility, while C5/6 and C6/7 were both fused. The AH of the inferior OVB significantly decreased from 1.29 cm at 1 week postoperatively to 0.84 cm at the final follow‐up. A middle‐aged female patient underwent C4/5, C5/6 CDR and C6/7 ACDF (E–H). There was no significant collapse of the superior or inferior OVB, and C6/7 had fused. Significant bone resorption was observed at the anterior edge of the superior OVB.
Bone Density Assessment and Its Implications Between HS and ACDF
One of the primary methods utilized to evaluate bone density involves the application of dual‐energy x‐ray absorptiometry (DXA). Utilizing a two‐dimensional method, bone density is measured at specific locations like the lumbar spine and hip joints. 32 Nevertheless, variations in bone mineral density were observed across different segments of the spine. In contrast, the utilization of DXA for the lumbar spine does not translate effectively to the cervical spine. 20 Currently, there is an increasing utilization of standard CT scans in the assessment of vertebral HU values in the cervical spine. Assessing the bone density of the cervical spine can be effectively achieved by utilizing Vertebral HU values. 33 Factors such as implant subsidence or collapse are related to bone density.34, 35 However, no significant abnormalities were observed in our study in HU values among the three groups during preoperative follow‐up, suggesting that this may not be the main influencing factor. Compared with implant subsidence or collapse, OVB was more strongly associated with stress concentration. Compared with conventional anterior cervical plate fixation over long segments, zero‐profile fixation resulted in more stress concentrated on the vertebral body, leading to a significant decrease in height at the anterior edge of the vertebral body. 36
Limitations and Strengths
This study has several limitations. Initially, the retrospective nature of this study being conducted in a single center could have introduced some bias. Moreover, there was variation in the average age of patients across the different groups, potentially introducing bias into the findings. Furthermore, there were limitations such as the relatively small sample size, particularly noticeable in patients from the Type II group who underwent HS, and the comparatively brief duration of the follow‐up period. Moreover, it was not possible to classify the types of implants in the OVB more finely. Third, only the Zero‐P or Zero‐P VA and Prestige‐LP systems were included in the study. Ultimately, it is conceivable that there may be differing vertebral alterations among individuals who received the treatment within this outlined time span. To validate these findings, it is recommended that studies should be carried out, focusing on prospective, multicenter, large‐scale research using a variety of prostheses.
Conclusions
Three‐level HS may have advantages over three‐level ACDF in terms of neck VAS and NDI scores. Three‐level HS appears to have advantages in reducing stress concentrations and alleviating morphological changes in OVB. Morphological changes in OVB are unrelated to bone density. The occurrence of more VBC in patients with OVB is associated with the use of Zero‐P or Zero‐P VA implants. Additional research studies involving multiple medical centers, larger participant numbers, and extended observation periods are necessary to confirm these results and investigate other factors that impact the occurrence of OVB and patient outcomes.
Author Contributions
Shihao Chen and Yaling Li wrote the article and contributed equally to this work and should be considered as co‐first authors. Beiyu Wang takes responsibility for the integrity of the work as a whole, from inception to published article, and should be considered as corresponding authors. Hao Liu, Beiyu Wang, and Kangkang Huang contributed to the concept and design of this study. Shihao Chen, Tingkui Wu, and Minghe Yao contributed to literature search, data extraction, bias assessment, and data analysis.
Conflict of Interest
The authors declare that they have no conflicts of interests.
Ethics Statement
This study was approved by the Institutional Review Board of West China Hospital. Informed consent was obtained from all individual participants included in this study.
Funding Information
National Natural Science Foundation of China (81902190), the Foundation of Science and Technology Department of Sichuan Province (2023NSFSC1741), Provincial Science and Technology Plan Project Special Fund Transfer Payment Project (2021‐YF08‐00113‐GX), and 1.3.5 project for Postdoctoral Foundation of West China Hospital of Sichuan University (2023HXBH080). There were no relevant financial activities outside the submitted work.
Acknowledgments
We thank the nursing staffs from our department and the patients enrolled in this study for their supports.
Shi‐hao Chen and Ya‐ling Li have contributed equally to this work and share the first authorship.
References
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