DOI: https://doi.org/10.21203/rs.3.rs-2306119/v1
Introduction: According to the different numbers and relative locations of cervical disc replacement (CDR) and anterior cervical discectomy and fusion (ACDF), three-level hybrid surgery (HS) has many constructs. The purpose of this retrospective study was to compare the sagittal alignment parameters of HS and ACDF for cervical degenerative disc disease (CDDD) and the association of the respective parameters.
Methods: This study involved patients with three-level CDDD who underwent ACDF or HS at our institution between June 2012 and August 2021. This follow-up included one-level CDR and two-level ACDF (type I group), two-level CDR and one-level ACDF (type II group) and three-level ACDF. Cervical sagittal alignment parameters included cervical lordosis (CL), segment alignment (SA), T1 slope (T1S), C2-C7 sagittal vertical axis (SVA), T1S-CL, C2 slope (C2S), occipital to C2 angle (O-C2A) and segment range of motion (ROM).Postoperative complications included adjacent segment degeneration (ASD), imbalance, prosthetic subsidence and heterotopic ossification (HO).
Results: The three groups with a total of 106 patients were better matched in terms of demographics. Patients who underwent HS had significantly higher CL than those who underwent ACDF at 1 week, 6 months, 12 months and the final follow-up after surgery, as well as significantly better SA at 12 months and the final follow-up. There was no significant difference in T1S, SVA, T1S-CL, C2S, O-C2A or segment ROM among the three groups after surgery. The T1S-CL was significantly associated with C2S in the type I and type II groups at the preoperative and final follow-up. There was no significant difference in postoperative complications among the three groups.
Conclusions: Most improvements in cervical sagittal alignment (CL, SA, T1S, SVA, T1S-CL, C2S, O-C2A, and segmental ROM) were observed in all three groups postoperatively. HS was more advantageous than ACDF in the maintenance of postoperative CL and SA. Thus, three-level HS may be better for maintaining cervical curvature. The number of replacement segments differed in those who underwent HS but did not affect the correlation between T1S-CL and C2S, both of which are well balanced.
Anterior cervical discectomy fusion (ACDF) is generally accepted as the standard surgical treatment for cervical degenerative disc disease (CDDD) because of its excellent postoperative results. However, it may lead to kinematic and biomechanical changes in the adjacent segments, which may result in accelerated adjacent segment degeneration (ASD) and the possible need for further surgery. Therefore, cervical disc replacement (CDR) has become increasingly prevalent in recent years as an alternative approach aimed primarily at preserving segmental range of motion (ROM) and reducing the risk of ASD. Although CDR has been shown to be superior to ACDF in terms of range of motion preservation, the optimal surgical approach for cervical range of motion and stability in patients with multilevel CDDD remains controversial. To overcome the limitations and drawbacks of both approaches, hybrid surgery (HS) combining ACDF and CDR is increasingly being used for multilevel CDDD. HS allows the optimal surgical approach to be tailored to each target segment based on the status of cervical disc degeneration. Many studies have demonstrated that HS is a safe and effective surgical approach for the treatment of multilevel CDDD1–4. At present, there is evidence in the literature supporting the radiological and clinical outcomes of one- and two-level ACDF and HS, while few studies on multilevel surgeries of the cervical spine exist5.
Over the past decade, cervical spine alignment has become primary aim of spine research. Cervical alignment plays an important role in compensating for spinal balance, transmitting axial loads, and maintaining mechanical function6. The study of cervical sagittal alignment began with normative data and expanded to include correlations with overall sagittal balance, prognosis in various conditions, surgical outcomes, definition and classification of cervical deformities, and prediction of ideal goals for cervical spine reconstruction7. Various imaging parameters have been proposed for the assessment of cervical spine alignment. Cervical lordosis (CL) plays an essential role in compensating for spinal balance, transmitting axial load and maintaining mechanical function. In patients with CDDD requiring surgical intervention, restoration and maintenance of CL is one of the most vital factors affecting clinical outcomes8,9. The loss of CL alters normal biomechanics and leads to cervical sagittal alignment imbalance, resulting in axial symptoms and potential complications. Therefore, it is crucial to maintain cervical sagittal alignment after HS, whereas most studies have concentrated only on CL. Other important cervical sagittal alignment parameters, including the C2-C7 sagittal vertical axis (SVA), T1 slope (T1S), T1 slope minus cervical lordosis (T1S-CL), C2 slope (C2S), and occipital to C2 angle (O-C2A), have been rarely studied10. Sagittal parameters have been relatively well maintained after multilevel fusion surgery11; however, there is a lack of clinical evidence on whether they can be well maintained in three- or multilevel HS.
The purpose of this study was to compare the sagittal alignment of consecutive patients undergoing three-level HS and ACDF and to investigate whether better sagittal parameters can be maintained after three-level HS surgery and the association of the respective parameters. The findings of this paper may provide information on which multilevel CDDD surgery can lead to better postoperative sagittal alignment.
A retrospective study was conducted involving patients with three-level CDDD who underwent ACDF or HS in our hospital between June 2012 and August 2021. 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 imaging (computed tomography (CT), magnetic resonance imaging (MRI), and X-rays); and (4) surgery on three levels between C3 and C712. The exclusion criteria consisted of (1) previous surgery at the cervical spine or (2) the existence of cervical stenosis, osteoporosis, tumor, and infection. The indications of CDR at the lesion segment were according to previous studies, which were without instability (sagittal plane translation > 3 mm and sagittal plane angulation > 11°), without an absence of motion < 3°, without a disc height loss > 50%, and without facet joint degeneration12. If instability, bridging osteophytes, and facet degeneration were observed in the radiological images, ACDF was performed. Ethical approval was provided by the medical ethics committee of our hospital (No. 2019 − 567). All patients provided written informed consent.
One senior spine surgeon performed all HS or ACDF surgeries in this study. The surgery was performed as previously described12. A standard Smith-Robinson approach was used to reveal the surgical segment. The normal anatomy is carefully preserved and identified in preparation for the next step of fusion or replacement. After discectomy decompression of all target segments, an appropriately sized Prestige-LP disc and channel are inserted into the endplate. The appropriate size Zero-P implant system was subsequently inserted at the ACDF level and filled with β-tricalcium phosphate. C-arm fluoroscopy was performed to confirm the correct position of the implant. Finally, the incision was closed after insertion of the drainage tube.
The data were collected preoperatively and at 1 week, 3 months, 6 months, and 12 months postoperatively and at the final follow-up. Perioperative parameters, including operative time and blood loss, were collected.
Cervical sagittal alignment parameters were measured on the lateral radiographs. The following cervical sagittal alignment parameters were evaluated: 1) CL; 2) SA; 3) T1S; 4) SVA; 5) T1S-CL; 6) C2S; 7) O-C2A; and 8) Segment ROM. CL is the angle between the tangent line of the inferior endplate of the C2 and C7 vertebral bodies. SA is the angle between the tangent line of the superior and inferior endplates of the operative segment. T1S is the angle between the tangent line of the superior endplate of the T1 vertebral body and the horizontal line. C2-7 SVA is the horizontal distance between the plumb line of the geometric central C2 vertebral body and the posterior superior angle of the superior endplate of the C7 vertebral body13. T1S-CL is obtained by subtracting the previously determined C2-C7 lordosis angle from the T1 slope14. C2S is the angle between the tangent line of the inferior endplate of the C2 vertebral body and the horizontal line15. O-C2A is the angle between the McGregor line and the line connecting the inferior endplates of the C2 vertebral body. Segment ROM is recognized as the extension-flexion segment angle. (Fig. 1)
ASD was defined based on the height of an adjacent level disc and anterior osteophyte formation on X-rays according to the classification reported by Goffin et al. 16. T1S-CL was used to evaluate the cervical sagittal balance (T1S-CL < 15°, balance; T1S-CL ≥ 15°, imbalance)13,17. Prosthetic subsidence was considered to be a change of > 5° in the tangential angle along the lower edge of the prosthesis to the posterior edge of the vertebral body between the final postoperative follow-up and 1 week postoperatively18. Heterotopic ossification (HO) was defined as the exposed bony end plates of the vertebral bodies at the surgical-level growth toward the artificial19.
All statistical analyses were performed using SPSS (version 24.0, SPSS, Chicago, IL, USA). Continuous variables are presented as the mean ± standard deviation (SD), and categorical variables are presented as the number of cases. ANOVA and Tukey tests were applied to compare the clinical and radiographic effects as qualitative data among the three groups. A paired t test was used to compare the clinical outcomes and sagittal alignment parameters pre- and postoperation. Student’s t test or the Mann‒Whitney U test was used to compare continuous variables depending on the normality of the data. A chi-square test or Fisher’s exact test was used to analyze categorical data. The correlations between sagittal alignment parameters were analyzed using the Pearson correlation coefficient. Statistical significance was defined as p < 0.05.
A total of 106 patients were included in the analysis according to the inclusion and exclusion criteria, including 47 patients in the type I group, 26 patients in the type II group, and 33 patients in the ACDF group. There were no significant differences between the three groups in terms of sex ratio, body mass index (BMI), surgical level distribution, mean blood loss, or mean follow-up time. The mean age of patients in the ACDF group was significantly older than that in the type II group (p < 0.05). The operative time in the type II group was 178.20 min ± 22.15 min, which was significantly longer than that in the ACDF group (p < 0.05). However, there was no significant difference between the ACDF group and the type I group or the type I group and the type II group. Detailed information is shown in Table 1.
| Type I | Type II | ACDF | p value | |
|---|---|---|---|---|
| N | 47 | 26 | 33 | |
| Gender, n | ||||
| Male | 20 | 13 | 17 | 0.692a |
| Female | 27 | 13 | 16 | |
| Age, year | 50.87 ± 8.20 | 47.12 ± 7.39 | 56.70 ± 12.59 | 0.002b |
| BMI | 24.33 ± 3.47 | 24.80 ± 3.87 | 24.48 ± 3.28 | 0.862b |
| Levels, n | ||||
| C3-6 | 14 | 10 | 10 | 0.724a |
| Ia/Ib/Ic | 6/7/1 | / | / | |
| IIa/IIb/IIc | / | 4/3/3 | / | |
| C4-7 | 33 | 16 | 23 | |
| Ia/Ib/Ic | 22/2/9 | / | ||
| IIa/IIb/IIc | / | 4/9/3 | / | |
| Operation time, min | 164.83 ± 20.78 | 174.39 ± 23.72 | 156.24 ± 28.38 | 0.035b |
| Blood loss, ml | 70.64 ± 21.00 | 70.77 ± 18.96 | 67.27 ± 17.19 | 0.704b |
| FU, mouths | 22.15 ± 13.61 | 21.50 ± 12.44 | 29.13 ± 9.3 | 0.378 b |
| ACDF, anterior cervical discectomy and fusion; BMI, body mass index; FU, follow-up. | ||||
| a Chi-square test for the three groups | ||||
| b ANOVA test for the three groups | ||||
At 12 months postoperatively and at the final follow-up, CL and SA were significantly lesser in the ACDF group than in the type I and type II groups (p < 0.05). Furthermore, CL in the ACDF group was also significantly lesser than that in the type I and II groups at 1 week and 6 months postoperatively (p < 0.05). A week after surgery, CL, SA, T1S and SVA were significantly more pronounced in all three groups than in the preoperative period (p < 0.05). Furthermore, SA and SVA were significantly higher in both the type I and type II groups at 3 and 6 months postoperatively (p < 0.05). For the final follow-up, there was no statistically significant difference in CL and SA of the three groups when compared to the preoperative period. However, both the type I and ACDF groups showed a significant decrease at the final follow-up when compared to the preoperative values (p < 0.05). (Table 2) (Fig. 2)
| Type I | Type II | ACDF | p value | ||
|---|---|---|---|---|---|
| CL | Pre | 7.1 ± 7.8 | 10.8 ± 10.0 | 6.0 ± 6.9 | 0.068a |
| Po-1w | 15.7 ± 7.8# | 16.3 ± 10.3# | 10.3 ± 6.8# | 0.003a | |
| Po-3m | 9.6 ± 7.6# | 10.5 ± 10.1 | 6.7 ± 5.6 | 0.087a | |
| Po-6m | 9.0 ± 6.9 | 10.5 ± 8.4 | 5.1 ± 5.9 | 0.009a | |
| Po-12m | 8.7 ± 7.0 | 9.9 ± 8.4 | 4.7 ± 6.2 | 0.012a | |
| FFU | 7.9 ± 7.5 | 8.7 ± 8.8 | 3.6 ± 6.4 | 0.016a | |
| SA | Pre | 3.9 ± 6.1 | 3.8 ± 3.0 | 3.4 ± 5.2 | 0.899a |
| Po-1w | 9.0 ± 5.0# | 9.1 ± 5.3# | 7.6 ± 5.3# | 0.405a | |
| Po-3m | 6.6 ± 5.4# | 6.8 ± 4.2# | 4.8 ± 4.4 | 0.179a | |
| Po-6m | 5.5 ± 5.0# | 6.5 ± 3.4# | 3.6 ± 5.7 | 0.069a | |
| Po-12m | 5.3 ± 5.4 | 6.0 ± 4.1# | 2.4 ± 5.6 | 0.013a | |
| FFU | 5.1 ± 5.0 | 5.1 ± 3.3 | 2.0 ± 5.8 | 0.015a | |
| T1S | Pre | 21.4 ± 7.0 | 22.0 ± 5.9 | 20.3 ± 6.2 | 0.583a |
| Po-1w | 27.3 ± 7.3# | 26.0 ± 7.8# | 23.8 ± 6.4# | 0.103a | |
| Po-3m | 23.6 ± 6.0# | 23.3 ± 7.8 | 21.2 ± 7.3 | 0.284a | |
| Po-6m | 22.2 ± 5.6 | 21.9 ± 7.8 | 19.0 ± 7.1 | 0.091a | |
| Po-12m | 20.9 ± 5.7 | 20.7 ± 7.9 | 18.6 ± 7.4 | 0.306a | |
| FFU | 19.1 ± 6.4a | 18.7 ± 7.8 | 16.7 ± 8.1aa | 0.334a | |
| SVA | Pre | 1.8 ± 0.8 | 1.7 ± 0.9 | 1.9 ± 1.1 | 0.693a |
| Po-1w | 2.2 ± 1.0# | 2.3 ± 0.8# | 2.3 ± 1.0# | 0.915a | |
| Po-3m | 2.1 ± 0.8# | 2.3 ± 0.8# | 2.1 ± 0.6 | 0.467a | |
| Po-6m | 2.0 ± 0.7# | 2.2 ± 0.9# | 2.3 ± 0.8# | 0.221a | |
| Po-12m | 2.0 ± 0.8 | 2.0 ± 1.0 | 2.2 ± 1.1# | 0.674a | |
| FFU | 2.0 ± 0.9# | 2.0 ± 1.0 | 2.2 ± 1.1# | 0.810a | |
| T1S-CL | Pre | 14.3 ± 9.3 | 11.1 ± 10.7 | 14.3 ± 8.6 | 0.339a |
| Po-1w | 11.6 ± 8.9 | 9.8 ± 10.9 | 12.7 ± 9.0 | 0.499a | |
| Po-3m | 14.0 ± 7.7 | 12.8 ± 9.8 | 14.5 ± 8.6 | 0.741a | |
| Po-6m | 13.1 ± 7.2 | 11.4 ± 8.1 | 13.9 ± 8.0 | 0.477a | |
| Po-12m | 12.2 ± 7.7 | 10.8 ± 9.9 | 14.0 ± 8.7 | 0.369a | |
| FFU | 11.3 ± 8.9# | 10.0 ± 9.5 | 13.1 ± 10.0 | 0.435a | |
| C2S | Pre | 12.4 ± 7.2 | 12.0 ± 7.3 | 13.4 ± 6.7 | 0.726a |
| Po-1w | 10.4 ± 7.3 | 9.3 ± 6.4 | 12.9 ± 6.3 | 0.109a | |
| Po-3m | 12.2 ± 6.8 | 11.8 ± 7.0 | 12.7 ± 8.6 | 0.889a | |
| Po-6m | 11.5 ± 6.2 | 11.0 ± 6.9 | 11.9 ± 7.6 | 0.885a | |
| Po-12m | 9.5 ± 5.8# | 9.5 ± 5.8 | 10.9 ± 6.8# | 0.585a | |
| FFU | 8.3 ± 5.7# | 8.4 ± 5.9# | 10.5 ± 7.6# | 0.258a | |
| O-C2A | Pre | 20.9 ± 7.5 | 18.7 ± 7.0 | 20.5 ± 7.3 | 0.433a |
| Po-1w | 16.6 ± 6.4# | 16.7 ± 8.0 | 18.8 ± 5.6 | 0.272a | |
| Po-3m | 20.3 ± 6.9 | 20.5 ± 9.3 | 21.9 ± 7.1 | 0.622a | |
| Po-6m | 20.5 ± 6.8 | 19.6 ± 8.8 | 20.3 ± 6.7 | 0.871a | |
| Po-12m | 19.6 ± 6.2 | 18.2 ± 8.4 | 19.6 ± 6.8 | 0.690a | |
| FFU | 18.2 ± 6.9# | 17.2 ± 8.5 | 15.7 ± 5.1# | 0.198a | |
| Segment ROM | Pre | 12.2 ± 4.5 | 11.0 ± 4.9 | 0.205b | |
| Po-1w | 5.5 ± 3.9# | 7.4 ± 5.1# | 0.036b | ||
| Po-3m | 6.9 ± 3.9# | 7.7 ± 4.4# | 0.327b | ||
| Po-6m | 7.4 ± 4.3# | 10.6 ± 4.5 | 0.000b | ||
| Po-12m | 8.8 ± 4.6# | 10.9 ± 3.5 | 0.014b | ||
| FFU | 9.2 ± 4.7# | 12.6 ± 4.1 | 0.000b | ||
| ACDF, anterior cervical discectomy and fusion; Pre, preoperative; Po, postoperative; FFU final follow-up; CL, cervical lordosis; SA, segment alignment; T1S, T1 slope; SVA, sagittal vertical axis; C2S, C2 slope; O-C2A, occipital to C2 angle; ROM, range of motion. | |||||
| # Significance on parameters between pre-op (p < 0.05) | |||||
| a ANOVA test for the three groups | |||||
| b Independent-Samples T Test | |||||
Segment ROM was better at 1 week, 6 months, 12 months and the final follow-up after type II surgery than after type I surgery (p < 0.05). The T1S-CL, C2S, O-C2A and segment ROM for the patients in the type I group were all significantly lesser at the final follow-up when compared to the preoperative values (p < 0.05). Compared to the preoperative period, both type I of O-C2A and type I and type II of segment ROM were significantly decreased at 1 week postoperatively (p < 0.05). However, the other parameters decreased but were not significantly different. The final postoperative follow-up of C2S was significantly lesser in all three groups than that of the preoperative period (p < 0.05). At all postoperative follow-ups, the ROM of type I segments was significantly lesser than that preoperatively, whereas type II segments decreased significantly only at 1 week and 3 months postoperatively. (Table 2) (Fig. 3).
CL was significantly correlated with O-C2A (rPre = -0.563; rFFU = -0.290, p < 0.05) and preoperative SVA (rPre = -0.341, p < 0.05). T1S-CL was significantly correlated with CL (rPre = -0.675; rFFU = -0.703, p < 0.05), T1S (rPre = 0.570; rFFU = 0.566, p < 0.05), SVA (rPre = 0.532; rFFU = 0.425, p < 0.05), C2S (rPre = 0.769; rFFU = 0.471, p < 0.05) and O-C2A (rPre = 0.446; rFFU = 0.324, p < 0.05). C2S was significantly correlated with CL (rPre = -0.674; rFFU = -0.321, p < 0.05), SVA (rPre = 0.533; rFFU = 0.338, p < 0.05) and O-C2A (rPre = 0.559; rFFU = 0.393, p < 0.05). T1S was significantly correlated with SVA (rPre = 0.323; rFFU = 0.290, p < 0.05). (Table 3)
| CL | SA | T1S | SVA | T1S-CL | C2S | O-C2A | ||
|---|---|---|---|---|---|---|---|---|
| Pre | ||||||||
| CL | 1 | 0.617# | 0.222 | -0.341# | -0.675# | -0.674# | -0.563# | |
| SA | 1 | 0.338# | -0.147 | -0.264 | -0.426# | -0.554# | ||
| T1S | 1 | 0.323# | 0.570# | 0.266 | -0.038 | |||
| SVA | 1 | 0.532# | 0.533# | 0.219 | ||||
| T1S-CL | 1 | 0.769# | 0.446# | |||||
| C2S | 1 | 0.559# | ||||||
| O-C2A | 1 | |||||||
| FFU | ||||||||
| CL | 1 | 0.421# | 0.188 | -0.256 | -0.703# | -0.321# | -0.290# | |
| SA | 1 | 0.189 | 0.066 | -0.216 | 0.034 | -0.070 | ||
| T1S | 1 | 0.290# | 0.566# | 0.279 | 0.111 | |||
| SVA | 1 | 0.425# | 0.338# | 0.187 | ||||
| T1S-CL | 1 | 0.471# | 0.324# | |||||
| C2S | 1 | 0.393# | ||||||
| O-C2A | 1 | |||||||
| Pre, preoperative; FFU final follow-up; CL, cervical lordosis; SA, segment alignment; T1S, T1 slope; SVA, sagittal vertical axis; C2S, C2 slope; O-C2A, occipital to C2 angle; ROM, range of motion. | ||||||||
| # Significant correlation between parameters (P < 0.05) | ||||||||
CL was significantly correlated with T1S-CL (rPre = -0.840; rFFU = -0.635, p < 0.05), C2S (rPre = -0.463; rFFU = -0.626, p < 0.05) and O-C2A (rPre = -0.536; rFFU = -0.450, p < 0.05). T1S-CL was significantly correlated with T1S (rPre = 0.395; rFFU = 0.495, p < 0.05), T1S-CL (rPre = 0.515; rFFU = 0.531, p < 0.05), final follow-up SVA (rFFU = 0.462, p < 0.05) and final follow-up O-C2A (rFFU = 0.495, p < 0.05). C2S was significantly correlated with final follow-up O-C2A (rFFU = 0.622, p < 0.05). (Table 4)
| Type II | CL | SA | T1S | SVA | T1S-CL | C2S | O-C2A | |
|---|---|---|---|---|---|---|---|---|
| Pre | ||||||||
| CL | 1 | 0.394# | 0.166 | -0.166 | -0.840# | -0.463# | -0.536# | |
| SA | 1 | 0.042 | -0.144 | -0.344 | -0.091 | -0.192 | ||
| T1S | 1 | -0.027 | 0.395# | 0.153 | -0.382 | |||
| SVA | 1 | 0.140 | 0.373 | 0.010 | ||||
| T1S-CL | 1 | 0.515# | 0.289 | |||||
| C2S | 1 | 0.376 | ||||||
| O-C2A | 1 | |||||||
| FFU | ||||||||
| CL | 1 | 0.182 | 0.357 | -0.243 | -0.635# | -0.626# | -0.450# | |
| SA | 1 | 0.115 | -0.238 | -0.074 | -0.025 | -0.064 | ||
| T1S | 1 | 0.285 | 0.495# | -0.063 | 0.092 | |||
| SVA | 1 | 0.462# | 0.343 | 0.173 | ||||
| T1S-CL | 1 | 0.531# | 0.495# | |||||
| C2S | 1 | 0.622# | ||||||
| O-C2A | 1 | |||||||
| Pre, preoperative; FFU final follow-up; CL, cervical lordosis; SA, segment alignment; T1S, T1 slope; SVA, sagittal vertical axis; C2S, C2 slope; O-C2A, occipital to C2 angle; ROM, range of motion. | ||||||||
| # Significant correlation between parameters (P < 0.05) | ||||||||
CL was significantly correlated with SVA (rPre = -0.265; rFFU = -0.250, p < 0.05), T1S-CL (rPre = -0.754; rFFU = -0.675, p < 0.05), C2S (rPre = -0.575; rFFU = -0.440, p < 0.05) and O-C2A (rPre = -0.560; rFFU = -0.363, p < 0.05). T1S-CL was significantly correlated with T1S (rPre = 0.491; rFFU = 0.536, p < 0.05), SVA (rPre = 0.365; rFFU = 0.439, p < 0.05), C2S (rPre = 0.664; rFFU = 0.491, p < 0.05) and O-C2A (rPre = 0.400; rFFU = 0.397, p < 0.05). C2S was significantly correlated with SVA (rPre = 0.467; rFFU = 0.340, p < 0.05) and O-C2A (rPre = 0.493; rFFU = 0.483, p < 0.05). (Table 5)
| I and II | CL | SA | T1S | SVA | T1S-CL | C2S | O-C2A | |
|---|---|---|---|---|---|---|---|---|
| Pre | ||||||||
| CL | 1 | 0.503# | 0.201 | -0.265# | -0.754# | -0.575# | -0.560# | |
| SA | 1 | 0.277# | -0.135 | -0.262# | -0.339# | -0.459# | ||
| T1S | 1 | 0.193 | 0.491# | 0.228 | -0.146 | |||
| SVA | 1 | 0.365# | 0.467# | 0.144 | ||||
| T1S-CL | 1 | 0.664# | 0.400# | |||||
| C2S | 1 | 0.493# | ||||||
| O-C2A | 1 | |||||||
| FFU | ||||||||
| CL | 1 | 0.337# | 0.260# | -0.250# | -0.675# | -0.440# | -0.363# | |
| SA | 1 | 0.160 | -0.022 | -0.173 | 0.018 | -0.066 | ||
| T1S | 1 | 0.288# | 0.536# | 0.139 | 0.104 | |||
| SVA | 1 | 0.439# | 0.340# | 0.181 | ||||
| T1S-CL | 1 | 0.491# | 0.397# | |||||
| C2S | 1 | 0.483# | ||||||
| O-C2A | 1 | |||||||
| Pre, preoperative; FFU final follow-up; CL, cervical lordosis; SA, segment alignment; T1S, T1 slope; SVA, sagittal vertical axis; C2S, C2 slope; O-C2A, occipital to C2 angle; ROM, range of motion. | ||||||||
| # Significant correlation between parameters (P < 0.05) | ||||||||
Summary of the patient complications.
There was no significant difference in the incidence of postoperative ASD (incidence: 31.9%, 26.9%, 42.4%, respectively, p = 0.424) or imbalance (incidence: 29.8%, 23.1%, 36.4%, respectively, p = 0.542) between the patients included in the type I, type II or ACDF group. There was no significant difference the incidence of postoperative prosthetic subsidence (incidence: 17.0% and 23.1%, respectively, p = 0.750) or HO (incidence: 40.4% and 57.7%, respectively, p = 0.157) between the patients included in either the type I or type II group. (Table 6)
| Type I | Type II | ACDF | p value | |
|---|---|---|---|---|
| N | 47 | 26 | 33 | |
| ASD | 15 | 7 | 14 | 0.424a |
| Imbalance | 14 | 6 | 12 | 0.542a |
| Prosthesis subsidence | 8 | 6 | 0.750b | |
| HO | 19 | 15 | 0.157b | |
| ACDF, anterior cervical discectomy and fusion; HO, heterotopic ossification; ASD, adjacent segment degeneration. | ||||
| a Chi-square test for the three groups | ||||
| b Chi-square test for the two groups | ||||
CDDD is a chronic, acquired deterioration of the cervical spine that can cause neck pain, radiculopathy, and/or myelopathy20. HS can be tailored to rebuild cervical stability at the target level, depending on the degree of degeneration of the different segments. Theoretically, an adequate range of motion is achieved at the level of joint replacement, and fixation is achieved at the level of joint fusion 21. Cervical instability due to disruption of the posterior tension band of the cervical spine has been identified as the cause22. The maintenance and reconstruction of cervical balance after HS and ACDF is due in large part to the protection of the posterior cervical ligamentous complex and fewer incisions. In a prospective review of studies, Chen et al23 found that both hybrid surgeries resulted in satisfactory neurological recovery. Compared with cervical laminoplasty, anterior hybrid surgery preserves cervical lordosis and has a lower rate of late complications. The safety and efficacy of HS in one- and two-level cervical spondylosis has been demonstrated 24. Three-level HS is now less studied, and few articles have been devoted to the results of sagittal parameter changes after three-level HS. However, sagittal parameters are critical to postoperative recovery outcomes in patients undergoing cervical spine surgery.
The cervical spine is a relatively complex structure with many factors affecting its alignment and balance. For patients undergoing spine surgery, elucidating compensatory mechanisms can be a key point in properly reconstructing cervical spine alignment. Cervical sagittal alignment is considered a diverse and significant component of the overall sagittal alignment. Cervical sagittal balance is associated with the development of cervical spine-related disorders and a decrease in health-related quality of life25. Ibrahim et al26 showed in a 2-year randomized controlled trial that maintaining cervical sagittal balance significantly reduced chronic cervicogenic headache in patients. A recent large retrospective study showed an increasing trend in cervical sagittal imbalance27. Therefore, it has become increasingly important to assess and correct cervical sagittal alignment during surgical treatment. Therefore, in this study, the effects of different surgical approaches on postoperative cervical sagittal parameters in patients with three-level CDDD were compared. The results showed that HS surgery was superior to ACDF in maintaining CL and SA, while there was no difference between them in other parameters. This result may suggest that three-level hybrid surgery is superior to ACDF in cervical sagittal alignment, while it may delay the development of ASD in the long term.
HS is the combination of ACDR and ACDF and is now one of the most common surgical procedures for treating patients with cervical spondylosis. Compared to ACDF, HS has the same outcomes and functional recovery for patients with cervical disc disease, with significantly better preservation of cervical ROM, suggesting that HS is an effective alternative treatment for multilevel cervical spondylosis28. Cervical sagittal alignment has been a heavily debated and controversial issue. Xu et al29 compared three-level HS (Prodisc-C and MC+) and ACDF through more than 5 years of follow-up, and most patients achieved cervical balance with HS and ACDF, but there was no difference in cervical sagittal alignment parameters between the two. However, in our previous research, we more accurately classified three-segment HS (Prestige-LP and Zero-P) as type I versus type II and showed that type II was superior in terms of cervical lordosis and range of motion12. The different prostheses and cages used may be the main factor in this difference. For three-level CDDD, it has been shown in many studies that HS can restore the anterior lordosis of the entire cervical spine and the surgical segment, preserving the range of motion of the cervical replacement segment and restoring the biomechanical function of the cervical spine30,31. In this study, a comparison of postoperative cervical sagittal parameters between HS and ACDF showed that HS is superior to ACDF in maintaining cervical curvature, while similar cervical sagittal balance can be obtained in all other aspects. Although the follow-up period for three-level HS is relatively short, the use of HS may be a more accepted procedure by more surgeons in the future. More studies are underway for improving the effectiveness of HS.
Multiple disorders of the cervical spine can lead to an imbalance in the sagittal alignment of the cervical spine32,33, and the linkage and interplay between cervical sagittal alignment parameters was demonstrated in this study. In both ACDF and HS, reconstruction of the CL is performed, making both cervical lordosis and T1S more pronounced. Both of these affect SVA simultaneously, with a greater CL causing a posterior shift of the head's center of gravity resulting in a lower SVA and a greater T1S causing an anterior shift of the head and cervical center of gravity resulting in a higher SVA. This is a compensatory mechanism to maintain horizontal gaze in response to changes in the overall sagittal alignment34. By showing that SVA is elevated after surgery in this retrospective study, the effect of T1S on SVA will be greater than the effect of CL on SVA, and the patient's head and cervical spine are anteriorly displaced after surgery.
C2S is a recently considered single, simplified measure of cervical deformity, similar to the T1S-CL measure. Shen et al35 showed that a greater C2S was associated with the presence of preoperative adjacent segmental pathology. C2S can adequately describe cervical deformity because of the association between O-C2A and CL, and both are closely related36. Mathematically, it can also be explained as follows: T1S - CL = T1S - (C7s - C2S), whereas in many patients, the T1 and C7 slopes are approximately equal, which means that they cancel each other in the equation, leaving only the C2S as the only variable to measure the aberration. Similarly, a similar trend as well as a significant correlation between C2S and T1S-CL was observed in both type I and type II groups in this study. The results suggest that the different number of replacement segments in HS does not affect the correlation between T1S-CL and C2S, and both are well-balanced. Similarly, in both type I and type II groups, this study indicates that CL is negatively correlated with T1S-CL, C2S and O-C2A, while T1S is positively correlated with T1S-CL.
This study has several limitations. First, it was a retrospective, single-center study, which may have been biased. In addition, the mean age of the patients in each group varied, which may have biased the results. Second, the sample size was relatively small, especially for patients in the type II group undergoing HS, and the follow-up period was relatively short. Third, only the Zero-P and Prestige-LP systems were included in the study. In the future, prospective, multicenter, large-scale studies with different prostheses should be conducted to confirm these results. Fourth, the focus of this study was the radiological results of HS; therefore, its clinical outcomes were not considered.
Most improvements in cervical sagittal alignment (CL, SA, T1S, SVA, T1S-CL, C2S, O-C2A, and segmental ROM) were observed in all three groups postoperatively. HS was more advantageous than ACDF in the maintenance of postoperative CL and SA. Thus, three-level HS may be better for maintaining cervical curvature. The number of replacement segments differed in those who underwent HS but did not affect the correlation between T1S-CL and C2S, both of which are well balanced.
CDR: Cervical disc replacement; ACDF: Anterior cervical discectomy and fusion; HS: Hybrid surgery; CDDD: Cervical degenerative disc disease; CL: Cervical lordosis; SA: Segment alignment; T1S: T1 slope; SVA: Sagittal vertical axis; C2: C2 slope; O-C2A: Occipital to C2 angle; ROM: Segment range of motion; ASD: Adjacent segment degeneration; HO: Heterotopic ossification; TIS-CL: T1 slope minus cervical lordosis; BMI: body mass index.
Acknowledgements
We thank the editors and reviewers for helping to process our manuscript.
Author contributions
SC wrote the original draft. BW contributed in the conceptualization, methodology, validation, and investigation; provided the resources; reviewed and edited the manuscript; and did the supervision. YD took part in the conceptualization, formal analysis, and validation and provided the resources. HL and TW provided the resources and did the supervision and funding acquisition. KH and JH provided the resources and did the supervision. The authors read and approved the final manuscript.
Funding
National Natural Science Foundation of China (81902190). There were no relevant financial activities outside the submitted work.
Availability of data and materials
Datasets are available from the corresponding author on a reasonable request.
Ethics approval and consent to participate
All participants provided signed, informed consent prior to study participation. This study was approved by the Ethics Committee on Biomedical Research, West China Hospital of Sichuan University (No. 2019-567) and was conducted following the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Consent for publication
Not applicable.
Competing interests
The authors declare that this research was conducted in the absence of any commercial or financial relationships that could have appeared to influence the work reported in this paper.
Author details
1 Department of Orthopedics, West China Hospital, Sichuan University, 37 Guoxue Lane, Chengdu 610041, Sichuan Province, China.