Cervical spine surgery can be generally divided into an anterior approach and a posterior approach. Anterior cervical discectomy and fusion (ACDF), one of the typical anterior surgical methods, was first put forward by Smith and Robinson and has a history of over half a century (1). It aims to decompress the spinal cord and nerves in order to relieve the symptoms of diseases such as cervical spondylosis and spine cord injury. With the help of plate fixation, ACDF has advantages of restoring intervertebral height and maintaining cervical spine stability (2, 3). However, it also has complications such as loosening of internal fixation, the injury of the esophagus and laryngeal nerve, and axial or root symptoms (4, 5). In addition, although the safety and clinical efficacy of 3-level ACDF have been demonstrated, more complications have been reported in multi-level ACDF (6). Cervical laminoplasty (LP) is one of the typical posterior surgical methods and has been developed as an alternative to cervical laminectomy. It has the merit of widening the spinal canal and relieving compression of the spinal cord caused by cervical spondylosis or spine cord injury (7). There are two main techniques: Hirabayashi’s open-door LP and Kurokawa’s double-door LP. Studies have found that there was no significant difference in clinical outcomes between open-door and double-door LP. LP has complications such as the injury of the spinal cord and vertebral artery, spinal deformity, and C5 palsy (7).

In recent years, the relationship between cervical spine surgery and cervical sagittal balance (CSB) has become a hot spot. CSB shows how the cervical spine is postured in the sagittal section and can be quantified by measuring relevant parameters such as the C2–7 angle, sagittal vertical alignment (SVA), C7, and T1 slope (8). Cervical spine surgery can be further assessed by analyzing CSB and comparing the perioperative data of patients. However, there are few articles on cervical spine surgery from a CSB perspective. Studies on CSB may help surgeons to view cervical spine surgery from a biomechanical perspective and improve their understanding of the impact of CSB on surgery and diseases (9). In addition, some studies have compared the anterior approach and posterior approach of cervical spine surgery and reported their safety and clinical efficacy (7, 10). However, studies on the comparison of 3-level ACDF and open-door LP are relatively rare. Therefore, this retrospective comparative study was conducted to compare the effect of 3-level ACDF and open-door LP on clinical evaluation and radiological outcomes from the perspective of CSB.

Surgical methods for multilevel cervical diseases include multilevel ACDF and open-door LP. Surgeons need to take many aspects into account to choose the appropriate approach, such as the etiology of the disease, degree of the deformity, neurological impairment, comorbidities and patient’s expectations. Many studies focused on the comparison of these two approaches. Multilevel ACDF achieves direct spinal canal decompression, cervical spine stability, and restoration of the cervical spine curvature. The open-door LP is more suitable for patients who cannot be treated with the anterior approach with diseases such as ossification of the posterior longitudinal ligament. It enables direct posterior decompression and leads to indirect anterior decompression due to spinal cord palsy. The aim of both surgical methods is to achieve complete decompression of the spinal canal, and both have been developed as mature surgical procedures for the treatment of diseases including cervical spondylosis and spine cord injury. However, CSB is a special topic in a few studies in the literature. In recent years, scholars have noticed the value of CSB for cervical surgery. Studies have emphasized the importance of CSB before and after surgery, which may be closely related to clinical prognosis. However, the literature on the effects of improving or preserving CSB remains controversial. Many details of CSB and the two approaches need to be further clarified.

The efficacy of anterior and posterior approaches in improving CSB is still a matter of discussion. A mini-review is presented in Table 5 (11–17). The assessment of postoperative CSB includes two aspects: cervical spine curvature reconstruction and lordosis maintenance. ACDF restores the curvature of the cervical spine, and multilevel ACDF may make cervical spine more lordotic (14). A review of prospective cohort studies by Sakai et al. found that cervical alignment and balance improved after ACDF but worsened after LP (13). Some studies reported that the multilevel anterior approach has advantages over the posterior approach mainly in terms of spine reconstruction (14). ACDF restores cervical alignment by pulling the vertebrae forward (18). Previous studies showed that ACDF was able to significantly improve overall and segmental lordosis by changing the parameters of CSB (12). In addition, ACDF may improve cervical muscle function by altering cSVA so as to reduce the incidence of postoperative axial symptoms. However, ACDF may be inferior to LP in maintaining lordosis. It was reported that some of the parameters of CSB after multilevel ACDF were lower than those after single-level ACDF (12, 14). It appeared that as the number of levels increased, the capacity to maintain lordosis decreased (14). Unlike ACDF, LP causes damage to the posterior cervical column and the muscle-ligament complex, leading to partial loss of the weight-bearing function and disorder of sagittal balance (16, 19). Cervical spine has a tendency to tilt forward after LP, resulting in the need for greater muscle strength at the back of the neck to maintain an upright neck. Therefore, continuous muscle contraction is required to maintain proper neck position, and further, muscle spasm may occur, which is an important cause of postoperative axial pain (16). It was also reported that LP reduces lordosis and straightens the cervical spine (19). Although CSB appears to be less important than lumbar-pelvic balance, it is worth noting that changes in lumbar-pelvic balance probably result from adjustments in body posture to accommodate cervical sagittal imbalance (20–23).

Spine sagittal balance plays an important role in the alignment against the axis of gravity with a minimum of energy expenditure (24). Spine sagittal imbalance is a significant factor not only for diseases but also for the planning of the perioperative period. CSB explains the posture of the cervical spine in the plane of sagittal, which shows the association between spine structure and relevant diseases. Cervical sagittal parameters are measured to evaluate cervical spine disorders and reflect the effect of surgery. Cervical lordosis is one of the major aspects of CSB. Parameters such as CCD, C2–7 angle, cSVA, C7S, and T1S were included in this study.

Cervical curvature is an important indicator of CSB. Borden et al. published the first study on cervical alignment in 1960 and proposed CCD to reflect cervical curvature (25). The advantage of this method is to minimize the impact of vertebral degeneration, but differences in bone and x-ray magnification are factors that affect the accuracy of measurement. For asymptomatic patients, restoring the curvature of the cervical spine through conservative treatment has a positive effect on preventing further degeneration of adjacent segments and even the entire cervical spine. For symptomatic patients, reconstructing the curvature of the cervical spine through cervical spine surgery can indirectly decompress the spinal canal and better restore the volume of the spinal canal. The Sagittal Cobb angle is clinically used in the measurement of spinal curvature, preoperative preparation, and postoperative evaluation for spine diseases. The C1–7 angle and C2–7 angle are measured for cervical lordosis because of their intra and interrater reliability and feasibility (26). Compared with the C2–7 angle, the C1–7 angle overestimates the lordosis of the cervical spine due to the hyperextension of C1 and C2 vertebrae. Therefore, the C2–7 angle is widely used in research studies on the cervical spine. cSVA is a classic sagittal parameter for assessing cervical spine alignment, which is closely related to cervical diseases and health-related quality of life. Studies have found that energy consumption increases as the center of gravity shifts, which indicates the importance of cSVA especially after cervical spine reconstruction. It was also reported that increased cSVA was associated with elevated intramedullary pressure in the spinal cord and was positively correlated with NDI scores (27, 28). In addition, regression studies show that T1S has a correlation with cSVA (15). The C7S and T1S are useful measurements for assessing CSB due to their great utility when full-length films are not available. Scholars tend to use T1S in their studies because C7S is strongly correlated with T1S, and the change of T1S in the pathological state is more obvious (29). Previous studies have shown that patients with T1S under 25° may have better CSB. However, patients with T1S over 25° are not meant to suffer from congenital or degenerative cervical diseases (30).

In our study, we compared 3-level ACDF with open-door LP from many perspectives, especially CSB. In terms of perioperative parameters, blood loss and drainage volume at 1 day after surgery in Group A was significantly less than that in Group B, indicating that 3-level ACDF had the advantages of small incisions, less trauma, and quick recovery. Therefore, the hospital stay of Group A patients was undoubtedly shorter than that of Group B patients. In addition, a significant difference was found in the NDI and JOA scores between the two groups postoperatively and at 1 month after surgery. Patients after 3-level ACDF recovered faster than open-door LP mainly in terms of function and life quality. However, there was no significant difference between the two groups with regard to NDI and JOA scores at FFU, which suggests that 3-level ACDF may benefit patients in the early stage of rehabilitation and there may be no difference between the long-term prognosis of the two surgical approaches. In terms of radiographic outcomes, patients after 3-level ACDF in our study reconstructed their cervical spine curvature and improved their cervical lordosis compared with those after open-door LP. The CCD of Group A increased significantly after surgery, indicating that 3-level ACDF increased cervical lordosis, while open-door LP did not change CCD significantly. In addition, 3-level ACDF showed advantages over open-door LP in terms of improving cervical spine curvature. Similar to CCD, the C2–7 angle increased significantly after 3-level ACDF, showing that cervical lordosis increased compared with open-door LP. No significant difference was observed in cSVA between both groups. From the results, conclusions can be drawn that the center of gravity did not shift significantly after 3-level ACDF and open-door LP, which guaranteed normal energy consumption in maintainin posture. Furthermore, T1S increased significantly after 3-level ACDF, which, in turn, increased cervical lordosis. Some studies have put forward the hypothesis that an increase of T1S may be a risk factor that aggravates symptoms, and therefore, reducing T1S may be beneficial to clinical recovery (30, 31). Also, it has been reported that excessive T1S may lead to spinal cord compression and cervical spondylosis (32). However, controversy still remains. T1S increases with age, and increased T1S may not be an exact variable to demonstrate clinical outcomes. Some scholars have attempted to use ratios such as C7S/T1S and Neck Tilt/T1S to replace T1S in their studies (29). More studies are needed to reveal the relationship between T1S and clinical prognosis.

This study had its limitations. Firstly, it was a retrospective comparative study. Secondly, the sample size was relatively insufficient. Thirdly, the research did not study further factors that affected cervical sagittal parameters. Therefore, a prospective randomized controlled study and a long-term follow-up with a large sample size are badly needed to analyze different cervical sagittal parameters after multilevel cervical spine surgery.

Patient-reported clinical outcomes improved after 3-level ACDF and open-door LP compared with those before surgery according to NDI and JOA scores. However, clinical outcomes showed a significant difference between the two groups postoperatively and at 1 month after surgery, indicating that patients who underwent 3-level ACDF benefited more in the early stage of rehabilitation. From a long-term perspective, patients’ clinical outcomes showed no significant difference. From radiographic outcomes, 3-level ACDF had the advantages of reconstructing cervical lordosis over open-door LP with increased CCD and the C2–7 angle. However, cSVA, C7S, and T1S were analyzed with no significant differences. Given the limited literature on the comparison of multilevel cervical spine surgery, more research studies are recommended to elucidate the relationship between CSB and clinical and radiological outcomes.