Historically, early clinical intervention and optimal surgical approach have been recognized as the prerequisites of a good surgical outcome. All kinds of risk factors affected surgical outcome in patients with CSM and CK. Several articles have been published that predictors of postoperative outcome in patients with CSM included age at operation, duration of symptoms and signal intensity of spinal cord.[14, 15] However, few studies paid close attention to clinical outcome after anterior hybrid surgery for patient with multilevel CSM and kyphosis deformity. Did cervical kyphosis impede the recovery of neurological function after surgery? Chavanne[16] found that change of cervical alignment would lead to the increasing of intramedullary pressure, especially cervical kyphotic deformity exceeded 21 degrees. Whereas, the correlation between correction of kyphosis alignment and postoperative outcome remained controversial.[10, 17, 18]
An appropriate surgical approach was one of the important factors to achieve good postoperative outcome. However, the selection of surgical approach was the once controversial notion. Anterior approach could directly remove the lesion of compression of spinal cord and correct more kyphotic angle. Unfortunately, anterior approaches were more vulnerable to complications which were C5 palsy, cerebrospinal fluid leakage and temporary dysphagia.[19] Posterior approach relieved spinal cord compression according to the drift backward of spinal cord and the enlarging of vertebral canal volume. Posterior approach would be an optimum selection when patients were accompanied by a consecutive ossification of posterior longitudinal ligament.[20] Whereas, cervical kyphotic alignment reduced the space of drift backward of spinal cord, which would influence clinical outcome. In previous study, Cabraja[11] showed that anterior approach had a better restored of cervical kyphosis than the posterior approach, and Suda[21] showed that posterior laminoplasty was best indication for patients with local kyphosis less than 13 degrees. Furthermore, Yang[22] showed a new-style: anterior controllable ante-displacement fusion (ACAF), which could enlarge the volume of the spinal canal and simultaneously correct cervical kyphosis for patients with m-CSM and stenosis. In this study, an anterior hybrid approach was selected to remove ossification of the posterior vertebral body and correct kyphotic deformity. This method could not only directly decompress spinal cord, but also avoid the occurrence of low fusion rate and implant translocation after multi-ACCF. Therefore, the selection of surgical approaches should be planned on an individual basis.
In this study, the change of local kyphotic angle between preoperative and last-follow was associated with surgical outcome according to the JOA score, particularly corrective angle more than 10.2 degree. However, the change of C2-7 Cobb angle was not statistically significant difference between good group and poor group. We considered that the cause was the occurrence of cervical “S” or reverse “S” type that lordosis and kyphosis existing side-by-side on the lateral films of cervical vertebra. Hence, the measurement of local kyphosis angle had greater meaningful to the prevention of poor postoperative outcome. In previous study, Uchida[10] explained also that correction of local cervical kyphosis was beneficial to improve the recovery of neurological function. Whereas, excessive correction of cervical kyphosis would give rise to short-term axial pain after surgery.[23]
Not all patients could maintain the effect of surgical correction with passage of time. In this study, there were seventeen patients with the worsening of postoperative local alignment as a result of each kind of suggestion factor. Although our research didn’t show that the worsening of postoperative local alignment was associated with poor outcome after surgery, the causes of worsening were necessary to study further. Lee[24] found that one of key factors of affecting cervical spine sagittal balance was T1 slope. Patients with cervical kyphotic deformity required low T1 slope angle to compensate for maintaining the sagittal balance. In addition, Katsuura[25] suggest that adjacent segment degeneration after anterior cervical fusion was also a key factor determining postoperative kyphotic change in the cervical fused segment. Our finding confirmed that the T1 slope and adjacent segment degeneration were associated with change of postoperative local alignment. The results expounded that surgical correction of cervical local kyphosis couldn’t effectively improve the T1 slope angle, so recurrence of kyphotic deformity aimed to compensate for the balance of cervical alignment. Furthermore, we founded also that implant subsidence and large preoperative C2-7 SVA were the important factors of worsening of postoperative local alignment. The implant subsidence would lead to the height difference of anterior and posterior margin in surgical segments. Frequent head-down tilt after surgery was crucial reason of the subsidence in front of implant. Understanding and preventing risk factors could obtain maximum improvement in quality of life after surgery.
In our study, several limitations were worth mentioning. Firstly, this was a retrospective study with relatively small number of patients and lacked long-term follow-up data for some patients. Secondly, the evaluation of surgical outcome only focused on improvement of JOA score and recovery rate, neglected the evaluation according to the SF-36 scale and the HR-QOL scale. Thirdly, the relationship between the change of cervical kyphotic alignment and thoracolumbar or spino-pelvic parameters were not considered. Finally, the adjacent segment degeneration was evaluated only at last fallow-up, which may continue to occur in the future.