RADIOGRAPHIC EVOLUTION AND CERVICAL SAGITAL BALANCE OF LAMINOPLASTY VERSUS LAMINECTOMY IN PATIENTS WITH CERVICAL SPONDYLOTIC MYELOPATHY

ABSTRACT Objective To compare radiographic findings of patients who underwent laminoplasty and laminectomy with arthrodesis for spondylotic cervical myelopathy. Methods Who were submitted to laminectomy with arthrodesis or laminoplasty to treat cervical spondylotic myelopathy with minimum follow-up of 6 months. The radiographic parameters related to the cervical spine evaluated were C0C2 lordosis (C0C2), cervical lordosis (CL), T1 slope (T1S), thoracic inlet angle (TIA), neck tilt (NT), cervical sagittal vertical axis (CSVA), and T1S – CL mismatch (T1S-CL). Results We evaluated 34 patients, 23 (68%) of whom were men. The mean age was 65 years (SD ± 13). There was no statistical difference in any of the preoperative radiographic parameters. Considering the patients submitted to laminectomy alone, a significant difference was observed for C0C2 (P = 0.045), CSVA (P = 0.0008), with differences between IPO and POS times (P = 0.026) and between PRE and POS (P = 0.0013) and T1S – CL mismatch (P = 0.0004), with a difference between IPO and POS (P = 0.0076) and between PRE and POS (P=0.001). Considering the patients submitted to laminoplasty alone, there was no difference over time for any radiographic parameters considered. Comparing the radiographic parameters between the laminectomy and laminoplasty groups in the three time periods, there was no significant difference for any of them. Conclusion This study suggests that patients with cervical spondylotic myelopathy who underwent laminectomy with instrumentation may present worse radiographic evolution as regards cervical sagittal alignment over time when compared to patients who underwent laminoplasty. Level of evidence III; Retrospective case series.


INTRODUCTION
Cervical spondylotic myelopathy (CSM) is the most common cause of non-traumatic spinal cord injury and can lead to high morbidity in the affected patient. 1 It is usually treated surgically, by either anterior or posterior approach, though the posterior approach is usually reserved for cases of multi-segment compression, more elderly patients, and more serious myelopathy without fixed kyphosis. 1 The two main posterior access techniques are laminoplasty and laminectomy associated with arthrodesis. Both have similar outcomes from a neurological recovery perspective and there is no consensus around the superiority of one technique over the other. 2 The influence of the sagittal balance of the thoracolumbar spine on the quality of life and the functional results of patients is increasingly recognized. 3,4 Due to the great complexity of the cervical spine, with broad compensatory mechanisms, the sagittal balance of this region is not yet widely understood. 5 However, there is evidence that changes in alignment can lead to a poorer quality of life 6 and a worsening of the myelopathy. 5 Some authors have demonstrated that postoperative sagittal cervical alignment following laminectomy and arthrodesis 7 can influence functional outcomes and even predict a worsening of radiographic alignment during postoperative follow-up. 8 The objective of this study is to compare sagittal cervical alignment and the radiographic progression of patients who underwent laminoplasty and laminectomy associated with arthrodesis for the treatment of cervical spondylotic myelopathy.

Patients
This is a retrospective study based on prospectively collected data. Following approval by the local Institutional Review Board (REC 2.546.077), the medical records and imaging examinations of patients who underwent surgical treatment for cervical spondylotic myelopathy and at least six months of follow-up at a single center.
All cases of myelopathy from other causes (traumatic, tumoral, and infectious), as well as anterior approach cases (discectomy and/or corpectomy), were excluded.
The patients were submitted to laminoplasty or laminectomy and arthrodesis surgery according to the preference of the assisting surgeon.

Radiographic analysis
The imaging evaluation was conducted with radiographs of the cervical spine, radiographs of the total spine, and magnetic resonance. All radiographs were taken at the same center following the same protocol with the patient in orthostasis. The only exceptions were patients with severe myelopathy who could not stand and whose radiographs were taken with them sitting.
The radiographic parameters evaluated were: 5

Statistical analysis
Statistical analysis was performed using R version 3.4 software (R Foundation for Statistical Computing, Vienna, Austria). The data consisted of quantitative variables and distribution normality was verified by the Shapiro-Wilk test. The comparison between the means of the laminectomy and laminoplasty groups was carried out using the Student's t test, following confirmation of the equality of variances of the groups using the F-test. The values of the PRE, IPO, and POS radiographic parameters were compared using repeated measures ANOVA, since a paired analysis was required. Finally, the evolution of the radiographic parameters of the two groups in the POS and IPO periods was analyzed by comparing the mean difference between the POS and IPO values using the Student's t test. The level of significance considered was 5%.

Population
A total sample of 34 patients was evaluated, 23 (68%) of whom were men and 11 (32%) of whom were women. The mean age was 65 years (SD: ±13), ranging from 37 to 88 years of age. There was no significant difference between the mean ages of the laminectomy (66 years, SD: ±10.7) and laminoplasty (64 years, SD: ±17.9) groups. Table 1 shows the preoperative mean and standard deviation of the preoperative radiographic sagittal alignment parameters of the cervical spine. There was no difference between any of the parameters of the patients in the laminectomy and laminoplasty groups, showing that the groups were radiographically similar.

Evolution of the radiographic parameters during monitoring
Analyzing the evolution of the radiographic parameters studied during the three monitoring periods (PRE, IPO, and POS), we observed different behaviors in the two groups.
Considering the patients submitted to laminectomy by themselves, we observed a significant difference in C0-C2 (P = 0.045), with no difference in the comparison between each time period using the complementary Bonferroni test ( Figure 3); in CSVA (P = 0.0008), where we observed a difference between IPO and POS (P = 0.026) and between PRE and POS (P = 0.0013) values ( Figure 4); and in the T1S -CL mismatch (P = 0.0004), with differences between IPO and POS (P = 0.0076) and PRE and POS (0.001) ( Figure 5). There were no significant differences in CL or T1S.
Considering the patients submitted to laminoplasty by themselves, there were no differences between the time periods for any of the radiographic parameters analyzed.
Comparing the radiographic parameters between the laminectomy and laminoplasty groups in the three monitoring time periods, there was no significant difference for any of the parameters (C0-C2, P = 0.898; CL, P = 0.557; CSVA, P = 0.459; T1S, P = 0.631; T1S -CL, P = 0.110).     Behavior of the radiographic parameters following the surgical procedure The comparison of the radiographic parameters studied between the laminectomiy and laminoplasty groups following the surgical procedure were conducted comparing the means of the difference between the POS and IPO values of each parameter. As can be seen in Table 2, there was no significant difference between the groups for any of the radiographic parameters.

DISCUSSION
The ideal surgical approach for the treatment of CSM is a subject of discussion in the literature. Generally, the posterior approach is reserved for more serious cases of myelopathy, more diffuse disease, and cases without fixed kyphotic deformity. The decision about the access route is usually only based on regional cervical spine radiographs and magnetic resonance data. 1 There are several studies showing the importance of cervical alignment to clinical and quality of life outcomes in certain patient populations. [14][15][16][17] However, the cervical spine is a complex region with a great range of motion. This mobility allows greater adaptation to the changes typical to aging. These adaptations occur in the cervical region, especially to maintain the line of vision on the horizon.
This study did not find any difference in preoperative sagittal alignment between the two groups evaluated. However, Lau et al. 12 showed that laminoplasty was more common in patients with high CL. This difference may be related to the fact that the choice of technique in our population was based on the preference of the surgeon rather than on any well-established criteria.
The LAMINOPLASTY group did not present any radiographic worsening over time. However, patients who underwent LAMINEC-TOMY presented worsening of C0-C2 lordosis, CSVA, and T1S-LL parameters. These results were not expected following arthrodesis, which theoretically should prevent worsening of alignment in the fixed segment. One hypothesis is that with the arthrodesis the segments lose the capacity to compensate, which can predispose the adjacent segments to degeneration and thus worsen the radiographic parameters. The patients with laminoplasty maintained alignment during the entire follow-up. These results conflict with some studies in the literature. For example, Lau et al. demonstrated that alignment worsened more following laminoplasty as compared to laminectomy. 12 Radiographic worsening related to laminoplasty was associated with T1S greater than 30°, which is a strong indicator of thoracolumbar sagittal inbalance. 15 This worsening following laminoplasty observed in other studies but not in our case series can be justified by the small number of patients in this group and for technical reasons in performing the surgeries (to avoid resecting the facet joint and a concern with preserving the cervical musculature that inserts into C2).
The increase in C0C2 lordosis observed in the laminectomy patients can probably be related to a compensatory mechanism of the cervical spine to ensure horizontal vision, as observed by other studies. 13 There was no difference between the groups at the three evaluation times.
This study has the following limitations: First, its retrospective nature, even though the data was collected prospectively.
In addition, the clinical parameters, which might be correlated to the radiographic differences in functional results observed between the groups, were not evaluated. This could be included in a future study.
A larger sample is necessary to make any inferences, which is difficult due to the rarity of the disease.

CONCLUSION
This study suggests that patients with cervical spondylotic myelopathy submitted to laminectomy with instrumentation may present worse radiographic evolution in terms of sagittal cervical alignment over time than patients submitted to laminoplasty.