Influence of Preoperative T1-Slope and Cervical Sagittal Vertical Axis on Postoperative Cervical Sagittal Alignment Following Posterior Cervical Laminoplasty

DISCUSSION

Posterior cervical laminoplasty is a common surgical technique utilized to decompress the cervical spinal cord with the goal to improve neurologic function and reduce pain.6,7 As postoperative CL has been shown to be correlated with postsurgical neck pain and disability,3 the goal of this investigation was to assess the influence of preoperative cervical alignment, particularly severity of cSVA and T1S, on postoperative cervical sagittal alignment. This study had 2 major findings: (1) patients with high preoperative T1S, irrespective of cSVA, were at risk of loss of CL postoperatively; and (2) patients with low preoperative T1S and cSVA <4 cm experienced a decrease in global sagittal cervical alignment without jeopardizing CL. These results are in concordance with and also add a unique dimension to the current literature on sagittal alignment following posterior cervical laminoplasty.

Changes in the sagittal profile following cervical posterior laminoplasty have been an area of great interest and investigation.8 As loss of sagittal cervical alignment is purported to jeopardize clinical outcomes, several studies have attempted to assess preoperative factors that predict the loss of CL following posterior cervical laminoplasty. Historically, the leading theories regarding loss of CL after laminoplasty centered around magnitude of CL. For example, Suk et al identified 3 preoperative risk factors that predicted postoperative kyphosis: (1) preoperative neutral position lordotic angle <10°, (2) preoperative diagnosis of cervical spondylotic myelopathy, and (3) a preoperative kyphotic angle during flexion that is greater than the extension lordotic angle.4 However, within this model, effects on changes on CL were mixed, likely due to the fact that other parameters of cervical sagittal alignment, including cSVA and T1S, were not considered.

More recently, the importance of cSVA and T1S on cervical alignment following laminoplasty has gained greater appreciation. For example, in an investigation of 174 patients without preoperative kyphotic alignment, Sakai et al found that an SVA measurement >4.2 cm measured from the center of gravity of the head to C7 and advanced age (>75 years) were predictors of postoperative kyphotic alignment following laminoplasty.9 In a retrospective review of 49 patients who underwent open door laminoplasty, Lee et al noted that laminoplasty has a high probability of resulting in loss of CL, and that the T1S was significantly associated with change in the postoperative Cobb angle.10 Specifically, it was reported that patients with higher T1Ss demonstrated loss of CL postoperatively.10 Miyazaki et al and Kim et al also demonstrated that loss of CL after laminoplasty is significantly correlated with preoperative T1S.11,12 Our findings corroborate these results, as we found that patients with high T1Ss (>20°), irrespective of the global sagittal cervical alignment (cSVA), demonstrate significant decreases in CL and cSVA postoperatively compared with patients with low T1Ss.

In contrast to the patients with high T1Ss, patients in our study with low T1Ss demonstrated an improvement, albeit slight, in CL after the operation. While the low T1S patients had a significant increase in cSVA, the average cSVA remained <4 cm. This highlights the notion that the preservation and improvement of CL after laminoplasty are most likely related to alignment of the thoracolumbar spine (ie, thoracic kyphosis), as manifested in the T1S.

Our study’s findings should be considered in the context of its limitations. Notably, there is heterogeneity in the study population with regard to age at the time of surgery and follow-up time. However, as all patients had 6-week postoperative radiographs, and that changes in the radiographic alignment parameters between 6 weeks and last follow-up are not significantly different, heterogeneity in latest follow-up likely does not influence the results. Other limitations include variations in levels of laminoplasty performed and by whom. Last, while the absence of clinical outcomes may be considered a limitation, the goal of this study was to purely assess radiographic changes in sagittal alignment after laminoplasty based on variations in preoperative sagittal alignment.