Postoperative cervical sagittal imbalance negatively affects outcomes after surgery for cervical spondylotic myelopathy

Abstract

Study design: Prospective observational cohort study.

Objective: To determine if postoperative cervical sagittal balance is an independent predictor of health-related quality of life outcome after surgery for cervical spondylotic myelopathy.

Summary of background data: Both ventral and dorsal fusion procedures for CSM are effective at reducing the symptoms of myelopathy. The importance of cervical sagittal balance in predicting overall health-related quality of life outcome after ventral versus dorsal surgery for CSM has not been previously explored.

Methods: A prospective, nonrandomized cohort of 49 patients undergoing dorsal and ventral fusion surgery for CSM was examined. Preoperative and postoperative C2-C7 sagittal vertical axis was measured on standing lateral cervical spine radiographs. Outcome was assessed with 2 disease-specific measures-the modified Japanese Orthopedic Association scale and the Oswestry Neck Disability Index and 2 generalized outcome measures-the Short-Form 36 physical component summary (SF-36 PCS) and Euro-QOL-5D. Assessments were performed preoperatively, and at 3 months, 6 months, and 1 year postoperatively. Statistical analyses were performed using SAS version 9.3 (SAS Institute).

Results: Most patients experienced improvement in all outcome measures regardless of approach. Both preoperative and postoperative C2-C7 sagittal vertical axis measurements were independent predictors of clinically significant improvement in SF-36 PCS scores (P = 0.03 and P = 0.02). The majority of patients with C2-C7 sagittal vertical axis values greater than 40 mm did not improve from an overall health-related quality of life perspective (SF-36 PCS) despite improvement in myelopathy. The postoperative sagittal balance value was inversely correlated with a clinically significant improvement of SF-36 PCS scores in patients undergoing dorsal surgery but not ventral surgery (P = 0.03 vs. P = 0.93).

Conclusion: Preoperative and postoperative sagittal balance measurements independently predict clinical outcomes after surgery for CSM.

Level of evidence: 2.

Conflict of interest statement

Potential Conflicts of Interest: For the remaining authors, none were declared.

Figures

Figure 1

C2-C7 SVA is the distance from a plumb line drawn at the midpoint of the base of C2 to the plumb line drawn at the mid-point of the base of C7 measured on a standing lateral cervical spine radiograph.

Figure 2

Scatter plots of postoperative C2-C7 SVA measurements and improvements in HR-QOL measures at one year.

Figure 3

(A) Predicted probability of clinically significant improvement in SF-36 PCS scores by postoperative C2-C7 SVA measurements. Fewer than 50% of patients with postoperative sagittal balance of greater than 40mm are predicted to experience clinically significant improvement after surgery for CSM. (B) Two-way scatter plots of change in SF-36 PCS scores from baseline to one year postoperatively stratified by dorsal and ventral approach demonstrating that patients who were treated with dorsal approaches and who had positive sagittal imbalance tended to have less improvement in SF-36 PCS score.

Figure 4

ANCOVA model of postoperative sagittal balance with preoperative sagittal balance and surgical approach.