62. What effect does T1 slope have on sagittal balance and the relationship with caudal end of 3- or more-level posterior cervical fusions?

Abstract

BACKGROUND CONTEXT

Previous studies have highlighted the biomechanical effect of high T1 slopes on lordic force and the subsequent acceleration of kyphosis in postoperative cervical laminoplasties. While the data and collective opinion remain varied when determining whether the caudal end of a posterior cervical fusion should routinely be in the cervical or thoracic spine, adjacent level stenosis and nonunion are leading precipitating factors of revision.

PURPOSE

The study investigated the effect of T1 slope on postoperative sagittal vertical axis (SVA) and whether extension of posterior cervical fusions into the upper thoracic spine provides improved sagittal balance in comparison to C7 caudal level. Our hypothesis was does extension of posterior cervical fusions across the cervicothoracic junction lead improved sagittal balance in comparison to C7 caudal level.

STUDY DESIGN/SETTING

Multicenter retrospective study.

PATIENT SAMPLE

A total of 224 adult spine patients.

OUTCOME MEASURES

Clinical and radiographic outcomes.

METHODS

A database of 327 patients who underwent a 3- or more-level posterior cervical fusion with 2-year follow-up was created. Two cohorts were created based on fusion caudal level, those whose fusion terminated at C7 and those whose fusions extended to T1 or T2. The cohorts were then divided again into two subgroups, high T1 slope (>25°) and low T1 slope (≤25°) and subject to comparative analysis.

RESULTS

A total of 224 patients were included in the C7 caudal cohort and 103 were included in the T1/T2 caudal cohort. The mean age of C7 and T1/T2 groups were 61±12 yrs and 63.1±12.6 yrs, respectively. Mean BMI of the C7 cohort was 28.9±6.8, and 29.1±5.8 in the T1/T2 cohort. Mean SVA was significantly higher in patients with high T1 slopes (mean range 34.2-44.1mm) as compared to patients with Low T1 slopes (mean range 21-28.9mm) across all time intervals (pre-op to 24 months post-op). Additionally, the 25^th percentile SVA of High T1 slopes were greater than the median SVA values of Low T1 slopes at all intervals. For both the high and low T1 slope cohorts, patients with a caudal T1/T2 had comparatively higher SVA values than their C7 counterparts at all intervals despite maintenance of cervical lordosis, however these differences were not statistically significant.

CONCLUSIONS

Increased sagittal imbalance was comparatively higher in patients with >25° T1 slope ranging across preoperative to 24 months postoperative radiographic measurements. Extension of the posterior cervical fusion to T1 or T2 did not improve sagittal balance in patients with high T1 slopes. In fact, extension of posterior cervical fusions across the junction lead to increased positive sagittal imbalance. The results of this study do not support routinely extending posterior cervical fusions into T1 or T2 to improve post-operative sagittal balance. Longer thoracic extension or other intra-operative measures must be sought in patients at high risk for sagittal decompensation.

FDA Device/Drug Status

This abstract does not discuss or include any applicable devices or drugs.