When Does the Construct Need to Extend further Into the Thoracic Spine in Patients Undergoing Correction for Cervical Deformity?
STUDY DESIGN: Retrospective cohort study of prospectively enrolled cervical deformity patients. OBJECTIVE: To investigate patients in whom fusion to the thoracic spine was warranted. SUMMARY OF BACKGROUND DATA: Thoracolumbar malalignment is often seen in patients presenting with cervical deformities. For cervical deformity (CD) patients, it is not always clear where in the thoracic spine to end the construct. METHODS: Patients were stratified into upper and lower thoracic groups: T1-T4 [Short Fusion], beyond T4 [Long Fusion]. Optimal outcome (OO) at 2 years postop was defined as: (1) did not have DJF and (2) had Virk et al good clinical outcome [≥2 of the following: NDI <20 or meeting MCID, mild myelopathy (mJOA ≥14), NRS-Neck ≤5 or improved by ≥2 points from baseline]. Univariate analysis compared variables between short and long fusion groups. Multivariate analysis analyzed associations between groups and factors related to treatment success and failures. RESULTS: One hundred forty-four cervical deformity patients were included (60.3±9.0 y, 60% F, 29.4±7.6 kg/m2, levels fused: 7.8±3.2). Eighty-two percent of patients had short fusions, whereas 18% had long fusions. 44.4% met the optimal outcome criteria, with no difference by fusion length (P=0.171). Factors associated with achieving OO in long fusions: baseline sacral slope ≤33.5 degrees (OR: 15.0), not undergoing high-grade osteotomy (OR: 12.3) and being Ames descriptor type C (OR: 13.5); all P<0.05. Factors associated with failure to achieve OO in short fusions: levels fused >6 (OR: 4.3), Ames descriptor type CT (OR: 11.5), Ames cSVA modifier grade 1 or 2 at BL (OR: 4.56), and Flatneck sagittal morphotype (OR: 4.5); all P<0.05. CONCLUSION: The choice of lower instrumented vertebra (LIV) in cervical deformity fusions may be influenced by multiple factors. In patients with global malalignment, severe frailty, flatneck deformity morphotype, and Ames type CT descriptor types, LIVs beyond T4 are associated with treatment success. LEVEL OF EVIDENCE: Level III.
