The cervical lordosis distribution index and its consideration of upper cervical region and morphology

Abstract

BACKGROUND CONTEXT: The cervical lordosis distribution in relation to its apex has not been characterized, nor has the impact of morphologic differences and upper cervical segments. PURPOSE: The goal of this study is assess whether tailored correction of cervical deformity by incorporating the cervical apex into a distribution index (CLDI) improves clinical outcomes while lowering rates of junctional failure. STUDY DESIGN/SETTING: Retrospective review of a prospectively-collected cohort; Multiple academic centers. PATIENT SAMPLE: A total of 84 patients met radiographic criteria for adult cervical deformity and at least 2-year follow-up. OUTCOME MEASURES: Optimal outcome is defined as meeting Virk et al Good Clinical Outcome (GCO): [Meeting 2 of 3: 1) NDI<20 or meeting MCID, 2) mJOA>=14, 3) NRS-Neck<=5 or improved by >2 points] and no occurrence of distal junctional failure (DJF). METHODS: C2-T2 lordosis was divided into cranial (C2-to-apex) and caudal (apex-to-T2) arches. A cervical lordosis distribution index (CLDI) was developed by dividing the cranial lordotic arch (C2 to apex) by the total segment (C2-T2) and multiplying by 100. Cross-tabulations developed categories for CLDI producing the highest chi-square values for achieving Optimal Outcome at two years and outcomes were assessed by multivariable analysis controlling for significant confounders. Patients stratified by Ames et al deformity classification then assessed against thresholds. Patients were further divided into those meeting thresholds with upper cervical compensation (defined by C0-C2 angle, C0 slope, McGregor's Slope [MGS]) vs without compensation. Multivariate regression analysis controlling for T1 slope assessed differences in classification and impact of upper cervical region. RESULTS: Cervical apex distribution postoperatively was: 1% C3, 42% C4, 30% C5, 27% C6. Mean cervical LDI was 117±138. Mean cranial lordosis was 23.2±12.5°. Using cross-tabulations, CLDI between 70 and 90 was defined as ‘Aligned’. Chi-square test revealed significant differences among CLDI categories for DJK, DJF, Good Clinical Outcome, and Optimal Outcome (all p<.05). Patients aligned in CLDI were less likely to develop DJK (OR: 0.1, [<0.1-0.9]), more like to achieve GCO (OR: 3.9, [1.2-13.2]) and Optimal Outcome (OR: 7.9, [2.1-29.3]) at two years. Patients aligned in CLDI developed DJF at a rate of 0%. Those meeting this CLDI threshold were more likely to be classified into primarily cervical deformity by Ames criteria (OR: 1.9, [3.2-10.6], p<.05). CONCLUSIONS: The cervical lordosis distribution index, classified through the cranial segment, takes each unique cervical apex into account and tailors correction to the patient in order to better achieve good clinical outcomes. While differences based on morphology exists, upper cervical region functions as a reserve in all deformity types. Consideration of regional and global factors allows for a comprehensive assessment and individualization of realignment surgery. FDA Device/Drug Status: This abstract does not discuss or include any applicable devices or drugs.