Investigating the Cervical Implant Width to Uncovertebral Width Ratio (IWUW) in Single-Level Anterior Cervical Discectomy and Fusions

Study Design: Retrospective cohort. Objective: Evaluating the implant width: uncovertebral width (IWUW) ratio on fusion status and patient-reported outcomes measurement information system (PROMIS) scores in single-level anterior cervical decompression and fusion (ACDF). Summary of Background Data: The uncovertebral joint contributes to cervical stability. Undersized implants have been associated with subsidence; however, the impact of the IWUW ratio on fusion status and PROMIS outcomes has not been previously reported. Methods: Adults older than or equal to 18 years who underwent an elective, single-level ACDF at a single institution over a seven-year period were included. PROMIS pain interference (PI) and physical function (PF) and dynamic cervical spine radiographs were required at ≥6 months follow-up. Uncovertebral width and fusion status (<1 mm interspinous motion on dynamic radiographs) were assessed. Relative risks were calculated using Poisson regression. t tests and χ 2 tests analyzed continuous and categorical data, respectively. Significance was P <0.05. Results: In total, 142 patients were included (allograft: 85, cage: 57). Fusion rate, time to fusion, age, and BMI were similar between cohorts; the allograft cohort had a higher proportion of females ( P =0.03). Fused patients had a higher mean IWUW (0.94 vs. 0.90, P =0.02); however, stratified trend analysis (RR: 1.11, P =0.41) and logistic regression ( P =0.09) were not significant between increasing IWUW and fusion. Receiver operator curve analysis yielded an area under the curve of 0.623 for predicting fusion. IWUW was not associated with achieving PROMIS PI or PF minimal clinically important difference. Increasing IWUW correlated to worsened PF ( P =0.03), but not PI ( P =0.13). IWUW was not associated with time to fusion, revision rate, or time to revision. Conclusions: IWUW is not predictive of fusion status, but higher ratios may worsen PROMIS PF despite higher mean IWUW among fused patients. IWUW between 0.8 and 1 may optimize outcomes. IWUW seems to have limited clinical value in single-level ACDF procedures. Level of Evidence: Level III.