Introduction: Pseudarthrosis remains a problem in ACDF1. A meta-analysis of single level ACDF showed a 4.8% pseudarthrosis rate2. We sought to demonstrate the optimal cage size for each cervical interspace.

Methods: We conducted radiographic and chart review of consecutive patients who underwent single level ACDF (C3-C7) with variable polyetheretherketone (PEEK) cage heights (6mm-9mm) at multiple institutions from 2012-2015. Primary outcome is fusion rate determined at 6 and 12 months postop by standing, flexion/extension X-rays or cervical CT. We excluded patients with inadequate imaging quality and < 6m follow up. Fusion criteria are <2mm interspinous movement on flexion/extension films, and bony trabeculation. Secondary outcomes are QoL scores as determined by Short-form 12 (SF-12) and Neck Disability Index (NDI). Multiple logistic regression will be used with fusion >6m and >12m as dependent variable and cage size, interspace, age, sex, smoking, osteoporosis and diabetes as independent variables. This is a pilot study to determine the baseline fusion rate in our local population for sample size calculation.

Results: We reviewed 381 patients and 232 were included in the analysis. Demographic information is noted in Table 1. The mean postoperative XR interval is 14.78 ± 8.1 months. Overall fusion rate was 83%. At the C3-4 level, there was a trend with increasing cage size and decreased fusion rates. This was not seen at C4-7 as shown in Table 2. SF-12 and ND post-operatively are displayed in Table 3. Utilizing a fusion rate of 83%, power of 0.8, alpha level of 0.05, we calculated a sample size of 633 patients.

Conclusions: Preliminary data on ACDF cage size and fusion rates shows an inverse trend at C3-4, which was not seen at C4-7. A full cohort of patients is needed for multivariate analysis of the optimal cage size in ACDF.

Patient Care: We seek to identify if cage size effects fusion rates in the sub axial cervical spine. If cage size is a significant predictor of fusion rates, it would be more optimal to place a well sized graft rather than a larger graft that may over distract the cervical interspace.

Learning Objectives: By the conclusion of this segment, participants should be able to: 1) Describe the importance of sample size calculation to draw correct conclusions in surgical cohorts. 2) Discuss, in small groups, the role of multiple variables in ACDF fusion rates. 3) Identify an optimal cage size for ACDF.

References: 1) Benzel EC, Francis TB. In: Spine surgery: techniques, complication avoidance, and management, 3rd edn. Philadelphia, PA: Elsevier/Saunders, 2012. 2) Shriver MF, Lewis DJ, Kshettry VR, Rosenbaum BP, Benzel EC, Mroz TE: Pseudoarthrosis rates in anterior cervical discectomy and fusion: a meta-analysis. The Spine Journal 15:2016–2027, 2015