99. Radiographic assessment of fusion: a comparison of interbody spacers, following anterior cervical decompression and fusion

Abstract

BACKGROUND CONTEXT While fusion in the context of anterior cervical discectomy and fusion (ACDF) has been reported to be as high as 97% at 4 years postop, little is known about the bridging of trabecular bone, radiolucency and interspinous motion (ISM) as definitive criterion for assessing fusion on radiographic X-ray imaging. While there is no conclusive method for quantifying interbody fusion (IBF), there is curiosity about whether these parameters can prove a spacer type to have a higher fusion rate than another. PURPOSE To determine whether the use of interbody cages (IC) promotes higher fusion rates in ACDF using plain X-ray studies. STUDY DESIGN/SETTING Single-center retrospective analysis of prospective consecutive database of multilevel ACDF. PATIENT SAMPLE This study included 94 patients and 232 levels were evaluated with 1-year postop images from August 2015 to November 2018. OUTCOME MEASURES Interspinous motion, bridging trabecular bone, fusion grade. METHODS A total of 32 published papers were reviewed to select the three best parameters for assessing cervical fusion: the passage of trabecula through the implant, the presence of a radiolucent line interfacing implant and vertebral plate, and the range of motion between two adjacent spinous processes. Radiolucency and bridging trabecular bone (BTB) parameters were combined to categorize each ACDF level as fused (≥75% BTB present) or not fused ( RESULTS A total of 234 surgical levels from 92 patients were included (age: 62.5, 42.4% F, BMI: 29.87). Median number of levels fused by patient was 2 (IQR: 1). Overall, 28.2% of the patients had at least 1 level with incomplete fusion. Patients with incomplete fusion (by BTM or ISM method) had longer ACDF than those with complete fusion (median=3 vs 2, p=0.022). No associations were found between demographic, smoking status and fusion rate (all p > 0.1). When investigating fusion level by level, using the BTB and ISM methods respectively, no significant differences were found based on IC type (bone graft vs cage; p=.867 and .585), iliac bone vs local (p =.869, .796) or allograft. Lower fusion rate was noticed for C6-C7 (58.1%) compared to more proximal disc spaces (71.4% to 78.7%, p = 0.049). Combination of IC and graft material revealed no significant difference (bonegraft + local=71.8% vs cage + iliac=66.7%, p = 0.517). Multivariate analysis, controlling for demographic and smoking status, demonstrated that only location of the fusion was an independent predictor of incomplete fusion. CONCLUSIONS There was no superiority within the allograft and autograft respective groups or between spacers, using the ISM or BTB techniques. More than 2mm of motion on dynamic X-ray studies, BTB and radiolucent interface between implant and endplates are efficient quantifiable methods to measure fusion on X-ray studies, as they are easily accessible and affordable within the health care field. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.