Radiographic Assessment of Successful Lumbar Spinal Fusion: A Systematic Review of Fusion Criteria in Randomized Trials

Study Type: Systematic Scoping Review. Introduction: Radiographic assessment is crucial for diagnosing symptomatic pseudarthrosis and evaluating spinal fusion outcomes, yet no consensus exists on defining successful lumbar fusion. This scoping review presents criteria for imaging-based assessment after posterolateral and interbody lumbar fusion, aiming to guide consistent evaluation methods. Methods: Following PRISMA guidelines, a comprehensive search of Medline, Embase, and Scopus identified eligible randomized controlled trials and Federal Drug Administration clinical trials involving lumbar fusion. Studies on revision surgeries, non-lumbar fusions, adult spinal deformity, traumatic fractures, tumors, infections, or lacking defined fusion assessment methods were excluded. Data extraction focused on classification and descriptive systems of fusion evaluation, analyzing parameters such as bony bridging, angular motion, translation, hardware failure, cage migration, radiolucency, and cleft within the fusion mass. Results: A total of 142 articles (1995-2024) were reviewed. Computerized tomography was the most common imaging modality (102, 71.8%), followed by static (96, 67.6%) and dynamic radiographs (88, 62%). Descriptive criteria were used in 108 studies (76.1%) and classification systems in 47 (33.1%). Interbody fusion was assessed in 90 articles (63.4%) and posterolateral fusion in 68 (47.9%). Bony bridging continuity was the most reported descriptive criterion (105, 73.9%), followed by angular motion (72, 50.7%) and translation (43, 30.3%). Radiolucency was reported around the cage (31, 21.8%), pedicle screws (17, 11.9%), and within the fusion mass (36, 25.4%) to describe nonunion. Common classification systems included Bridwell (10 studies), Brantigan (9), and Lenke (9). Conclusions: This scoping review highlights the variability in lumbar fusion assessment across RCTs and FDA trials. Over time, assessment methods have evolved from static radiographs to greater use of dynamic imaging and classification systems in the mid-2000s, with CT emerging as the dominant modality in the past decade. Despite these advancements, fusion assessment criteria remain inconsistent across studies.