ArticleJournal of clinical orthopaedics and trauma2026
Multicenter reliability study of the universal long bone nonunion classification.
Article in Journal of clinical orthopaedics and trauma, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
Background: A universal classification providing a clinically relevant and anatomically comprehensive framework for long bone nonunions has been recently introduced. This study aimed to evaluate its inter- and intra-observer reliability and compare its performance with the widely used Weber-Cech classification. Methods: This multicenter, three-stage validation study included 191 cases meeting the FDA definition of nonunion. Four expert raters participated. In Stage 1, cases were classified using existing systems: AO/OTA for anatomical location and Weber-Cech for biological type. In Stage 2, 133 eligible cases were independently classified using the Universal Long Bone Nonunion Classification (ULBNC) in two rounds, two weeks apart. Stage 3 involved refinement of classification criteria based on feedback and statistical analysis, followed by re-assessment of 90 cases. Inter-observer reliability was assessed using free-marginal Fleiss' kappa; intra-observer reliability using Cohen's kappa with linear weighting. Results: Substantial to almost perfect inter-observer agreement was observed for type classification (κ = 0.85), with the highest reliability in diaphyseal nonunions (κ = 0.90). Incorporating pathological mobility significantly improved agreement compared to Weber-Cech (κ = 0.38, p < 0.05). Periarticular nonunions showed substantial agreement (κ = 0.72). Group-level agreement improved from moderate (κ = 0.42-0.57) to substantial (κ = 0.79-0.82) after refining criteria. Subgroup agreement was excellent (κ = 0.89-1.00). Intra-observer reliability ranged from substantial to almost perfect across all levels. Conclusion: ULBNC is a reliable and reproducible classification system for long bone nonunions. Incorporation of clinical features-such as pathological mobility, alignment, and correction strategy-enhances its clinical utility and supports standardization in treatment and research.
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