Multicenter evaluation of four large language models for automated spine imaging diagnosis.

Accurate interpretation of spine imaging is essential for clinical decision-making, yet the diagnostic potential of large language models (LLMs) for radiological report analysis remains inadequately evaluated in terms of sample size, multi-model comparison, reproducibility, and cross-institutional generalisability. Here, we conducted a multicentre cohort study using 20,277 authentic clinical spine radiological reports from three teaching hospitals in China, systematically comparing the diagnostic performance, output consistency, and generalisability of four LLMs-GPT-4o, Claude-4, Qwen-3 Max, and DeepSeek-V3.1-across nine modality-region combinations under two input modes (with-option and without-option). All models showed high overall diagnostic performance, with specificity exceeding 90% and negative predictive value exceeding 96%. Cross-institutional validation demonstrated stable recall generalisability, with recall coefficients of variation ranging from 0.7% to 5.0%. However, performance was uneven across the disease spectrum: for low-prevalence conditions, precision declined by 19-42 percentage points, indicating a persistent long-tail diagnostic deficit. Input mode and prompt formulation also produced model-specific shifts in diagnostic behaviour. These findings suggest that LLMs may support report-based spine imaging diagnosis as clinical assistive tools, but deployment should account for disease prevalence, prompt sensitivity, and the need for domain-specific optimisation.