Multi-Plane Hybrid Fusion for Robust Knee MRI Diagnosis

Automated knee MRI analysis requires deep learning models that are not only accurate but also robust and clinically interpretable across different anatomical planes. In this study, we systematically evaluated four architectures: Baseline MRNet, Mamba, Hybrid, and a proposed Hybrid Fusion framework for ACL and meniscus tear classification using sagittal, coronal, and axial knee MRI from the MRNet dataset. Experiments were conducted using three independent random seeds, and performance was reported as mean ± standard deviation to assess both diagnostic accuracy and training stability. The proposed Hybrid Fusion framework achieved strong and competitive performance across most experimental settings. In ACL classification, the highest single-plane performance was obtained on sagittal MRI with an AUC of 0.976, while the three-plane Hybrid Fusion configuration achieved an AUC of 0.949, demonstrating the ability to integrate complementary anatomical information across multiple MRI planes. In meniscus classification, which remained more challenging across all architectures, the proposed framework achieved competitive performance with AUC values of 0.791 in sagittal and 0.826 in axial MRI. Interestingly, the Mamba-based architecture consistently demonstrated lower mean AUC values and higher variance compared with CNN-based approaches, suggesting that long-range sequential dependency modeling may provide limited benefit in plane-specific knee MRI analysis where diagnostically relevant findings are often localized within adjacent slices and anatomical regions. In contrast, CNN-based representations provided more stable feature learning under limited-data clinical settings. To improve interpretability and clinical reliability, Grad-CAM visualizations were additionally incorporated, demonstrating that the proposed framework focuses on anatomically relevant joint structures during decision making. Overall, the findings suggest that anatomically informed hybrid fusion strategies provide a promising and clinically meaningful direction for robust multi-plane knee MRI analysis.