A validated SSAM-FEA framework for the rat knee reproduces varus-induced contact redistribution in a...

To characterize tibiofemoral contact mechanics in a rat knee under progressive varus loading, evaluate whether a statistical shape and appearance model (SSAM) can reproduce specimen-specific biomechanical behavior, and assess whether this meniscus-deficient computational-experimental framework can serve as a controlled preclinical platform for studying load redistribution.

Three-dimensional rat knee models were reconstructed from micro-CT images of 10 hind limbs from 5 male Sprague Dawley rats. Each limb model was alternately designated as the target, while the remaining limb models served as the training dataset for principal component analysis (PCA) to develop the SSAM. Finite element analysis (FEA) was used to assess maximum contact pressure and contact area in the medial and lateral compartments under simulated standing posture at 0%, 50%, and 100% varus loading. Because the finite element model did not include the menisci, experimental validation was performed in a matched meniscus-deficient setting using a custom biomechanical testing apparatus. Analysis of variance (ANOVA) was used to compare biomechanical outcomes among loading conditions and model types.

Both FEA and experimental results demonstrated consistent patterns in maximum contact pressure and contact area across varus loading levels. Compared with 0% varus, 50% and 100% varus loading increased medial maximum contact pressure and contact area by up to 0.55 MPa and 1.28 mm², respectively. The lateral compartment showed reductions, with maximum decreases of 0.43 MPa and 1.76 mm². No statistically significant differences were detected between the specimen-specific FEA models and the corresponding SSAM-predicted models across the tested loading conditions (P > 0.05).

Progressive varus loading shifted contact mechanics toward the medial compartment in both FEA and experimental tests, and the SSAM reproduced these trends with good agreement to specimen-specific models. These findings support the use of the present SSAM-FEA framework as a controlled biomechanical tool for investigating varus-induced contact redistribution in a rat meniscus-deficient knee. However, because the model excludes the menisci, uses simplified material assumptions, and applies static loading, the results should be interpreted primarily within a post-meniscectomy biomechanical context rather than as a direct surrogate for naturally occurring human knee osteoarthritis.