From theory to tissue: Constitutive modeling and underlying assumptions in cartilage biomechanics

Articular cartilage is a charged, multiphasic tissue whose mechanical response emerges from coupled solid–fluid–ion interactions. Modeling this complexity remains a major challenge in computational biomechanics. This scoping review maps cartilage constitutive models and provides a structured, mechanics-informed appraisal of their physiological representation, constitutive assumptions, and numerical implementation practices. Database searches (1995–2025) identified 84 eligible studies. Models were classified into monophasic, biphasic, triphasic, and other constitutive families. To systematically assess modeling assumptions, a mechanics-oriented appraisal framework structured around five evaluation axes (M1–M5) was applied, addressing constitutive closure, dissipative mechanisms, internal physical admissibility constraints, model–problem coherence, and verification/validation practices. Biphasic models dominate current practice, whereas triphasic formulations better capture osmotic and electrochemical effects. Physiological features were represented unevenly across studies: stress relaxation (86.9%), fluid exudation (69.0%), strain-dependent permeability (48.8%), zonal anisotropy (51.2%), and electrochemical coupling (16.7%). Degeneration mechanisms were incorporated in only 23.8% of studies. Across the corpus, most models demonstrated strong model–problem coherence but frequently lacked explicit admissibility constraints and robust verification and validation practices. Numerical transparency was also limited: although software platforms were often reported, solver configuration, convergence criteria, and computational cost were rarely specified. These findings highlight a persistent gap between constitutive sophistication and empirical validation. Advancing predictive cartilage modeling will require closer integration between constitutive formulation, experimental validation, parameter identifiability, and reproducible numerical implementation. • Scoping review of 84 cartilage constitutive models (1995–2025). • Mechanics-oriented appraisal grid covering consistency, fidelity, robustness, adequacy, validation. • Quantifies key phenomena: relaxation, exudation, anisotropy, permeability. • Identifies major gaps in reporting of solvers, convergence and runtimes.