Beyond flexibility: Unraveling the mechanics and assessment of digital stiffness

Digital stiffness, defined as reduced articular mobility due to impaired tissue plane gliding, contrasts with rigidity and mechanical resistance to deformation. Viscoelastic tissue properties, primarily determined by collagen and elastin, govern the response to force, while edema exacerbates stiffness by increasing interstitial fluid resistance. Accurate assessment is critical for treatment selection. Subjective end-feel evaluation is limited, while objective tools such as torque range of motion (TROM) and torque-angle curve (TAC) analysis provide reliable, quantitative insights into tissue mechanics. Understanding viscoelastic and edema-related contributions enables the development of tailored interventions, thereby improving rehabilitation outcomes. Future research should integrate advanced technologies for real-time monitoring. This report aimed to explore the biomechanical principles underlying digital stiffness, differentiate it from rigidity, and highlight the role of viscoelastic properties and edema in movement restriction. By discussing both subjective and objective assessment methods, this report highlights the importance of quantitative tools, such as TROM and TAC analysis, in enhancing diagnostic accuracy and rehabilitation outcomes.