Post-traumatic osteoarthritis (PTOA) is common following severe ankle injuries, such as tibial pilon intra-articular fractures (TP-IAFs). TP-IAFs often lead to chronic elevated contact stress during daily activities, with debilitating PTOA predictably following. Exploring the potential efficacy of post-operative carbon fiber custom dynamic orthoses (CDOs) in mitigating PTOA risk by reducing plantarflexor muscle force, joint reaction force (JRF), and corresponding contact stress is the topic of the research here reported. A multi-faceted approach was employed, combining multi-scale computational musculoskeletal (MSK) modeling and cadaveric testing.

Kinematic and kinetic gait data from nine healthy subjects ambulating under various CDO conditions that were collected as part of a separate study were used as modeling input. A sequential multi-scale computational MSK modeling framework, implemented in OpenSim, was used to simulate the influence of CDO rotational stiffness on ankle loading and contact mechanics. This was followed by the first-time implementation of concurrent MSK modeling for the ankle, implemented in OpenSim using the previously reported Concurrent Optimization of Muscle Activations and Kinematics (COMAK) algorithm, to improve simulation accuracy. The concurrent framework enforces dynamic consistency between whole-body kinematics and joint-level contact stress. As proof-of-concept, input data from one healthy subject were used to study the influence of varied CDO stiffness upon contact stress.

Complementary cadaveric testing was also conducted to study the influence of CDO rotational stiffness on tibiotalar joint mechanics. A servohydraulic load frame was used to test five cadaver ankles, with axial loading and pneumatic actuation of the Achilles tendon serving to quasistatically model multiple points in the stance phase of gait. Three CDO rotational stiffness conditions were tested. JRF and contact stresses were measured using a piezoresistive pressure sensor inserted into the tibiotalar joint. CDO use decreased JRF, with associated decreases in contact stress, but results varied based upon CDO characteristics.

Taken together, results obtained using this complementary experimental and computational modeling framework demonstrate that CDOs can effectively support ankle moments, thereby reducing plantarflexor muscle force, JRF, and contact stress during midstance to terminal stance in healthy walking. However, the relationship between CDO characteristics studied and the resulting amount of stress reduction underscore the need for personalized CDO prescription.