Effects of a Medial Knee Unloading Implant on Tibiofemoral Joint Mechanics During Walking

The Atlas™ unicompartmental knee system is a second‐generation extra‐articular unloading implant for patients with mild to moderate medial knee osteoarthritis. The technology acts to reduce a portion of the weight‐bearing load exerted on the medial knee during physical activity thereby, reducing the mechanical stress imposed on a degenerative joint. The purpose of the present study was to evaluate the effects of the Atlas™ on tibiofemoral joint mechanics during walking. A computer‐aided design assembly of the Atlas™ was virtually implanted on the medial aspect of a previously validated finite element tibiofemoral joint model. Data for knee joint forces and moments from an anthropometrically matched male were applied to the model to quasi‐statically simulate the stance phase of gait. Predictions of tibiofemoral joint mechanics were computed pre‐ and post‐virtual implantation of the Atlas™. Compressive force in the medial tibiofemoral compartment was reduced by a mean of 53%, resulting in the decrement of mean cartilage–cartilage and cartilage–meniscus von Mises stress by 31% and 32%, respectively. The Atlas™ was not predicted to transfer net loading to the lateral compartment. The tibiofemoral joint model exhibited less internal–external rotation and anterior–posterior translation post‐Atlas™, indicating a change in the kinematic environment of the knee. From a biomechanical perspective, extra‐articular joint unloading may serve as a treatment option for patients recalcitrant to conservative care. Evaluation of mechanical changes in the tibiofemoral joint demonstrate the potential treatment mechanism of the Atlas™, in accordance with the available clinical data. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2149–2156, 2019