The Knee Loading Apparatus: Axial, Anterior, and Compressive Loading With Magnetic Resonance Imaging

Abstract

When magnetic resonance (MR) images are collected while applying a load to the knee joint, additional information about the joint response to loading can be acquired such as cartilage deformation, whole joint and ligament stiffness, or physiological estimates of weight-bearing joint positions. To allow load application and controlled lower limb movement in supine MR imaging, the knee loading apparatus (KLA) was designed to apply safe and physiologically relevant controlled loads to the knee joint, position the knee through a range of flexion angles, and operate successfully in a magnetic environment. The KLA is composed of three main components: a remotely operated custom hydraulic loading system, a logic system that interfaces with the user, and modular non ferromagnetic positioning frames. Three positioning frames are presented for application to anterior tibial loading, tibiofemoral compression, and patellofemoral compression at multiple knee flexion angles. This system design makes improvements over current devices. Safe remotely applied loads (hydraulic loading system) can be applied by either subject or tester and in multiple locations simultaneously. Additionally, loads can be altered at any time in a continuous manner without electrical interference. Transportability was improved due to a smaller footprint. The KLA has the flexibility to attach any positioning frame with many possible loading scenarios without changing the loading mechanism or logic systems, and allows force values over time to be output rather than estimated. An evaluation of the load repeatability (within 7% of applied load) and accuracy (0.5–14.9%) demonstrates the feasibility of this design for investigations into in vivo knee joint responses to loading.