A Magnetic Resonance Imaging–Compatible Device to Perform In Vivo Anterior Knee Joint Loading

Abstract

Context: Greater anterior knee laxity (AKL) is associated with impaired sensory input and decreased functional knee stability. As functional magnetic resonance imaging (MRI) is the gold standard for understanding brain function, methods to load the anterior cruciate ligament in the MRI environment could further our understanding of the ligament’s sensory role in knee joint stability. Objective: To design and validate an MRI-compatible anterior knee joint loading device. Design: Descriptive laboratory study. Setting: University laboratory study. Participants: Sixteen healthy and physically active females participated (age = 23.4 [3.7] y; mass = 64.4 [8.4] kg). Interventions: The AKL was assessed by a commercially available arthrometer. The AKL was also assessed with a custom-made, MRI-compatible device that produced anterior knee joint loading in a manner similar to the commercial arthrometer while obtaining dynamic structural MRI data. Main Outcome Measurements: The AKL (in millimeters) at 133 N of loading was assessed with the commercial knee arthrometer. Anterior displacement of the tibia relative to the femur obtained at 133 N of loading was measured from dynamic MRI data obtained during usage of the custom device. Pearson correlations were used to examine relationships between the 2 measures. The 95% limits of agreement compared the absolute differences between the 2 devices. Results: There was a 3.2-mm systematic difference between AKL (6.3 [1.6] mm) and anterior tibial translation (3.2 [1.0] mm) measures. There was a significant positive correlation between values obtained from the commercial arthrometer and the MRI-compatible device values (r = .553, P = .026). Conclusions: While systematic differences were observed, the MRI-compatible anterior knee joint loading device anteriorly translated the tibia relative to the femur in a similar manner to a commercial arthrometer design to stress the anterior cruciate ligament. Such a device may be beneficial in future functional magnetic resonance imaging study of anterior cruciate ligament mechanoreception.