Flex-Knee: A Low-Cost Passive Haptic Model for Injury Assessment Training

We present the design and development of a lowcost ($ 400 CAD), scalable, and modular haptic knee model to support training in manual musculoskeletal assessments of injuries. Our model aims to help inexperienced practitioners learn the Valgus test, a clinical test to assess medial collateral ligament (MCL) injuries. The valgus test is typically taught on classmates or patients, which limits available training time and exposure to anatomical diversity and injury conditions. Designed with a certified clinician, our model uses a generic mechanical joint, silicone approximating human skin look and feel, a metamaterials-based approach to reproduce MCL injuries, and pressure sensors to capture user-applied forces. We evaluated the model in three stages: internal calibration with our collaborating clinician to configure it for four conditions (healthy, grades 1-3) using the staircase procedure; acceptance testing with 6 additional clinicians; and a showcase with students in a kinesiology class. Certified professionals distinguished healthy, partially-torn, and fully-torn MCLs with sensitivities of 0.83, 0.75, and 1.00; students also recognized these differences, though refinements are needed for grades 1 and 2. Participants praised the model's skin texture and shape. This work highlights the potential of low-cost haptic simulators to deliver standardized and repeatable training experiences.