Real-Time Tendon Strain Estimation of Rotator-Cuff Muscles during Robotic-Assisted Rehabilitation

In this research, we propose a novel method to estimate and monitor rotator cuff tendon strains during active robotic-assisted rehabilitation. This is a significant step forward from our previous work which estimated these tendon strains during passive exercises (i.e., no muscle activity). Physiotherapists adopt a cautious approach to rehabilitation treatment to prevent (re-) injury given the limited available information about the shoulder's internal condition. By leveraging a robotic device and a musculoskeletal model, our approach provides quantitative information on the risk of re-injury by monitoring the strains of the rotator cuff tendons during shoulder movements with the application of external loads. Muscle strains depend on the shoulder kinematic state and muscle activations, which makes it crucial to obtain physiologically realistic joint kinematics to estimate real-time muscle function. To obtain the strains, we utilize our muscle redundancy solver that incorporates constraints on model accelerations, the glenohumeral joint reaction forces, and active muscle dynamics. Using this algorithm along with force and pose data from a collaborative robotic arm, we demonstrate the ability to update our tendon strain estimates based on muscle activation during robotic-assisted rehabilitation exercises. The findings of our research pave the way for establishing improved therapy that considers the risk of injury to individual muscles and explores a broader and more personalized range of motion. By providing physiotherapists with valuable quantitative information on rotator cuff tendon strains, our method empowers them to optimize rehabilitation protocols and deliver more personalized and effective care. In addition, the system and method presented here comprise a tool capable of offering new insights into the relationship between the rotator cuff muscles, external forces, and shoulder kinematics.