Measurements of the Static Friction Coefficient Between Bone and Muscle Tissues

This study aimed at measuring the static coefficient of friction $(μ)$ between bone and skeletal muscle tissues in order to support finite element (FE) modeling in orthopaedic and rehabilitation research, where such contact conditions need to be defined. A custom-made friction meter (FM) that employs the load cell and motion-controlled loading arm of a materials testing machine was designed for this study. The FM was used to measure $μ$ between fresh ulna bones and extensor muscles surrounding the ulna, which were harvested from five young adult pigs. Mean bone-muscle $μ$ were between 0.36 and 0.29, decreased with the increase in loads applied on the bone $(p<0.05)$ and plateaued at a mean $∼0.3$ for loads exceeding 4 N. Hence, for FE modeling of bone-muscle contacts through which loads with magnitudes of kgs to 10s-of-kgs are transferred, assuming $μ$ of $∼0.3$ appears to be appropriate.