quaternion

Sufficient axial rotation range of motion is critical for performing such simple tasks as reaching into your back pocket (internal axial rotation), or combing your hair (external axial rotation). I previously described how axial rotation can be measured in a physically meaningful manner. In this project, I explore how scapular motion can generate axial rotation. This mechanism has not been previously described in biomechanics literature and provides a more comprehensive view of shoulder motion.

For long bones, axial rotation is defined as a rotation around the axis running through the shaft of the bone. Sufficient axial rotation range of motion is critical for performing such simple tasks as reaching into your back pocket (internal axial rotation), or combing your hair (external axial rotation). Restoration of axial rotation range of motion is a critical consideration in shoulder replacement surgery and upper extremity prosthetic implant design. Yet, there is no consensus in the biomechanics community on how to measure axial rotation in a physically meaningful manner. This project 1) measures axial rotation in a physically meaningful manner for a cohort of 20 subjects performing arm elevation and rotation, 2) describes why commonly utilized techniques incorrectly measure axial rotation, 3) provides a JavaScript webapp for visualizing and quantifying physiologic arm motion (shoulder kinematics).