Ultrasound Imaging of Wrist Muscle Moment Arms: A Phantom Experiment and In Vivo Case Study

Jonathan Charles

Authors:  Jonathan P. Charles, Jennifer A. Nichols, Ph.D.

Faculty Mentor:  Jennifer A. Nichols, Ph.D.

College:  Herbert Wertheim College of Engineering


Joints in the human body utilize torque to create movement, where a force F acts at a distance, r, from a rotation point. In biomechanics, F is generated by muscles acting on the joint, and r is the distance between the joint’s center of rotation (COR) and the muscle line of action. The distance r is also known as a geometric moment arm (GMA). Changes in GMAs may be correlated with loss of muscle and hand function in people due to aging, injury, or pathology. To comprehensively evaluate GMAs, efficient and inexpensive in vivo measurement methods are needed. This study explores whether ultrasound is valid for quantifying the GMA of muscles crossing the wrist. The capitate was defined as the wrist’s COR due to its central location within the joint, and the measured GMA was defined between this COR and the flexor digitorum superficialis (FDS) muscle. An agar-gel phantom study determined if distance measurements from 20 ultrasound images were accurate compared to four baseline distances. A subsequent in vivo case study explored whether ultrasound could measure GMAs within a human wrist. Both studies returned data that exhibited low measurement variability over consecutive days and provided proof that ultrasound can accurately measure wrist GMAs.

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5 Responses
  1. Jonathan P. Charles

    Hey everyone! Thanks for taking the time to stop by if you did, and please leave any questions or comments here and I’ll do my best to get back to everyone. Stay healthy!

  2. Catherine Martinez

    Hello, this is very interesting!

    As someone that is not in the medical field, I do not know – why would you want to image and measure human wrist GMAs? Does this pertain to being able to determine if someone has a broken bone in their wrist?


    1. Jonathan P. Charles

      Hi Catherine!

      So this project is the foundational work needed for a larger grant through our lab – essentially we are looking to use wrist GMAs to see if changes in the length of certain GMAs in your wrist can be correlated, or linked to wrist pathologies (deformities, carpal tunnel etc), aging (why do you lose hand and wrist function/strength as you age? Could it be due to your GMAs increasing/decreasing with time), or post-operational trauma (wrist surgery).

      So the ultimate goal is for a clinician to use ultrasound to measure the GMAs of their patient, and see if their GMA lengths correspond to issues that patient has been having with their wrist joint.

      Thanks for the question! I hope that cleared some things up.