Biomechanical Assistance Equipment for Surgical Tendon Transfer

Cyth Systems was honored to be selected by the UC San Diego VA Medical Center to help the Department of Orthopedics and Bioengineering develop a device to assist with both training doctors and assisting during surgery to reattach the Brachioradialis tendon during arm surgeries. The results were published in numerous industry publications including the Journal of Hand Surgery when the system matured from training surgeons to being used in cadaver tests and eventually patient surgeries.

From the publication: "One of the most critical steps in performing a surgical tendon transfer, is the tensioning of the donor's muscle as it is reattached to the recipient site. Correct tensioning of a transferred muscle is critical for proper muscle force production, for use of stenosis to aid function, and to provide the necessary appearance that accompanies the transfer. Unfortunately, for most surgeons proper tensioning of muscle-tendon units remains an art. A scientific rationale for proper tensioning of a transfer requires information such as the normal operating range of the muscle, the passive mechanical properties of the muscle, and the muscle sarcomere length at the time of transfer. In general, none of these parameters is known for muscles of the upper extremity. In an attempt to provide criteria for the tensioning procedure numerous recommendations for proper tensioning have been proposed that are based on the feel of the muscle, the excursion of the muscle determined intraoperatively, the joint posture, or a combination of all of these. Almost invariably these recommendations are based on assumptions regarding the relationship between a muscle’s feel (ie, its passive tension sensed intraoperatively) and its function, which—with few exceptions —is never actually measured... Although [the] active sarcomere length-tension relationship is extremely well founded the relationship between passive muscle tension and active force generation is understood poorly."

Cyth designed a created a machine using a motor in position control with torque feedback to record the force of the tendon as it was pulled by the motor, and the force versus length was recorded. The motor was moved using a non-linear acceleration pattern to maximize and study the sarcomere reaction to speed of motion if desired. The data was collected from the motor using LabVIEW over an RS232 connection, and the measurements recorded into data files. In early trials, the system was reversed and put into torque control mode so that the torque could be increased or decreased as the motor was pulled upon. Therefore one of three modes could be utilized: 1) The system could record the unique properties of a tendon, 2) the system could be used to "playback" the tension as a doctor pulled on a string connected to the motor, and 3) the system would self-tension the optimal distance at the peak of tension.

The system has been used for quite some time and taken on some variations in order to grow from one research experiment to another. Experiments performed at numerous conferences taught the industry more about the properties of the tendons and muscles of the arm and went on to influence hand surgeries such as carpal tunnel and another injury repair to be more effective.

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