A novel technique to measure active tendon forces: application to the subscapularis tendon.

This paper describes the design and use of a novel system for quantification of active tendon forces. An arthroscopically implantable force probe (AIFP) was inserted arthroscopically into the subscapularis tendon of the shoulder in vivo. The output response of this device was calibrated in situ with known forces applied to the tendon using an arthroscopic technique. On recovery of motor control following interscalene regional anaesthesia, the force within the tendon during active muscle contraction was measured. The AIFP was then retrieved through an arthroscopic portal. The technique showed that the subscapularis may produce forces of 250 N during maximum internal rotation of the shoulder.