In vivo measurement of ligament/tendon strains and forces: a review.

Accurate and precise measurements of ligament and tendon biomechanics in living humans are needed to better understand function and injury and to optimize treatment. The complex structure and loadings of these internal soft tissues makes in vivo measurements difficult to obtain. A noninvasive method that can be used in the field during normal unrestricted activity would be optimal, though this goal has yet to be achieved. Instrumentation has been developed to directly measure the strains and forces in human ligaments and tendons in vivo. The current strain measurement techniques include devices that attach directly to the tissue (e.g. Differential Variable Reluctance Transducer). The current force measurement techniques include the Buckle transducer, fiber optic sensors, and other implantable force probes that are placed in or around the mid-substance of the tissue. Noninvasive methods (e.g. ultrasonography, magnetic resonance imaging) have recently emerged to measure soft tissue strains and they show considerable promise. In this paper, the different techniques are reviewed with an emphasis on their advantages, limitations, and hence clinical relevance. These must be clearly understood in order to interpret the data reported in the literature that were obtained from such technologies, to design experiments that utilize these technologies, or to improve upon these technologies.