Evaluation of the implantable force transducer for chronic tendon-force recordings

In vivo force measurements from tendons and ligaments have become an important technique to determine internal forces, joint loading, and mechanisms of neuromotor control. The most frequently used transducers for such force recordings were placed external to the target tissue. Because of space restrictions and the associated impingement artifacts, these external transducers cannot be used for force measurements in all tendons and ligaments. In these situations, transducers placed inside the target tissue have been used recently; however, the suitability and performance characteristics of these internal transducers have not been assessed systematically. The purpose of this study was to assess the suitability and performance characteristics of an internally placed force transducer which has been used previously. The results indicated that small angular displacements of the transducer within the target tissue, as well as small relative rotations of the corresponding bones, resulted in substantially changed transducer output for given externally applied loads. Also, the transducer output was found to depend on the rate of load application. It was concluded that, although the internal force transducer gave reliable signals within a given experiment, and thus, could be used to assess relative changes in tissue forces pre- and post-interventions, it would be difficult to use the transducer for the accurate determination of the actual tissue forces during unrestrained animal locomotion.