Tribology at Your Fingertips: Frictional Forces in Tendon Repair

Despite recent advances, tendon repair often results in a finger that does not move normally. The goal of my research has been to improve the results of tendon repair by addressing two interrelated issues:

• Wolff's law of Soft Tissue: The effect of loading on wound healing and soft tissue material properties. In tendon, this especially affects the nature of the rehabilitation protocol, timing of initiation of motion, and timing and gradation of loading of the repair.
• Tendon Gliding Beneath Pulleys: The effect of tendon repair and lubrication on tendon gliding.

These two factors interact, as the ease of gliding will dictate how well the tendon moves under loading, and how much loading is needed to initiate motion, while the amount of loading needed to initiate motion will affect the strength requirements of the tendon repair.

One of our NIH-funded research projects is addressing these factors. Past research quantified the mechanics and kinematics of the tendon-pulley interaction, identified structural differences within tendon based on the loading environment, and also showed that these environments differed in the rate and quality of healing after similar injury. This was followed by work that tested the tribology and material properties of various tendon repair constructs, first in vitro and then in vivo. In addition, we compared the relative motion induced by various tendon gliding rehabilitation regimens in vivo. We noted that low friction repairs, combined with rehabilitation that provided better gliding, gave the best results in terms of tendon healing and final digit motion. Our current research is investigating the impact of more complex gliding regimens on tendon healing, wich include the timed augmentation of gliding with new therapies and the development of strong, low friction tendon repairs. We are currently investigating the effect of tissue engineering strategies on tendon healing and the reduction of adhesions. Specifically, we are investigating the fixation of lubricating substances such as hyaluronan and lubricin on the surface of tendon repairs and tendon grafts. Future research will investigate the effect of gene therapy on tendon healing, both in vivo and in cell and tissue cultures.

Such therapies may also have an effect on other tendon-associated pathologies where impaired tendon gliding appears to be a factor, such as carpal tunnel syndrome, and adhesions complicating tendon grafting procedures. Therefore, we are also pursuing similar strategies to address these other clinical problems as well. Finally, we are investigating the use of ultrasound for the early diagnosis of tendon adhesions and carpal tunnel syndrome.

Most recently, we have begun to investigate the possibility that tendon friction may be one of the precipitating factors in carpal tunnel syndrome (CTS). We have received a second NIH grant to study this pehenomenon more closely, and with it have developed an animal model to investigate the etiology of CTS.