Investigators: Dennis R. Carter, PhD and Gary S. Beaupré, PhD Project Staff: Tishya A.L. Wren, PhD; Scott A. Yerby, PhD; R. Lane Smith, PhD; John E. Drace, MD; Loretta B. Chou, MD; and Garry E. Gold, MD Project Categories: Arthritis / Osteoporosis - 2000 Many individuals suffer from tendon injuries, especially injuries of the Achilles tendon, and these injuries are becoming increasingly common as the population ages and becomes more involved in health and fitness activities. We hypothesize that both acute and chronic tendon injuries result from the accumulation of loading-induced damage. The long term objective of this study is the prevention of tendon injuries through a basic understanding of damage accumulation in tendons and through the prediction and early detection of damage accumulation. This study examines the injury mechanism of damage accumulation in human tendons using multiple approaches including computational modeling, in vitro mechanical testing of cadaver tendons, and magnetic resonance (MR) imaging of tendons in vitro and in vivo. The specific aims of this study are: (1) to develop a computer model that can predict the amount of damage accumulated in a tendon; (2) to characterize loading-induced damage accumulation in human Achilles tendons in vitro using mechanical measures, histology, and MR imaging; and (3) to evaluate the feasibility of using MR imaging for the in vivo detection of damage accumulation in tendons. Findings to Date: Our models suggest that tensile strains are an important mechanical parameter governing tendon adaptation and injury. Our models demonstrate how tendons may adapt their mechanical properties in response to cyclic strains, thereby reducing high strains that might lead to injury in the absence of this adaptive response. Our models also indicate, however, that there may be physical limits on the extent to which a given tendon can adapt. A tendon that reaches these limits is at increased risk of injury since it will be exposed to higher strains. Our mechanical testing suggests that the Achilles tendon is one such tendon. We have shown that the Achilles tendon has material properties similar to other tendons even though it is exposed to much higher in vivo stresses. The Achilles tendon therefore experiences much higher strains than most other tendons. We believe this helps to explain the high incidence of Achilles tendon injuries. To improve the prevention of loading-induced injuries, we are imaging Achilles tendons in vivo using new MRI techniques which capture more signal from tendons than is obtained during conventional MRI. This additional signal may allow earlier detection of damage accumulation in tendons and therefore earlier intervention to prevent injury. Publications and Presentations: Wren TAL, Beaupré GS, Carter DR: A model for loading-dependent growth, development, and adaptation of tendons and ligaments. J Biomech 31:107-114, 1998. Wren TAL, Beaupré GS, Carter DR: Computational predictions of tendon and ligament adaptation to exercise and immobilization. In Press J Rehab R&D, 37(2), 2000. Wren TAL, Yerby SA, Beaupré GS, Carter DR: The Achilles tendon does not have high mechanical properties despite high in vivo loading. Trans Orthop Res Soc, 25:188, 2000. Wren TAL, Yerby SA, Beaupré GS, Carter DR: Interpretation of calcaneus DXA measurements in the assessment of osteopenia and fracture risk. Accepted to the Journal of Bone and Mineral Research. Wren TAL, Yerby SA, Beaupré GS, Carter DR: Influence of bone mineral density, age, and strain rate on the failure mode of human Achilles tendons. Submitted to the American Journal of Sports Medicine. Wren TAL, Yerby SA, Beaupré GS, Carter DR: Re-interpreting calcaneus DXA measurements to assess osteopenia and fracture risk. Trans Orthop Res Soc, 25:757, 2000. Wren TAL, Beaupré GS, Carter DR: Mechanobiology of tendon adaptation to compressive loading through fibrocartilaginous metaplasia. J Rehab Res Dev, 37:135-151, 2000. Wren TAL, Beaupré GS, Carter DR: Tendon and ligament adaptation to exercise, immobilization, and remobilization. J Rehab Res Dev, 37:217-224, 2000. Funding Source: VA RR&D Merit Review |
