Upon microscopic evaluation at low and high magnification, no abnormality or structural change could be identified in the arrangement of the collagen in the patellar tendon complexes (Fig. 2). There was no evidence of vascular changes or inflammatory cells. The two sides appeared identical histologically.
Several different surgical techniques have been described for chronic tendon problems. Debridement of damaged tissue is sometimes the primary goal (17,24). One technique, longitudinal tenotomy, has a primary goal of creating bleeding within the tendon (17,20). Blood is a rich source of growth factors, which can stimulate fibrocyte migration and activation (8,9). Additionally, there are factors in blood, such as endothelial cell growth factor, that can help induce neovascular ingrowth (12,21). Clotted blood has been used both experimentally and clinically to stimulate fibrous tissue healing in the meniscus model (2,3,26,28). We found one published article using blood products (fibrin glue) to augment the repair of Achilles tendon ruptures. In a poster exhibit, Hansen et al. (7) reported using autologous blood injection on 22 patients with lateral epicondylitis. They had all failed conservative care. Their success rate was 86% with no apparent complications. Other forms of injection therapy are being used clinically. There is anecdotal evidence that injecting dextrose-phenol solution (prolotherapy) may be of help in treating chronic tendon problems in addition to other areas of chronic pain (27).
The purpose of this study was to identify long-term safety of blood injection. As such, we did not look at the early inflammatory stages of soft tissue healing, including tenocyte activation and collagen deposition. By 6 wk, the soft tissue healing process would have been in the maturation and remodeling stage. This would explain the normal histology. This maturation of the collagen would have continued between 6 and 12 wk (17). We hypothesize this collagen maturation explains the increase in strength between 6 and 12 wk.
The objective of this study was to assess the safety and biomechanical and histological effects of autologous blood injection on animal tendons. We found that injecting blood directly into normal tendons caused no apparent harm. At 6 and 12 wk after the injection, there was no difference in the histology from normal tendon tissue. Biomechanically, at 6 wk there was an early trend for increased stiffness and strength; however, the tendons were statistically stronger (15.5%) at 12 wk after blood injection compared with controls without further increases stiffness. Our data suggest that further evaluation of injecting blood into a chronically nonhealing tendon would be safe.
This project was funded by a grant from Mark Taylor, M.D. We are grateful to Ms. Suzanne Smith for her assistance with manuscript preparation, Mr. Vince Kish for performing the mechanical tests, Gerry Hobbs, Ph.D., Department of Statistics, for statistical support, and Patsy Willard and Dr. Choudari Kommineni, NIOSH of Morgantown, WV, for assistance with the histological preparation and analysis.
Address for correspondence: Timothy L. Norman, Ph.D., Department of Orthopedics, P.O. Box 9196 Health Sciences Center, West Virginia University, Morgantown, WV 26506-9196; E-mail: firstname.lastname@example.org.
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