The Effects of Aging, Antiinflammatory Drugs, and Ultrasound on the In Vitro Response of Tendon Tissue.

The Effects of Aging, Antiinflammatory Drugs, and Ultrasound on the In Vitro Response of Tendon Tissue

Almekinders LC, Deol G (Department of Orthopedic Surgery, Sports Medicine Section, University of North Carolina School of Medicine, Chapel Hill, NC), Am J Sports Med. 1999;27:417-421.

Chronic tendon injuries, such as microtears, are commonly associated with repetitive use of tendons, particularly in sports activities, and are expected to result in a local inflammatory response in tendons. According to the authors, histologic investigations of such cases, however, do not reveal definitive signs of tendinitis; rather, they suggest a degenerative process in the chronically injured tendons, termed tendinosis. The authors' review of the sports medicine literature suggests that aging should be considered an important factor in the etiology of tendinosis, in addition to the generally accepted factor of "repetitive mechanical overload." The authors investigated the role of aging and certain treatments on rat patellar tendon specimens in vitro, and they suggested that aging was associated with a decline in the metabolic activity of the tendons.

In part 1 of the study, the role of aging was examined in 24 male Sprague-Dawley rats (aged 21 days to 6 months). In part 2, the effect of indomethacin (a nonsteroidal anti-inflammatory drug), dexamethasone (a steroidal antiinflammatory drug), or ultrasound on the tendon's metabolic activity was investigated in another 24 rats, aged 4 to 6 months. In part 1, the patellar tendons were removed from 3 groups of rats (8 per group) under anesthesia, each tendon was cut in half longitudinally, and each half was incubated separately in specific culture media for 12, 24, or 48 hours at 37 [degrees] C. Subsequently, the DNA and protein synthesis by the tendon specimens was determined by the uptake of radioactive thymidine and proline, respectively. In part 2, using the same in vitro model, tendon specimens (n = 16 for each group) from the rats that were 4 to 6 months old were incubated (1) in a controlled culture medium, (2) in a medium containing either low-dose or high-dose indomethacin (5 or 50 [micro]mol, respectively) or low-dose or high-dose dexamethasone (0.5 or 5 [micro]mol, respectively), or (3) in a medium exposed to 50% pulsed ultrasound for 20 minutes. The control group for the ultrasound category consisted of specimens exposed to a sham ultrasound treatment.

In part 1, the analyzed data demonstrated that, with increasing age, there was a significant decline in the incorporation rate of both thymidine and proline by the tendon specimens. The results from part 2, however, indicated that neither the proline nor the thymidine uptake by the aging tendon specimens was significantly altered in the presence of indomethacin. Conversely, dexamethasone at higher concentrations caused a significant decline in the thymidine, but not the proline, uptake by the specimens. Also, the ultrasound treatment did not alter the rate of uptake of either thymidine or proline by the specimens, as compared with the control groups.

According to the authors, the data from this study support the hypothesis that aging is associated with a decline in the synthesis of DNA and protein by the tendon in vitro. The steroidal drug, dexamethasone, at high concentration had a small but significant negative effect on the tendon's metabolic activity. Indomethacin and ultrasound treatments had no such negative effect. The authors argued that extensive in vivo and clinical studies are needed to determine whether similar effects are operative in real-life situations.

Kamran Tavakol, PT, PhD Howard University Washington, DC