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The purpose of this study was to compare selected rabbit tendons and ligaments morphologically and biochemically. Five representative structures from each of six age-and sex-matched rabbits were compared. Biochemical analyses included total collagen, reducible collagen cross-links, quantitative collagen typing, DNA, and glycosaminoglycans. Histological and chemical differences were demonstrated between the tendons and the ligaments. Smaller differences were also found between the individual ligaments (collateral and cruciate) and between the two tendons (patellar and Achilles) that were examined. These findings suggest that ligaments are more metabolically active than tendons, having more plump cellular nuclei, higher DNA content, larger amounts of reducible cross-links, and the presence of more type I11 collagen, as compared with tendons. They also contain slightly less total collagen than tendons and more glycosaminoglycans. We conclude that the tendons and ligaments studied have unique histological and biochemical characteristics, despite their gross similarities. Relatively increased metabolic activity in ligaments, implied by our findings, may be species specific, age related (transient), or may truly represent a structural expression of functional need for more rapid adaptation. Further investigation of other similarities or differences between particular ligaments (or tendons) is indicated, and attention is directed toward the importance of such variables in development of models for tendon and ligament studies. Key Words: Tendon-Ligament-DNA concentration-Collagen cross-linking-Glycosaminoglycans-Comparison.Chronic knee ligament instabilities are most commonly treated by functional replacement with other periarticular structures, mainly tendons. These replacements have included the use of various parts of the quadriceps tendon mechanism (1 1,20,28), pes anserinus (39), semitendinosis tendon (8,36), biceps femoris tendon (38), gracilis tendon (43), iliotibial bank (17,31,34), and lengths of fascia lata twisted or rolled into tendonlike forms (24,25).

With the known action of the matrix metalloproteinases and tissue inhibitors of metalloproteinase in extra-cellular matrix remodeling, these findings suggest that their roles in remodeling of rotator cuff tears should be further investigated.

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Elastic bandages are often used to treat musculoskeletal disorders, even though there is little scientific evidence currently to support this generalized practice. We tested the hypothesis that elastic bandages improve proprioception of the bandaged joint during their use, and that this benefit was more than temporary. The uninjured human knee was used as a model. Fifty-four volunteers (54 knees), aged 22 to 40 years, were asked to identify a prior set joint angle as their knee was passively extended. Each knee was tested without the elastic bandage, immediately after bandage application, after 1 hour of bandage wear, and finally after removal of the bandage. Results showed that elastic bandages significantly improved knee joint proprioception in the uninjured knee during the entire interval of their use (mean decrease in inaccuracy of 1.0 degree, equivalent to 25% improvement, P < 0.05), and that this benefit was lost when the bandage was removed. The magnitude of the improvement, or the potential beneficial effect of the bandage, was inversely related to the participant's inherent knee proprioceptive ability, which was demonstrated in the test group before the initial application of the bandage.

Corticosteroids are used in musculoskeletal diseases, and offer patient relief. Injections of corticosteroids are recommended for management of osteoarthritis (OA). Current data have shown the role of corticosteroids in ameliorating pain. We hypothesized that repeated intra-articular injections of high dose dexamethasone would protect the cartilage from damage in a post-traumatic model of OA. Eighteen female New Zealand White rabbits were used. Twelve underwent surgery to induce OA; six of them received intraarticular injections of dexamethasone every 3 days for 3 weeks. The other six rabbits served as operated controls. Six additional rabbits served as non-operated controls. All animals were euthanized 3 weeks post-surgery. Knees were assessed grossly. Cartilage, synovium, and fat pad were assessed histologically. Synovium and fat pad were analyzed with qPCR and Western blots. Surgical controls had cartilage damage which was supressed with dexamethasone. Dexamethasone significantly decreased synovial expression of interleukin1b and collagen I, and a trend to decrease synovial matrix metalloproteinase3 expression. There were also significantly lower levels of interleukin-1b protein with dexamethasone treatment. Dexamethasone significantly decreased fat pad expression of matrix metalloproteinase13, basic fibroblast growth factor, and interleukin8, and a trend to decrease matrix metalloproteinase3 and transforming growth factorb expression. Dexamethasone decreased joint inflammation and joint tissue degradation and was chondroprotective in this unique model of PTOA. ß

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SUMMARYHeterotopic tendon mineralization (ossification or calcification), which may be a feature of tendinopathy or which may develop following surgical trauma (repair or graft harvest), has not received much attention. The purpose of this article is to review the prevalence, mechanisms and consequences of heterotopic tendon mineralization and to identify the gaps in our current understanding. We focus on endochondral heterotopic ossification and draw on knowledge of the mechanisms of this process in other tissues and conditions. Finally, we introduce a novel murine Achilles tendon needle injury model, which will enable us to further study the mechanisms and biomechanical consequences of tendon mineralization.