Biochemical, histological, and biomechanical analyses of canine tendon

Abstract

To define the matrix composition and architecture of canine flexor tendon, and to correlate tissue structure with applied mechanical loading, five anatomical regions of flexor tendon were studied. Histologically, two prominent fibrocartilaginous areas were observed on concave aspects of the tendon. The location of the major fibrocartilaginous area at the metacarpophalangeal joint correlated well with the region predicted by biomechanical modeling to be under greatest compressive loads during standing and claw movement. Comparative biochemical analysis showed an elevated water content, a five-fold higher hexuronic acid content, and a larger hydroxylysine/hydroxyproline ratio in this region relative to that for more tendinous areas. The major glycosaminoglycan component of fibrocartilaginous areas was chondroitin sulfate, whereas in other areas dermatan sulfate and hyaluronic acid dominated. Cell density and DNA analyses indicated a slightly higher cellularity for fibrocartilaginous areas and the region of vinculum insertion. These data document the existence of discrete areas of specialization within the flexor tendon that appear to be an adaptation to nutritional and mechanical factors.

Expression and mapping of lubricin in canine flexor tendon

“…22 Consistent with these findings, we found variations in lubricin expression along the FDP, corresponding to regions that differ in mechanical environment. 24 Regions B to F of the canine FDP tendon glide within a synovial sheath and sustain more shear force and compression than region A in routine canine activity. These are also the weight-bearing zones of the tendon.…”

“…14 In our study, the larger variants V1 and V2 were noted particularly in region B/C, in which the FDP tendon is compressed by the metacarpal head during walking. 24 The tensile characteristics of tendons depend on the level of collagen organization and on the orientation of collagen fibrils and bundles. 33,34 Sliding between fibrils occurs as mechanical loading is applied to tendons.…”

“…1) were harvested separately: region A, proximal vascularized area outside of the digital sheath; combined regions B and C, dorsal fibrocartilaginous and ventral fibrous segments, respectively; a weight bearing zone; region D, avascular isthmus between proximal and distal pulleys; region E, the vincular insertion region; and region F, a small distal fibrocartilaginous segment underneath the distal pulley). 24 Tissue samples were embedded in Tissue-Tek, Optimal Cutting Temperature (OCT) (Sakura Finetek USA Inc., Torrance, CA) and subsequently sectioned longitudinally or transversely at 10 mm and placed on Superfrost/Plus Microscope slides (Fisher Scientific, Pittsburgh, PA). The sections were immunostained with a modification of a previously described method.…”

“…23 Similar zones have been identified in animal models, such as the dog, an important model for in vivo tendon research. 24 The importance of FDP lubrication has been recognized. [25][26][27] More recently, lubricin, the principal boundary lubricant in articular cartilage, has also been identified in tendon, 6 but little is currently known regarding the distribution of lubricin or lubricin variants within the distinct anatomic zones of the FDP.…”

Optimization of surface modifications of extrasynovial tendon to improve its gliding ability in a canine model in vitro

“…One of the major differences between intrasynovial and extrasynovial tendons is that the extrasynovial tendon is surrounded by a multilayer paratenon, with an irregular surface, while the intrasynovial tendon surface is covered with a thin, smooth layer of synovial lining cells that secretes lubricants such as hyaluronic acid (HA). [3][4][5] However, the availability of intrasynovial tendon for a donor graft is limited. Because extrasynovial tendons produce higher friction against a pulley compared to intrasynovial tendons, 6,7 it is possible that the rougher surface of extrasynovial tendon is a factor leading to the formation of adhesions.…”