MACROSCOPIC DEGENERATION OF EQUINE SUPERFICIAL DIGITAL FLEXOR TENDON IS ACCOMPANIED BY A CHANGE IN EXTRACELLULAR-MATRIX COMPOSITION

Injuries to the superficial digital flexor tendon are common in horses required to gallop and jump at speed, Partial rupture of this tendon usually occurs in the central core of the mid-metacarpal region and ma y be preceded by localised degenerative changes. Post mortem examinati on of apparently normal equine flexor tendons has revealed an abnormal macroscopic appearance in the central core, characterised by a reddis h discolouration, We have previously shown that there is also physical damage to the collagen fibres, In the present study we tested the hyp othesis that the abnormal appearance is accompanied by changes in the composition of the extracellular matrix of the tendon. Biochemical ana lysis of the extracellular matrix demonstrated an increase in total su lphated glycosaminoglycan content, increase in the proportion of type III collagen and decrease in collagen linked fluorescence in the centr al core of 'degenerated' tendons relative to tissue from the periphera l region of the same tendon. Dry matter content and total collagen con tent were not significantly different between tendon zones or normal a nd 'degenerated' tendons. These changes suggest a change in cell metab olism and matrix turnover in the central core of the tendon and are li kely to contribute to a decrease in mechanical properties in this part of the tendon, predisposing to the characteristic partial rupture of the tendon.