Page 317 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

292 CHAPTER 1

VetBooks.ir CONDITIONS AFFECTING THE TENDONS AND LIGAMENTS

SUPERFICIAL DIGITAL FLEXOR
TENDINOPATHY (TENDON DISEASE) ‘tendinitis’ and ‘tendinopathy’. A consensus con-
ference was held in 2007 in Iceland to propose a
standard in evaluation protocols and terminology
Definition/overview (Havemeyer Symposium) for future research and
‘Tendonitis’ is a common condition affecting all reference. The term ‘tendon disease’ or ‘tendino-
breeds, but particularly racehorses, eventers and pathy’ was accepted as the most suitable to describe
other horses engaged in high-speed pursuits. this condition.
Progressive, exercise-induced degeneration of the
collagen matrix leads to acute, partial rupture of the Aetiology/pathophysiology
tendon (‘tendinopathy’). After injury, healing is slow The aetiology is still incompletely understood,
and characterised by a high rate of recurrence. although recent advances in cell and matrix biol-
Tendon disease is a major source of economic loss ogy have markedly improved our knowledge and
in the equine industry. Alternative names include revealed the tremendous complexity of involved
‘bowed tendon’, ‘tendon strain’, ‘tendon break-down’, mechanisms. The main cause of ligament and tendon
injuries is probably mechanical failure of the colla-

1.552 gen fibre-based parenchyma, due to recurrent over-
stretching of the fibres beyond the tolerance of the
tissue. Although naturally very elastic, the SDFT is
stretched to near its physiological limits during fast
exercise, as the fetlock drops to near ground level
(Fig. 1.552). Cyclic strain involves fast stretching–
release cycles at fast paces, which appear to gradu-
ally weaken the tendon. In most cases, subclinical
microtears occur during training or fast exercise.
They form quicker than they can heal, progressively
weakening the tendon. There is increasing evidence
that chronic, recurrent overuse has a tremendous
effect on matrix composition and properties. Ageing
and cell apoptosis are probably significant factors in
older animals, and it has been suggested that hor-
mone-induced changes in older females (oestrogen
impregnation) can lead to severe, spontaneous rup-
ture. An acute, severe episode, involving rupture
of a major proportion of the weakened fibres, can
occur with a normal level of exercise. Predisposing
factors include work type (racing, athletic activities
versus leisure or pleasure activities), genetics, age
and career duration. There are major biomechani-
Fig. 1.552 View of the distal limb of a racehorse cal influences from the hoof shape (especially long
at full gallop. The fetlock drops at maximum weight toe/low heel conformations), ground surface quality
bearing during the stance phase of the stride because (especially soft, deep soil and uneven surfaces) and
of stretching of the flexor tendons and interosseous method of training (duration and length of high-
ligament. The SDFT, being most palmar, is stretched speed training).
to a greater degree, nearing its physiological limits Repeat cyclic trauma leads to gradual alterations
(yield point). of the collagen matrix. Normally, the tendon consists