Page 145 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

120 CHAPTER 1

VetBooks.ir is sepsis of the DDFT and the flexor cortex of the Aetiology/pathophysiology
Primary injury to the DDFT may be the result
navicular bone. Both can have a negative impact and,
in addition, concurrent infection of the other syno-
stance phase, repetitive overload stress, or a com-
vial structures is likely to deteriorate the prognosis. of acute traumatic fibre tearing at the end of the
Furthermore, persistent severe lameness in one limb bination of both. Predisposition to primary ten-
predisposes the animal to contralateral support limb don injury may increase as degenerative ageing
laminitis. Historically, the prognosis for survival has changes accumulate in the tendon. Injury to the
been poor (50% or less) and for return to athletic distal portion of the tendon may also result from
function even worse at around 30%. Recent reports distal extension of tendinopathy at the level of the
suggest that the prognosis has significantly improved, DDFT sheath. Possible risk factors include hoof
although they are somewhat variable, with survival conformation, the angle of the distal phalanx and
rates of 80% or better and return to function rates the horse’s athletic discipline. Horses jumping over
60% or better, following bursoscopy or bursotomy. fences have a significantly higher risk of injuring
However, another recent study in which many of the the digital portion of the tendon than horses that
injuries also involved the DIP joint, reported a lower are used for other sporting endeavours. Horses
survival rate of between 50% and 60%. Careful con- that have undergone a palmar digital neurectomy
sideration of clinical reports is always necessary as are at significant risk of deterioration of existing
some do not always account for horses euthanased tendon pathology.
because of the expense of treatment, which can be
considerable, or the fact that clinicians are still jus- Clinical presentation
tifiably cautious about the prognosis for return to There are generally no visible or palpable abnor-
function. In comparison, puncture wounds of the malities in horses with distal tendinopathy of the
foot that do not involve a synovial structure have a DDFT. Occasionally, distension of the DDFT
very significantly better overall prognosis. sheath is present in horses with a lesion that extends
proximally to the level of the sheath. Even more
DEEP DIGITAL FLEXOR rarely, a focal, painful, firm soft-tissue swelling
TENDINOPATHY IN THE FOOT can be appreciated on the palmarodistal aspect of
the pastern. Flexion and extension tests of the digit
Definition/overview produce variable results but are not specific. Toe
Since the advent of equine foot MRI, it has become elevation, with a wooden wedge, makes some horses
clear that tendinopathy or tendinitis of the DDFT is worse, but it does not distinguish between horses
the most common soft-tissue injury causing lameness with tendon pain and other forms of palmar foot
in the horse’s foot. It is responsible for around 30–50% pain. Surprisingly, in a considerable number of ten-
of all foot lameness without radiographic abnormali- don injury cases, elevation of the heel with a wooden
ties. Tendinitis of the digital portion of the DDFT wedge of 15–20° results in marked exacerbation of
may occur alone, in conjunction with navicular bone lameness. Lameness varies substantially in severity,
pathology or as one component of a complex of mul- but some horses will experience episodes of severe
tiple soft-tissue injuries in the foot. Pathological sur- lameness and may be seen intermittently point-
veys have recognised four different lesion types in the ing the affected foot at rest. Approximately 50% of
distal portion of the DDFT: core lesions; dorsal abra- horses are presented with an acute-onset, moderate
sions and tears; sagittal plane and oblique splits; and to severe lameness while the other 50% experience
insertional lesions (including entheseopathy). It is a more insidious disease progression. Some horses
thought that these lesions may be primarily degener- are presented for poor performance evaluation and
ative in nature. Lesions occur most commonly at the may not even show lameness when trotting in a
level of the navicular bone and proximal aspect of the straight line. All affected horses are lame when trot-
navicular bursa, less commonly at the insertion and ting in a circle on hard ground, especially when the
least of all at the level of the proximal interphalangeal affected limb is on the inside. Lameness is unilateral
joint and proximal phalanx. in approximately 60% of horses.