Page 392 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.8 Soft-tissue injuries 367

VetBooks.ir tears. Tears may be very superficial, most frequently and careful palpation is always warranted with acute
tenosynovitis.
on the lateral aspect in the distal fetlock region
or immediately distal to the ergot. Some tears, on
the other hand, can extend through part, or all, of Differential diagnosis
the thickness of the tendon, sometimes spreading Other causes of tenosynovitis and tendonitis of the
through the parenchyma in a reticulated pattern SDFT or its branches need to be considered for
(with multiples tears). Central core lesions are also DDF tendonitis in the fetlock and pastern regions.
encountered; these may or may not extend to the
periphery of the tendon. They are most commonly Diagnosis
found in the fetlock region and tend to be relatively Radiography
short (1–3 cm in length). Radiography is of little use for DDFT injuries in the
Healing of lesions in contact with the synovium digital sheath but may be useful to rule out other
is often slow and delayed and occurs through fibrosis pathology in the fetlock/pastern area. Ectopic min-
and fibrocartilaginous metaplasia. This is suppos- eralisation in the tendon and/or sheath boundaries
edly due to synovial tissue and/or fluid invasion of may be visualised. Contrast studies (with injection
the lesion. These have a tendency to persist in the of air or iodinated contrast medium in the sheath)
long term. have limited applications and have been superseded
Central core lesions usually heal, although not by ultrasonography.
always with restoration of a properly aligned fibrous
tissue. The lesions often remain hypoechogenic Ultrasonography
despite resolution of the lameness in the long term Four types of lesions of the DDFT have been
and this has been associated with fibrocartilage identified in the digital sheath region on ultra-
formation (metaplasia). Mineralisation can occur sonography: diffuse enlargement and change in
within the metaplastic foci. Tenosynovitis is usually the shape of the tendon, with asymmetric thick-
severe, particularly if the lesion communicates with ening of one or both lobes (Fig. 1.727); focal
the sheath lumen, and often becomes a major com- hypoechoic lesions within the tendon (core lesions)
ponent of the disease. or on its margins (Figs. 1.727, 1.728); mineralisa-
tion within the DDFT (Fig. 1.729); and marginal
Clinical presentation tears (Fig. 1.730). The latter may require teno-
DDF tendonitis in the DFTS is always associated scopic exploration to identify the lesion definitively,
with marked distension and inflammation of the although they may be identified ultrasonographi-
synovial sheath. It is more common in the hindlimb, cally as a focal cleft or superficial hypoechogenic
especially in ponies and cobs. Lameness varies from area on the tendon periphery. Typically, the tendon
mild to severe and is usually unilateral and acute outline is lost and the synovium is displaced locally.
in onset, although the sheath distension may have There may be an associated, echogenic ‘mass’ or
been long-standing. Accurate palpation of structures tissue thickening in the adjacent sheath cavity. In
within the sheath is difficult, but pain is often elic- addition, adhesions can develop in more chronic
ited by distal flexion and/or direct pressure applied cases, identified directly or on dynamic examination
to the tendon. Digital flexion markedly increases the (Fig. 1.731). The lesions are often reticular in pat-
lameness. Intrathecal analgesia of the digital sheath tern and may combine several of the above charac-
and distal metacarpal perineural analgesia (low teristics. Chronic injuries often lead to dystrophic
four-point nerve block) will improve the lameness, mineralisation. Acute or chronic digital sheath syno-
although this may only be partial. vitis is usually evident and severe.
Puncture wounds may be difficult to diagnose
unless there is an obvious wound on the palmar Magnetic resonance imaging
aspect of the limb. There is often marked soft-tissue MRI may also be useful to assess DDFT lesions in
swelling and a focal haematoma. Clipping the hair the distal fetlock area, where ultrasonography may