Page 396 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.8 Soft-tissue injuries 371

VetBooks.ir Differential diagnosis 1.733
Other swellings on the caudal distal crus, including
crurotarsal joint effusion, deep capped hock (calca-
neal bursitis), false thoroughpin (deep gastrocnemius
bursitis) and sympathetic effusion. Tarsal check liga-
ment desmitis may have a similar presentation.

Diagnosis
Clinical examination
The swelling must be differentiated from joint or
(calcaneal or gastrocnemius) bursa swelling. Careful
palpation is generally diagnostic. Intrathecal injec-
tion of local anaesthetic solution (5–8 ml) is useful to
confirm that pain is due to sheath involvement.

Radiography
Four standard projections of the tarsus and a flexed
caudoproximal plantarodistal (‘skyline’) view of the
calcaneus should be obtained. These will confirm
sustentaculum tali fragmentation and/or erosion
(Fig. 1.733). Lytic osteitis may be present in asso-
ciation with wounds. In chronic cases, entheseo-
phytes may be visible along the medial edge of the
sustentaculum tali and on the axial insertion of the Fig. 1.733 Dorso 45° medial/plantarolateral
sheath on the plantaromedial calcaneus. Injection of radiograph of the tarsus of a horse that had sustained
contrast medium into the sheath may help to detect a kick injury to the medial aspect of the hock. There is
fistulas in the presence of a wound or trauma to the an obvious defect and fragmentation of the edge of the
medial hock. sustentaculum tali of the calcaneus. (Photo courtesy
Graham Munroe)
Ultrasonography
The sheath is easily identified cranial to the flexor also be present and can be challenging to visualise,
tendons along the caudal aspect of the tibia and then although adherent, echogenic pannus on the tendon
around the LDF tendon over the plantaromedial surface should arouse some suspicion. Erosion of
aspect of the hock. It extends distally to the proximal the fibrocartilage may be obvious, creating irregu-
one-quarter to one-third of the metatarsus, between lar, focal defects (Fig. 1.738). Fragmentation of the
the DDFT and tarsal check ligament (AL-DDFT). edge of the sustentaculum tali is often associated
The ultrasonographic signs are as described for the with thickening and decreased echogenicity of the
digital sheath, with synovial membrane thicken- plantar retinaculum (Fig. 1.739). Where wounds
ing (hypoechogenic in acute stages, then increas- are detected, careful examination for a contiguous
ing in echogenicity) and fluid distension. Adhesions fistula should be made.
are often large and fibrous (Figs. 1.734, 1.735).
Chronic tenosynovitis often leads to the production Management
of large synovial masses that obliterate the proximal The approach is similar to that described for digi-
pouch (Fig. 1.736). LDF tendon lesions are variable tal tenosynovitis. Chronic cases are often non-
in appearance, but are often diffuse and longitudi- responsive to conservative management and surgical
nally arranged, forming large clefts in the tendon treatment is recommended. Tenoscopic examina-
(Fig. 1.737). Thin, superficial longitudinal tears may tion, debridement of erosive lesions and partial