Page 395 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

370 CHAPTER 1

VetBooks.ir TENOSYNOVITIS OF THE TARSAL Clinical presentation
SHEATH (THOROUGHPIN)
Typically, distension causes swelling of the proximal
Definition/overview sheath pouch in the distal crus, particularly laterally
and medially between the tibia and common calca-
The tarsal sheath is the synovial sheath of the lat- neal tendon (Fig. 1.732). A lesser swelling is visible
eral digital flexor (LDF) tendon. This large ten- or palpable medial to the DDFT in the proximal
don runs over the medial aspect of the hock and third of the metatarsus. There should be no confu-
sustentaculum tali of the calcaneus to join up with sion with distension of the calcaneal bursa or plantar
the medial digital flexor tendon in the proximal pouch of the tarsocrural joint. In cold distension,
metatarsus to form the DDFT. ‘Thoroughpin’ there is no associated lameness. There may, however,
refers to distension of the sheath, whatever the be pain on limb flexion due to increased pressure.
cause. Tenosynovitis causes moderate to severe lameness,
with restricted hock flexion and decreased foot flight
Aetiology/pathophysiology arc. In severe cases, lameness may be marked to
The causes are the same as in the digital sheath. non-weight bearing. This is most notably the case in
‘Cold’ idiopathic distension is by far the most com- septic tenosynovitis.
mon cause. It is therefore paramount that other
causes of lameness are ruled out. Other common
causes include spontaneous injury to the tendon 1.732
(LDF tendinopathy) or other sheath components
(tears of the mesotenon, erosions of the sustentacu-
lum tali), probably as a result of overextension of the
digit while the hock is flexed, and direct trauma (e.g.
kick injuries, interference with the opposite limb).
LDF tendinopathy is rare but causes a similar syn-
drome to DDF tendinopathy in the digit. In most
cases, superficial tears on the tendon surface are
associated with severe tenosynovitis.
Direct trauma to the medial hock tends to cause
damage to the prominent sustentaculum tali of the
fibular tarsal bone (calcaneus), with frequent frag-
mentation of its plantaromedial edge. This also leads
to tenosynovitis. If a wound is present, septic teno-
synovitis is common. Septic (infectious) tarsal teno-
synovitis may be caused by puncture wounds, open
wounds or iatrogenic contamination due to intrathe-
cal injections.
Chronic or recurrent sheath inflammation leads
to adhesion formation. These are often restrictive
and tend to tear repeatedly because of the large
range of movement of the tendon over the sustentac-
ulum tali, leading to repeated haemorrhage, chronic
inflammation and marked pain. In severe cases the Fig. 1.732 Substantial tarsal sheath distension
fibrocartilage covering the sustentaculum tali is clearly visible as a fluid-filled pouch laterally (right),
eroded and leads to contact/shearing lesions on the and less obviously medially and distomedially.
overlying tendon. (Photo courtesy Graham Munroe)