Page 138 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.3 The foot 113

VetBooks.ir foot placement, with the quarters of the foot at differ- Differential diagnosis
Physical examination findings, except for the pres-
ent heights, results in rotation and sliding of the distal
and middle phalanges in both the transverse and fron-
cause of moderate lameness arising within the foot:
tal planes. This type of ‘collateral motion’ is encoun- ence of lameness, are usually unremarkable. Any
tered mainly during the stance phase of asymmetric navicular disease; bruising; DIP joint pain; pedal
propulsion, such as moving in circles, and places par- osteitis; sheared heels.
ticular stress on the collateral ligaments of the DIP
joint. Injury at the bone/ligament interface is referred Diagnosis
to as entheseopathy, while desmitis affects the body Improvement on regional analgesia of the foot is
of the ligament. Injury may consist of mild to moder- variable: only about a quarter of horses improve fol-
ate fibre damage (sprain) or severe fibre damage with lowing intra-articular anaesthesia of the DIP joint
elongation or separation resulting in joint instability while two-thirds improve to a palmar digital nerve
(partial or complete rupture with subluxation or luxa- block. An abaxial sesamoid nerve block should
tion), although the latter is extremely rare. abolish lameness completely. Uniaxial analgesia of
the palmar or palmar digital nerves is not always
Aetiology/pathophysiology effective in removing lameness. Analgesia of the
Although acute traumatic strain injury is possible, navicular bursa does not cause any improvement in
most cases seem to be associated with chronic repet- lameness.
itive strain injury. The cause of injury is believed
to be concurrent sliding and rotation of the joint
superimposed on pre-existing degenerative changes 1.197
within the ligament and at its insertion. Lateral slid-
ing of the distal phalanx and medial rotation causes
great strain in the medial collateral ligament, which
is the most commonly injured. OA as a sequela of
collateral desmitis appears to be uncommon.

Clinical presentation
Most horses with collateral desmitis do not display
any localising signs. Distension of the dorsal pouch
of the DIP joint may be present but is not a char-
acteristic finding. A discrete, palpable swelling may
occasionally be found at the level of the origin of a
collateral ligament, immediately proximal to the dor-
somedial or dorsolateral aspect of the coronary band
(Fig. 1.197). Lameness may be unilateral or bilateral,
and of variable severity. It may be worsened by the
use of lateral or medial hoof wedges. It is typically
mild to moderate and has all the hallmarks of palmar
foot pain. Acute-onset severe lameness with a history
of trauma is atypical. Lameness is usually worse on a
circle, especially on hard ground, when the injured
ligament lies on the outside, thus being subjected to Fig. 1.197 View of a horse with a medial collateral
increased strain. Horses with collateral desmitis of ligament injury of a forelimb showing clearly a
the body of the ligament may be more likely to react unilateral swelling above the coronary band, which
painfully to digital flexion than those with an enthe- was confirmed by ultrasonography and MRI. (Photo
seopathy, although this is individually variable. courtesy Graham Munroe)