Page 34 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.1 A pproach to the lame horse 9

VetBooks.ir toe with the cannon and tibia parallel to the ground of inflammatory reaction they cause in tissues. Only
In a full flexion test the limb is supported at the
lameness due to pain (i.e. not mechanical or neuro-
(Fig. 1.19):
logical types of lameness) is suitable for this approach
to lameness diagnosis. The blocks should ideally be
• A distal hindlimb flexion test consists of flexing carried out sequentially, starting distally and pro-
the foot and fetlock by supporting the limb at gressing proximally (Fig. 1.20). The selection of
the toe with the cannon perpendicular to the blocks is based on the previous clinical examination.
ground and the hock and stifle at 90°. For example, if a forelimb foot lameness is suspected,
• A proximal hindlimb flexion test involves a palmar digital nerve block may be carried out first.
supporting the limb at the cannon parallel to the If marked joint distension is present in the metacar-
ground and held fully flexed at the hock and stifle. pophalangeal (MCP) joint and a markedly positive
• A hip abduction test is used by some clinicians fetlock flexion test is observed, intrasynovial analge-
to abduct the hindlimb away from the horse sia of the MCP joint may be appropriate. If no appar-
in order to test the hip region, but it can be ent signs for a particular region are identified from
dangerous and must be used with care. previous examinations, it is prudent to start as dis-
tally as possible and work proximally with perineural
Due to the reciprocal apparatus of the hindlimb, analgesia techniques. Note that in suspected fracture
flexion tests may not be as specific as in the forelimb. cases, diagnostic analgesia may be contraindicated,
Extension tests may also be carried out to exac-
erbate a degree of lameness in a certain region. For
example, placement of a reverse heel wedge under a 1.20
foot is used by some clinicians to evaluate suspected
caudal hoof pain.
Evaluation at the trot, after direct digital pressure
to a painful region (e.g. over a collateral ligament
insertion) or after hoof tester application to a sus-
picious region of the solar surface of the foot, may
sometimes be useful manipulative tests.

DIAGNOSIS

Diagnostic analgesia
If the lameness is significant (grade 4 or 5/5) and
there are localising signs of pain or anatomical
abnormalities, these regions should be subjected to
diagnostic imaging before any attempt at diagnostic
analgesia techniques. If the lameness is mild or mod-
erate, identifying the painful region during physi-
cal examination might be difficult. In these cases,
the use of diagnostic analgesia to isolate a structure
or area of pain is very helpful. Diagnostic analgesia
(perineural nerve blocks, local infiltration and intra-
synovial joint/sheath/bursa blocks) is used to abolish
lameness temporarily in the limb being investigated
and thereby further isolate a site of pain. The most Fig. 1.20 This horse has had sequential regional and
commonly used local anaesthetics are mepivicaine, intra-articular analgesia carried out up to the level of
lidocaine and prilocaine. They differ in their time the stifle joints in an attempt to localise the source of
of onset and duration of analgesia, and the degree the hindlimb lameness.