Page 36 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.1 A pproach to the lame horse 11

VetBooks.ir 1.21 1.22

Fig. 1.22 An example of diagnostic analgesic
technique. The left hindlimb superficial and deep
peroneal (fibular) nerves are being injected with local
Fig. 1.21 Lateromedial radiograph of the foot anaesthetic as part of analgesia of the tarsus and
confirming the correct placement of a needle into the entire distal hindlimb. This nerve block is routinely
navicular bursa before the local anaesthetic is injected. combined with a tibial nerve block.

1.23 due to a depletion of hyaluronan, but a similar
colour to normal. Varying degrees of haemorrhage
will be present depending on sampling technique
or the presence of a haemarthrosis. Septic fluid is
also less viscous and often cloudy and discoloured
(Fig. 1.25). Small amounts of fibrin may be present.
Parameters routinely measured include cytology
and total protein concentration. Cytological analysis
Fig. 1.23 Lateromedial radiograph of the dorsal is most useful for identifying and monitoring sepsis
spinous processes of a horse with back pain showing or post-injection reactions. Total protein concentra-
needles in the interspinous spaces prior to the tions normally tend to be higher in the larger joints.
injection of local anaesthetic. The horse responded Hyaluronan concentration is not normally measured
very clearly to the local infiltration.
since there is a large variation between individual
horses. When an infectious cause is suspected, bac-
Synovial fluid collection and analysis terial culture from joint fluid should be attempted,
Sites for diagnostic intrasynovial (joint/sheath/ although culture of microorganisms from synovial
bursa) analgesia may also be used for synovial fluid fluid is often difficult. The chances of a positive
collection for analysis if this is indicated (e.g. sus- culture are increased by placing the fluid directly
picion of a synovial septic process). Clipping the in blood culture medium immediately after col-
hair and aseptic preparation of the collection site lection. Polymerase chain reaction (PCR) analysis
are mandatory. The fluid is aspirated and placed in may be useful in the near future to reveal bacterial
EDTA and plain tubes for analysis (Fig. 1.24). DNA in suspected septic joint samples where cytol-
Visual assessment of normal joint fluid reveals ogy is equivocal. The normal parameters of synovial
it to be slightly viscous and a clear, straw colour. fluid and ranges for certain conditions are shown in
Fluid from inflamed joints tends to be less viscous Table 1.2.