Page 35 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

10 CHAPTER 1

VetBooks.ir and examination should continue with survey radio- the use of intravenous acepromazine or shorter-acting
alpha-2 agonists (e.g. xylazine) may be necessary. The
graphs of the region under suspicion.
A partial or complete response to diagnostic anal-
gesia warrants further investigation of that region by dosage required depends on the individual animal’s
behaviour. The horse is re-examined once the seda-
appropriate diagnostic imaging such as radiography tion has worn off, usually after 20–45 minutes. Horses
and ultrasonography. If a contralateral limb lameness are usually re-examined 5–30 minutes after blocking
is revealed, this limb should be examined with diag- (depending on the block used), at the trot in a straight
nostic analgesia, starting distally as before. Imaging line and/or on the lunge. This minimum amount of
is then carried out after the site of lameness in this time generally allows the nerve targeted to be suf-
limb is confirmed (e.g. bilateral forefoot lameness). ficiently anaesthetised to allow interpretation of the
The sites for perineural nerve blocks should be block, while minimising the spread of the drug to
cleaned and can be clipped if identification of anatomi- other anatomical sites. Intrasynovial blocks such as the
cal landmarks is difficult or the coat is dirty. For all large scapulohumeral and stifle joints are re- examined
intrasynovial blocks, aseptic precautions, after clipping after a longer period of time (30–60 minutes) by some
the hair, are a prerequisite for this technique. Physical clinicians. Certain perineural nerve blocks may be
restraint and consideration of personnel safety are tested for efficacy by loss of skin sensation prior to
advisable in the majority of horses. Placement of a re- examination (e.g. lightly pressing a pen into the
nose twitch, if the horse tolerates this, and having an bulbs of the heel is normally strongly resented by the
assistant lift a contralateral limb for forelimb blocks or horse but is not felt after successful palmar digital
ipsilateral forelimb for hindlimb blocks may be use- nerve block). The interpretation of the results of diag-
ful methods of physical restraint. Chemical restraint nostic analgesia are based on a knowledge of which
is occasionally required for intractable patients, and region the block desensitises (Table 1.1).

Table 1.1 More commonly used perineural nerve blocks, local infiltration and intrasynovial blocks for the
forelimb and hindlimb

FORELIMB HINDLIMB
Perineural blocks Palmar digital Plantar digital
Abaxial sesamoid Abaxial sesamoid
Low 4-point Low 6-point
High 4-point (subcarpal) Deep branch of the lateral plantar nerve
Lateral palmar High 6-point
Median/ulnar/musculocutaneous Tibial/superficial and deep fibular (peroneal) (Fig. 1.22)
Local infiltration Painful exostoses including ‘splints’ Painful exostoses including ‘splints’
Origin of the suspensory ligament Origin of the suspensory ligament
Dorsal spinous processes (Fig. 1.23)
Sacroiliac region
Intrasynovial blocks Navicular bursa (Fig. 1.21) Navicular bursa
Distal interphalangeal joint Distal interphalangeal joint
Proximal interphalangeal joint Proximal interphalangeal joint
Metacarpophalangeal joint Metatarsophalangeal joint
Digital sheath Digital sheath
Intercarpal joint (communicates with the Tarsometatarsal joint
carpometacarpal joint) Central tarsal joint
Antebrachiocarpal joint Tarsocrural joint
Carpal sheath Tarsal sheath
Humeroradial joint Femoropatellar joint
Bicipital bursa Medial femorotibial joint
Scapulohumeral joint Lateral femorotibial joint
Coxofemoral joint