Page 46 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.1 A pproach to the lame horse 21

VetBooks.ir are transported in formalin, whereas samples for his- GAIT ANALYSIS
tochemical analysis require fixation in methylbutane
and chilling in liquid nitrogen. Placing such samples Biomechanics, equine lameness and
in saline-soaked gauze in a watertight container on objective lameness evaluation systems
ice is an alternative. The field of biomechanics explores the mechanics
(physics) behind biological events. During the exam-
Electromyography ination of a lame horse two key areas of mechanics
The diagnosis of neuromuscular problems such as play an important role and explain the empirical
specific areas of muscle atrophy or fasciculations clinical evaluation of a lame horse: kinematics, which
can be helped by performing electromyography studies the movement; and kinetics, the study of
(EMG). This involves measuring electrical activity forces acting on the body. Kinematics is therefore
via needle electrodes placed in the affected muscles the basic science behind the dynamic visual assess-
(Fig. 1.44). Normal muscle exhibits little spontane- ment of lameness and which limbs are affected.
ous electrical activity unless it contracts or the horse The vast majority of lameness cases are caused by
moves. Where there are abnormalities in the elec- pain arising from an orthopaedic structure (hoof,
trical conduction system of the muscle or denerva- bone, joint, sheath, tendon or ligament) and during
tion of motor units, spontaneous electrical activity locomotion, pain is directly related to the forces act-
in the form of fibrillation potentials, positive sharp ing through these structures (stress). Peak force (mag-
waves, myotonic discharges or complex repetitive nitude) and the time over which this force is applied
discharges may be seen. (called impulse) are the two components altered in a

1.43 1.44

Fig. 1.43 A muscle biopsy has just been taken from
the semimembranosus muscle in the right hindlimb of
a Thoroughbred racehorse with recurrent exertional
rhabdomyolysis.

Fig. 1.44 Performing electromyography on the
neck of a horse with neck pain and quadrilateral limb
neurological deficits.