Page 157 - Adams and Stashak's Lameness in Horses, 7th Edition

Examination for Lameness 123

SUBJECTIVE ASSESSMENT OF LAMENESS

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The word “lame” stems from the Proto‐Indo‐ horses with bilateral pain or disease to move symmetri­
European language root lem, meaning literally “broken,” cally, at least in some strides, especially when moving in
with comparative usage in Old English (lame), Old a straight line. But one limb is usually slightly worse,
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Norse (lami), and Proto‐Germanic (lahm). The word and an average asymmetry of movement, or lameness,
lame is an adjective, as in a lame limb. In modern veteri­ over all strides is retained. Axial skeletal disease in
nary usage, we use a derivative of the word as the noun particular may cause relatively equal amounts of pain
lameness, the state of being lame. Lameness is a clinical during both steps in a stride so that lameness may not be
sign not a disease. 32,48 A synonym is limp, also used as a displayed. However, most horses with musculoskeletal
verb, as in “the horse limps.” A horse with lameness is a disease will display lameness, and many horses that dis­
limping horse. play lameness have musculoskeletal disease.
Most lameness is caused by pain during weight‐ bearing, The asymmetric movement in horses with musculo­
with shifting of load away from the source limb onto the skeletal or neurologic abnormality causes a decrease in
other three, non‐ or less afflicted, limbs. In human medi­ resultant ground reaction forces, because most pain or
cine lameness due to pain on weight‐bearing is called dysfunction occurs during weight‐bearing. Some abnor­
antalgic (“against pain”) gait and is considered the medi­ malities may also cause pain in the swing (non‐weight‐
cal term for “limping.” In the bipedal human the main bearing) phase of the stride, but there is objective
feature of antalgic gait is decreased duration of stance evidence that the abnormal movement due to pain or
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time of the affected versus unaffected limb. But this is dysfunction in the swing phase of the stride affects kin­
frequently not true in the quadruped equine unless the ematics (and likely ground reaction forces) also in the
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lameness is severe, and, instead, it is a decrease in peak stance phase of the stride. In other words, pure swing­
vertical ground reaction force on the affected limb that is ing limb lameness conditions without weight‐bearing
the primary effect of weight‐bearing pain. 10,54,55 But also signs have not been shown to exist and if they do exist
decreased vertical ground reaction force can be a sign of are not common. In addition, asymmetric limb move­
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a comparative unilateral weakness, neurologic dysfunc­ ment without asymmetry in weight‐bearing, though
tion, anatomical asymmetry, and, to a limited degree and technically defined as lameness, is more likely simply a
uncommonly, even primary functional asymmetry (hand­ sign of conformational difference or handedness and
edness, laterality), a dominance of one side of the brain in not clinically significant as a sign of disease.
controlling particular activities. Horses without pain, Movement of the midline of the horse’s body, more
neurologic abnormality, or weakness in the limbs or torso precisely movement of the head and pelvis, in the same
usually move symmetrically and are not lame. sagittal plane of the body’s center of mass, is directly
Detection of the clinical sign of lameness by observing related to vertical ground reaction forces on the limbs
the horse move in most situations is a simple concept. It is during weight‐bearing. Movements of the abaxial
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the recognition of asymmetric gait. However, it is more appendages are more naturally variable (right vs. left
difficult in practice because of inherent limitations in spa­ and stride by stride) and more affected by idiosyncratic
tial and temporal resolution of unaided human eyesight. factors, like conformation and handedness (predomi­
In contrast, determination of the cause and importance of nance or preference of one side of the body over the
lameness is frequently both difficult and complex, requir­ other). Higher variability and more complex association
ing detailed knowledge of anatomy; understanding of to multiple causative factors decrease the usefulness of
how movement of the head, torso, and limbs are affected specific limb movements to reliably signal painful
by limb loading and unloading; a complete and systematic weight‐bearing lameness. 1,44,45 For these reasons, obser­
palpation and manipulation of the entire limb and torso; vation of how the midline (head and torso) moves is
knowledge of breed‐ and use‐specific diseases that cause more sensitive and specific for weight‐bearing lameness
lameness; localization of the focus of pain with local anes­ detection than evaluation of limb movement. Exceptions
thesia; and quality imaging. Obtaining relevant history, to this generalization include dorsiflexion of the fetlock
visual examination of the horse at rest, and palpation and during weight‐bearing and amplitude of hindlimb pro­
manipulation of the limbs and torso are covered in earlier traction, both of which, when decreased, have been
chapters. Subjective evaluation of the horse during move­ shown to be reliable indicators of abnormality. 12,19,30
ment to detect and assess lameness is the purpose of this These are discussed later in this section.
chapter. However, there are a few musculoskeletal/neurologi­
A horse without lameness moves symmetrically, with cal abnormalities that are most easily recognized as spe­
equal amplitude of movement in the head, torso, cific “odd” limb movements and, if seen unilaterally,
and limbs during the right and left halves of the stride. satisfy the definition of lameness. Fibrotic myopathy of
A horse with lameness due to pain in a limb moves the stifle flexor muscles, stringhalt, momentary or inter­
asymmetrically. This does not mean that all horses mittent upward fixation of the patella, gastrocnemius
with musculoskeletal or neuromuscular abnormality muscle injury, peroneus tertius rupture, and “shivers”
move asymmetrically or show lameness. It is possible for can be recognized merely by observing limb movement