Page 179 - Adams and Stashak's Lameness in Horses, 7th Edition

Examination for Lameness 145

both hindlimbs such that false hindlimb lameness could occur, which could damage tissue or cause pain, or both.
be measured in both sides. Primary forelimb lameness Although less is known about secondary lameness pat­
VetBooks.ir toward the back half of the body during the stance phase certain patterns in trotting horses have been suggested
terns (because it is difficult to study experimentally),
causes the horse to shift its center of gravity slightly
based on clinical impression. In horses that trot, primary
of the affected forelimb. This causes the pelvis to fall
more in the contralateral hindlimb compared with the forelimb lameness will most likely overload the opposite
ipsilateral hindlimb, mimicking impact‐type lameness in forelimb or the opposite hindlimb, but it will unlikely
the opposite hindlimb, ipsilateral to the primarily lame overload the ipsilateral hindlimb. Primary hindlimb
forelimb. However, the horse moving forward will push lameness will equally likely overload the contralateral
off less from the opposite/diagonal hindlimb (contralat­ fore‐ or hindlimb, but will unlikely overload the ipsilat­
eral to the forelimb with primary lameness) to lessen eral forelimb (Figure 2.134). Secondary lameness should
shifting of weight forward onto the primarily lame fore­ not reduce immediately when the primary lameness is
limb, causing the pelvis to rise less and giving the appear­ reduced with blocking. Secondary lameness, because it is
ance of a contralateral pushoff‐type hindlimb lameness. caused by physiologic overload that may damage ana­
Thus, primary forelimb lameness may cause compensa­ tomic structures that span a length of the limb, for
tory movements that mimic ipsilateral hindlimb impact‐ example, the suspensory apparatus or flexor tendons, is
type lameness but contralateral pushoff‐type hindlimb also more difficult to block completely with lower limb
lameness. Generally the ipsilateral impact‐type “false” blocks, and frequently small or partial improvements
hindlimb lameness is small and less common than the are seen with successively higher blocks.
contralateral pushoff‐type “false” hindlimb lameness. Following the logic of Occam’s razor (the principle of
Compensatory pelvic movement patterns with primary parsimony), which states that the simplest explanation
forelimb lameness are regularly measured with the of competing explanations for a series of observations is
increased sensitivity of the inertial sensors, and these usually the most correct, and our knowledge of compen­
patterns are useful for helping to detect and evaluate satory (previous section) and secondary lameness pat­
forelimb and multiple limb lameness (Figure 2.133). terns, one can make a reasonable and evidence‐based
Compensatory pelvic movements with primary forelimb guess as to which limb in a multiple limb lameness is the
lameness are not commonly observed subjectively. primary source of lameness. In a study of over 1200
Compensatory lameness should reduce when the pri­ horses evaluated for lameness, multiple limb lameness
marily lameness is reduced with blocking. Compensatory was measured in just over half (57%) of horses with
lameness patterns are seen when the horse is trotting in lameness when trotting in a straight line. Therefore,
a straight line and while lunging. During lunging, com­ when measuring lameness in horses actually presented
pensatory patterns are additive to directional patterns, for lameness, multiple limb lameness is the norm rather
sometimes exacerbating and sometimes masking multi­ than the exception.
ple limb effects. Considering both impact‐ and pushoff‐type forelimb
Known compensatory lameness patterns were lameness together, but hindlimb impact and pushoff
described in the previous section. However, there may be lameness as separate quantities, there are only eight pos­
other reasons for an apparent multiple limb lameness. sible “types” of multiple limb lameness:
Secondary lameness arises when a primary lameness
causes weight shifting away from the primary limb to 1. Forelimb lameness with ipsilateral hindlimb lame­
other limbs. If this weight shifting compensation over­ ness that is both decreased impact and decreased
loads the other limb(s), supraphysiologic strain may pushoff (Figure 2.135).

Front Front

Compensatory 1°

LF RF LF RF

Compensatory Compensatory
1° pushoff impact

Hind Hind
LH RH LH RH
A B
Figure 2.133. Known compensatory lameness patterns. (A) First of the law of sides. Concurrent forelimb and either compensatory
part of the law of sides. Concurrent apparent ipsilateral forelimb and contralateral hindlimb pushoff or ipsilateral hindlimb impact (or both)
hindlimb lameness is usually a primary hindlimb lameness and an lameness. Compensatory contralateral compensatory hindlimb
ipsilateral compensatory (false) forelimb lameness. (B) Second part pushoff lameness is more common and usually more prominent.