Page 159 - Adams and Stashak's Lameness in Horses, 7th Edition

Examination for Lameness 125

for forelimb compared with hindlimb lameness, most elimination of signs at higher speed gaits, and rarely
likely because of higher percent of total body weight causing clinically significant restricted use or decrease
VetBooks.ir the walk. Limb position and foot placement under the that the condition also causes decreased hindlimb
in function. However, recent kinematic studies prove
borne by the forelimbs compared with the hindlimbs at
propulsion with characteristic decreased rise of the
body, as well as head height from the ground (in fore­
limb lameness), can also be assessed during turning. The pelvis after affected hindlimb stance, i.e. a lack of
outside limb swings forward and lands quickly, crossing hindlimb vertical propulsion. Moreover, when the
over the lame inside limb. Head movement trajectory restriction in movement is eliminated by transection
during turning with forelimb lameness is typical of an of the fibrosis, the abnormal swing movement and
impact‐type forelimb lameness seen at the walk and the decreased hindlimb propulsion are both eliminated.
trot, with the head moving upward greatly during 2. Stringhalt: Stringhalt causes lameness of presumed
impact of the lame, inside, forelimb. neurologic origin characterized as a sudden hyper­
Lameness conditions that can usually be recognized flexion of the hindlimb. Known causes are chronic
and diagnosed almost solely by evaluation of gait at the toxicity from ingestion of certain species of weeds
walk include: (dandelion family) in times of drought and prior
trauma to the dorsal surface of the hindlimb meta­
1. Fibrotic myopathy: Injury to the stifle flexor muscles tarsus and tarsus. The hindlimb hyperflexion can be
(biceps femoris, semimembranosus, semitendinosus) slight or dramatic and may vary in amplitude from
most likely occurs with stifle hyperextension when stride to stride. When severe, it appears to disturb
the hindlimbs are protracted forward and the horse the horse, but in many cases the horse seems indiffer­
either falls or the hind torso lowers as in a sliding ent when it occurs. It is generally thought only to
stop. Injury to the stifle flexors can result in pain soon cause dysfunction during the hindlimb hyperflexion,
after injury, but fibrosis or ossification at the muscu­ but this author has also measured decreased weight‐
lotendinous junction, which can be palpated, is a bearing in the affected limb, and treatment by surgi­
common, more chronic result. This injury leads to a cal removal of a length of long digital extensor
characteristic hindlimb swing trajectory beginning tendon/muscle can eliminate the hyperflexion and
with increased retraction, followed by the limb swing­ decrease both lameness and apparent discomfort in
ing forward with low flight arc and slightly shortened severe cases.
length of protraction, and ending with an elevation of 3. Upward fixation of the patella: Momentary or inter­
the hoof, which precedes an unusual, goose‐stepping‐ mittent upward fixation of the patella is dysfunction
like retraction of the hoof backward immediately in the normally smooth locking and then unlocking
before impact (Figure 2.114). In contrast the normal of the patella over the top of the medial condyle of
hoof flight trajectory has shorter retraction, higher the femur during an otherwise normal hindlimb
swing trajectory, and greater protraction, with the movement. At the end of limb extension, before lift‐
hoof ending its flight moving forward and down­ off of the hindlimb foot, to prepare for initiation of
ward. It was previously believed that this condition swinging the limb forward, quadriceps muscle activ­
was an isolated swinging limb lameness seen espe­ ity elevates the patella, unlocking it from the femur
cially and primarily at the walk, with a decrease or
and allowing stifle flexion. Delayed or incomplete

Figure 2.114. Hoof flight trajectories during fibrotic myopathy of positions. Upper trajectory is that of the contralateral normal
the stifle flexor muscles (biceps femoris, semitendinosus, semimem- hindlimb foot. Lower trajectory is that of the affected hindlimb foot.
branosus) with associated still video frames indicating limb