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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
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