Page 158 - Adams and Stashak's Lameness in Horses, 7th Edition

124 Chapter 2

during the swing phase of the stride or when not weight lamer forelimb and lowest during stance of the not lame
bearing. Although these are thought to be pure “swing­ or less lame forelimb. This corresponds only vaguely to
VetBooks.ir isolated to the swing phase of the stride, and therefore narians and taught to veterinary students of the horse’s
the concept of “head nod” understood by many veteri­
ing limb” lameness conditions, with pain or dysfunction
head moving “down on the sound” limb and “up on the
exceptional to biomechanical descriptions of weight‐
bearing lameness, the author has measured horses with lame” limb. This explanation of “head nod,” however, is
these conditions and found that decreases in vertical actually not precisely true, and a more accurate descrip­
movement of the torso are likewise seen. Thus, in these tion of “head nod” during the trot will be developed
few exceptional conditions, the descriptions of asym­ later in this section.
metric vertical movement of the head and pelvis may not Vertical movement of the pelvis at the walk does not
adequately explain the quantity of dysfunction, but they follow this downward and then upward trajectory.
remain valid for describing side of lameness. Detection Instead it is upward and then downward with the low
of these lameness conditions by observing characteristic positions at the beginning of, and the high positions,
abnormal limb movement is discussed later. during stance. Also with two and three limbs alter­
nately bearing weight at the same time, vertical pelvic
EVALUATION OF THE HORSE FOR LAMENESS movement (VPM) at the walk may not be a simple
AT THE WALK biphasic pattern. Total vertical pelvis movement is also
less than that of the head, and the amount of asymme­
Because limb and torso movements are slower when try between right and left hindlimb strides is more dif­
walking, it is the easiest gait in which to observe lame­ ficult to see. These characteristics make detecting
ness. However, for disease of mild severity, vertical hindlimb lameness using VPM at the walk more diffi­
ground reaction force may not reach a minimum thresh­ cult than using head movement to detect forelimb
old for pain, but the horse walks without visible asym­ lameness at the walk. Alterations in hindlimb move­
metric movement and is not subjectively lame. It is ment like decreased hindlimb protraction, prominent
thought that sometimes, and for some conditions, lame­ circumduction, or excessive rotation are more obvious
ness is more visible at the walk than at other gaits, but than asymmetry of VPM.
for weight‐bearing lameness, this is most likely because Other forelimb and hindlimb movement parameters,
movement speed is within the temporal resolution of besides vertical head and pelvic movement, which indi­
unaided human sight. Weight‐bearing lameness at the cate lameness, may also be seen at the walk, but these
trot measures greater than lameness at the walk. 4 will also be seen at the trot.
The trajectory of vertical head movement during the Evaluation for lameness at the walk can be enhanced
walk of a horse with unilateral forelimb lameness is by turning the horse in a tight circle, especially on hard
asymmetric (Figure 2.113). At the walk, as in other gaits surfaces or on surfaces with high frictional forces
at slow speeds, the front limbs acts almost exclusively between the bottom of the foot and the ground. If
like a strut or crutch, so head movement trajectory in a weight‐bearing or torque of the inside limb elicits pain,
horse with forelimb lameness is usually shaped like then the outside limb will display accelerated protrac­
depicted below, being highest from the ground right tion and earlier‐than‐expected initiation of weight‐
before or during the first part of stance of the lame or bearing. This abnormal movement is more prominent

A
Stance phase
of right forelimb
C

D

B

Stance phase
of right forelimb Stance phase of left forelimb

Figure 2.113. Typical vertical head trajectory of a briskly phase of lame or more lame forelimb that is higher than that during
walking horse with a forelimb lameness (in this specific case a left stance phase of the non‐lame or less lame forelimb (D). (C) Local
forelimb lameness). (A) Highest head height immediately before maximum head position right before impact of the non‐lame or less
impact of the lame or more lame (left) forelimb (note bandage: lame forelimb that is lower than before impact of the lame or more
inferior check ligament previously injected with collagenase to lame forelimb (A). (D) Lowest head position during stance phase of
induce lameness). (B) Local minimum head position during stance the non‐lame or less lame forelimb.