• In the case of pain-mediated lameness, we perceive adjustments that the horse makes in an attempt to avoid pain.
• In the case of biomechanical lameness, we perceive adjustments that the horse makes in an attempt to accommodate a physical restriction or exaggeration in movement.
• In the case of neurologic lameness, we perceive adjustments that the horse makes in an attempt to maintain balance.
Improved pattern recognition enables:
Owners to recognize lameness in their horses more quickly.
Veterinarians to assist in owner recognition of lameness more quickly.
Veterinarians to more accurately classify and characterize lameness during clinical examination, thereby streamlining the diagnostic process.
Let’s imagine for a moment that a horse’s lame limb would visibly change color for us, making it much easier to distinguish it from the other limbs. Most of us have had the ability to discriminate between colors since childhood, so this scenario would make determining the horse’s affected limb a breeze.
Now let’s imagine that the affected half of the limb (upper or lower) would glow brightly for us. In addition to seeing the affected limb, we would instantly know which aspect of the limb harbored the problem.
Finally, imagine that the specific source of the horse’s lameness (such as a certain joint) would flicker for us. In this instance, we could determine the source of the problem simply by looking at the horse. Visual lameness assessment of the horse would accordingly seem much less intimidating to the average observer.
Obviously, we don’t have the luxury of using colors and flickering lights to help us determine the anatomic source of a horse’s lameness. There are other visual markers, however, that can be just as obvious and just as definitive. It is the goal of this book to make the reader aware of these markers as well as their physiologic implications. The fundamental methodology of proper lameness assessment is highlighted in Figure 4.1 and detailed in section VI (see p. 157) of this book.
4.1 Basic Method of Visual Assessment
A. Initially, you scrutinize the adjustments the horse makes in its median anatomy to avoid or accommodate the problem. The visible expression of these adjustments helps you to identify which region(s) or limb(s) might be afflicted. In this instance, the right forelimb is lame.
B. Next, you determine the nature of the horse’s lameness. This can help you to discriminate which aspect of the region or limb is likely harboring the problem. In this example, the horse exhibits a combination lameness that suggests that the problem likely resides within the mid-aspect of right forelimb.
C. Finally, you can use the horse’s display of characteristic or unique gait deficits to establish a list of potential causes for the lameness. Based on the appearance of this horse’s combination lameness, for instance, you might suspect a problem along the right fore fetlock region.
5 Obscure (Hidden) Lameness
Obscure lameness manifests when the horse is unable or unwilling to make the physical adjustments that we as observers require to assess the problem. It is appreciably easier to see lameness when the right side of the horse moves decidedly differently than the left. In the case of unilateral lameness, the horse may favor one side by transferring body weight to the other side (fig. 5.1 and see VL 5a). This manifests as asymmetrical movement and is readily detected by our eyes.
5.1 Unilateral Transfer of Weight
Lame horses will often transfer weight off the uncomfortable (lame) side and onto the comfortable (sound) side.
VL 5a Scan/Click to view video. www.getsound.com/tutorials/5a
Bilateral Lameness
It may be more difficult to perceive bilateral lameness, especially when both sides are comparably (equally) affected. The relative lack of asymmetry displayed by the bilaterally lame horse can make accurate visual assessment somewhat challenging, especially if the visible disparity between sides is less than 25%.6 It is for this reason that many horses with bilateral gait deficits of similar appearance and degree are deemed to be sound.
In the case of bilateral lameness, the horse may not be permitted to adjust its movement to avoid one problem without exacerbating a separate problem in the contralateral limb (fig. 5.2 and see VL 5b).
5.2 Bilateral Suppression of Lameness
A horse may not want to favor one limb if it exacerbates a problem (such as pain) in the contralateral limb. In this case, the horse may be unable to underload a sore right front limb without overloading a sore left front limb.
VL 5b Scan/Click to view video. www.getsound.com/tutorials/5b
As you remember, the horse alters movement to avoid pain, accommodate a biomechanical restriction, and/or maintain balance. But what if something prohibits the horse from making the desired physical adjustments? In this case, our visual perception of the lameness may become more obscure even though the source of the problem persists. For example, if both of your knees were equally painful you might walk funny but not necessarily “limp.” This is because your bilateral discomfort poses a dilemma: to which leg can you transfer weight without exacerbating your pain? Your inability to visibly limp in this instance doesn’t mean that your knees don’t hurt—it just becomes more difficult for others to discern that you have a problem.
Multifactorial Lameness
We may also have difficulty perceiving asymmetric movement in horses exhibiting certain forms of multifactorial lameness, especially if pathology coexists in a compensating limb. For example, a trotting horse with severe foot pain in the right hind limb will often choose to transfer weight to the left front limb, which constitutes the other limb of the respective diagonal pair. As observers, we try to use this visible shift in weight to identify and characterize the horse’s lameness. However, concurrent left front foot pain might preclude this horse from comfortably and effectively transferring weight