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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 off the right hind limb (fig. 5.3 and see VL 5c). This presents a quandary because the horse doesn’t have a comfortable place to which to transfer the weight. The observer is also in a predicament because the lack of obvious body adjustment may give the false impression that the horse is relatively comfortable.

5.3 Multifactorial Suppression of Lameness

A horse may not want to favor one limb if it exacerbates a problem (such as pain) in a compensating limb. In this case, the horse may be unable to underload a sore right hind limb without overloading a sore left front limb.

VL 5c Scan/Click to view video. www.getsound.com/tutorials/5c

Axial Lameness

Axial structures are those situated along or near the horse’s midline or centerline. They include the head, neck, chest, back, and rump. Due to their proximity to the horse’s centerline, asymmetric movement between right and left axial anatomy may be difficult to discern for the observer. This is because disparities in movement become harder to detect as we assess analogous structures that reside closer to one another (fig. 5.4 and see VL 5d). Dissimilarities are much easier to see when they are associated with structures farther away from the midline, toward the periphery of the horse.

5.4 Axial Suppression of Lameness

The farther away a structure is from the centerline of the horse’s body, the easier it is to discern a difference in movement between it and its contralateral counterpart. By contrast, it is more difficult to detect asymmetric movement between contralateral structures located closer to the horse’s midline.

VL 5d Scan/Click to view video. www.getsound.com/tutorials/5d

In general, the closer that contralateral counterparts are from one another, the more difficult it is to discern asymmetric movement between the two. Consider the manner in which a seesaw displays movement, for example. It is relatively easy to visually appreciate that the ends of the board are moving dissimilarly from one another: one rises as the other lowers. Of course, reciprocal movement is also occurring along portions of the board located near its pivot point at the center of the seesaw. Yet, motion along this area is considerably more challenging to perceive with our eyes.

To further convolute our frustration, horses often respond to back and neck pain by evading movement along the affected area(s) rather than altering it. And as you might imagine, it is nearly impossible for most horses to brace one side of the neck or back without significantly limiting movement of the other side. The understated discrepancy in movement between corresponding axial structures coupled with their mitigated activity (as the horse attempts to avoid pain) can make proper assessment of the median anatomy very challenging for the observer. Even the most seasoned equine performance professionals will usually choose to pursue hands-on palpation, physical manipulation, and diagnostic imaging to supplement their visual impressions and build confidence in their assessment.

We should always remember that our lame horses are “talking” to us. They’re using a form of “sign language” that is expressed through altered movement. Similar to the way people use gestures to illuminate conversation, horses use them to illustrate what they are experiencing as they move. As effective observers, it is imperative that we learn to listen with our eyes instead of our ears.

Horses suppressing axial pain that exists independent of any limb deficits will often exhibit general stiffness, resistance and/or poor behavior rather than overt lameness (VL 5e). In many instances, a problem is “felt” by the rider rather than seen by a spectator. On the other hand, the size and configuration of the horse’s axial anatomy does lend itself to fairly clear expression of inappropriate position, orientation, and carriage. These visible aberrations are characterized in chapter 23 (p. 161).

VL 5e Scan/Click to view video. www.getsound.com/tutorials/5e

Moreover, we have ways of exposing most forms of “hidden” lameness to facilitate our assessment. The principle function of the lameness examination, for instance, is to create a setting intended to increase the horse’s asymmetric or irregular movement, thereby allowing the observer to more easily detect the presence of one or more problems. Environmental manipulation strategies are discussed in chapter 26 (p. 183).