Christy West, TheHorse.com Webmaster
February 14 2005, Article # 5394
"I used to think I knew how to evaluate a horse's movement for lameness, until I started to look more carefully. Two different highly experienced practitioners can evaluate a lame horse, and come up with different [lame] legs," said Kevin Keegan, DVM, MS, Dipl. ACVS, associate professor of veterinary medicine and surgery at the University of Missouri, in his presentation on lameness evaluation. He discussed the conclusions he and his co-authors have drawn about interpreting lameness via head and pelvic movement, using their observations of more than 100 horses evaluated on a treadmill with video and computer-assisted gait analysis.
Keegan noted that most equine practitioners use head movement to determine forelimb lameness, and pelvis movement to clarify hindlimb lameness. "However, the specific components of the head or pelvic motion that are important for the evaluation of equine lameness have not been clearly described or agreed on by veterinarians," he commented. Furthermore, multiple lamenesses can certainly complicate the issue.
Conventional veterinary wisdom makes two statements regarding head nod and forelimb lameness, he said: With forelimb lameness, the head nods up when the lame limb is on the ground, and the head goes down when the sound limb lands (the "down when sound" maxim). "The first statement is true sometimes, and the second one false sometimes," he stated.
To illustrate the variability of horses' carriage changing with different lamenesses, Keegan first showed a video of a normal horse trotting on a treadmill with a graphic evaluation of his head position (seen head-on). His perfectly consistent wave pattern of head up and down movement contrasted notably with the next video, that of a lame horse (one forelimb) that showed less downward movement of the head only and no change in upward movement. Another lame horse (one forelimb) only had more upward head movement when pushing off of the lame limb. Graphs showing the movement of markers on their heads very clearly showed the differences in the movement patterns between all three horses.
Similar principles apply when evaluating hindlimb lameness, Keegan said. Traditionally, veterinarians have watched horses move away from them to look for a "hip hike," in which the sore limb is carried higher to identify the lame leg. Rather, he prefers to look at the entire vertical movement of the pelvis when left and right hind limbs land and push off. "To me, this is a lot easier than looking at rotation of the pelvis (evaluating the hips separately, or rotation of the pelvis)," he commented. "Look at the pelvis like it's a big head."
Also, he said evaluating pelvic rotation is not always accurate. To illustrate this point, he showed a video of a sound horse that looked slightly lame from behind while trotting because of pelvic rotation; however, this horse had the same pelvic rotation when standing still--a conformational abnormality rather than a lameness.
Again, he showed several videos of hindlimb-lame and sound horses to illustrate his points, along with graphs of the movement of hip markers to further clarify the movement abnormalities.
"We've had hundreds of horses on the treadmill; all [hindlimb] lame horses had asymmetrical movement of the pelvis (comparing vertical movement during right and left hind limb landings), regardless of pelvic tilt," he explained. "You see symmetrical movement of the pelvis in a sound horse, even if the pelvis is rotated to one side, because the vertical movement of the pelvis is symmetrical. The most sensitive measurement of lameness is the vertical movement of the head and of the pelvis. Stride length and other characteristics are much more variable and can give you false negatives."
To summarize the presenting characteristics of lame horses, Keegan offered the following observations of head carriage changes with forelimb lameness:
* The head moves down less during the stance phase of the lame limb and up less after the stance phase of the lame limb when the pain occurs maximally at hoof impact or within the first half of the stance phase of the stride.
* The head moves down less during the stance phase of the lame limb when the pain occurs maximally at full weight-bearing.
* The head moves up more after the stance phase of the lame limb when the pain occurs maximally during the second half of the stance phase of the stride.
* The head does not move up appreciably during the stance phase of the lame limb until the lameness is severe.
The following observations pertain to hindlimb lameness:
* The pelvis moves down less during the stance phase of the lame limb and up less after the stance phase of the lame limb when the pain occurs maximally within the first half of the stance phase of the stride.
* The pelvis moves up less after the stance phase of the lame limb when the pain occurs maximally within the second half of the stance phase of the limb.
* The pelvis does not move up appreciably during the stance phase of the lame limb until the lameness is severe.
Compensatory lameness appears as follows:
* During primary hindlimb lameness, the head moves down less during the stance phase of the ipsilateral forelimb, mimicking a forelimb lameness. The false, compensatory forelimb lameness can be "severe" enough to overshadow the primary hindlimb lameness.
* During primary forelimb lameness, the pelvis moves up less after the stance phase of the contralateral hindlimb, mimicking a hindlimb lameness. The false, compensatory hindlimb lameness is usually much milder than the primary forelimb lameness.
"A more objective and specific description of the various head and pelvic movements seen during lameness will assist equine practitioners in their clinical lameness evaluations," he said.