Page 178 - Adams and Stashak's Lameness in Horses, 7th Edition

144 Chapter 2

Hindlimb strides The lameness values give a more quantitative descrip­
tion of the hindlimb lameness. Hindlimb lameness is
VetBooks.ir –30 Left hind lameness Right hind lameness 30 pelvic position between left and right hindlimb strides
quantified by calculation of the difference in maximum
Pushoff
Pushoff
(Diff Max Pelvis) and the difference in minimum pelvic
position between left and right hindlimb strides (Diff
–Diff Max (mm) –20 20 +Diff Max (mm) Min Pelvis). Diff Max Pelvis and Diff Min Pelvis are
calculated for every stride collected, and the mean and
standard deviation over all strides are reported. The
10
–10
signs of Diff Max Pelvis and Diff Min Pelvis determine
side and timing of lameness. Positive values indicate
right hindlimb lameness, and negative values indicate
0 0 left hindlimb lameness. High Diff Max Pelvis absolute
values indicate pushoff‐type hindlimb lameness. High
Diff Min Pelvis absolute values indicate impact‐type
–Diff Min (mm) –10 10 +Diff Min (mm) hindlimb lameness. The approximate reference range for
lameness for both measures is ±3 mm, which are confi­
dence intervals of the measure when hindlimb mean
–20
20
subjective AAEP score = 0. These confidence intervals
Impact Impact were determined and should be interpreted like the ref­
erence ranges of Diff Max Head and Diff Min Head for
–30 30 forelimb lameness.
0 10 20 30 0 10 20 30
Stride Stride
Metrics Detecting Compensatory Lameness
Thresholds for Max/Min Pelvis: ±3mm In trotting quadrupeds a primary lameness in the
Diff Max Pelvis: Mean: 5.8mm SD: 2.6mm front half of the body will sometimes cause compensa­
Diff Min Pelvis: Mean: 2.2mm SD: 2.7mm tory movements in the back half of the body and vice
versa, such that an apparent multiple limb lameness is
present. Interpretation of these compensatory move­
Q Score (hind): R 5.8 Push /R 2.2 lmp ments is sometimes referred to as the “law of sides.” The
Figure 2.132. Output of Lameness Locator® indicating right first principle of the “law of sides” states that an appar­
hindlimb pushoff lameness. Most red rays (Diff Max Pelvis) are on ent ipsilateral lameness, i.e. forelimb and hindlimb lame­
right side. This indicates most Diff Max Pelvis are + in sign, i.e. the ness on the same side of the body, is likely primary
pelvis is thrust up less after pushoff of right hindlimb compared with hindlimb lameness and a compensatory but false fore­
left hindlimb. Diff Max Pelvis > reference range of ±3 mm. Standard limb lameness. The second principle of the “law of sides”
deviation of Diff Max Pelvis less than mean of Diff Max Pelvis, states that an apparent contralateral lameness, i.e. fore­
indicating consistent lameness. limb and hindlimb lameness on opposite sides of the
body, is likely primary forelimb lameness and a compen­
The hindlimb lameness display is a qualitative satory but false hindlimb lameness.
description of the hindlimb lameness. The left side of the Experimental studies have determined that the first
display represents qualities of the left hindlimb function. principle of the law of sides is, for the most part,
The right side of the display represents qualities of the true. 38,40,41,70,72 Pain during stance in the hindlimb will
right hindlimb function. Each vertical line on the display cause the horse to shift weight forward onto the simul­
moving from left to right is a measure of either the defi­ taneously weight‐bearing contralateral forelimb, and
ciency of impact (pelvic fall) or the deficiency of pushoff the head will fall more than normal. Normal falling of
(pelvic rise) for that stride. The length of the line is rep­ the head during weight‐bearing of the opposite forelimb
resentative of the amplitude of lameness. will be less, giving the appearance of an ipsilateral fore­
Display of hindlimb lameness, with two subplots, one limb lameness (“low on sound”). Although there is sig­
representing function of the left and the other represent­ nificant variability from horse to horse, which is likely
ing function of the right hindlimb, is different from dis­ dependent on the type of primary hindlimb lameness,
play of forelimb lameness, as one plot combining Diff even slight primary hindlimb lameness may cause com­
Max Head and Diff Min Head. Why? The displays are pensatory movement in the head that mimics significant
different because the biomechanical model of VPM with forelimb lameness. This suggests the possibility, depend­
hindlimb pain is different from that of vertical head ing on the sensitivity of detection, of missing the identi­
movement for forelimb pain. VPM is modeled as a single fication of the primary hindlimb lameness because of the
free body falling less due to factors occurring in the first more apparent compensatory but false forelimb lame­
half of stance, which are different from factors causing ness. The increased sampling frequency of the inertial
less pelvic rise during pushoff of a hindlimb in the sec­ sensors compared to the unaided human eye decreases
ond half of stance. Diff Max Head and Diff Min Head the chance of this confusion.
are dependent quantities caused by the same thing (head The second principle of the “law of sides” is less true
moving upward at moment of peak pain), whereas Diff and less straightforwardly explained. 23,38,73,74 Primary
Max Pelvis and Diff Min Pelvis are independent quanti­ forelimb lameness can cause compensatory movements
ties caused by different things. in the vertical movement of the pelvis attributable to