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Compensatory Lameness Patterns
Law of Sides
Ipsilateral suggests 1º hind limb lameness - THIS IS TRUE!!!!! WATCH OUT
Contralateral suggests 1º forelimb lameness - This is partly true…
Diff Max Head
the difference in maximum head height that occurs before RF weight bearing compared to before LF weight bearing. Ref range: -6.0 to +6.0 mm
Diff Max Pelvis
the difference in maximum pelvis height that occurs before RH weight bearing compared to before LH weight bearing. Ref range: -3.0 to +3.0 mm
Diff Min Head
the difference in minimum head height that occurs during RF mid stance compared to during LF mid stance. Ref range: -6.0 to +6.0 mm
Diff Min Pelvis
the difference in minimum pelvis height that occurs during RH mid stance compared to during LH mid stance.Ref range: -3.0 to +3.0 mm
If the foot does not create a depression or a divot in the ground, the surface should be considered hard. Hard preset surfaces = asphalt, concrete, packed dirt, gravel/stone, wood, frozen, treadmill, hard synthetic, hard (generic).
The head sensor device contains an accelerometer that tracks vertical head acceleration.
Indications of Severity
Indications of severity are based on a general range of amplitude of lameness, with levels increasing from “very mild”, “mild”, “mild/moderate”, “moderate”, and “moderate/severe”.
**The veterinarian should keep in mind that the severities are a range, and should not be used to compare two trials for consistency of amplitude (such as in establishing a stable baseline between two trials) or to assess change in amplitude (such as before and after a block, or change over time).
quantitative data from the collected trial. Calculated lameness metrics include 1) mean values of Diff Max head, Diff Min head, Diff Max pelvis and Diff Min pelvis; 2) standard deviations for each respective mean Diff Max and Diff Min; 3) Total Diff Head (mean vector sum) of the forelimb data; and 4) The Q Score for both forelimb and hind limb data.
The pelvic sensor device contains an accelerometer that tracks vertical pelvic acceleration.
Right Forelimb Sensor
The right forelimb sensor device contains a gyroscope that measures angular velocity in the sagittal plane. It is used as an event marker to determine right forelimb stance. It is also used to calculate a median stride rate.
If the foot creates a depression or a divot in the ground, the surface should be considered soft. Soft preset surfaces = loose sand, grass/turf, soft/deep, mud, soft synthetic, soft (generic).
Stabilizing the Lameness
Following viewing the initial baseline straight evaluation, repeat the trial to confirm stability of lameness measurements!
the graphical representations of the trial data.
the variability of the lameness measure (Diff Max Head, Diff Min Head, Diff Max Pelvis, Diff Min Pelvis) from stride to stride over the course of a single data collection trial. Stride-by-stride variability is assessed in the Lameness Locator® report by comparing the standard deviation to the absolute value of the mean for that measure. If the standard deviation is significantly greater than the mean (currently this is arbitrarily set at 120% of the mean), the confidence in, or strength of evidence for, lameness (in limb, amplitude and/or timing) is reduced.
The Quantification (Q) Score
the Q score is a summary of the side, timing and amplitude of the asymmetry.
Total Diff Head (Vector Sum)
Can be considered the amplitude of total head movement asymmetry, taking into account both Diff Max and Diff Min of the head.
As the side and timing of forelimb lameness is dependent upon both Diff Max Head and Diff Min Head, this single variable can be more easily used to estimate the overall level of forelimb lameness.
Total Diff Head is the Vector Sum of the mean Diff Max and mean Diff Min values, and is calculated using Pythagorean Theorem (a2 + b2 = c2), where a is the value of Diff Max head, b is the value of Diff Min head, and c is Vector Sum. (a) is plotted on the X axis, (b) is plotted on the Y axis, and the hypotenuse that forms that triangle is the Vector Sum. Total Diff Head is indicated by the RED ray on the forelimb plot.
The Total Diff Head (Vector Sum) reference range is 0 to 8.5mm. The upper reference range value of 8.5 is derived from the VS calculation when Diff Max Head and Diff Min Head are at their upper reference range values of |6|. 62+62=VS2
Owner, horse, and trial specific data (including date, time and type of trial conducted).
Trial-to-trial variability = the variability of the mean lameness measure between two trials. I.e. is the measure repeatable? Trial-to-trial variability is assessed by comparing the lameness measures between two trials and whether they are within the 95% confidence intervals of repeatability. If a particular measure in two back-to-back trials is not within the 95% CI, then that lameness is not stable.
Reported when the standard deviation is between 50 and 120% of the mean.
Lameness measure is within reference range.
If asymmetry of head or pelvic movement is within reference range and the variability is very low, “weak or moderate evidence” of “very mild asymmetry” may be reported. Note that this is sub-threshold asymmetry, reported only as an alert to the veterinarian that very mild asymmetry with low variability is present. Only the veterinarian can confirm any asymmetry, above or below established reference ranges, as clinically significant lameness.
Reported when the standard deviation is less than 50% of the mean Diff Min head (since Diff Min Head determines the side of forelimb lameness, it is the more important measure to assess for variability); or Mean Diff Min and/or Diff Max pelvis.
Reported when the standard deviation is greater than 120% of the mean.
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