Algometry device for measuring pain reaction from pressure

Technology for Enforcement:
Pressure Algometry
g
y
Kevin K. Haussler,, DVM,, DC,, PhD
Examination for Soring
g
Visual inspection of pastern region
• Signs of inflammation
• Proliferative granulation tissue
• Open wounds
Digital palpation of the distal forelimbs
• Identify
yp
presence of p
pain
• Abnormal tissue indicative of illegal therapy
United States Department of Agriculture, Animal and Plant Health Inspection Service (2004)
2004 DQP/VMO Horse Protection Act Training Manual. pp 3131-33.
Positive Pain Response
p
• Repeatable to digital palpation
• Ensure that the reaction is not due to anxiety
or excitement
Perceived Limitations of Current Exam
Inconsistent application of thumb pressure
• Not quantified
• May
M vary between
b t
examiners
i
Comments of owners and trainers of “positive”
positive
horses
• Too much pressure was applied
• Any normal horse would respond to the applied
pressure
Pressure Algometry
g
y
Mechanical nociceptive threshold (MNT)
• The minimum pressure which induces pain or a pain response
A high pressure measurement
indicates a high pain threshold
or a low pain response
Fischer AA. Pain 1987; 30(1): 115
115--126.
Pressure Algometry
g
y
Haussler KK, et al. Equine Vet J 2006; 38: 70-75.
Haussler KK, et al. Amer J Vet Res 2007; 68: 1167-1176.
Objectives
j
1 Assess how nonsored Tennessee Walking Horses
1.
respond to mechanical pressures ≤ 10 kg/cm2
• Nonsored Tennessee Walking Horses can tolerate mechanical
pressures > 10 kg/cm2 within the pastern region of both
thoracic limbs
• By experienced Veterinary Medical Officers (VMOs) responsible
for enforcement of the Horse Protection Act (HPA)
2. Establish reference mechanical nociceptive thresholds
((MNTs)) within the p
pastern region
g
Materials and Methods
Tennessee Walking Horses (N=26)
• Housed on a single farm
• All
ll actively
l showing
h
• Average duration of 3 years (range 11-10 years)
• Flat shod in the fore feet
• Unshod in the hind feet
• No
N signs
i
off lameness
l
• Pass a Horse Protection Act (HPA) inspection for soring
• 2 experienced
i
d APHIS veterinary
t i
medical
di l officers
ffi
(VMOs)
(VMO )
Horses
1 horse excluded
• Intolerant to pressure algometry procedure
25 horses
• 11 mares,, 11 geldings,
g
g , 3 stallions
• Age – 7 years (3
(3--12 years)
• Body
y weight
g – 405 kg
g ((341(341-490 kg)
g)
• Height at withers – 153 cm (144(144-166 cm)
All horses
h
passed
d examination
i ti for
f soring
i
Mechanical Nociceptive
p
Thresholds
4 sites commonly
y found to be p
painful in sored horses
• Pastern – Dorsal, lateral, medial, and palmar
Mechanical Nociceptive
p
Thresholds
1.
1 Response to applied pressure
• 5 VMOs - Inexperienced in pressure algometry
• Pressure algometer – Upper limit of 10 kg/cm2
• 3 consecutive measurements at each site
2. Reference MNTs
• 1 person - Experienced in pressure algometry
• Pressure algometer – Upper limit of 30 kg/cm2
• Measured last
• Limit trauma associated with increased applied pressure
MNT Measurements
• 4 pastern sites
• 3 consecutive measurements/site
• 4 or 5 examiners per limb
• 48 to 60 MNTs per limb
• 96 to 120 MNTs per horse
• 25 horses
• Total of 2,628
2 628 MNT measurements
MNT Values of 5 VMOs
Hypothesis:
100
• Nonsored Tennessee Walking
Overall > 10 kg/cm
g/ 2
• 80% (range 53 to 98%)
80
% of MNT M easurements
Horses tolerate mechanical
pressures > 10 kg/cm2
90
70
60
50
40
30
20
10
0
1
2
3
Examiners
4
5
MNT Values ((≤ 10 kg/cm
g/ 2) of 5 VMOs
Overall = 9.5 ± 0.3 kg/cm
g/ 2 ((range
g 6.4 to 10.0))
2
Mechanical Nociceptive Thrresholds (kg/cm )
10
8
6
4
2
0
1
2
3
Examiners
4
5
Reference MNT Values of Pastern
2
Mecha
anical Nociceptivve Thresholds (kg/cm )
30
25
20
15
10
5
0
Lateral
Dorsal
Medial
Palmar
Haussler KK, et al. Equine Vet J 2008.
Adaptation
p
and Sensitization
70 ± 15%
90
80
Proportion of M
P
Measuremen ts
70
60
50
40
17 ± 14%
13 ± 12%
30
20
10
0
Adapatation
No Change
Sensitization
Skin Lesions
6 (24%) horses
• Unilateral skin lesions
or mild scarring
No significant MNT
differences
• To opposite limb
• Other horses without
skin lesions
No Significant
g
Differences
• Age,
Age sex,
sex body weight
weight, wither height
• Recent exercise
• Order of measurements
• Hand
H d dominance
d i
off examiners
i
Mental Status
Separate nonblinded examiner
Mental status during MNT measurements
Grades (1 to 5)
• 1 – Very calm, stood quietly during all measurements
• 2,
2 3,
3 4 - Intermediate
I
di
gradations
d i
off increasing
i
i anxiety
i
• 5 – Extremely anxious and unmanageable
H
Hypothesis
h i
• Calmer horses (grade 1) have higher MNTs (lower pain)
Mental Status Scores
Average score = 1.3
1 3 ± 0.7
0 7 (range 11--5)
10 horses had mental status scores > 1 across all 6 examiners
Distribution of scores
• Grade 1 (N=120)
• Grade 2 (N=20)
• Grade 3 (N=6)
• Grade 4 (N=3)
• Grade 5 (N=1)
(N 1)
Horses with high initial mental status scores tended to have
lower scores after repeat
p
MNT examinations
Tolerance to Procedure
Overall willingness or tolerance to stand quietly on each
thoracic limb by each examiner
Grades (1 to 5)
• 1 – Stood completely quietly and readily tolerated all
measurements
• 2, 3, 4 - Intermediate
d
gradations
d
off decreasing
d
tolerance
l
• 5 – Repeated lifting of the limb and inability to stand on the limb
for the majority
j
y of measurements
Hypothesis
• Tolerant horses (grade 1) have higher MNTs (lower pain)
Tolerance to Procedure Scores
Average score = 1.3
1 3 ± 0.6
0 6 (range 11--4)
13 horses had tolerance scores of 1 across both limbs
and
d 6 examiners
i
Distribution of scores
• Grade 1 (N=162)
• Grade 2 (N=48)
• Grade
G d 3 (N=8)
(N 8)
• Grade 4 (N=1)
• Grade 5 (N=0)
(N 0)
Correlations Between Scores
Mental status scores
• No correlation with MNT values
• Calm horses did not have higher MNTs
• Anxious horses did not have lower MNTs
Tolerance to procedure scores
• No
N significant
i ifi
lleftleft
f -right
i h li
limb
b diff
differences
• No correlation with MNT values
P iti correlation
Positive
l ti between
b t
mental
t l status
t t and
d
tolerance to procedure scores
• Calmer horses had higher tolerance scores
• Anxious horses had lower tolerance scores
Hypothesis
yp
Tennessee Walking Horses are “more
more sensitive”
sensitive
• Lower mechanical nociceptive thresholds
Compare similar sites within the digit to a population
of mixed breed horses (N=24)
Forelimb MNTs ((N=24 horses))
Mechanical Nocicceptive Threshold
ds (kg/cm2)
35
30
25
20
15
10
5
0
C5TP
C5M
Neck
N k
T3M
SCAP SHDR
Sh ld
Shoulder
TRI
ULNA ECR
Elb
Elbow
AC
IC
RC
C
Carpus
C3
MC3
MC4
SUSP
C
Cannon
FTK
CBND
Di i
Digit
Haussler KK, et al. Amer J Vet Res 2007; 68(11): 11671167-1176.
Forelimb MNTs ((N=24 horses))
Tennessee Walking
g Horses ((N=25))
2
Mechanical Nociceptive
e Thresholds (kg
g/cm )
35
30
25
20
15
10
5
0
C5TP
C5M
Neck
T3M
SCAP SHDR
Shoulder
TRI
ULNA
ECR
Elbow
AC
IC
RC
Carpus
C3
MC3
MC4
Cannon
SUSP
FTK
CBND
Digit
Digital
g
Palpation
p
Apply thumb pressure with enough force to
• Flatten the flesh of the thumb
• Partially
P i ll blanch
bl
h the
h thumbnail
h b il
• Approximately 2.3 kg (1 pound) of force
• Thumb
Th b surface
f
area = 4 to
t 6 cm2
• Equals 0.4 to 0.6 kg/cm2 of pressure
Comparison
p
of Applied
pp
Pressures
47-70 X
25
33-49 X
2
Applied Presssure (kg/cm )
20
15
80% - > 10 kg/cm2
10
11-16 X
5
0.5 kg/cm2
0
Blanch Thumbnail
VMOs using 10-kg PA
Methods of Pressure Application
Reference MNT
Limitations of Study
y
Flat shod
• Long toes, pads, weighted shoes, action devices
Non--sored horses
Non
• Sored horses are expected to have lower MNTs
Upper limit of 1010-kg algometer
• Repetitive
p
measurements and p
potential tissue injury
j y
No formal interinter- and intraintra-examiner repeatability
No correlation between skin lesions or scarring
g and MNTs
• Areas of pain could have been present, but were not measured
Home environment
• Not at a novel or show environment
• Effect on mental status and tolerance to procedure scores
Conclusions
• Reference MNTs of the pastern region of nonnon-sored
Tennessee Walking horses provide an objective
standard for the evaluation of p
potentially
y sored horses
• Pressure algometry, in lieu of digital pressure, can
quantify mechanical pressure applied during soring
inspections and provide consistency between
examiners
i
Acknowledgements
g
• Funding provided by the United States Department
of Agriculture, Animal and Plant Health Inspection
Service,, Animal Care,, Horse Protection Program
g
• Dr. Clement Dussault for initial conception of the
study
• Drs. Todd Behre, Lynn Bourgeois, Kurt Hammel,
Susan Kingston, John Poe, and Tanya Tims for
technical assistance
Source for Pressure Algometer
g
Wagner Instruments
• Force gauge, Model FPK 60
• 0 to 30 kg/cm2
• 1 cm2 rubber plunger
• www.wagnerinstruments.com
The
E d
End
MNT Measurements
MNT Measurements
Feet
Q
Questions
• Description of technology
• How it might detect soring
• Costs to train and equip an inspector
• Equine research and testing already been completed
• Legally supportable in ticketing soring
• How quickly and efficiently could an inspection for soring be done
•
•
•
•
before entering show ring
Successful in court cases
Detect soring even if covered up by stewarding or local anesthetics
Applied to horses after a show class that appear sore
Does a sore horse have a better chance of testing sore after a class
Soring
g
The practice of inflicting pain on the limbs of a
horse with the purpose of accentuating gait
United States Department of Agriculture, Animal and Plant Health Inspection Service (2001)
The Horse Protection Act. Understanding the scar rule. Program Aid No. 1685.
Soring
g Examination
• Lameness examination
• Observation of any pain behavior
• Physical examination of the forelimbs from
the carpus distally
• Inspection of the shoes, pads and action
devices
United States Department
epartment of Agriculture,
griculture, Animal
nimal and Plant
lant Health
ealth Inspection
nspection Service ((2005)
005)
The Horse Protection Act. Program Aid No. 1827.
Thermography
g p y
• Significant thermographic differences within
the distal forelimb have been reported for
treated and nontreated limbs within the
same horse
van Hoogmoed L, Snyder JR, Allen AK, et al. Use of infrared
thermography to detect performance enhancing techniques in
horses. Equine Vet Educ 2000; 12(2): 132
132--138.
Effect of Hand Dominance
• All 6 examiners were rightright-handed
• Compared MNTs at medial and lateral pastern
sites
i
Pressure Algometry
g
y
• Able to quantify applied pressure
• Determine normal mechanical nociceptive thresholds
• Axial skeleton
Haussler KK, Erb HN. Mechanical nociceptive thresholds in the axial skeleton
of horses.
horses Equine Vet J 2006; 38(1): 70
70--75.
75
• Thoracic limb
Haussler KK,
KK Hill AE
AE, Frisbie DD
DD, et al
al. Determination and use of
mechanical nociceptive thresholds of the thoracic limb to assess pain
associated with induced osteoarthritis of the middle carpal joint in horses.
Amer J Vet Research 2007;; 68(11):
( ) 1167
1167--1176.
Materials and Methods
2 (of 5) VMOs – Selected at random
• Lameness – Figure 8 pattern
• Digitally palpated unweighted thoracic limbs from
carpus to hoof
• Pain or inflammation in pastern region
• Light digital pressure
• Visual examination of pastern region
• Skin lesions or scarring – Graded: Mild, moderate or severe
MNT Measurements
Pressure applied perpendicular to 4 pastern sites
• Rate - 5-10 kg/cm2/second
• Duration – 2-3 seconds
• Avoidance reaction
• Lift thoracic limb or pull limb away
• Maximal recordable pressure of instrument
3 consecutive measurements
• Within
Within--site repeatability
p
y
Wait 2 minutes between the each MNT measurement session by
4 or 5 different examiners per horse
• 20 minutes per horse
MNT Values of 5 VMOs
Hypothesis:
100
• Nonsored Tennessee Walking
90
Horses tolerate mechanical
pressures > 10 kg/cm2
• 80% (range 53 to 98%)
Overall ≤ 10 kg/cm2
• 20% (range 2 to 47%)
70
Percentage o
of MNTs
Overall > 10 kg/cm2
80
60
50
40
30
20
10
0
1
2
3
Examiners
4
5
VMOs ≤ 10 kg/cm2
• Left
Left--right differences - 0.1 ± 0.2 kg/cm2
30--kg
30
g Algometer
g
Reference MNTs
• 3 consecutive MNTs across sites and horses
Compare leftleft-right MNTs
• Pool MNT values
Si
Signalment
l
t effects
ff t
• Age - < 7 years; ≥ 7 years
• Sex – Female; Male
• Body weight - < 410 kg; ≥ 410 kg
• Wither height - < 154 cm; ≥ 154 cm
• Exercise status – Recently exercised; Unexercised
Statistical Tests
• Left
Left--right paired MNTs
• Left
Left--right tolerance scores
• Order of MNTs
• Effect of hand dominance on MNTs
• Pastern site differences in MNTs
• Presence or absence of skin lesions on MNTs
• Signalment
Si
l
– Age,
A
sex, weight,
i h height,
h i h exercise
i
• Correlations – MNTs, mental status, tolerance to
procedure
Adaptation
p
and Sensitization
Assess 3 consecutive measurements at each site
• Sequential increases > Adaptation
• Sequential
S
ti l d
decreases > Sensitization
S iti ti
• No change or consistent pattern
Proportions of above patterns
Median of 3 consecutive measurements
• Site
Site--specific baseline MNT within horse
Reference MNTs
Proportion of patterns of 3 consecutive
measurements
• No significant leftleft-right differences
Mean range
Mea
a ge o
of 3 co
consecutive
secut ve measurements
easu e e ts
• 2.1 ± 1.6 kg/cm2
Left--right paired differences
Left
• 0.7 ± 2.8 kg/cm
g/ 2
The
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End