Wireless Transmission of Torso Acceleration and Fault

Detection to Evaluate Lameness in Horses

Marco Lopes

, Kevin Keegan

, P. Frank Pai

, Yoshiharu Yonezawa

and Hiromitchi Maki

Department of Veterinary Medicine and Surgery, College of Veterinary Medicine

University of Missouri, Columbia, 65211, Missouri, U.S.A.

Department of Mechanical and Aerospace Engineering, College of Engineering

University of Missouri, Columbia, 65211, Missouri, U.S.A.

Department of Electrical and Digital Systems Engineering, Hiroshima Institute of Technology

Hiroshima, Japan

Abstract. Lameness is the most common clinical problem affecting horses. In

cases of mild lameness, experienced veterinarians do not consistently detect

lameness using subjective evaluation. The classic methods of kinematics and

kinetics for objective detection of lameness are effective but not practical for

the clinical setting. An inertial sensor system has been developed for objective

lameness detection in horses. The sensors sample vertical acceleration of the

head and pelvis and angular velocity of the right forelimb at 200 Hz. Data is

transmitted in real time to a hand-held tablet computer. Using an adaptation of

vibration analysis for fault detection vertical torso movement is processed and

analyzed. Evaluation of lameness with the inertial sensor system is precise, ac-

curate, and more sensitive than traditional subjective evaluation.

1 Background

Lameness is a change in the gait due to a functional or structural change in the

locomotor system [3]; [19]. Lameness is the most common clinical problems that

affects the horses’ wellbeing and causes severe losses to the equine industry [8]; [1].

In many cases, the initial condition causing lameness is reversible if promptly diag-

nosed and treated. Delayed diagnosis and treatment may lead to progression of dis-

ease and delayed recovery. In many cases, without prompt diagnosis and treatment,

irreversible lesions may develop, which can incapacitate the horse for further use [3];

[9].

The first step for lameness diagnosis is lameness detection, which is identification

of the affected limb(s). This is a crucial step, which is then followed by other diag-

nostic procedures for locating the affected structure(s) and the pathologic process(s)

associated with lameness. Traditionally, veterinarians identify lameness in horses by

Lopes M., Keegan K., Frank Pai P., Yonezawa Y. and Maki H..

Wireless Transmission of Torso Acceleration and Fault Detection to Evaluate Lameness in Horses.

DOI: 10.5220/0003879200510059

In Proceedings of the International Workshop on Veterinary Biosignals and Biodevices (VBB-2012), pages 51-59

ISBN: 978-989-8425-94-2

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

observing the horse moving at the walk and at the trot and then subjectively grading

lameness severity using an integer scale [20]; [3]. Small changes in severity of lame-

ness may be missed. The naked eye has limited temporal resolution and small changes

in movement with mild or early dysfunction may be missed [18]; [21]. The limitations

of the human eye explain the limited results of subjective evaluation of lameness even

when performed by experts [6]; [7]; [10]; [12]. The human brain stores limited visual

information [22]; [23] so that effective comparisons of sequential evaluations (e.g.,

before and after flexion, before and after nerve block, before and after treatment)

cannot be performed. Also, subjective evaluation can be biased [2].

Objective evaluation of lameness lacks many deficiencies of subjective evalua-

tion. Objective evaluation for detection of lameness in horses has been performed

with both kinetic and kinematic approaches [11]; [13]. The use of a stationary force

plate, a kinetic approach which measures the ground reaction forces to one limb at a

time, is considered by some to be a gold standard for lameness detection in horses.

However, kinematic evaluation using cameras to record motion has also been shown

to be useful as an objective method for lameness detection. Although accepted as

accurate methods to objectively study lameness, current kinetic and kinematic evalua-

tion approaches are limited. The artificial conditions required for data collection af-

fect normal locomotion. Current methods are laborious and time consuming. Special-

ized equipment, facility and expertise are required. These limitations generally restrict

objective lameness evaluation in horses to the laboratory environment and make tra-

ditional kinetic and kinematic methods not practical for routine clinical use [11].

Fig. 1. Periodic signal representing normal vertical movement of the head or pelvis of horses

moving at the trot. Local minimums are reached at middle of the stance of each limb (i.e., front

limb for head movement, hind limb for pelvic movement) and local maximums occur after

stance of each limb.

Kinematic studies of normal horses and lame horses moving at the trot have

demonstrated that the head and pelvis move up and down twice during each stride.

Head and pelvic height reach lowest position in the middle of and highest position

after the stance phase of each diagonal pair (Figure 1) [5]; [4]; [13]. Lameness mani-

fests as perturbation of the normal sinusoidal-like vertical movement of the head and

pelvis (at twice stride frequency) by a recurring component (at 1x stride rate) (Figure

2) [13].The aim of this article is to describe this approach of objective lameness eval-

uation using wireless transmission of body mounted inertial sensors and to demon-

strate that it can be used practically in clinical cases trotting naturally over ground.

Fig. 2. Deformation of the normal vertical periodic motion of head or pelvis (gray solid line)

by a component at 1x stride rate (gray dashed line) in lame horses moving at the trot. The black

wave line represents the deformed periodic motion of a lame horse. Timing of lameness com-

ponent relative to the phase of stride (arrows) indicates affected limb and phase of stance (be-

ginning, middle, end) affected. The stances of the front limbs (if graphs represent head move-

ment) or hind limbs (if graphs represent pelvic movement) are indicated as black (right limb)

and white (left limb) rectangular figures.

2 Features of the Inertial Sensor-based System for Lameness De-

tection in Horses

2.1 Sensors

This device is composed of three small wireless inertial sensors each weighing 32 g

and measuring 3.2 x 3.8 x 1.9 cm. Each sensor consists of a surface-mounted,

microelectrical-mechanical device (accelerometer

or gyroscope

), radio transceiver

(open wireless technology standard) and antenna

, 4.2-V lithium-polymer battery

microcontroller,

and associated circuitry. The sensors are sampled synchronously at

200 Hz. Two of the sensors are uniaxial accelerometers, one attached to the head

(Figure 3A) and one to the pelvis (Figure 3C). A third sensor is a gyroscope attached

to the dorsal aspect of the right front distal limb (Figure 3B), measuring rotation of

the digit on the sagittal plane. Fault detection algorithms are implemented to quantify

vertical torso perturbation. This perturbation causes asymmetry of vertical torso

movement, which is measured and reported to the user.

2.2 Computer

A tablet PC equipped with a class 1 Bluetooth receiver (Figure 4) receives and stores

raw data, conducts data analysis, generates a report of the analysis, and stores the

results of data analysis.

2.3 Software

Data acquisition and analysis software were custom written

6,7

to perform multiple

tasks including a moving window error correction, double integration and decomposi-

tion into periodic and random components (Figure 5). After the random component is

extracted, asymmetry of vertical torso movement (i.e., lameness) is quantified by

calculating the ratio of the amplitude of the first harmonic (a1) to the amplitude of the

second harmonic (a2) (Figure 5) and by calculating differences in local head and

pelvis maximums and minimums between right and left strides (Figure 6). Means and

standard deviations are calculated over all strides collected. Peak detection algorithms

are used to automatically select strides to be analyzed. A report is generated at the end

of data analysis (Figure 7).

__________________________

MMA7260QT, ± 1.5 to 6 g, Freescale Semiconductor, Austin TX, USA.

Gyrostar ENC-03M, Murata Electronics North America, Smyrna, GA, USA.

EYSF1SAJJ, Taiyo Yuden Co Ltd, Tokyo, Japan.

Hyper Power Co Ltd, Shenzhen, China.

PIC18LF452/PQ(44), Microchip Technology Inc, Chandler, AZ, USA.

Delphi, Borland Software Corp, Austin, Tex.

MATLAB, The Mathworks Inc, Natick, Mass.

Fig. 3. Inertial sensor based system for lameness detection in horses: A and C - Vertical accel-

erometer positioned on the top of the head (poll) and top of the croup (between the sacral

tuberosities); B – Gyroscope positioned on the dorsal aspect of the pastern of the right front

limb.

Fig. 4. Data collection with the inertial sensor based system for lameness detection in horses: A

tablet PC equipped with a long-range class 9 Bluetooth receiver stores and analyses data ob-

tained by the inertial sensors.

3 Validation of the Inertial Sensor-based System for Lameness

Detection in Horses

This system has been validated by comparison with traditional kinematics using hors-

es with and without lameness trotting on the treadmill, with stationary force plate

evaluations (kinetics) and with subjective evaluation by expert veterinarians. The

inertial sensor system has shown to be precise [14], accurate [15]; [16] and more

sensitive than subjective evaluation performed by experienced veterinarians [17].

Results of evaluation with the inertial sensor system correlate with results of tradi-

tional kinematic evaluation [16] and, for forelimb evaluation, with the results of eval-

uation with the stationary force plate [15]. Correlation between the evaluation with

the inertial sensor system and evaluation with the stationary force plate has not been

investigated yet.

Fig. 5. Decomposition of the sinusoidal-like curves of vertical displacement signals of the head

or pelvis into periodic components and random moving average. The stances of the front limbs

(if graphs represent head movement) or hind limbs (if graphs represent pelvic movement) are

indicated as black (right limb) and white (left limb) rectangular figures under the horizontal

axis. The first periodic harmonic with frequency equal to frequency of the stride is the lame-

ness component. The second harmonic with frequency equal to twice the frequency of the

stride represents the normal vertical oscillation of the head or pelvis. Lameness severity is

proportional to the ratio between the amplitude of the lameness component and the normal

component (a1/a2).

Fig. 6. Calculation of the difference between the maximal positions of the head or pelvis

(maxdiff) after the stance of each diagonal limb pair. Calculation of the difference between the

minimal positions of the head or pelvis (mindiff) during the stance of each diagonal limb pair.

Fig. 7. Report of an evaluation performed with the inertial sensor system. Results of the front

limbs are on the left side and results of the hind limbs are on the right side. Graphs and the data

reported below each graph should be considered while interpreting the results.

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