Equiping the horse with body-mounted inertial sensors (Lameness Locator®
by EquinosisTM)
Lameness Locator® was specifically designed as an aid to the practicing equine
veterinarian for detection and evaluation of lameness in horses. It was developed by
equine veterinarians and engineers at the University of Missouri in collaboration with
the Hiroshima Institute of Technology in Japan. It is licensed to EquinosisTM in
Columbia, Missouri, for further development and commercialization and is currently
the most widely used system of objective measurement of lameness in equine
clinical practice.
Lameness Locator® consists of 3 inertial sensors (2 accelerometers and 1
gyroscope), a tablet PC for data analysis, a sensor battery charger, and accessories
for attaching the sensors to the horse’s body. The inertial sensors are attached to the
head (accelerometer 1), the pastern of the right forelimb (gyroscope) and the dorsal
midline of the pelvis (accelerometer 2). Vertical accelerations of the head and pelvis
and angular velocity of the right distal forelimb are measured and wirelessly
transmitted in real time to a handheld tablet computer. The range of transmission is
up to 150 meters. Custom-designed algorithms are used to detect and quantify
forelimb and hind limb lameness when the horse is trotting. Trotting strides are
automatically detected by the software when the horse is moving.
Lameness Locator® algorithms were developed from previous kinematic research.
Vertical head and pelvic acceleration are converted to distance and separated into
components by custom error-correction algorithms. Random movement is discarded.
Remaining periodic movement is separated into movement due to lameness at stride
frequency and natural vertical motion at twice the stride frequency. Lameness is
detected and quantified by reporting (1) the ratio of vertical movement due to
lameness to the natural vertical movement, and (2) the means and standard
deviations of the differences between the maximum and minimum height of the head
position (for forelimb lameness evaluation) and pelvis position (for hind limb
lameness evaluation). Location of lameness to limb and timing of peak lameness
within the stride phase of a limb are determined by the association of head and
pelvic movement to angular velocity of the right forelimb. Lameness evaluation
results are reported in a graphical display that depicts amplitude of impact and
propulsion asymmetry in each stride. Lameness Locator® has been commercially
available since December 2009.
Detecting Forelimb Lameness with Lameness Locator®
There are 2 principle causes of vertical head movement in the trotting horse. The
first principle states that the head follows the down-and-up motion of the torso as the
horse is trotting, down during the first half of stance and up during the second half of
stance of each forelimb. The second principle implies that the head moves up
because of pain causing lameness. Moving the head upward reduces vertical
ground reaction forces. The total vertical movement of the head is simply a
summation of both these causes. Another interesting fact is supported by
observation and measurement. The shape of the trajectory of vertical head
movement provides information about the timing of forelimb lameness, i.e. whether
the pain is greatest in the first half of stance, when the torso is decelerating
downward, or in the second half of stance, when the torso is accelerating upward.
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
37