Objective—To measure the effect of subject velocity
on hind limb ground reaction force variables at the
walk and to use the data to predict the force variables
at different walking velocities in horses.
Animals—5 clinically normal horses.
Procedure—Kinematic and force data were collected
simultaneously. Each horse was led over a force plate
at a range of walking velocities. Stance duration and
force data were recorded for the right hind limb. To
avoid the effect of horse size on the outcome variables,
the 8 force variables were standardized to body
mass and height at the shoulders. Velocity was standardized
to height at the shoulders and expressed as
velocity in dimensionless units (VDU). Stance duration
was also expressed in dimensionless units
(SDU). Simple regression analysis was performed,
using stance duration and force variables as dependent
variables and VDU as the independent variable.
Results—Fifty-six trials were recorded with velocities
ranging from 0.24 to 0.45 VDU (0.90 to 1.72 m/s).
Simple regression models between measured variables
and VDU were significant (R2 > 0.69) for SDU,
first peak of vertical force, dip between the 2 vertical
force peaks, vertical impulse, and timing of second
peak of vertical force.
Conclusion and Clinical Relevance—Subject velocity
affects vertical force components only. In the
future, differences between the forces measured in
lame horses and the expected forces calculated for
the same velocity will be studied to determine
whether the equations can be used as diagnostic criteria.
(Am J Vet Res 2001;62:901–906)
Objective—To evaluate the locomotor mechanics of the tölt in Icelandic horses.
Animals—10 adult Icelandic horses with no history of lameness.
Procedures—Force platform data were captured for 27 trials for horses ridden at a tölt in a lateral sequence single-foot gait at a steady speed from 0.89 to 5.98 m/s. Simultaneous kinematic data were obtained by tracking retroflective markers overlying the right fore- and hind limbs. These kinetic and kinematic data were combined to evaluate 3 mechanical approaches, duty factor, Froude number, and center of mass (COM) mechanics, and to evaluate the capacity to recover mechanical energies during tölting via inverse pendulum and spring-mass (bouncing) mechanics.
Results—Tölting horses had in-phase fluctuations of gravitational potential and kinetic energies of their COM and a capacity to recover mechanical energy through elastic recoil of spring elements in their limbs. These characteristics, along with Froude numbers exceeding values expected for the walk-run transition, are indicative of bouncing mechanics and, hence, most strongly ally tölting with running. Only the footfall pattern of a lateral sequence single-foot gait and low vertical excursions of the COM are more commonly associated with walking.
Conclusions and Clinical Relevance—At the tölt, horses have unique mechanical characteristics that should be understood for veterinary care. Differences in interlimb coordination between tölting and trotting mask the overall similarities in most other aspects of their locomotor dynamics.
Objective—To determine the gross morphology of the multifidus, longus colli, and longus thoracis muscles in the cervical and cranial thoracic portions of the equine vertebral column.
Sample—15 horse cadavers.
Procedures—The vertebral column was removed intact from the first cervical vertebra (C1) to the seventh thoracic vertebra (T7). After removing the superficial musculature, detailed anatomic dissections of the multifidus, longus colli, and longus thoracis muscles were performed.
Results—The multifidus cervicis muscle consisted of 5 bundles/level arranged in lateral, medial, and deep layers from C2 caudally into the thoracic portion of the vertebral column. Fibers in each bundle attached cranially to a spinous process then diverged laterally, attaching caudally on the dorsolateral edge of the vertebral lamina and blending into the joint capsule of an articular process articulation after crossing 1 to 4 intervertebral joints. The longus colli muscle had ventral, medial, and deep layers with 5 bundles/level from C1 to C5 that attached cranially to the ventral surface of the vertebral body, diverged laterally and crossed 1 to 4 intervertebral joints, then attached onto a vertebral transverse process as far caudally as C6. The longus thoracis muscle consisted of a single, well-defined muscle belly from C6 to T5-T6, with intermediate muscular attachments onto the ventral aspects of the vertebral bodies, the intervertebral symphyses, and the craniomedial aspects of the costovertebral joint capsules.
Conclusions and Clinical Relevance—Results indicated that there were multiple, short bundles of the multifidus cervicis, multifidus thoracis, and longus colli muscles; this was consistent with a function of providing sagittal plane intersegmental vertebral column stability.
Objective—To determine the magnitude and location of skin movement attributable to the cutaneus trunci muscle reflex in response to localized stimulation of the skin of the dorsolateral aspect of the thoracic wall in horses.
Procedures—A grid of 56 reflective markers was applied to the lateral aspect of the body wall of each horse; markers were placed at 10-cm intervals in 7 rows and 8 columns. A motion analysis system with 10 infrared cameras was used to track movements of the markers in response to tactile stimulation of the dorsolateral aspect of the thoracic wall at the levels of T6, T11, and T16. Marker movement data determined after skin stimulation were used to create a skin deformation gradient tensor field, which was analyzed with custom software.
Results—The sites of maximal skin deformation were located close to the stimulation sites; the centers of the twitch responses were located a mean distance of 7.7 to 12.8 cm ventral and between 6.6 cm cranial and 3.1 cm caudal to the stimulation sites.
Conclusions and Clinical Relevance—Findings of this study may have implications for assessment of nerve conduction velocities of the cutaneus trunci muscle reflex and may enhance understanding of the responses of horses to placement of tack or other equipment on skin over the cutaneus trunci muscles.
Objective—To calculate forces in the flexor tendons
and the influence of heel wedges in affected and contralateral
(compensating) forelimbs of horses with
experimentally induced unilateral tendinitis of the
superficial digital flexor (SDF) tendon.
Animals—5 Warmblood horses.
Procedure—Ground reaction force and kinematic
data were obtained during a previous study while
horses were trotting before and after induction of tendinitis
in 1 forelimb SDF and after application of 6°
heel wedges to both forehooves. Forces in the SDF,
deep digital flexor (DDF), and the suspensory ligament
(SL) and strain in the accessory ligament (AL) of
the DDF were calculated, using an in vitro model of
the distal region of the forelimb.
Results—After induction of tendinitis, trotting
speed slowed, and forces decreased in most tendons.
In the affected limb, SL force decreased more
than SDF and DDF forces. In the compensating
limb, SDF force increased, and the other forces
decreased. After application of heel wedges, SDF
force in both limbs increased but not significantly.
Furthermore, there was a decrease in DDF force
and AL strain.
Conclusions and Clinical Relevance—The increase
in SDF force in the compensating forelimb of horses
with unilateral SDF tendinitis may explain the high secondary
injury rate in this tendon. The lack of decrease
of SDF force in either limb after application of heel
wedges suggests that heel wedges are not beneficial
in horses with SDF tendinitis. Instead, heel wedges
may exacerbate the existing lesion. (Am J Vet Res
Objective—To develop a method for arthrocentesis
of the temporomandibular joint in adult horses.
Animals—7 equine cadaver heads and 6 clinically
normal adult horses.
Procedure—Fluoroscopy, contrast radiography, and
computed tomography were used on cadaver specimens
to locate the temporomandibular joint, identify
externally palpable landmarks for joint access, guide
needle placement into the joint, and illustrate regional
anatomy. The arthrocentesis technique was performed
on 6 live healthy adult horses to determine
efficacy and safety of this procedure.
Results—Externally palpable structures were identified
as landmarks for temporomandibular arthrocentesis,
including the lateral border of the condylar
process of the mandible, the zygomatic process of
the temporal bone, and the lateral pericapsular fat
pad. Arthrocentesis was successful in all 6 joints in
the live horses, and no complications developed.
Conclusions and Clinical Relevance—The technique
identified will improve the ability to examine
and treat the temporomandibular joint in horses. (Am J Vet Res 2001;62:729–735).
Objective—To assess the reliability of the center-ofpressure
(COP) values obtained from a force platform
for analysis of postural sway in horses.
Animals—Six 2-year-old horses that were free from
lameness and neurologic disease.
Procedure—Horses stood stationary with all 4
hooves on a force platform; COP data were collected
at 1,000 Hz and 3-dimensional kinematics collected at
60 Hz for 10 seconds. Five trials were recorded at
each of 3 time periods (15-minute intervals) or at 1
time period on 3 separate days. Mean values for each
set of 5 trials and actual, normalized, and relative COP
variables were calculated. The reliability was quantified
by use of agreement boundary.
Results—The COP results within and across days
were similar and provided small agreement boundary
limits (eg, across days, in order of least relative reliability:
area, ± 62 mm2; mediolateral range, ± 8 mm;
radius, ± 2 mm; craniocaudal range, ± 4 mm; and
velocity, ± 3 mm/s). Head height possessed the greatest
relative intraday reliability (12%) but a high agreement
boundary limit (± 0.15 m).
Conclusions and Clinical Relevance—The use of a
force platform to analyze postural sway in a group of
young healthy horses was found to produce reliable
results and may provide a simple and sensitive measure
for assessing balance deficiencies in horses.
Agreement boundaries provide 95% confidence intervals
for use as limits of error and variability in measurements
that, if exceeded, may signify meaningful
effects. (Am J Vet Res 2003;64:1354–1359)
Objective—To compare effects of 4 types of stimulation devices attached to the hind feet on hoof flight, joint angles, and net joint powers of trotting horses.
Animals—8 clinically normal horses.
Procedures—Horses were evaluated under 5 conditions in random order: no stimulators, loose straps (10 g), lightweight tactile stimulators (55 g), limb weights (700 g), and limb weights with tactile stimulators (700 g). Reflective markers on the hind limbs were tracked during the swing phase of 6 trotting trials performed at consistent speed to determine peak hoof heights and flexion angles of the hip, stifle, tarsal, and metatarsophalangeal joints. Inverse dynamic analysis was used to calculate net joint energies. Comparisons among stimulators were made.
Results—Peak hoof height was lowest for no stimulators (mean ± SD, 5.42 ± 1.38 cm) and loose straps (6.72 ± 2.19 cm), intermediate for tactile stimulators (14.13 ± 7.33 cm) and limb weights (16.86 ± 15.93 cm), and highest for limb weights plus tactile stimulators (24.35 ± 13.06 cm). Compared with no stimulators, net tarsal energy generation increased for tactile stimulators, limb weights, and limb weights plus tactile stimulators, but only the weighted conditions increased net energy generation across the hip joint.
Conclusions and Clinical Relevance—The type and weight of foot stimulators affected the magnitude of the kinematic and kinetic responses and the joints affected. These findings suggest that different types of foot stimulators are appropriate for rehabilitation of specific hind limb gait deficits, such as toe dragging and a short stride.
Objective—To develop a method of measuring 3-dimensional kinematics of the temporomandibular joint (TMJ) in horses chewing sweet feed.
Animals—4 mature horses that had good dental health.
Procedure—Markers attached to the skin over the skull and mandible were tracked by an optical tracking system. Movements of the mandible relative to the skull were described in terms of 3 rotations and 3 translations. A virtual marker was created on the midline between the rami of the mandibles at the level of the rostral end of the facial crest to facilitate observation of mandibular movements.
Results—During the opening stroke, the virtual midline mandibular marker moved ventrally, laterally toward the chewing side, and slightly caudally. During the closing stroke, the marker moved dorsally, medially, and slightly rostrally. During the power stroke, the mandible slid medially and dorsally as the mandibular cheek teeth moved across the occlusal surface of the maxillary cheek teeth. The 4 horses had similar chewing patterns, but the amplitudes varied among horses.
Conclusions and Clinical Relevance—The TMJ allows considerable mobility of the mandible relative to the skull during chewing. The method presented in this report can be used to compare the range of motion of the TMJ among horses with TMJ disease or dental irregularities or within an individual horse before and after dental procedures.
Objective—To identify differences in intersegmental bending angles in the cervical, thoracic, and lumbar portions of the vertebral column between the end positions during performance of 3 dynamic mobilization exercises in cervical lateral bending in horses.
Animals—8 nonlame horses.
Procedures—Skin-fixed markers on the head, cervical transverse processes (C1–C6) and spinous processes (T6, T8, T10, T16, L2, L6, S2, and S4) were tracked with a motion analysis system with the horses standing in a neutral position and in 3 lateral bending positions to the left and right sides during chin-to-girth, chin-to-hip, and chin-to-tarsus mobilization exercises. Intersegmental angles for the end positions in the various exercises performed to the left and right sides were compared.
Results—The largest changes in intersegmental angles were at C6, especially for the chin-to-hip and chin-to-tarsus mobilization exercises. These exercises were also associated with greater lateral bending from T6 to S2, compared with the chin-to-girth mobilization or neutral standing position. The angle at C1 revealed considerable bending in the chin-to-girth position but not in the 2 more caudal positions.
Conclusions and Clinical Relevance—The amount of bending in different parts of the cervical vertebral column differed among the dynamic mobilization exercises. As the horse's chin moved further caudally, bending in the caudal cervical and thoracolumbar regions increased, suggesting that the more caudal positions may be particularly effective for activating and strengthening the core musculature that is used to bend and stabilize the horse's back.