Objective—To provide a quantitative description of the
architecture of superficial digital flexor (SDF) and deep
digital flexor (DDF) muscles in adult horses to predict
muscle-tendon behavior and estimate muscle forces.
Sample Population—7 forelimb specimens from 7
Procedure—Muscle and tendon lengths and volumes
were measured from 6 fixed forelimbs. After processing,
fiber bundle and sarcomere lengths were
measured. Optimal fascicle lengths and muscle
length-to-fascicle length, muscle length-to-free tendon
length, and fascicle length-to-tendon length ratios
were calculated, as were tendon and muscle physiologic
cross-sectional areas (PCSAs). Pennation angles
were measured in 1 embalmed specimen.
Results—The SDF optimal fascicle lengths were uniformly
short (mean ± SD, 0.8 ± 0.1 cm), whereas DDF
lengths ranged from 0.9 ± 0.2 cm to 10.8 ± 1.6 cm.
The DDF humeral head had 3 architectural subunits,
each receiving a separate median nerve branch, suggestive
of neuromuscular compartmentalization.
Pennation angles were small (10o to 25o). The PCSAs
of the SDF and DDF muscle were 234 ± 51 cm2 and
259 ± 30 cm2, with estimated forces of 4,982 ± 1148
N and 5,520 ± 544 N, respectively.
Conclusions and Clinical Relevance—The SDF
muscle appears to provide strong tendinous support
with little muscle fascicular shortening and fatigueresistance
properties. The DDF muscle combines
passive and dynamic functions with larger tension
development and higher shortening velocities during
digital motion. Architectural parameters are useful for
estimation of forces and have implications for analysis
of muscle-tendon function, surgical procedures
involving muscle-tendon lengthening, and biomechanical
modeling. (Am J Vet Res 2004;65:819–828)
Objective—To compare variables for screw insertion, pushout strength, and failure modes for a headless tapered compression screw inserted in standard and oversize holes in a simulated lateral condylar fracture model.
Sample Population—6 pairs of third metacarpal bones from horse cadavers.
Procedure—Simulated lateral condylar fractures were created, reduced, and stabilized with a headless tapered compression screw by use of a standard or oversize hole. Torque, work, and time for drilling, tapping, and screw insertion were measured during site preparation and screw implantation. Axial load and displacement were measured during screw pushout. Effects of drill hole size on variables for screw insertion and screw pushout were assessed by use of Wilcoxon tests.
Results—Drill time was 59% greater for oversize holes than for standard holes. Variables for tapping (mean maximum torque, total work, positive work, and time) were 42%, 70%, 73%, and 58% less, respectively, for oversize holes, compared with standard holes. Variables for screw pushout testing (mean yield load, failure load, failure displacement, and failure energy) were 40%, 40%, 47%, and 71% less, respectively, for oversize holes, compared with standard holes. Screws could not be completely inserted in 1 standard and 2 oversize holes.
Conclusions and Clinical Relevance—Enlarging the diameter of the drill hole facilitated tapping but decreased overall holding strength of screws. Therefore, holes with a standard diameter are recommended for implantation of variable pitch screws whenever possible. During implantation, care should be taken to ensure that screw threads follow tapped bone threads.
OBJECTIVE To determine the effects of racetrack surface and shoe characteristics on formation of wear grooves in the horseshoes of racehorses.
SAMPLES 1,121 horseshoes from 242 Thoroughbred racehorses collected during routine horseshoeing procedures at 4 racetracks with dirt or synthetic surfaces.
PROCEDURES Data for 1,014 horseshoes from 233 racehorses were analyzed. Horseshoes were photographed, and length and width of grooves formed at the heels of the solar surface of horseshoes were measured on the photographs. Effects of racetrack, racetrack surface, and shoe characteristics (eg, shoe size, clips, and nails) on length and width of grooves were assessed by use of a mixed-model anova.
RESULTS Length and width of wear grooves differed significantly on the basis of racetrack, nail placement, and limb side (left vs right). Differences in groove dimensions between types of racetrack surface (dirt vs synthetic) were less apparent than differences among racetracks.
CONCLUSIONS AND CLINICAL RELEVANCE Measurements of the length and width of wear grooves in the horseshoes of racehorses may be useful for understanding some aspects of hoof interactions with various racetrack surfaces. Interpretation of differences in wear grooves for various racetrack surfaces will likely require quantitation of the mechanical behavior of the surfaces.
Objective—To determine a range of limb loading
activity for healthy adult horses confined to box stalls
in an equine veterinary teaching hospital and determine
the effects of hospital environmental factors on
load rates and daily limb loading patterns.
Animals—6 mature healthy horses of various ages,
breeds, and sexes, and 1 horse with a repaired
Procedure—Step monitors were placed on 2 limbs of
adult horses confined to box stalls. Relocation steps
and weight shifts were recorded, as loading events,
for 24 hours. Influence of forelimb versus hind limb
and environmental factors on load rate (loading
events per hour) were assessed with repeated-measures
Results—Loading activity was greater for the forelimb
than the hind limb and was greater during the
day than the night. Loading activity differences were
not associated with daytime environmental factors.
Conclusions and Clinical Relevance—Horses with
normal locomotor activity appear to have higher load
rates for forelimbs compared with hind limbs and
higher load rates during the day compared with night.
Knowledge of influence of environmental factors and
mechanical restraint on limb loading activity may be
useful in management of horses with musculoskeletal
disorders. This information may also be used for in
vitro simulation of in vivo loading of limbs during
cyclic biomechanical investigations.(Am J Vet Res
Objective—To quantify the passive contribution of
the biceps brachii muscle-tendon unit to the limits of
elbow joint extension during shoulder joint flexion in
Sample Population—Normal right forelimb specimens
from 6 Thoroughbred cadavers.
Procedure—Specimens included the scapula,
humerus, radius-ulna, biceps brachii muscle-tendon
unit, and stabilizers of the shoulder and elbow joints.
Specimens were mounted to a rigid board by transfixation
pins through the humerus and instrumented
for mechanical manipulation of the limb and joint
angle and load measurements. Flexion and extension
limits of shoulder and elbow joint ranges of motion
were measured in each joint separately, while the
other joint was fixed. Measurements were made
before and after transection of the biceps brachii muscle-
Results—The biceps brachii muscle-tendon unit limited
elbow joint extension when the shoulder joint was
fixed in flexion, limited shoulder joint flexion when the
elbow joint was fixed in extension, and inhibited
shoulder joint extension to a lesser degree when the
elbow joint was fixed at midrange angles of 75° to 90°.
Conclusions and Clinical Relevance—Clinical
manipulation of the elbow joint into hyperextension
during shoulder joint flexion is indicative of biceps
brachii injury. (Am J Vet Res 2005;66:391–400)
Objective—To define a 3-dimensional (3-D) coordinate
system with clear definitions of origins and axes
relative to hoof anatomic features and determine
whether solar surfaces of Thoroughbred racehorse
hooves have geometric asymmetry in the mediolateral
and dorsopalmar directions.
Sample Population—Left forelimb hooves from 20
Thoroughbred racehorse cadavers.
Procedure—A right-handed 3-D coordinate axes system
centered on the collateral sulci was defined for
the left front hoof. Orthogonal distances of anatomic
features from the dorsopalmar axis and the plane
coincident with the ground were measured and compared
between medial and lateral sides and between
dorsal and palmar regions of the hoof.
Results—The hoof was wider and had a greater
radius laterally than medially. The most distal part of
the lateral bar of the frog was further from the dorsopalmar
axis than that of the medial bar. Overall,
mediolateral asymmetries in depth were not
observed. The sole at the perimeter was deeper
medially in the dorsal part of the hoof and laterally in
the palmar part, with depth overall being greater palmarly
than dorsally. Most features had dorsopalmar
Conclusions and Clinical Relevance—When the
angle bisected by the collateral sulci is used to determine
the dorsopalmar axis of the hoof, most central
structures (bars and collateral sulci) have mediolateral
symmetry. However, the hoof wall and sole have
some mediolateral asymmetries and most structures
have dorsopalmar asymmetry. These findings may
assist the development of devices for attachment to
hooves and studies of the interaction of hooves with
bearing surfaces. (Am J Vet Res 2003;64:1030–1039)
Objective—To determine the relative contributions of
the muscles, tendons, and accessory ligaments to
the passive force-length properties of the superficial
(SDF) and deep digital flexor (DDF) myotendinous
Sample Population—8 cadaveric forelimbs from 6
Procedure—In vitro, limb configurations during slack
position and myotendinous lengths during subsequent
axial loading of forelimbs were recorded before
and after transection of accessory ligaments.
Expressions were derived to describe the forcelength
behavior of each muscle, tendon, and accessory
ligament-tendon unit; linear stiffness was computed
for these components. The elastic modulus
was established for the SDF and DDF tendons.
Results—Linear stiffness was 2.80 ± 0.38 kN/cm for
the SDF muscle, 3.47 ± 0.66 kN/cm for the DDF muscle,
2.73 ± 0.18 kN/cm for the SDF tendon, 3.22 ±
0.20 kN/cm for the DDF tendon, 6.46 ± 0.85 kN/cm
for the SDF accessory ligament, 1.93 ± 0.11 kN/cm for
the SDF accessory ligament-tendon unit, and 2.47 ±
0.11 kN/cm for the DDF accessory ligament-tendon
unit. The elastic modulus for the SDF and DDF tendons
was 920 ± 77 and 843 ± 56 MPa, respectively.
Conclusions and Clinical Relevance—Both the
muscle-tendon and ligament-tendon portions of SDF
and DDF myotendinous complexes had important
roles in supporting the forelimb of horses. Although
muscle tension can be enhanced by elbow joint flexion
and active contraction, the accessory ligaments
transmitted more force to the distal tendons than did
the muscles under the conditions tested. (Am J Vet
Objective—To compare fit and geometry of reconstruction
of femoral components of 4 canine cemented
total hip replacement implants and determine
which implants are most compatible with current principles
of cemented arthroplasty.
Sample Population—Paired femurs from 16 adult
Procedure—Femurs were prepared for femoral stem
implantation of either the Bardet, BioMedtrix,
Mathys, or Richards II implant. Mediolateral and craniocaudal
radiographs were obtained with femoral
components in situ. Cross-sectional analysis of
implant fit was performed on transected cemented
specimens. Computer-aided analyses of digitized
images were performed.
Results—The Bardet and Richards II implants
reconstructed the original femoral head position significantly
better than the other 2 implants. None of
the implants allowed neutralization of the implant
axis in the sagittal plane or were routinely centralized
in the femoral canal. The Bardet implant had the
smallest minimum distal tip offset in the sagittal
plane. Greatest tip to cortex distance was provided
by the Richards II implant in the transverse plane
and the Mathys implant in the sagittal plane. The
thinnest cement mantle regions for all implants
were in the central longitudinal third of the femoral
Conclusions and Clinical Relevance—The Bardet
and BioMedtrix implants had stem design characteristics
that were most compatible with principles of
cemented stem fixation. None of the implants completely
satisfied the theoretically optimal conditions of
centralization and neutralization of the femoral stem.
Innovative design modifications, therefore, may be
needed if these conditions are important to the longterm
success of canine total hip replacement. (Am J
Vet Res 2000;61:1113–1121)
To assess the motion of the proximal sesamoid bones (PSBs) relative to the third metacarpal bone (MC3) of equine forelimbs during physiologic midstance loads.
8 musculoskeletally normal forelimbs (7 right and 1 left) from 8 adult equine cadavers.
Each forelimb was harvested at the mid-radius level and mounted in a material testing system so the hoof could be moved in a dorsal direction while the radius and MC3 remained vertical. The PSBs were instrumented with 2 linear variable differential transformers to record movement between the 2 bones. The limb was sequentially loaded at a displacement rate of 5 mm/s from 500 N to each of 4 loads (1.8 [standing], 3.6 [walking], 4.5 [trotting], and 10.5 [galloping] kN), held at the designated load for 30 seconds while lateromedial radiographs were obtained, and then unloaded back to 500 N. The position of the PSBs relative to the transverse ridge of the MC3 condyle and angle of the metacarpophalangeal (fetlock) joint were measured on each radiograph.
The distal edge of the PSBs moved distal to the transverse ridge of the MC3 condyle at 10.5 kN (gallop) but not at lower loads. The palmar surfaces of the PSBs rotated away from each other during fetlock joint extension, and the amount of rotation increased with load.
CONCLUSIONS AND CLINICAL RELEVANCE
At loads consistent with a high-speed gallop, PSB translations may create an articular incongruity and abnormal bone stress distribution that contribute to focal subchondral bone lesions and PSB fracture in racehorses.
Objective—To evaluate a Markov-chain model for the
development of forelimb injuries in Thoroughbreds
and to use the model to determine effects of reducing
sprint distance on incidence of metacarpal condylar
fracture (CDY) and severe suspensory apparatus
Sample Population—Weekly exercise and injury
data for 122 Thoroughbreds during racing or training.
Procedure—Weekly data were used to construct a
Markov-chain model with 5 states (uninjured [UNINJ],
palpable suspensory apparatus injury [PSAI], SSAI,
CDY, and lost to follow-up [LOST]). Transition probabilities
between UNINJ and PSAI were estimated as a
function of weekly sprint distance by use of linear
regression analysis. The model was used to predict
distributions of annual CDY and SSAI incidences in
southern California racehorses and was validated by
using CDY incidence reported by racetrack practitioners.
The model was modified by reducing the number
of sprint distances that were > 6 furlongs (> 1.20 km)
by 20%, and CDY and SSAI incidences were compared
with those generated by the baseline model.
Results—The model accurately fit development of
injuries in the sample population but overestimated
development of injuries in the southern California
racehorse population. Development of and recovery
from PSAI were correlated with distance run at high
speeds. Reducing by 20% the number of sprints run
at distances > 6 furlongs significantly reduced modeled
annual CDY and SSAI incidence by 9%.
Conclusions and Clinical Relevance—Reducing the
number of sprints at distances > 6 furlongs, particularly
among horses with PSAI, reduces risk of CDY
and SSAI. (Am J Vet Res 2003;64:328–337)