Objective—To test the sensitivity to measurement
and modeling errors of a method for noninvasive calculation
of flexor tendon forces in the equine forelimb
and to calculate tendon forces for Dutch Warmblood
horses during trotting.
Sample Population—A normative set of kinematic
and ground-reaction force (GRF) data obtained from
horses during trotting in another study.
Procedure—Forces in the flexor tendons were calculated
from the data set before and after addition of
fixed relative and absolute errors. Amount of error
was based on normal accuracy of the variables. A
similar analysis was performed for a measure of strain
of the accessory ligament of the deep digital flexor
Results—The only errors that had a substantial influence
on accuracy were modeling errors in the mechanical
properties of the suspensory ligament and measurement
errors in the point of application of the GRF
and position of the marker on the distal interphalangeal
joint. Influence of the measurement errors could be
minimized by applying usual correction methods.
Conclusion and Clinical Relevance—After correction
of measurement errors, the method can be used
to calculate mean tendon forces for a group of horses
and to evaluate the influence of factors such as surface
properties, type of shoe, speed, and fatigue on
tendon forces. The method could become an important
tool for use in research on the cause, prevention,
and treatment of tendon injuries in horses. (Am J Vet
Objective—To describe a method to calculate flexor
tendon forces on the basis of inverse dynamic analysis
and an in vitro model of the equine forelimb and to
quantify parameters for the model.
Sample Population—38 forelimbs of 23 horses that
each had an estimated body mass of ≥ 500 kg.
Procedure—Longitudinal limb sections were used to
determine the lines of action of the tendons.
Additionally, limb and tendon loading experiments
were performed to determine mechanical properties
of the flexor tendons.
Results—The study quantified the parameters for a
pulley model to describe the lines of action.
Furthermore, relationships between force and strain
of the flexor tendons and between fetlock joint angle
and suspensory ligament strain were determined,
and the ultimate strength of the tendons was measured.
Conclusion and Clinical Relevance—The model
enables noninvasive determination of forces in the
suspensory ligament, superficial digital flexor tendon,
and distal part of the deep digital flexor (DDF) tendon.
In addition, it provides a noninvasive measure of loading
of the accessory ligament of the DDF tendon for
within-subject comparisons. However, before application,
the method should be validated. The model
could become an important tool for use in research of
the cause, prevention, and treatment of tendon
injuries in horses. (Am J Vet Res 2001;62:1585–1593)
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 determine the effects of exercise on
biomechanical properties of the superficial digital flexor
tendon (SDFT) in foals.
Animals—43 Dutch Warmblood foals.
Procedure—From 1 week until 5 months of age, 14
foals were housed in stalls and not exercised, 14 foals
were housed in stalls and exercised daily, and 15 foals
were maintained at pasture. Eight foals in each group
were euthanatized at 5 months, and remaining foals
were housed together in a stall and paddock until
euthanatized at 11 months. After euthanasia, SDFT
were isolated and fit in a material testing system.
Mean cross-sectional area (CSA) was measured and
traction forces recorded. Normalized force at rupture
(forcerup), normalized force at 4% strain, strain at rupture,
stress at 4% strain (stress4%strain), and stress at
rupture were compared among and within groups.
Results—At 5 months, mean CSA and normalized
forcerup were significantly greater and stress4%strain
significantly less in the pastured group, compared
with the other groups. At 11 months, CSA and normalized
forcerup were not significantly different
among groups, because forcerup increased significantly
from 5 to 11 months in the nonexercised
group and decreased significantly in the pastured
Conclusions and Clinical Relevance—Exercise significantly
affected the biomechanical properties of
the SDFT in foals. Evenly distributed moderate- and
low-intensity exercise at a young age may be more
effective for development of strong, flexible tendons
in horses than single episodes of high-intensity
exercise superimposed on stall rest. This effect
may impact later susceptibility to SDFT injury.
(Am J Vet Res 2001;62:1859–1864)