Objective—To describe a single-portal cranial arthroscopic
approach to the stifle joint in horses and to
determine the clinical outcome in horses with
femorotibial joint disease in which this approach was
Animals—23 adult horses.
Procedure—Medical records were reviewed to
obtain information on clinical outcome in horses in
which the single-portal cranial arthroscopic approach
Results—Twenty-nine stifle joints of 23 horses were
examined arthroscopically, using the described
approach. Subchondral bone cysts were treated in 19
medial femoral condyles of 12 horses. Unilateral cruciate
ligament desmitis (4 horses), meniscal tearing
(3), or both (2) were identified in 9 horses. Evidence
of degenerative joint disease without cystic lesions or
soft tissue trauma was found in 2 horses. Information
on clinical outcome was obtained for 21 of 23 horses.
A successful outcome was obtained in 15 of 21 horses
and was defined as return to sound performance
at a degree equal to or better than that prior to injury
and lameness. Eight of 12 horses treated for medial
femoral condylar cysts had a successful outcome.
Four show horses treated for cruciate ligament
lesions alone successfully returned to showing activity.
None of the 3 horses with meniscal tearing were
able to perform successfully.
Conclusions and Clinical Relevance—The
femorotibial joint was evaluated through a single-portal
cranial arthroscopic approach, using the
femoropatellar joint as the point of access. This
approach was easy to perform, allowed controlled
access to the femorotibial joint, avoided accidental
damage to articular structures, and required fewer
access portals. (J Am Vet Med Assoc 2002;220:
Objective—To evaluate changes in strain patterns in
normal equine hooves following 4-point trimming,
using photoelastic stress analysis.
Sample Population—15 equine front limbs with normal
Procedure—Limbs were disarticulated at the carpometacarpal
joint. Weight-bearing surfaces of each
hoof were trimmed level to ensure 100% ground contact.
Hoof walls were coated with a custom-made
strain-sensitive plastic, and limbs were loaded to a
third of body weight. Using a polariscope, strain distribution,
magnitudes, and directions were evaluated
in level hooves as well as before and after standardized
4-point trimming. Repeated-measures ANOVA
was used to compare strain magnitudes and directions
before and after trimming.
Results—In leveled specimens, strain fields were
symmetrically distributed above the heels and at
quarter-toe junctions along a line between the middle
and distal thirds of the hoof wall. After 4-point trimming,
strain epicenters localized above the contact
points, whereas strain magnitudes significantly
increased by approximately 50%. Decreasing contact
area by 50% resulted in an additional significant
increase (32%) in strain magnitude. Trimming did not
have a significant effect on strain orientations.
Conclusion and Clinical Relevance—This study documents
that 4-point trimming results in strain concentration
above the hoof contact points and that
strain magnitude is dependent on contact area. (Am J
Vet Res 2001;62:467–473)
Objective—To demonstrate myofibroblasts in the
accessory ligament of the deep digital flexor tendon
(ie, distal check ligament) and deep digital flexor tendon
of clinically normal foals.
Sample Population—Tissue specimens from 25
foals that were necropsied for reasons unrelated to
this study and unrelated to musculoskeletal disease.
Procedure—The distal check ligament and deep digital
flexor tendon of both forelimbs were examined
histologically. Myofibroblasts were identified by
immunohistochemical staining specific for alphasmooth
muscle actin (α-SMA).
Results—Most of the cells in the distal check ligament
and deep digital flexor tendon of all foals
stained positive for α-SMA.
Conclusion and Clinical Relevance—Myofibroblasts
made up most of the cells in the distal check ligament
and deep digital flexor tendon of clinically normal
foals. These cells have contractile ability and therefore,
may play a role in flexure contracture of these
tendons. The ability of tetracycline to chelate calcium
or decrease the expression of the contractile protein
α-smooth muscle actin could inhibit the myofibroblasts'
ability to contract, thus providing a rationale for
tetracycline administration as a treatment of distal
interphalangeal joint flexor deformity in foals. (Am J
Vet Res 2001;62:823–827)
Objective—To determine the microvascular anatomy of the suspensory ligament of the forelimb of horses.
Sample—17 cadaveric forelimbs from 9 adult horses with no known history of forelimb lameness.
Procedures—The median artery of the forelimb was cannulated proximal to the antebrachiocarpal joint and injected with contrast medium for CT evaluation of the gross vasculature (n = 2) or India ink to evaluate the microvasculature (12). Routine histologic evaluation was performed on an additional 3 forelimbs to confirm the microvascular anatomy.
Results—The vascular supply of the suspensory ligament of the forelimb originated from branches of the medial and lateral palmar and palmar metacarpal vessels as well as the proximal and distal deep palmar arches. An abundant, longitudinally oriented microvascular supply was evident throughout the length of the suspensory ligament without distinct variation among the proximal, midbody, and distal regions. The intraligamentous blood supply originated from a periligamentous vascular plexus that surrounded the suspensory ligament throughout its length. Histologic findings indicated the presence of a periligamentous connective tissue plexus, which contained vessels that penetrated and anastomosed with an extensive network of intraligamentous vessels throughout the length of the suspensory ligament.
Conclusions and Clinical Relevance—The suspensory ligament of the equine forelimb had an abundant intraligamentous microvascular supply throughout its entire length. The absence of an obvious hypovascular area suggested that regional variations in healing rates of the suspensory ligament are not associated with the microvascular anatomy.
Case Description—3 foals were referred for treatment of tympany of the auditory tube diverticulum (guttural pouch).
Clinical Findings—Bilateral guttural pouch tympany was diagnosed in all 3 foals on the basis of clinical signs and results of radiographic and endoscopic evaluations and gutturocentesis. In each foal, previous medical or surgical interventions or both had failed to correct the problem.
Treatment and Outcome—Bilateral surgical resection of the plica salpingopharyngeus was performed. Follow-up telephone interviews with owners 8 months to 3 years after surgery revealed that long-term resolution of the tympany had been achieved in each foal, with few to no postsurgical complications.
Clinical Relevance—Surgical correction of refractory bilateral guttural pouch tympany can be accomplished by resection of the plica salpingopharyngeus within the pharyngeal opening of the Eustachian tube. In the foals of this report, permanent resolution of tympany was apparently achieved without interfering with upper airway function, providing support for the use of surgical resection of the plica salpingopharyngeus in the treatment of bilateral guttural pouch tympany.
Objective—To evaluate the safety and efficacy of thoracoscopically
guided pulmonary wedge resection in
Animals—10 horses (5 control horses and 5 horses
affected with recurrent airway obstruction [ie,
Procedure—Each horse underwent a thoracoscopically
guided pulmonary wedge resection. Before, during,
and after surgery, heart rate, respiratory rate,
arterial blood gases, and systemic and pulmonary
arterial pressures were measured. Physical examination,
CBC, and thoracic radiography and ultrasonography
were performed 24 hours before and 2 and 48
hours after surgery. Pulmonary specimens were
assessed by histologic examination. A second thoracoscopic
procedure 14 days later was used to evaluate
the resection site.
Results—The technique provided excellent specimens
for histologic evaluation of the lung. Heart and
respiratory rates decreased significantly after horses
were administered sedatives. A significant transient
decrease in PaO2 was detected immediately after pulmonary
wedge resection, but we did not detect significant
effects on arterial pH, Paco2, or mean arterial
and pulmonary arterial pressures. All horses except 1
were clinically normal after thoracoscopic surgery;
that horse developed hemothorax attributable to iatrogenic
injury to the diaphragm. The second thoracoscopy
revealed minimal inflammation, and there
were no adhesions.
Conclusion and Clinical Relevance—Thoracoscopically
guided pulmonary wedge resection provides
a minimally invasive method for use in obtaining specimens
of lung tissues from healthy horses and those
with lung disease. This technique may be useful for the
diagnosis of diseases of the lungs and thoracic cavity.
(Am J Vet Res 2002;63:1232–1240)
Objective—To compare endoscopic findings of the
upper portion of the respiratory tract in Thoroughbred
yearlings with their subsequent race records to determine
whether subjective assessment of airway function
may be used as a predictor of future racing performance.
Animals—427 Thoroughbred yearlings.
Procedures—Endoscopic examination findings were
obtained from the medical records and the videoendoscopic
repository of the Keeneland 1996
September yearling sales. Racing records were
requested for the yearlings through the end of their 4-year-old racing season (1997–2000). Twenty-nine measures
of racing performance were correlated with
endoscopic findings. Subjective arytenoid cartilage
movement grades were determined, using a 4-point
grading scale (grade 1 = symmetrical synchronous
abduction of the arytenoid cartilages; grade 4 = no
substantial movement of the left arytenoid cartilage).
Results—Of the 427 Thoroughbred yearlings included
in this study, 364 established race records, and 63 did
not. Opinions regarding suitability for purchase, meeting
conditions of the sale, and the presence of
epiglottic abnormalities had no significant association
with racing performance. Arytenoid cartilage movement
grades were significantly associated with many
of the dependent variables. However, palatine abnormalities
were not predictive of inferior racing performance.
Conclusions and Clinical Relevance—Thoroughbred
yearlings with grade-1 and -2 arytenoid cartilage
movements had significantly better racing performance
as adults, compared with yearlings with grade-
3 arytenoid cartilage movements. In contrast, epiglottic
and palatine abnormalities were not predictive of
inferior racing performance. Therefore, evaluation of
laryngeal function, but not epiglottic or palatine abnormalities,
using the 4-point grading system, should be
the major factor in developing recommendations for
prospective buyers. (J Am Vet Med Assoc 2001;219:
Objective—To record respiratory sounds in exercising
horses and determine whether spectrum analysis
could be use to identify sounds specific for laryngeal
hemiplegia (LH) and dorsal displacement of the soft
Animals—5 Standardbred horses.
Procedure—Respiratory sounds were recorded and
pharyngeal pressure and stride frequency were measured
while horses exercised at speeds corresponding
to maximum heart rate, before and after induction
of LH and DDSP.
Results—When airway function was normal, expiratory
sounds predominated and lasted throughout
exhalation. After induction of LH, expiratory sounds
were unaffected; however, all horses produced inspiratory
sounds characterized by 3 frequency bands
centered at approximately 0.3, 1.6, and 3.8 kHz. After
induction of DDSP, inspiratory sounds were unaffected,
but a broad-frequency expiratory sound, characterized
by rapid periodicity (rattling) was heard
throughout expiration. This sound was not consistently
detected in all horses.
Conclusions and Clinical Relevance—The technique
used to record respiratory sounds was well tolerated
by the horses, easy, and inexpensive.
Spectrum analysis of respiratory sounds from exercising
horses after experimental induction of LH or
DDSP revealed unique sound patterns. If other conditions
causing airway obstruction are also associated
with unique sound patterns, spectrum analysis of respiratory
sounds may prove to be useful in the diagnosis
of airway abnormalities in horses. (Am J Vet Res
Objective—To determine the effects of oxytetracycline
on matrix metalloproteinase-1 (MMP-1) mRNA
expression and collagen gel contraction by equine
myofibroblasts in an effort to explain the mechanistic
basis for the pharmacologic treatment of flexural
deformities in foals.
Sample Population—Cultured myofibroblasts from
the accessory ligament (distal check ligament) of 6
Procedure—Collagen gel scaffolds seeded with
equine myofibroblasts were cultured in individual culture
dishes containing complete media (Dulbecco's
modified Eagle medium with 10% fetal bovine serum)
and oxytetracycline (0, 12.5, 25, or 75 µg/mL) for 48
hours. After 24 hours, the gels were released from
the bottom of the culture plate and allowed to contract.
Photographs were taken at 0, 1, 2, 4, 6, 8, and
24 hours after release to assess the degree of collagen
gel contraction. Additional gels were harvested at
2 hours after release for RNA isolation and reverse
transcriptase-polymerase chain reaction assessment
of the degree of MMP-1 mRNA expression.
Results—Oxytetracycline induced a dose-dependent
inhibition of collagen gel contraction by equine myofibroblasts.
Oxytetracycline also induced a dose-dependent
decrease in MMP-1 mRNA expression by equine
Conclusions and Clinical Relevance—Results of
this study indicate that oxytetracycline inhibits tractional
structuring of collagen fibrils by equine myofibroblasts
through an MMP-1 mediated mechanism. In
young foals, oxytetracycline administration may make
the developing ligaments and tendons more susceptible
to elongation during normal weight-bearing.
Inhibition of normal collagen organization may provide
the mechanistic explanation for the results seen following
the pharmacologic treatment of flexural deformities
in foals by oxytetracycline administration. (Am
J Vet Res 2004;65:491–496)