Objective—To compare gentamicin concentrations achieved in synovial fluid and joint tissues during IV administration and continuous intra-articular (IA) infusion of the tarsocrural joint in horses.
Animals—18 horses with clinically normal tarsocrural joints.
Procedure—Horses were assigned to 3 groups (6 horses/group) and administered gentamicin (6.6 mg/kg, IV, q 24 h for 4 days; group 1), a continuous IA infusion of gentamicin into the tarsocrural joint (50 mg/h for 73 hours; group 2), or both treatments (group 3). Serum, synovial fluid, and joint tissue samples were collected for measurement of gentamicin at various time points during and 73 hours after initiation of treatment. Gentamicin concentrations were compared by use of a Kruskal-Wallis ANOVA.
Results—At 73 hours, mean ± SE gentamicin concentrations in synovial fluid, synovial membrane, joint capsule, subchondral bone, and collateral ligament of group 1 horses were 11.5 ± 1.5 μg/mL, 21.1 ± 3.0 μg/g, 17.1 ± 1.4 μg/g, 9.8 ± 2.0 μg/g, and 5.9 ± 0.7 μg/g, respectively. Corresponding concentrations in group 2 horses were 458.7 ± 130.3 μg/mL, 496.8 ± 126.5 μg/g, 128.5 ± 74.2 μg/g, 99.4 ± 47.3 μg/g, and 13.5 ± 7.6 μg/g, respectively. Gentamicin concentrations in synovial fluid, synovial membrane, and joint capsule of group 1 horses were significantly lower than concentrations in those samples for horses in groups 2 and 3.
Conclusions and Clinical Relevance—Continuous IA infusion of gentamicin achieves higher drug concentrations in joint tissues of normal tarsocrural joints of horses, compared with concentrations after IV administration.
Objective—To develop a method for continuous infusion
of gentamicin into the tarsocrural joint of horses,
to determine pharmacokinetics of gentamicin in synovial
fluid of the tarsocrural joint during continuous
infusion, and to evaluate effects of continuous infusion
of gentamicin on characteristics of the synovial
Animals—12 healthy adult horses.
Procedure—An infusion catheter consisting of flow
control tubing connected to a balloon infuser was
used. Gentamicin solution (100 mg/ml) was infused in
the right tarsocrural joint and balanced electrolyte
solution was infused in the left tarsocrural joint for 5
days. Synovial fluid and serum gentamicin concentrations
were measured by use of a fluorescence polarization
Results—17 of the 24 (71%) infusion catheters initially
placed functioned without complications for the entire
5-day infusion period. Median gentamicin concentration
in synovial fluid from treated joints during the 5-day infusion
period ranged from 287.5 to 982 μg/ml. Median
serum gentamicin concentration during this period
ranged from 2.31 to 2.59 μg/ml. Mean (± SD) elimination
half-life and total clearance of gentamicin from the
synovial fluid were 6.25 ± 1.01 hours and
1.52 ± 0.96 ml/min, respectively.
Conclusions and Clinical Relevance—An infusion
catheter can be used for continuous infusion of gentamicin
into the tarsocrural joints of horses for up to 5
days. At a gentamicin dosage of 0.17 ± 0.02 mg/kg/h,
continuous intra-articular infusion results in synovial
fluid gentamicin concentrations greater than 100
times the minimal inhibitory concentration reported
for common equine pathogens. (Am J Vet Res 2000;61:407–412)
To compare heat generation and mechanical bone damage achieved with 2 tapered and 1 cylindrical transfixation pin taps in third metacarpal bones from equine cadavers.
18 pairs (36 specimens) of third metacarpal bones from euthanized horses with no known metacarpal disease.
In each bone, an investigator drilled 3 holes for placement of a 6.3-mm cylindrical transfixation pin, a 6.3-mm tapered pin using a prototype tapered tap, and a 6.3-mm tapered pin using a revised tapered tap. One bone of each pair was tapped by hand and the other with an electric drill. Temperatures of the drill bits, reamers, and taps were measured and used to compare heat generation among tap groups and tapping methods (hand vs power tapping). Macrodamage (all bone pairs) and microdamage (6 bone pairs) were assessed.
The revised tapered tap resulted in less heat generation and less total thread microdamage, compared with the prototype tapered and cylindrical taps. Power tapping created less bone damage but higher temperatures than did hand tapping for all bone groups.
CONCLUSIONS AND CLINICAL RELEVANCE
The revised tap design for tapered pin insertion was superior to the prototype tap design and yielded similar or less bone damage than achieved with cylindrical pin insertion in equine third metacarpal bone specimens. We recommend careful hand tapping for tapered pin insertion rather than power tapping, which generated greater heat. The revised tapered tap could be expected to perform better than a cylindrical pin tap in terms of thermal and mechanical microdamage and should be used for insertion of tapered transfixation pins.
Objective—To determine synovial fluid gentamicin concentrations and evaluate adverse effects on the synovial membrane and articular cartilage of tarsocrural joints after implantation of a gentamicin-impregnated collagen sponge.
Animals—6 healthy adult mares.
Procedures—A purified bovine type I collagen sponge impregnated with 130 mg of gentamicin was implanted in the plantarolateral pouch of 1 tarsocrural joint of each horse, with the contralateral joint used as a sham-operated control joint. Gentamicin concentrations in synovial fluid and serum were determined for 120 hours after implantation by use of a fluorescence polarization immunoassay. Synovial membrane and cartilage specimens were collected 120 hours after implantation and evaluated histologically.
Results—Median peak synovial fluid gentamicin concentration of 168.9 μg/mL (range, 115.6 to 332 μg/mL) was achieved 3 hours after implantation. Synovial fluid gentamicin concentrations were < 4 μg/mL by 48 hours. Major histologic differences were not observed in the synovial membrane between control joints and joints implanted with gentamicin-impregnated sponges. Safranin-O fast green stain was not reduced in cartilage specimens obtained from treated joints, compared with those from control joints.
Conclusions and Clinical Relevance—Implantation of a gentamicin-impregnated collagen sponge in the tarsocrural joint of horses resulted in rapid release of gentamicin, with peak concentrations > 20 times the minimum inhibitory concentration reported for common pathogens that infect horses. A rapid decrease in synovial fluid gentamicin concentrations was detected. The purified bovine type I collagen sponges did not elicit substantial inflammation in the synovial membrane or cause mechanical trauma to the articular cartilage.
Objective—To determine the effects of a continuous
intra-articular infusion of gentamicin on the synovial
membrane and articular cartilage in the tarsocrural
joint of horses.
Animals—6 healthy adult horses.
Procedure—A balloon infusion system attached to a
catheter placed in the plantarolateral pouch of both
tarsocrural joints in each horse was used for continuous
gentamicin solution (GM) or balanced electrolyte
solution (BES) delivery for 5 days. Cartilage and synovial
membrane specimens were collected on day 5
from 3 horses and on day 14 from the remaining 3
horses. Both infused joints from each horse were
assessed, using gross evaluation and histologic scoring
Results—Significant differences in the histologic
scores of synovial membrane specimens between
the GM- and BES-treated joints at either 5 or 14 days
were not observed. Safranin-O-fast green staining
scores were similar between cartilage specimens
from GM- and BES-treated joints. Although the synovial
membrane histologic scores and safranin-O-fast
green staining scores improved from day 5 to 14, the
changes in scores were not significant. Loss of synovial
intimal cells from villi was found more commonly
in sections of synovial membrane from GM-treated
joints, compared with BES-treated joints.
Conclusions and Clinical Relevance—Continuous
infusion of GM into the tarsocrural joint of horses
does not have significant effects on histologic scores
of articular cartilage or synovial membrane, compared
with those infused with BES. Continuous infusion of
GM into the tarsocrural joint of horses for 5 days is an
acceptable method for the treatment of septic arthritis.
(Am J Vet Res 2002;63:683–687)
Objective—To determine the effect of 2 hydroxyapatite pin coatings on heat generated at the bone-pin interface and torque required for insertion of transfixation pins into cadaveric equine third metacarpal bone.
Sample Population—Third metacarpal bone pairs from 27 cadavers of adult horses.
Procedures—Peak temperature of the bone at the cis-cortex and the hardware and pin at the trans-cortex was measured during insertion of a plasma-sprayed hydroxyapatite (PSHA)—coated, biomimetic hydroxyapatite (BMHA)—coated, or uncoated large animal transfixation pin. End-insertional torque was measured for each pin. The bone-pin interface was examined grossly and histologically for damage to the bone and coating.
Results—The BMHA-coated transfixation pins had similar insertion characteristics to uncoated pins. The PSHA-coated pins had greater mean peak bone temperature at the cis-cortex and greater peak temperature at the trans-cortex (70.9 ± 6.4°C) than the uncoated pins (38.7 ± 8.4°C). The PSHA-coated pins required more insertional torque (10,380 ± 5,387.8 Nmm) than the BMHA-coated pins (5,123.3 ± 2,296.9 Nmm). Four of the PSHA-coated pins became immovable after full insertion, and 1 gross fracture occurred during insertion of this type of pin.
Conclusions and Clinical Relevance—The PSHA coating was not feasible for use without modification of presently available pin hardware. The BMHA-coated pins performed similarly to uncoated pins. Further testing is required in an in vivo model to determine the extent of osteointegration associated with the BMHA-coated pins in equine bone.
Objective—To compare the bone temperature and final hole dimensions associated with sequential overdrilling (SO) and single 6.2-mm drill bit (S6.2DB) methods used to create transcortical holes in the third metacarpal bones (MCIIIs) of horse cadavers.
Sample—60 MCIIIs from 30 horse cadavers.
Procedures—In phase 1, hole diameter, tap insertion torque, peak bone temperature, and postdrilling bit temperature for 6.2-mm-diameter holes drilled in the lateral or medial cortical region of 12 MCIIIs via each of three 2-bit SO methods with a single pilot hole (diameter, 3.2, 4.5, or 5.5 mm) and the S6.2DB method were compared. In phase 2, 6.2-mm-diameter transcortical holes were drilled via a 2-bit SO method (selected from phase 1), a 4-bit SO method, or a S6.2DB method at 1 of 3 locations in 48 MCIIIs; peak bone temperature during drilling, drill bit temperature immediately following drilling, and total drilling time were recorded for comparison.
Results—Hole diameter or tap insertion torque did not differ among phase 1 groups. Mean ± SD maximum bone temperature increases at the cis and trans cortices were significantly less for the 4-bit SO method (3.64 ± 2.01°C and 8.58 ± 3.82°C, respectively), compared with the S6.2DB method (12.00 ± 7.07°C and 13.19 ± 7.41°C, respectively). Mean drilling time was significantly longer (142.9 ± 37.8 seconds) for the 4-bit SO method, compared with the S6.2DB method (49.7 ± 24.3 seconds).
Conclusions and Clinical Relevance—Compared with a S6.2DB method, use of a 4-bit SO method to drill transcortical holes in cadaveric equine MCIIIs resulted in smaller bone temperature increases without affecting hole accuracy.
Objective—To evaluate the effect of ovariectomy on insulin sensitivity in horses and determine whether the effects of suppression of the hypothalamo-pituitary-adrenal axis differ before and after ovariectomy.
Animals—6 healthy mares.
Procedures—The horses underwent an IV glucose tolerance test (IVGTT), an insulin sensitivity test, and a dexamethasone suppression test before and 5 weeks after ovariectomy. Body weight, serum cortisol and plasma ACTH concentrations, serum insulin-to-blood glucose concentration ratios, and changes in blood glucose concentration with time after injection of glucose or insulin were compared before and after ovariectomy.
Results—The dexamethasone injection resulted in a decrease in serum cortisol concentration before and after ovariectomy. In all horses, baseline plasma ACTH concentrations were within the reference range before and after ovariectomy. For each mare, results of an IVGTT before and after ovariectomy were considered normal. No significant differences in basal blood glucose concentration or time to reach baseline glucose concentration after an IVGTT were observed. Basal serum insulin concentration and serum insulin-to-blood glucose concentration ratios were not significantly different before or after ovariectomy, nor was the mean time to attain a 50% decrease in blood glucose concentration after insulin injection.
Conclusions and Clinical Relevance—Results indicated that ovariectomy does not appear to modify dexamethasone response in horses and that it does not modify short-term measures of insulin sensitivity. Findings suggested that horses undergoing ovariectomy are not at higher risk of developing equine metabolic syndrome or hypothalamo-pituitary-adrenal axis dysfunction and associated morbidity.
OBJECTIVE To compare results obtained with a handheld reference point indentation instrument for bone material strength index (BMSi) measurements in the equine third metacarpal bone for various testing conditions.
SAMPLE 24 third metacarpal bones.
PROCEDURES Third metacarpal bones from both forelimbs of 12 horses were obtained. The dorsal surface of each bone was divided into 6 testing regions. In vivo and ex vivo measurements of BMSi were obtained through the skin and on exposed bone, respectively, to determine effects of each testing condition. Difference plots were used to assess agreement between BMSi obtained for various conditions. Linear regression analysis was used to assess effects of age, sex, and body weight on BMSi. A mixed-model ANOVA was used to assess effects of age, sex, limb, bone region, and testing condition on BMSi values.
RESULTS Indentation measurements were performed on standing sedated and recumbent anesthetized horses and on cadaveric bone. Regional differences in BMSi values were detected in adult horses. A significant linear relationship (r2 = 0.71) was found between body weight and BMSi values. There was no difference between in vivo and ex vivo BMSi values. A small constant bias was detected between BMSi obtained through the skin, compared with values obtained directly on bone.
CONCLUSIONS AND CLINICAL RELEVANCE Reference point indentation can be used for in vivo assessment of the resistance of bone tissue to microfracture in horses. Testing through the skin should account for a small constant bias, compared with results for testing directly on exposed bone.
OBJECTIVE To compare heat generation and mechanical bone damage for tapered and cylindrical transfixation pins during drilling, tapping, and pin insertion in equine third metacarpal bones.
SAMPLE 16 pairs of cadaveric equine third metacarpal bones.
PROCEDURES For cylindrical pin insertion, a 6.2-mm hole was drilled and tapped with a cylindrical tap, and then a standard 6.3-mm pin was inserted. For tapered pin insertion, a 6.0-mm hole was drilled, reamed with a tapered reamer, and tapped with a tapered tap, and then a 6.3-mm tapered pin was inserted. Paired t tests and 1-way ANOVAs were used to compare heat generation (measured by use of thermocouples and thermography), macrodamage (assessed by use of stereomicroscopy), and microdamage (assessed by examination of basic fuchsin–stained histologic specimens) between cylindrical and tapered pins and between tapered pins inserted to various insertion torques.
RESULTS Tapered pin insertion generated less heat but resulted in more bone damage than did cylindrical pin insertion when pins were inserted to the same insertion torque. Insertion of tapered pins to increasing insertion torques up to 16 N•m resulted in increased heat generation and bone damage.
CONCLUSIONS AND CLINICAL RELEVANCE Tapered pin insertion resulted in lower heat production than did cylindrical pin insertion. However, tapered pin insertion resulted in greater bone damage, which likely was attributable to differences in the tapered and cylindrical taps. A tapered pin may be preferable to a cylindrical pin for insertion in equine cortical bone provided that improvements in tap design can reduce bone damage during insertion.