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Abstract

Objective

To investigate the effect of late gestation, age, and parity on material properties of third metacarpal (MCIII) cortical bone in mares.

Animals

8 healthy mares (treatment group) that died or were euthanatized within 24 hours after parturition because of foaling complications and 6 age-matched, healthy, nonpregnant mares (control group).

Procedures

After random assignment for mechanical testing and microradiography, the dorsal half of transverse mid-diaphyseal sections of each MCIII bone was divided into lateral, dorsal, and medial regions. Cylinders of bone from each of the 3 regions were tested in compression in a single cycle to failure. Contact microradiographic views were taken of 100-µm-thick sections prepared from methylmethacrylate-embedded transverse dorsal region specimens, which were further divided into periosteal, intracortical, and endosteal regions for assessment of bone mineral density and porosity.

Results

Postpartum mares had lower yield strain in the dorsal and medial regions and failure strain in the medial region. Increasing parity was associated with decreasing elastic modulus in the dorsal region and yield stress and failure stress in the lateral region. Age and parity were positively correlated (r = 0.865; P = 0.0001), but significant correlations were not found between treatment group and age or between treatment group and parity. Increasing age and parity were associated with increasing porosity in the periosteal region.

Conclusions and Clinical Relevance

On the basis of the material properties evaluated for MCIII cortical bone in late pregnancy, any increased risk for fractures in mares in late gestation may be related to parity or age or both, and less likely to pregnancy per se. (Am J Vet Res 1997;58:182–187)

Free access
in American Journal of Veterinary Research

Abstract

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 horses.

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- tendon unit.

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)

Full access
in American Journal of Veterinary Research

Abstract

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 metatarsal fracture.

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 ANOVA.

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 2000;61:234–237)

Full access
in American Journal of Veterinary Research

Abstract

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 adult Thoroughbreds.

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)

Full access
in American Journal of Veterinary Research

Abstract

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.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To assess individual and combined associations of high-speed exercise and horseshoe characteristics with risk of forelimb proximal sesamoid bone fractures and proximal sesamoid bone midbody fractures in Thoroughbred racehorses.

Animals—269 deceased Thoroughbred racehorses.

Procedures—A case-control study design was used to compare 121 horses with a fracture of at least 1 of 4 forelimb proximal sesamoid bones (75 horses had a midbody fracture) and 148 horses without a forelimb proximal sesamoid bone fracture. Univariable and multivariable logistic regression analyses were used to evaluate potential risk factors for association with proximal sesamoid bone fracture.

Results—Compared with horses that died without proximal sesamoid bone fractures, horses that died with proximal sesamoid bone fractures were more likely to be sexually intact males, spend more time in active trainingand racing, complete more events, train and race longer since their last layup, have higher exercise intensities during the 12 months prior to death, and have greater cumulative distances for their career. Horses with proximal sesamoid bone midbody fractures were more likely to be sexually intact males, train and race longer since their last layup, and have higher exercise intensities during the 12 months prior to death.

Conclusions and Clinical Relevance—Limitingexercise intensity and the continuous time spent in activity duringa horse's career may decrease the frequency of forelimb proximal sesamoid bone fractures in Thoroughbred horses.

Full access
in American Journal of Veterinary Research

Abstract

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 mixed-breed dogs.

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 stem.

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)

Full access
in American Journal of Veterinary Research

Abstract

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 complexes.

Sample Population—8 cadaveric forelimbs from 6 adult Thoroughbreds.

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 Res 2004;65:188–197)

Full access
in American Journal of Veterinary Research

Abstract

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.

Full access
in American Journal of Veterinary Research

Abstract

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 injury (SSAI).

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)

Full access
in American Journal of Veterinary Research