Search Results

Abstract

Objective—To determine the degree to which components of the training program of 2-year-old Thoroughbred racehorses influence their susceptibility to fatigue injury of the third metacarpal bone (bucked shins).

Animals—226 two-year-old Thoroughbred racehorses.

Procedure—Daily training information and health reports on 2-year-old Thoroughbreds were compiled from records provided from 5 commercial stables. For each horse, data (exercise variables) were collected that comprised distance jogged (approx speed of 5 m/s), galloped (approx 11 m/s), and breezed (approx 15 to 16 m/s) until a single instance of bucked shins was reported. Data were coded for analysis using cross-tabulation, graphic, and survival techniques.

Results—Of 226 horses, 56 had bucked shins, 9 completed the observation period without bucked shins, and 161 were lost to follow-up. Distinct training strategies were used at stables resulting in significantly different survival profiles among stables. Mean (± SD) allocation of exercise to breezing was 0.15 ± 0.13 miles/wk (maximum, 0.64 miles/wk), to galloping was 4.47 ± 1.52 miles/wk (maximum, 9.56 miles/wk), and to jogging was 2.34 ± 1.70 miles/wk (maximum, 8.53 miles/wk). Survival (ie, lack of bucked shins during 1 year of monitoring) was found to be significantly reduced by exercise allocation to breezing, significantly increased by exercise allocation to galloping, and uninfluenced by exercise allocation to jogging. The log of the hazard ratio was reduced by 4.2 ± 1.5/mile breezed and increased by 0.3 ± 0.1/mile galloped.

Conclusions and Clinical Relevance—Relationships between different gaits and speeds in the training regimen influence the incidence of bucked shins. To reduce the incidence of bucked shins, trainers should consider allocating more training effort to regular short-distance breezing and less to long-distance galloping. (Am J Vet Res 2000;61:602–608)

Summary

Bilateral, midshaft metacarpal osteotomies were performed in 11 sheep and bilateral, midshaft radial osteotomies were performed in 7 sheep. The lesions were repaired with bone plates. One of each pair of plates was luted with polymethylmethacrylate and all screws were tightened uniformly with a torque screwdriver. Sheep were allowed unrestricted exercise after surgery. At 8 weeks, 10 of 11 sheep with metacarpal osteotomies were sound and both osteotomies were healing. Seven were lame on the limb with the unluted plate during the first 3 weeks; 4 were never lame on either limb. The screws of the unluted plates were significantly (P < 0.01) looser at 8 weeks than those in the luted plates. All of the sheep with radial osteotomies were lame in the limb with the unluted plate. Four of 7 sheep had overt loosening of the unluted plates. One sheep only had mild screw loosening with continued alignment of the osteotomy. Two of 7 sheep fractured the radius with the luted plate; these 2 sheep were lame in the limb with the unluted plate and were using the limb with the luted plate vigorously. Excluding the 2 sheep with fractures, all had substantially more screw loosening in the unluted plate. Histologically, there were no discernible differences in the vascularity or porosity of the bone under the luted vs the unluted plates. The only adverse consequence of the luting technique was introduction of a small amount of polymethylmethacrylate into the osteotomy gap in 5 bones.

Summary

Eight untrained 2-year-old Thoroughbred horses were used in a study of the remodeling response of the proximal sesamoid bone (psb) to training-related stimuli. Two horses each were assigned to 1 of 4 groups: group 1, untrained, pasture turnout (control); group 2, modified-classically trained, dirt track; group 3, classically trained, dirt track; and group 4, classically trained, wood chip track. Horses were given fluorochromic bone labels every 28 days during training. All horses were euthanatized after 5 months of training, and the proximal sesamoid bones (psb) were removed. A midsagittal section of bone 85- to 95- μm thick was prepared for histomorphometric analysis by use of computerized image analysis and epifluorescent microscopy. Porosity (percent), trabecular width (micrometer), extent of anisotropy (percent), mineralizing surface (percent), fractional mineralizing surface (percent), and mineral apposition rate (micrometers per day) were determined at 5 circular regions of each specimen. Region 1 was located within the apex of the psb, regions 2, 3, and 4 were subjacent to the subchondral plate, and region 5 was within the basilar articular margin. Data were pooled to allow comparison by training group and by region.

The psb from horses trained on dirt tracks (groups 2 and 3) had significantly (P < 0.05) lower porosities and greater trabecular width, compared with the control group. The psb from all training group specimens had significantly larger mineralizing surfaces than control group specimens. The fractional mineralizing surface revealed a rapid and vigorous response of the endosteal surface of the psb in horses trained on dirt tracks. When group data were pooled, region 2 was found to have the lowest porosity and greatest trabecular width of any region. Region 1 was found to have the highest porosity and lowest structural anisotropy of any region. Structural anisotropy of the cancellous bone was greatest at regions 2, 3, and 4.

The results of this study demonstrate a substantial stress adaptive remodeling response of the psb to training-related stimuli. Regional morphologic variations were found that presumably reflect the load history of the psb in vivo. Adaptive changes may allow the psb to withstand without failure large stresses generated during maximal exercise.

SUMMARY

In vitro local fatigue testing of the third metacarpal bone from Thoroughbred and Standardbred racehorses was performed, using fully reversed cyclic bending. Strain number of cycle data were accumulated and indicated that significant difference did not exist between the 2 breeds. It was concluded that the marked difference in the incidence of fatigue failure in the third metacarpal bone (bucked shins, dorsal metacarpal disease) seen in Thoroughbreds and Standardbreds was not related to any differences between the 2 breeds in mechanical properties of the bone.

Abstract

Objective—To evaluate stiffness and bone-pin interface stress for a transcortical tapered-sleeve pin (TSP) that incorporates bilateral tapered sleeves over a transcortical pin.

Sample Population—14 third metacarpal bones (MCIII) collected from adult horses of various breeds.

Procedure—Each MCIII was cut in half to provide 2 test specimens. Pins (conventional and TSP) of 3 diameters (6.35, 7.94, and 9.50 mm) were inserted in specimens (3 specimens for each diameter and each type of pin). The test fixture simulated a typical sidebar- span skeletal fixation device for horses. Single cycle load-deflection tests were performed. Cyclic fatigue tests of TSP were performed to evaluate fatigue characteristics and stress conditions at the bone-pin interface. Maximum stress and strain were calculated, and results were compared with existing data on fatigue characteristics of bone.

Results—Significant increases in stiffness (loaddeflection) and higher loads at yield point were detected for the TSP (stiffness for conventional 9.50- mm pins, 4,500 N/mm; stiffness for TSP, 19,988 N/mm). Results of cyclic tests revealed a close correlation with existing data on fatigue characteristics.

Conclusions and Clinical Relevance—The TSP described here is stiffer than conventional transcortical pins, and stress across the bone-pin interface is more evenly distributed. Use of this TSP should minimize major problems encountered during external fixation associated with the transcortical pin and bone-pin interface (ie, bone necrosis, infection of the pin track, pin loosening, and bone failure). ( Am J Vet Res 2001;62:955–960)

SUMMARY

The third carpal bone (C₃) was collected from both forelimbs of 27 Thoroughbreds. On the basis of age, training, and history, specimens were assigned to 1 of 5 groups: yearling, untrained horses (group 1, n = 4); 2- to 3-year-old, untrained horses (group 2, n = 7); trained 2-year-old horses (group 3, n = 6); trained 3-year-old horses (group 4, n = 6); and 3-year-old, trained horses with carpal pathologic features (group 5, n = 4). A transverse section of subchondral bone 5-mm thick was cut in a precise fashion 10 mm below the proximal articular surface of all specimens. After high-detail radiography was done, indentation testing was performed on the proximal surface of the section at points 5 mm apart. The stiffness of the subchondral cancellous bone was determined from the slope of the load vs displacement curve. Topographic plots of stiffness measurements were compared with radiographs of each specimen. Point determinations were averaged to derive measures for the radial and intermediate facets, and for regions 5, 10, 15, and 20 mm from the dorsal margin of C₃. Area fraction (1-p; p = porosity) was measured for the radial and intermediate facets, using an automated image analysis system.

Significant (P < 0.05) increases in stiffness and area fraction were found in the C₃ from trained horses (groups 3 to 5), compared with untrained horses (groups 1 to 2). Stiffness and area fraction of the radial facet of pathologic C₃ were significantly higher than the same variables measured in C₃ from any other group. A typical profile of regional subchondral stiffness was identified in C₃ from normal horses, with maximal stiffness measured 10 mm from the dorsal articular margin. A different pattern was found in pathologic C₃, with significantly greater stiffness 15 and 20 mm from the dorsal articular margin when compared with normal horses. A highly significant (P < 0.0001) direct linear correlation between stiffness and area fraction at the radial facet was found. Topographic and radiographic analysis demonstrated good correlation between stiffness and radiographic density of the bone sections. The observed patterns of normal and pathologic C₃ were contrasted. In particular, a large gradient in subchondral stiffness was identified in pathologic C₃ at the dorsomedial aspect of the bone.

Abstract

Objective—To report the outcome of surgical treatment of comminuted fractures of the proximal phalanx in horses.

Design—Retrospective study.

Animals—64 horses.

Procedure—Medical records and radiographs were reviewed to obtain information regarding signalment, fracture classification, and treatment. Follow-up information was obtained by telephone conversation or evaluation of production records.

Results—Thirty-eight horses had moderately comminuted fractures of the proximal phalanx. Two horses were euthanatized immediately. Fractures of the proximal phalanx in 36 horses were repaired with open reduction and internal fixation with a successful outcome in 33 (92%) horses. Reconstruction of the fracture was performed in most horses by use of a long curved incision, transection of the collateral ligament of the metacarpophalangeal or metatarsophalangeal joint, and open exposure of the proximal articular surface of the proximal phalanx. Twenty-six horses had severely comminuted fractures of the proximal phalanx. Six horses were euthanatized immediately. One horse was euthanatized after 9 days of treatment with a cast alone. Severely comminuted fractures of the proximal phalanx in 13 horses were treated with an external skeletal fixation device, and fractures healed in 8 of those horses. Six horses with severely comminuted fractures of the proximal phalanx were treated with transfixation pins incorporated into a fiberglass cast, and fractures healed in 4 horses.

Conclusions and Clinical Relevance—Moderately comminuted fractures of the proximal phalanx can be successfully repaired; however, fractures that are too severe to permit accurate reconstruction of the fragments remain difficult to treat and horses have only a fair prognosis for survival. (J Am Vet Med Assoc 2004; 224:254–263)

Abstract

Objective—To describe the pool-raft recovery system protocol and to evaluate the clinical outcome inhorses that underwent recovery from general anes-thesia using this system.

Design—Retrospective study.

Animals—393 horses that underwent recovery fromgeneral anesthesia in the pool-raft system.

Procedure—Anesthetic records were examined fromhorses recovered from anesthesia in the pool-raft sys-tem between January 1984 and December 2000.Complete medical records of horses were examinedwhen available. Information regarding the anestheticand recovery period was recorded. Horses first recov-ered from general anesthesia in the pool-raft and,once awake, were transported to a recovery stall andlowered to the floor in a standing position.

Results—351 horses underwent 1 pool-raft recovery,and 42 horses underwent multiple pool-raft recover-ies. Most horses were recovered from general anes-thesia within the pool-raft system to safeguard repairof a major orthopedic injury. During 471 pool-raftrecoveries, 34 (7%) horses had complications withinthe recovery pool and 62 (13%) had complicationswithin the recovery stall. Deaths resulted from complete failure of internal fixation, pulmonary dysfunc-tion, or a combination of pulmonary dysfunction andfixation failure in 2% (10/471) of horses that under-went pool-raft recoveries.

Conclusions and Clinical Relevance—The pool-raftsystem is a good option for recovery from generalanesthesia. Although not a fail-safe system, itappears to decrease the complications of recoveringhorses in a high-risk category. Potential disadvan-tages of this system are added expense and man-power necessary in building, maintenance, andusage, as well as size limitations of the raft itself. (J Am Vet Med Assoc 2002;221:1014–1018)

Abstract

Twenty-two horses with ulnar fractures were treated, using tension band wires alone or tension band wires in combination with pins or cortical bone screws. Age of the horses ranged from 2 weeks to 12 years (median, 4 months), and body weight ranged from 68 to 477 kg (median, 181 kg). Fractures were classified according to the Donecker and Bramlage ulnar fracture classification and included type 1-a (4 horses), type 1-b (4), type-2 (6), type-3 (1), type-4 (3), and type-5 (4) fractures. Tension band wires alone were used in 7 horses. Tension band wires were used in conjunction with unthreaded pins in 10 horses. In 3 horses, 5.5-mm cortical bone screws were inserted longitudinally instead of pins. A combination of a 5.5-mm cortical bone screw and a pin was used in 2 horses. In addition to pins and tension band wires, 4.5-mm cortical bone screws were placed in lag fashion to aid reduction of comminuted or oblique fractures in 7 of the 22 horses. Fractures healed in 18 (82%) horses. Four horses were euthanatized because of complications that included catastrophic failure of fixation during recovery from general anesthesia in 1 foal, septic arthritis and hyperextension of the contralateral metacarpophalangeal joint in 1 foal, and wound infection with partial disruption of repair in 2 horses. Nonfatal complications developed in 6 horses and included incision infection, partial wound dehiscence, carpal contraction, carpus varus of the contralateral forelimb, slight distraction of proximal fragments of the fractures, bent implants, and distal migration of pins. Long-term monitoring was performed on 17 horses. Of these 17 horses, 13 (76%) were able to achieve athletic performance activities, 3 had residual lameness restricting athletic performance, and 1 had severely limited activity as a result of lameness. Tension band wires can be used successfully for repair of ulnar fractures in selected horses.