Effect of maturation and aging on the histomorphometric and biochemical characteristics of equine superficial digital flexor tendon.

OBJECTIVE: To assess tendon morphology and non-reducible crosslink concentration, and associations of these findings with horse age and previously reported mechanical and ultrasonographic findings. SAMPLE POPULATION: Superficial digital flexor tendon samples were obtained from 23 horses aged 2 to 23 years. The tendons had undergone ultrasonography and were submitted to biomechanical testing in the physiologic range prior to sample acquisition. PROCEDURE: Samples were sectioned in a transverse plane; then dorsal, palmar, central, lateral, and medial regions were evaluated for fascicle cross-sectional area (CSA), septal width, and vessel density (the product of vessel numbers and vessel CSA per field). Contiguous samples were analyzed for collagen crosslinking. RESULTS: Central fascicles were significantly larger than fascicles in other tendon regions. Fascicle CSA decreased significantly with increasing age. Because total tendon CSA is unrelated to increasing age, fascicle numbers appeared to increase with increasing age. Regional or age effects on septal width were not found. There was no age or regional effect on vessel numbers, density, or fractional area. Fascicle CSA was positively correlated with total tendon CSA; fascicle CSA was negatively correlated with elastic modulus. Hydroxypiridinium concentration tended to increase with increasing horse age; this effect was associated with a positive correlation between hydroxypiridinium values and elastic modulus. CONCLUSIONS: Equine superficial digital flexor tendon undergoes an increase in structural organization and an increase in nonreducible crosslinks with maturation and aging. These changes are associated with an increase in elastic modulus.

Gunshot injuries in horses: 22 cases (1971-1993)

Twenty-two horses were examined because of firearm injuries. Nine had been shot with .22-caliber bullets, 2 with BB pellets, 6 with buckshot, 1 with a .35-caliber bullet, and 1 with an airgun pellet. Injury was confined to the skin or skeletal muscles in 8 horses. Of these, 7 returned to their previous use. In 14 horses, injuries to additional structures were incurred, including the sinus and pharynx (n = 2), mandible (n = 1), tooth (n = 1), aorta (n = 1), eye (n = 3), tibia (n = 1), gastrointestinal tract (n = 3), joint (n = 1), and trachea (n = 1). The 3 horses that had only eye injuries were discharged to their owners. Of the other 11 horses with injuries to deep/vital structures, 3 died, 5 were euthanatized, and 3 survived.

Ultrasonographic cross-sectional area and mean echogenicity of the superficial and deep digital flexor tendons in 50 trained thoroughbred racehorses.

Fifty Thoroughbred horses were examined. All horses had been in race training for a minimum of 4 months before examination and had worked at racing speed; 24 horses had raced. All horses were clinically sound at the time of examination. Ultrasonography was performed, using a 7.5-MHz transducer with built-in fluid offset. Videotaped images of the palmar soft tissue structures were obtained at 4, 8, 12, 16, 20 and 24 cm distal to the base of the accessory carpal bone (DACB). Images were digitized, and each image was calibrated. Values for cross-sectional area (CSA) and mean echogenicity (ME) were then determined from the cross-sectional images of the superficial digital flexor (SDF) and the deep digital flexor (DDF) tendons, using an image-analysis program. The SDF tendons were compared between right and left forelimbs at each level, and from proximal to distal on each limb, as were the DDF tendons. The relation between the SDF and DDF tendons for the same forelimb was determined at each level. There were no significant differences in CSA or ME at equivalent levels of the left and right SDF tendons. Mean (+/- SD) CSA was 1.01 +/- 0.12) cm2 at 4 cm DACB, 0.95 (+/- 0.14) cm2 at 12 cm DACB, and 1.12 (+/- 0.15) cm2 at 24 cm DACB. Adjusted ME was 2.34 (+/- 0.34) at 4 cm DACB, 2.03 (-/+- 0.38) at 12 cm DACB, and 2.04 (+/- 0.35) at 24 cm DACB. The left and right DDF tendons did not have significant differences in CSA or ME at any level. Cross-sectional area was 1.13 (+/- 0.18) cm2 at 4 cm DACB, 1.01 (+/- 0.12) cm2 at 12 cm DACB, and 1.75 (+/- 0.29) cm 2 at 24 cm DACB. Adjusted ME was 2.60 (+/-0.46) at 4 cm DACB, 2.49 (+/- 0.49) at 12 cm DACB, and 2.50 (+/- 0.44) at 24 cm DACB. At all levels, the left and right SDF tendons were smaller and less echoic than the DDF tendons of the same limb. The SDF and DDF tendons had an hour glass shape, with smallest CSA at 12 cm DACB. Mean echogenicity generally decreased for the SDF and DDF tendons from proximal to distal on the limb. These results indicate that for clinically normal trained Thoroughbred racehorses, there should be no significant difference in CSA or echogenicity between the left and right SDF tendons at equivalent distances DACB. There should be no significant differences in the left and right DDF tendons at equivalent levels DACB. The SDF tendon is usually smaller and less echoic than the corresponding DDF tendon at each level.

Ultrasonography as a method to determine tendon cross-sectional area.

Ultrasonographic cross sectional area (CSA) measurements of equine superficial digital flexor (SDF) tendon were obtained to determine the feasibility of ultrasonography for CSA measurement of tendon in vivo and in vitro. Ultrasonographic measurements were compared with a more traditional CSA measurement method, ink-blot analysis. In addition, values for ultrasonographic SDF tendon mean echogenicity were obtained in vivo and in vitro. The left forelimb SDF tendons of 23 horses were evaluated ultrasonographically. Cross sectional images were acquired at 4-cm intervals distal to the base of the accessory carpal bone (DACB) to the level of the proximal sesamoid bones while horses were standing squarely. After euthanasia, the left forelimbs were mounted in a materials testing system (MTS) and loaded under tension to standing load. Ultrasonographic images were again acquired at the same locations. The ultrasonographic images were digitized, and values for ultrasonographic CSA and mean echogenicity were obtained for each level. immediately after mechanical testing, a 1-cm-thick transverse section of SDF tendon at 12 cm DACB was removed. Three ink blots were prepared from each end of the removed tendon section and digitized. The 6 CSA values were averaged to generate a value for morphologic CSA for each SDF tendon at 12 cm DACB. Standing ultrasonographic tendon CSA at 12 cm DACB was consistently smallest (mean +/- SD CSA 86 +/- 11 mm2), followed by MTS ultrasonographic CSA (mean, 95 +/- 12 mm), with ink-blot morphologic CSA being largest (mean, 99 +/- 15 mm2). Comparison of standing and MTS ultrasonographic CSA values at 12 cm DACB revealed a strong positive linear correlation between methods (R2 = 0.74, P = 0.001). Comparison of ink blot CSA at 12 cm DACB with standing and MTS ultrasonographic CSA revealed strong positive linear correlations (R2 = 0.64, P = 0.001 and R2 = 0.72, P = 0.001, respectively). For ultrasonographic mean echogenicity, standing values insignificantly exceeded MTS values at each level. The authors conclude that ultrasonography is a useful technique for the noninvasive assessment of SDF tendon CSA that can be applied in vivo and in vitro.

Effect of maturation and aging on material and ultrasonographic properties of equine superficial digital flexor tendon.

Results of studies in human beings and other species have indicated that aging significantly influences the strength, modulus of elasticity, and energy storage ability of tendon. We wanted to determine the effects of aging on the material and ultrasonographic properties of equine superficial digital flexor (SDF) tendon. Ultrasonographic measurements of left forelimb SDF tendon cross-sectional area and mean echogenicity were made in 23 standing horses ranging in age from 2 to 23 years. All horses had not been in work for a minimum of 6 months prior to the study. After euthanasia, left forelimb bone-muscle-tendon-bone specimens were mounted in a materials testing system. The SDF tendon was cyclically loaded sinusoidally 100 times at 0.5 Hz from 1.5 to 5.0% strain, then was submitted to 10-minute creep-and-stress relaxation tests. Modulus of elasticity, load at 3% strain, and creep-and-stress relaxation were determined for each specimen. A significant positive correlation was found between elastic modulus and age. Correlation was not found between age and SDF tendon cross-sectional area or mean echogenicity. When 2-year-old horses were compared with older horses, the latter had tendons with a significantly (P = 0.007) greater modulus of elasticity. The authors conclude that increasing age through maturity is associated with a corresponding increase in equine SDF tendon elastic modulus.

Digital flexor tendon lacerations in horses: 50 cases (1975-1990).

The medical records of 50 horses examined because of lacerations of the tendon of the superficial or deep digital flexor muscle were reviewed to determine whether any injury or treatment factors could be associated with outcome. Median age of horses treated was 4.5 years (range, 1.5 years to 15 years), and the median follow-up time was 5 years (range, 1.5 to 16 years) after injury. Horses were considered to have survived if they were alive more than 1 year after injury. Twelve of 16 horses that had 1 or the other tendon transected survived; 13 of 16 horses that had both tendons transected survived; and 14 of 18 horses that had partial tendon disruptions of 1 or both tendons survived. Of the 39 surviving horses, 27 horses returned to their original use, and 32 horses were sound for riding. Nine horses with 1 or both tendons transected were being used for athletic activities. Lacerated tendons were sutured in 16 horses, and 15 of these survived. Tendons were not sutured in 34 horses, and 24 of these survived. We were not able to detect any association between outcome and tendon sheath involvement or between outcome and limb involvement (forelimb vs hind limb).

Perioperative intratumoral administration of cisplatin for treatment of cutaneous tumors in equidae.

Twenty-seven horses (and 1 mule) with 32 histologically confirmed cutaneous tumors were studied to evaluate the effects of intratumoral injection of cisplatin initiated at the time of surgery. As a result of surgery, 9 of the wounds were closed primarily (5 sarcoids, 4 carcinomas) and 23 were left open to granulate (16 sarcoids, 6 carcinomas, 1 hamartoma). Chemotherapy consisted of 4 treatment sessions of intratumoral injection of cisplatin in purified sesame oil at 2-week intervals. The first treatment session was administered intraoperatively. A controlled-release formulation of cisplatin in sesame oil was used to limit drug egress from the injection site. Dosage was 1 mg of cisplatin/cm3 of tissue. The mean relapse-free interval was 41 +/- 3.7 months. The estimates of overall relapse-free survival rates were 92 +/- 5% at 1 year and 77 +/- 11% at 4 years. Cisplatin-related local toxicosis was minimal and wound healing was not compromised. Intratumoral injection of cisplatin appears safe and effective when administered in the perioperative period for selected tumors in equidae.

Surface oximetry for intraoperative assessment of colonic viability in horses.

Surface oximetry was used to evaluate viability of the ascending colon in 60 horses with naturally occurring colonic volvulus or displacement. Tissue surface oxygen tension (PsO2) was measured on the serosal surface of the pelvic flexure after anatomic correction of the colonic obstruction. Horses with PsO2 > 20 mm of Hg were predicted to have viable colon; whereas, horses with PsO2 < or = 20 mm of Hg were predicted to have nonviable colon. Results of surface oximetry were compared with final outcome. For surface oximetry, sensitivity (ability to accurately identify colon that was nonviable) was 53%, but specificity (ability to accurately identify bowel that was viable) was 100%. Negative predictive value (probability that a horse with PsO2 < or = 20 mm of Hg truly had nonviable bowel) was 87%, and positive predictive value (probability that a horse with PsO2 < or = 20 mm of Hg truly had nonviable bowel) was 100%. The overall accuracy was 88%. Of the 45 horses that had a colonic PsO2 > 20 mm of Hg and survived, 7 had been given, on the basis of subjective assessment of visual criteria, a good prognosis, 28 had been given a guarded prognosis, and 10 had been given a poor prognosis. Of the horses that had a colonic PsO2 > 20 mm of Hg but died after surgery because of further colonic infarction, confirmed at necropsy, 4 had been given a poor prognosis, and 3 had been given a guarded prognosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrasonographically detected changes in equine superficial digital flexor tendons during the first months of race training.

The forelimb superficial digital flexor (SDF) tendons of 6 Thoroughbreds were examined clinically and ultrasonographically during the first 4 months of race training. Sonograms were interpreted clinically and by use of computer-aided analysis. Tendon tissue from all horses was examined histologically at the end of the study. Computer-aided analysis of sonograms of the SDF tendons revealed trends toward an increase in mean cross-sectional area and a decrease in mean echogenicity over time with training. An inverse relation was found between increase in cross-sectional area and decrease in mean echogenicity over time in training. Two of the trained horses developed clinical signs of mild SDF tendonitis. Ultrasonography revealed an increase in cross-sectional area and decrease in mean echogenicity of clinically affected areas of the SDF tendons of 1 horse, compared with changes observed prior to the onset of tendonitis (these changes were not statistically significant). Blood vessels and lymphatics supplying the clinically and ultrasonographically affected tendon sites were large and thick-walled. These changes were not observed in the tendons of the other horses at the end of the study. The authors conclude that equine SDF tendons adapt to the early months of race training by increasing in size and decreasing in echogenicity, as determined by ultrasonography.

Prepurchase evaluation of horses: 134 cases (1988-1990).

To quantify some components of prepurchase evaluations in horses, records from 134 evaluations performed during a 2-year period were reviewed and the outcome was determined via telephone follow-up interview. Sixty-two percent of the prepurchase evaluations had been performed at the clinic and 38% had been performed in the field by the ambulatory service. All evaluations included physical and lameness examinations, whereas radiography (49%), endoscopy (15%), nerve blocking (5%), transrectal palpation (3%), hematologic analysis (2%), electrocardiography (2%), drug testing for analgesic agents (2%), and ultrasonography of the flexor tendons (1%) were not always performed. Fifty-nine percent of horses evaluated at the clinic were radiographed, compared with 33% of horses evaluated in the field (P less than 0.05). Thirty-seven percent of horses evaluated were judged serviceable for their intended use. Thirty-five percent of horses evaluated at the clinic were assessed to be serviceable, compared with 41% of those evaluated in the field (P less than 0.05). Horses used for pleasure riding (48%) tended to be considered serviceable more often than horses used for more athletic endeavors (3-day eventing, 33%; hunter/jumper, 24%; show, 31%; dressage, 30%). The most common basis for finding a horse unserviceable was lameness (88%).(ABSTRACT TRUNCATED AT 250 WORDS)

Surgical treatment of colic in American miniature horses: 15 cases (1980-1987).

A study of 15 American miniature horses (AMH) that underwent surgical treatment for colic was performed. Information obtained from the medical records included signalment, clinical signs, type and location of gastrointestinal lesion, and postoperative complications. All 15 AMH had intraluminal obstructions, attributable to feed impactions (11 horses), enteroliths (2), and sand (2). The most common location of obstruction was the small colon, which was involved in 9 of the 15 cases. All 15 AMH survived and were discharged from the hospital. Six of the 15 AMH underwent subsequent surgical treatment for abdominal disorders. Elapsed time between the first and second operations ranged from 1 month to 5 years. Intestinal adhesions were observed in all AMH that were surgically treated twice. Thus, despite the fact that most of the AMH had a simple intraluminal obstruction, 40% (n = 6) developed adhesions that required or complicated a second surgery. Of the 15 AMH, 87% (n = 13) survived at least 12 months after the initial exploratory celiotomy. These findings suggest that most surgical abdominal conditions in AMH can be corrected; however, precautions should be taken to avoid or minimize adhesion formation.

Clinical investigations of halothane and isoflurane for induction and maintenance of foal anesthesia.

Fifty-eight foals were divided into two groups for study of aspects of the clinical anesthetic management of foals and to characterize effects of halothane (n = 30) and isoflurane (n = 28) in foals. There were no significant differences (P greater than 0.05) in the demographics of the two groups. Results of hemograms and biochemical analysis of venous blood samples before and after anesthesia were either not influenced or only mildly (clinically unimportant) affected by either agent. Like adult horses, foals have an increased PaCO2 when anesthetized with inhaled anesthetics. We could detect no difference in the magnitude of increase in PaCO2 with either anesthetic. Anesthetic induction and recovery was most rapid with isoflurane. The quality of induction and recovery was similarly acceptable with either agent. Heart rate during isoflurane was not significantly different from conscious conditions but during halothane, heart rate was significantly less than control except at 91-120 min when statistical significance was not detected. These results support the clinical impression that foals can be safely and reliably anesthetized with either agent.

Malignant melanoma in the foot of a horse.

A 24-year-old horse had a malignant melanoma of the right forefoot. Because surgical excision of the melanoma was incomplete, as determined by histologic examination of the excised tissue margins, the tumor margins were injected with a matrix therapeutic implant containing cis-diamminedichloroplatinum, epinephrine, and purified bovine collagen matrix. The foot healed and the horse remained clinically free of disease for 26 months before recurrence of malignant melanoma. Surgical exploration of the digit revealed extensive involvement of the foot, and the horse was euthanatized.

Traumatic disruption of the suspensory apparatus in foals.

Traumatic disruption of the suspensory apparatus is a catastrophic injury in the horse. Although this injury has been described in the adult, little information is available in the foal. This paper describes 3 foals with metacarpophalangeal joint instability caused by traumatic disruption of the suspensory apparatus. Two foals had biaxial proximal sesamoid fractures in a single forelimb, and 1 foal had avulsion of the distal sesamoidean ligaments in 1 forelimb plus biaxial proximal sesamoid fractures in the other forelimb. The foals with single forelimb involvement were managed with splints, and the foal with bilateral disruption of the suspensory apparatus was euthanatized. Both treated foals resumed natural exercise at pasture. Both continue to be pasture sound 2 and 3 years after injury and are to be used for breeding. Management of disruption of the suspensory apparatus causing metacarpophalangeal joint instability using external support was effective for salvage of these 2 valuable foals for breeding.

Pathologic findings and pathogenesis of racetrack injuries.

Many lesions of the musculoskeletal system of racing horses are either acute traumatic lesions or are chronic biomechanically induced lesions that become suddenly unstable and provoke acute clinical signs. The latter lesions along with those of DJD are much more common and are of much greater overall economic importance to the racing industry than are the acute traumatic injuries. Chronic biomechanical lesions occur at predictable sites and are the result of an imbalance between repetitive microtrauma sustained in athletic performance and adaptive repair mechanisms of skeletal tissues. The distribution of these lesions in the limbs reflects the patterns of biomechanical forces placed on the skeleton during work at racing speeds and, therefore, reflects the type of racing activity for which the horse was bred. Lesions result when there is a failure of the stressed skeletal structures to adapt to the biomechanical forces placed upon them. Rest or a reduction in the level of training activity permit the healing of many asymptomatic and presumably some symptomatic lesions of the bony tissues. Articular cartilage, tendons, and ligaments have a lower capacity to resolve the damage and return to normal structure and function.

Upper airway function during maximal exercise in horses with obstructive upper airway lesions. Effect of surgical treatment.

Upper airway pressure was measured during maximal exercise in 10 Thoroughbred racehorses with naturally occurring upper airway obstruction. Left laryngeal hemiplegia and arytenoid chondropathy resulted in substantial increases (30-40 cm H2O) in inspiratory upper airway pressure (Pl), whereas complicated aryepiglottic entrapment and subepiglottic cysts produced only modest increases (15 cm H2O) in Pl. Uncomplicated aryepiglottic entrapment and grade IV pharyngeal lymphoid hyperplasia produced only slight increases (3-5 cm H2O). In general, surgical procedures restored airway pressures to within normal limits. Subtotal arytenoidectomy improved but did not normalize airway pressures in horses with arytenoid chondropathy. Pharyngeal lymphoid hyperplasia appeared to have little effect on upper airway function.

Effects of left recurrent laryngeal neurectomy, prosthetic laryngoplasty, and subtotal arytenoidectomy on upper airway pressure during maximal exertion.

Upper airway pressure was measured with a nasotracheal catheter system and a portable pressure transducer in 10 normal horses during maximal exercise before and after left recurrent laryngeal neurectomy. Measurements were repeated 16 weeks after prosthetic laryngoplasty (5 horses) or subtotal arytenoidectomy (5 horses). During maximal exertion, prosthetic laryngoplasty was more effective than subtotal arytenoidectomy in reversing the increases in upper airway pressure that followed left recurrent laryngeal neurectomy.

Laryngotracheal lesions following routine orotracheal intubation in the horse.

Sequelae of routine orotracheal intubation under clinical conditions were characterised in 38 healthy horses presented at three veterinary medical teaching hospitals. Four of these were necropsied and their tissues studied histologically. To minimise variation, 30 mm id cuffed silicone endotracheal tubes or Cole cuffless tubes were used in all patients. Fibreoptic endoscopic examination of upper respiratory and tracheal areas was accomplished pre-intubation, immediately post extubation and after 24 h. Endoscopy revealed that intubation was associated with laryngeal and/or tracheal lesions in all horses. Observations included abundant tracheal mucus, epithelial ecchymoses, basement membrane haemorrhage and mucus covered diphtheritic membrane plaques. Histological examination of lesions from the upper respiratory system of the four necropsied horses confirmed that the damage was comparable to that associated with tracheal intubation and reported in other species.

Survival after small intestine resection and anastomosis in horses.

The authors examined factors influencing survival in 140 horses that recovered from anesthesia after small intestinal resection between 1968 and 1986, using Kaplan-Meier estimated survival curves and the Cox proportional hazards regression model. Seventy-two horses (51%) died during the initial postoperative period, 19 horses (14%) died after discharge from the hospital, 33 horses (24%) were alive, and 16 horses (11%) were classified as censored. Mean age at surgery was 8 years. Horses 15 years of age or older, Arabians and Stallions, were overrepresented in the hospital population. The most common reason for resection was strangulation of bowel through a mesenteric rent. The mean and 50% median survival times were 1540 and 27 days, respectively. Horses admitted after January 1, 1980, had a significantly longer survival than those admitted before that time. Survival was longer after anastomosis of two small intestinal segments than after anastomosis of a small intestinal segment to the cecum; however, the length of bowel resected and the method of anastomosis had no demonstrable influence on survival. Of the variables studied, the heart rates at presentation and 24 hours after surgery were the most accurate predictors of survival.

Strangulating volvulus of the ascending colon in horses.

Of 57 horses with strangulating volvulus of the ascending colon, 42 were mares (including 21 postparturient mares), 8 were stallions, and 7 were geldings. Volvulus occurred most frequently in the summer (n = 24) and spring (n = 17). Pain was evaluated as severe in 41 horses, moderate in 9, and mild in 4. The abdominal fluid from 30 horses varied from clear yellow in 19 horses, to cloudy yellow in 3 horses, and serosanguineous in 8 horses. Protein content and nucleated cell count in the abdominal fluid were 2.5 +/- 1 g/dl and 1,000 +/- 900 microliters, respectively. Fifty horses had greater than or equal to 360 degrees volvulus and 7 had a 270 degrees volvulus, with 49 occurring in a counterclockwise direction. The site of volvulus in all horses was at the mesenteric attachment of the colon, except for a 360 degrees volvulus at the sternal and diaphragmatic flexures in 1 horse. Survival rates for horses with a greater than or equal to 360 degrees and a 270 degrees volvulus were 36% and 71%, respectively. The difference in survival rates reflected the severe vascular occlusion in the colon of horses with greater than or equal to 360 degrees volvulus. In nonsurvivors, hemorrhage in the submucosa and lamina propria (P less than 0.005) and edema in the submucosa (P less than 0.01) were greater than those in survivors. In nonsurvivors, greater than 97% of the superficial epithelium was lost. In horses that survived, only 60% of the cells were lost or degenerated.(ABSTRACT TRUNCATED AT 250 WORDS)