Measurement of tidal breathing flow-volume loop indices in horses used for different sporting purposes with and without recurrent airway obstruction

Tidal breathing flow-volume loop (TBFVL) indices in healthy horses and in horses suffering from mild and moderate to severe recurrent airway obstruction (RAO) were measured. In addition, the ability of these indices to differentiate healthy controls from horses with mild RAO by separating the horses according to their usage was investigated. The horses were assigned to three sporting categories: 1 Leisure horses; 2 Horses competing at events with a duration of more than five minutes (eventing, coaching and endurance); and 3 Horses competing at events with a duration of less than five minutes (dressage and show jumping). Flow-volume curves were recorded with an ultrasonic spirometer and TBFVL indices were calculated with specially dedicated software. The sporting usage of the horses had a significant effect on the differentiating ability of TBFVL indices in diagnosing different degrees of RAO. The index TIF50 differentiated control horses from horses with minor RAO in all sporting categories.     

New approach for quantitative assessment of articular cartilage degeneration in horses with osteoarthritis

OBJECTIVE: To evaluate a modified digital imaging technique for quantitative assessment of the grade of osteoarthritis across the proximal articular surface of the first phalanx in horses. SAMPLE POPULATION: 6 metacarpophalangeal (fet-lock) joint specimens from 6 horses with various stages of osteoarthritis. PROCEDURE: First phalanx specimens, together with 4 gray scale reference calibration targets, were positioned in a bath with the proximal articular cartilage surface submerged in saline (0.9% NaCl) solution. Digital images were obtained from the articular surface before and after staining with Indian ink. Computer-controlled gray level analysis of the nonstained and Indian ink-stained cartilage surfaces and gray scale reference calibration targets was performed by use of the mean pixel value (based on 255-gray scale). An increase in the mean pixel value after staining was used to calculate the cartilage degeneration index (CDI). RESULTS: The CDI of the proximal articular cartilage surface of the first phalanx specimens ranged from 9.2 +/- 5.7 (early stage osteoarthritis) to 41.5 +/- 3.6% (late stage osteoarthritis). The effect of repeating the measurement 6 times in nonstained (including repositioning) and stained specimens (including repositioning and restaining) was not significant. Up to 10 measurements of nonstained specimens could be made without refreshing the bath solution. In stained specimens, mean gray level increased significantly after the sixth measurement. CONCLUSIONS AND CLINICAL RELEVANCE: The modified digital imaging technique allowed quantitative assessment of cartilage degeneration across the articular cartilage surface. The CDI is the first quantitative measure for osteoarthritis-induced cartilage degeneration over an entire joint surface in horses.     

Comparative biokinematic study of young and adult Andalusian horses at the trot

The purpose of this study was to determine basic kinematic parameters (linear, temporal and angular) in young and adult Andalusian horses (P.R.E.) at the trot, using a normal computer-aided videography system. The trotting gaits of 16 horses were analysed: seven young horses (3.7 +/- 0.2 years old, height at withers 167.1 +/- 4.1 cm) and nine adult stallions (12.3 +/- 2.9 years old, height at withers 162.9 +/- 3.6 cm) were recorded at least 6 times at the trot using a 25-Hz video-camera filming from the side. Video images were processed with a real-time digital system (SMVD). Speeds averaged 3.84 and 3.75 m/s for young and adult horses, respectively. Differences between age groups for speed and linear and temporal parameters of the stride were not significant. However, variations in angular parameters were detected: adults showed a greater ARM than younger horses for most forelimb joints. In the hind limb, hip, stifle, and, to a lesser degree, the tarsal joint, a smaller degree of extension during the stance phase was observed in adult horses.     

Desmitis of the distal digital annular ligament in seven horses: MRI diagnosis and surgical treatment

Objective— (1) To describe the clinical signs and abnormalities observed on magnetic resonance imaging (MRI) in 7 horses with desmitis of the distal digital annular ligament (DDAL); (2) to describe the normal magnetic resonance (MR) appearance and thickness of the DDAL in health; and (3) to describe a tenoscopic surgical technique for treating horses with desmitis of the DDAL.
Study Design— Retrospective study.
Animals— Horses (n=7) with desmitis of the DDAL.
Methods— MR examinations of 20 sound horses were reviewed to determine the normal appearance of the DDAL. Dimensions obtained from these images were compared with MR findings from 7 horses with DDAL desmitis. Desmitis of the DDAL was treated by tenoscopic surgery and outcome assessed.
Results— Horses with DDAL desmitis had lameness (grade 2–3 out of 5) that improved after a palmar digital nerve block. The affected DDAL was enlarged and had an abnormal signal on MR images of the feet. After tenoscopy and DDAL transection, 5 horses returned to athletic performance, including 2 horses that failed to respond to medical treatment and rest before surgery.
Conclusion— Primary desmitis of the DDAL is a cause of lameness in horses. Transection of the DDAL allowed 5 horses with this injury to return to athletic performance.
Clinical Relevance— DDAL desmitis should be included in the differential diagnoses of horses with lameness that improves after a palmar digital nerve block but have no abnormalities observed on radiographs of the feet. Tenoscopic surgical transection of the DDAL is an effective treatment for some horses.     

Quantification of hepatic and renal cortical echogenicity in clinically normal cats

OBJECTIVE: To quantitatively determine echogenicity of the liver and renal cortex in clinically normal cats. ANIMALS: 17 clinically normal adult cats. PROCEDURE: 3 ultrasonographic images of the liver and the right kidney were digitized from video output from each cat. Without changing the ultrasound machine settings, an image of a tissue-equivalent phantom was digitized. Biopsy specimens of the right renal cortex and liver were obtained for histologic examination. Mean pixel intensities within the region of interest (ROI) on hepatic, renal cortical, and tissue-equivalent phantom ultrasonographic images were determined by histogram analysis. From ultrasonographic images, mean pixel intensities for hepatic and renal cortical ROI were standardized by dividing each mean value by the mean pixel intensity from the tissue-equivalent phantom. RESULTS: The mean (+/- SD) standardized hepatic echogenicity value was 1.06 +/- 0.02 (95% confidence interval, 1.02 to 1.10). The mean standardized right renal cortical echogenicity value was 1.04 +/- 0.02 (95% confidence interval, 1.01 to 1.08). The mean combined standardized hepatic and renal cortical echogenicity value was 1.02 +/- 0.05 (95% confidence interval, 0.99 to 1.04). CONCLUSIONS AND CLINICAL RELEVANCE: Quantitative determination of hepatic and renal cortical echogenicity in cats is feasible, using histogram analysis, and may be useful for early detection of diffuse parenchymal disease and for serially evaluating disease progression.     

Acquired flexural deformity of the metacarpophalangeal joint in five horses associated with tendonous damage in the palmar metacarpus.

Five cases of acquired flexural deformity of the metacarpophalangeal joint (MCPJ) in older horses and ponies were studied. The mean age of affected horses was 14-8 years. Four deformities developed following desmitis of the accessory ligament of the deep digital flexor tendon (ALDDFT) and superficial digital flexor tendon (SDFT) and one following tendonitis of the SDFT alone. All cases were markedly lame and demonstrated variable degrees of flexural deformity. Ultrasonographic examination was performed on all cases which revealed extensive adhesion formation between the ALDDFT and SDFT and reduced cross-sectional area of the deep digital flexor tendon in each case. A variety of treatments were unsuccessfully employed to treat this condition. The prognosis for acquired flexural deformity of the MCPJ in old horses following tendonous damage in the palmar metacarpus is likely to be poor.     

COMPARISON OF COMPUTED RADIOGRAPHY AND CONVENTIONAL FILM-SCREEN RADIOGRAPHY OF THE EQUINE STIFLE

Major advantages of computed radiography are the potential reduction of dose and the possibility of postprocessing. In our study, we compared conventional radiographs to digital radiographs of the equine stifle by subjective evaluation of diagnostic quality when using a decreasing photon flux (mAs). Twelve equine stifle joints from horses of different weight and size were examined. Conventional and digital radiographs were performed identically in a caudocranial projection with the tube angled 15 degrees. A series of four radiographs was performed in each technique with an increasing photon flux starting with 2.5 mAs and going up to 5, 10, and 20 mAs. All radiographs were evaluated subjectively in a blinded fashion by seven readers in terms of contrast, bone structure, and diagnostic value and were graded using a 1-5 scale. Results from conventional and digitized radiographs were compared, and differences between the individual observers were analyzed statistically. Contrast, bone structure, and diagnostic value from digital images were rated significantly better than from conventional images (p < .001). For both techniques, a decrease in ranking was found with a decrease of photon flux. There was only slight interobserver variability. A dose reduction up to a factor of 4 compared to a 100 speed film-screen system seems to be possible without loss of information. Weight and size of the horse are not major influences.     

Analysis of video-recorded images to determine linear and angular dimensions in the growing horse.

Studies of growth and conformation require statistical methods that are not applicable to subjective conformation standards used by breeders and trainers. A new system was developed to provide an objective approach for both science and industry, based on analysis of video images to measure aspects of conformation that were represented by angles or lengths. A studio crush was developed in which video images of horses of different sizes were taken after bone protuberances, located by palpation, were marked with white paper stickers. Screen pixel coordinates of calibration marks, bone markers and points on horse outlines were digitised from captured images and corrected for aspect ratio and 'fish-eye' lens effects. Calculations from the corrected coordinates produced linear dimensions and angular dimensions useful for comparison of horses for conformation and experimental purposes. The precision achieved by the method in determining linear and angular dimensions was examined through systematically determining variance for isolated steps of the procedure. Angles of the front limbs viewed from in front were determined with a standard deviation of 2-5 degrees and effects of viewing angle were detectable statistically. The height of the rump and wither were determined with precision closely related to the limitations encountered in locating a point on a screen, which was greater for markers applied to the skin than for points at the edge of the image. Parameters determined from markers applied to the skin were, however, more variable (because their relation to bone position was affected by movement), but still provided a means by which a number of aspects of size and conformation can be determined objectively for many horses during growth. Sufficient precision was achieved to detect statistically relatively small effects on calculated parameters of camera height position.     

Use of quantitative analysis of sonographic brightness for detection of early healing of tendon injury in horses

OBJECTIVES: To determine whether quantitative analysis of sonographic brightness could be used to detect healing of an induced injury of the superficial digital flexor tendon in horses and whether rate of healing was influenced by equine recombinant growth hormone. ANIMALS: 8 clinically normal Standardbreds. PROCEDURES: A localized injury was created in the left and right superficial digital flexor tendons of each horse by injection of 2,000 units of collagenase. After injury, 4 horses received equine recombinant growth hormone, a possible promoter of tendon healing. Sonographic images (7.5 MHz) of the flexor tendons and ligaments of the metacarpal region were recorded on videotape prior to injury and weekly for 7 weeks after injury. Images were digitized, and sonographic brightness of tendons and ligaments was calculated. RESULTS: Collagenase-induced injury was sonographically similar to naturally occurring injury. After injury, sonographic brightness of the tendon decreased; after 3 weeks, brightness progressively increased, although by 7 weeks brightness had not returned to preinjury value. Equine recombinant growth hormone had no significant effect on the rate of tendon healing, as evaluated sonographically or at necropsy. CONCLUSIONS AND CLINICAL RELEVANCE: As healing developed, alterations in sonographic brightness of injured tendons coincided with real changes in tendon structure. Quantitative sonographic brightness could be used to accurately monitor healing of equine tendon and ligament injuries and investigate the efficacy of various treatment regimens.     

ANATOMICAL STUDY OF CRANIAL NERVE EMERGENCE AND SKULL FORAMINA IN THE HORSE USING MAGNETIC RESONANCE IMAGING AND COMPUTED TOMOGRAPHY

For accurate interpretation of magnetic resonance (MR) images of the equine brain, knowledge of the normal cross‐sectional anatomy of the brain and associated structures (such as the cranial nerves) is essential. The purpose of this prospective cadaver study was to describe and compare MRI and computed tomography (CT) anatomy of cranial nerves' origins and associated skull foramina in a sample of five horses. All horses were presented for euthanasia for reasons unrelated to the head. Heads were collected posteuthanasia and T2‐weighted MR images were obtained in the transverse, sagittal, and dorsal planes. Thin‐slice MR sequences were also acquired using transverse 3D‐CISS sequences that allowed mutliplanar reformatting. Transverse thin‐slice CT images were acquired and multiplanar reformatting was used to create comparative images. Magnetic resonance imaging consistently allowed visualization of cranial nerves II, V, VII, VIII, and XII in all horses. The cranial nerves III, IV, and VI were identifiable as a group despite difficulties in identification of individual nerves. The group of cranial nerves IX, X, and XI were identified in 4/5 horses although the region where they exited the skull was identified in all cases. The course of nerves II and V could be followed on several slices and the main divisions of cranial nerve V could be distinguished in all cases. In conclusion, CT allowed clear visualization of the skull foramina and occasionally the nerves themselves, facilitating identification of the nerves for comparison with MRI images.     

Lameness in 46 horses associated with deep digital flexor tendonitis in the digit: diagnosis confirmed with magnetic resonance imaging

REASONS FOR PERFORMING STUDY: The differential diagnosis of foot pain has long proved difficult and the use of magnetic resonance imaging (MRI) offers the opportunity to further the clinical understanding of the subject. OBJECTIVES: To determine the incidence of deep digital flexor tendon (DDFT) injuries in a series of 75 horses with lameness associated with pain localised to the digit, with no significant detectable radiographic or ultrasonographic abnormalities, using MRI; and to describe a variety of lesion types and relate DDF tendonitis with anamnesis, clinical features, response to local analgesic techniques and nuclear scintigraphic and ultrasonographic findings. METHODS: All horses undergoing MRI of the front feet between January 2001 and October 2002 were reviewed and those with DDFT injuries categorised according to lesion type; horses with primary tendonitis (Group I) and those with concurrent abnormalities of the navicular bone considered to be an important component of the lameness (Group II). The response to perineural analgesia of the palmar digital nerves and palmar (abaxial sesamoid) nerves, intra-articular analgesia of the distal interphalangeal (DIP) joint and analgesia of the navicular bursa were reviewed. The result of ultrasonography of the pastern and foot was recorded. Lateral, dorsal and solar pool and bone phase nuclear scintigraphic images were assessed subjectively and objectively using region of interest (ROI) analysis. RESULTS: Forty-six (61%) of 75 horses examined using MRI had lesions of the DDFT considered to be a major contributor to lameness. Thirty-two horses (43%) had primary DDFT injuries and 14 (19%) a combination of DDF tendonitis and navicular bone pathology. Lesions involved the insertional region of the tendon alone (n = 3), were proximal to the navicular bone (n = 23) or were at a combination of sites (n = 20). Lesion types included core lesions, focal and diffuse dorsal border lesions, sagittal plane splits, insertional injuries and lesions combined with other soft tissue injuries. Many horses had a combination of lesion types. Lameness was abolished by palmar digital analgesia in only 11 of 46 horses (24%). Twenty-one of 31 horses (68%) in Group I showed > 50% improvement in lameness after intra-articular analgesia of the DIP joint, whereas 11 of 12 horses (92%) in Group II had a positive response. Twelve of 18 horses (67%) in Group I had a positive response to analgesia of the navicular bursa. Nineteen horses had lesions of the DDFT extending proximal to the proximal interphalangeal joint seen using MRI, but these were identified ultrasonographically in only 2 horses. Scintigraphic abnormalities suggestive of DDFT injury were seen in 16 of 41 horses (41%), 8 in pool phase images and 8 in bone phase images. CONCLUSIONS AND POTENTIAL RELEVANCE: DDFT injuries are an important cause of lameness associated with pain arising from the digit in horses without detectable radiographic abnormalities. Lameness is not reliably improved by palmar digital analgesia, but may be improved by intra-articular analgesia of the DIP joint in at least 68% of horses. Ultrasonography is not sensitive in detecting lesions of the DDFT in the distal pastern region, but a combination of pool and bone phase scintigraphic images of the digit is helpful in some horses. Further follow-up information is required to determine the prognosis for horses with lesions of the DDFT in the digit and to establish whether this is related to lesion severity and/or location.     

MAGNETIC RESONANCE IMAGING CHARACTERISTICS OF THE FOOT IN HORSES WITH PALMAR FOOT PAIN AND CONTROL HORSES

Palmar foot pain is a common cause of lameness. Magnetic resonance imaging (MRI) has the potential to detect damage in all tissues of the equine foot, but an understanding of the differences in magnetic resonance (MR) images between feet from horses with and without palmar foot pain is required. This study aimed to describe MR findings in feet from horses with no history of foot-related lameness, and to compare these with MR findings in horses with lameness improved by palmar digital local analgesia. Thirty-four limbs from horses euthanized with a clinical diagnosis of navicular syndrome (ameness >2 months duration, positive response to palmar digital nerve blocks and absence of other forelimb problems) (Group L), and 25 feet from age-matched horses with no history of foot pain (Group N) were examined. For each anatomic structure, MR signal intensity and homogeneity, size, definition of margins, and relationships with other structures were described. Alterations in MR signal intensity and homogeneity were graded as mild, moderate, or severe and compared between Groups L and N. Results revealed that there were significant differences in MR images between Groups N and L. Multiple moderate-severe MR signal changes were present in 91% of limbs from Group L and moderate (none were graded severe) in 27% of limbs from Group N. In most Group L limbs, more than three structures and frequently six to eight structures were abnormal. Concomitant abnormalities involved most frequently the deep digital flexor tendon, distal sesamoidean impar ligament, navicular bone, collateral sesamoidean ligament, and navicular bursa (with significant associations in severity grade between these structures), sometimes with involvement of the distal interphalangeal joint and/or its collateral ligaments. It was concluded that findings on MR images were different between horses with and without foot pain, and that pain localized to the foot was associated with MR changes in a variety of structures, indicating that damage to several structures may occur concurrently and that MR imaging was useful for evaluation of foot pain.     

Effects of intramuscular administration of acepromazine on palmar digital blood flow, palmar digital arterial pressure, transverse facial arterial pressure, and packed cell volume in clinically healthy, conscious horses

Objective— To determine the magnitude and duration of effects of acepromazine administered intramuscularly (IM) on digital and systemic hemodynamic variables in clinically healthy horses.
Study Design— Experimental study.
Animals— Healthy adult horses (n=12).
Methods— An ultrasonic Doppler flow probe was surgically implanted around the medial palmar digital artery before the study. Catheters were inserted in the transverse facial artery, lateral palmar digital artery, and jugular vein. A treatment group (n=6) was administered 0.04 mg/kg body weight of acepromazine IM; control horses (n=6) were administered an equivalent volume of saline IM. Palmar digital blood flow, and digital and facial arterial pressures were measured at baseline and for 6 hours after administration. Venous blood was collected for measurement of packed cell volume (PCV).
Results— Horses administered acepromazine had significantly lower facial arterial pressure compared with control horses administered saline. Palmar digital arterial blood flow in acepromazine-treated horses was not significantly different from that in control horses but increased significantly post-administration, compared with the respective baseline values for acepromazine-treated horses. PCV significantly decreased in horses administered acepromazine compared with their respective baseline value.
Conclusion— IM acepromazine causes hypotension and increases palmar digital blood flow over time but the magnitude of the effect on digital blood flow was not sufficient to yield differences compared with saline-treated horses.
Clinical Relevance— IM acepromazine has a modest effect on palmar digital blood flow, facial arterial pressures and PCV in healthy horses with minimal sedation.     

MULTISCALE IMAGE PROCESSING AND ANTISCATTER GRIDS IN DIGITAL RADIOGRAPHY

Scatter radiation is a source of noise and results in decreased signal-to-noise ratio and thus decreased image quality in digital radiography. We determined subjectively whether a digitally processed image made without a grid would be of similar quality to an image made with a grid but without image processing. Additionally the effects of exposure dose and of a using a grid with digital radiography on overall image quality were studied. Thoracic and abdominal radiographs of five dogs of various sizes were made. Four acquisition techniques were included (1) with a grid, standard exposure dose, digital image processing; (2) without a grid, standard exposure dose, digital image processing; (3) without a grid, half the exposure dose, digital image processing; and (4) with a grid, standard exposure dose, no digital image processing (to mimic a film-screen radiograph). Full-size radiographs as well as magnified images of specific anatomic regions were generated. Nine reviewers rated the overall image quality subjectively using a five-point scale. All digitally processed radiographs had higher overall scores than nondigitally processed radiographs regardless of patient size, exposure dose, or use of a grid. The images made at half the exposure dose had a slightly lower quality than those made at full dose, but this was only statistically significant in magnified images. Using a grid with digital image processing led to a slight but statistically significant increase in overall quality when compared with digitally processed images made without a grid but whether this increase in quality is clinically significant is unknown.     

The origin and foot condition of horses slaughtered in Australia for the human consumption market

Reasons for performing study: There are ethical concerns regarding the loss of horses from various equine industries and their corresponding slaughter. However, to date, no empirical evidence regarding the extent of this loss, nor of the condition of horses involved, exists within Australia. Objectives: To determine the approximate ages, brand type and condition of feet of horses relinquished to an export abattoir in Australia. Method: Data were collected from 340 horses processed at an Australian abattoir from November 2007‐January 2008. Foot abnormalities, injuries and hoof indicators of overgrown and untrimmed hooves were assessed together with a dental inspection. Observations of brand were used to determine horse origin. Results: The dental age of 60% of horses was ≤7 years, and 53% originated from the racing industry (40% Thoroughbred and 13% Standardbred). A total of 81% of the horses had overgrown or untrimmed hooves. Standardbred horses had fewer grass cracks and more injuries to the coronary band than Thoroughbreds, probably due to pacing and trotting activities. Conclusions: Just over half of the horses slaughtered at an Australian abattoir on 3 working days were aged ≤7 years and emanated from the racing industry. Foot problems were common. Potential relevance: Future research should identify means of reducing the number of horses slaughtered and preventative measures for foot disorders.     

SCINTIGRAPHIC EVALUATION OF THE STIFLE IN NORMAL HORSES AND HORSES WITH FORELIMB LAMENESS

We tested the hypotheses that mature horses without lameness have a repeatable radiopharmaceutical uptake pattern in the stifle, which is bilaterally symmetric; immature horses have a different radiopharmaceutical uptake pattern; and forelimb lameness alters the radiopharmaceutical uptake pattern in the stifle. The objectives of the study were to describe the normal radiopharmaceutical uptake patterns using region of interest (ROI) analysis; to compare uptake patterns between left and right stifles of the same horse and between mature and immature horses; to compare radiopharmaceutical uptake in mature normal horses with those with forelimb lameness. Lateral scintigraphic images of the stifle from 51 horses aged 2-16 years were evaluated using seven ROIs and a reference site (midfemur). After subtraction of a background count, ratios between the mean counts per pixel for each ROI to the reference site were calculated. There was a repeatable radiopharmaceutical uptake pattern in mature normal horses that was bilaterally symmetrical. The caudoproximal aspect of the tibia and the patella had the highest ratios. Radiopharmaceutical uptake patterns in horses with forelimb lameness were not significantly different. Immature normal horses had a different symmetric pattern, with greatest radiopharmaceutical uptake ratios in the caudoproximal aspect of the tibia and the tibial crest. It was concluded that there are symmetric, repeatable radiopharmaceutical uptake patterns in both immature and mature horses, which are not altered by forelimb lameness.     

Alterations of Endothelium-Dependent Digital Vascular Responses in Horses Given Low-Dose Endotoxin

Low doses of endotoxin cause vasoconstriction and hypoperfusion of the digit, small intestine, and cecum in horses. To determine the potential cause of these vascular alterations, in vitro vascular responses of palmar digital arteries and veins were determined in 8 horses after intravenous (IV) infusion of 1 L 0.9% NaCl (control) and 0.1 μg/kg Escherichia coli 055:B5 endotoxin in 1 L of 0.9% NaCl (endotoxin-treated). Vessels were surgically removed under general anesthesia, cut into 4-mm vascular rings, suspended in tissue baths, and attached to force displacement transducers for measurement of vascular tension. Cumulative concentration response curves to acetylcholine, bradykinin, nitroprusside, norepinephrine, 5-hydroxytryptamine (serotonin), and endothelin were determined. Maximal relaxation or contraction and the concentrations needed to produce 50% maximal relaxation or contraction were determined. Palmar digital arteries from endotoxin-treated horses relaxed significantly less in response to acetylcholine and bradykinin (endothelium-dependent), but not to nitroprusside (endothelium-independent) when compared with arteries from control horses. Digital arteries from endotoxin-treated horses also contracted significantly more with norepinephrine but less with serotonin. Digital veins responded less than digital arteries. In another study, vascular reactivity experiments documented that acetylcholine and bradykinin were endothelium-dependent vasodilators (endothelium-denuded vessels relaxed less than control vessels) in palmar digital vessels. Additionally, maximal relaxations for both vasodilators were significantly inhibited by N-nitro-L-arginine methyl ester (L-NAME), a nitric oxide antagonist, suggesting that acetylcholine and bradykinin cause relaxation through the nitric oxide pathway. The data from these studies indicate that low dose endotoxin impairs endothelium-dependent relaxation and augments adrenergic contraction of palmar digital arteries in horses.     

Effect of exercise on age-related changes in collagen fibril diameter distributions in the common digital extensor tendons of young horses

OBJECTIVE: To determine whether specific treadmill exercise regimens would accelerate age-related changes in collagen fibril diameter distributions in the common digital extensor tendon (CDET) of the forelimbs of young Thoroughbreds. ANIMALS: 24 female Thoroughbreds. PROCEDURE: Horses were trained for 18 weeks (6 horses; short term) or 18 months (5 horses; long term) on a high-speed treadmill; 2 age-matched control groups (6 horses/group) performed walking exercise only. Horses were (mean +/- SD) 24 +/- 1 months and 39 +/- 1 months old at termination of the short-term and long-term regimens, respectively. Midmetacarpal CDET specimens were obtained and processed for transmission electron microscopy. Diameter and area of at least 1,000 collagen fibrils/specimen were measured by use of computerized image analysis. Mass-average diameter (MAD) of collagen fibrils and collagen fibril index were calculated for each horse. RESULTS: Collagen fibril MAD for the older horses was significantly less than that for the younger horses. Exercise did not significantly affect fibril diameter or distributions in either age group, and collagen fibril index did not differ significantly between groups. CONCLUSIONS AND CLINICAL RELEVANCE: Age-related reduction in collagen fibril MAD agreed with findings for other tendons and species. Training did not accelerate age-related change in the CDET in contrast to a reported decrease in collagen fibril MAD in the superficial digital flexor tendon of horses trained long term. Our results support the concept that the functionally distinct nature of the CDET and superficial digital flexor tendon in horses results in fundamentally different responses to high-speed exercise regimens.     

Injuries of the calcaneal insertions of the superficial digital flexor tendon in 19 horses

Reasons for performing study: Injuries of the calcaneal insertions of the superficial digital flexor tendon and their relationship to displacement of the tendon from the calcaneus have not previously been reported. Objectives: To describe findings made on clinical cases with disruption of the calcaneal insertions of the superficial digital flexor tendon (SDFT) including observations on their role in horses with unstable subluxation of the tendon. To describe novel surgical techniques and the results of treatment. Hypotheses: Disruption of the calcaneal insertions of the SDFT is associated with lameness and distension of the calcaneal bursa. Unstable displacement of the SDFT from the calcaneus is a more complex injury than incomplete disruption of one of its calcaneal insertions. Methods: The case records and diagnostic images of horses with lesions involving the calcaneal insertions of the SDFT, which were confirmed by endoscopic evaluation of calcaneal bursa between 2005 and 2009, were reviewed. Results: Nineteen horses were identified including 7 that had unstable displacement of the tendon from the calcaneus. Following endoscopic surgery, 9 of 12 horses with stable tendons and 6 of 7 horses with unstable displaced SDFTs returned to work. Conclusion: Tearing of the calcaneal insertions of the SDFT is associated with lameness and distension of the calcaneal bursa; endoscopic removal of the torn tissue carries a good prognosis. Horses with unstable displacement of the tendon have also disruption of the tendon fibrocartilage cap. Removal of this results in stable subluxation and can return horses to athletic activity. Both lesions can be detected by preoperative ultrasonography. Potential relevance: Tearing of the calcaneal insertions of the SDFT should be included in the differential diagnoses of lame horses with distended calcaneal bursae. Tearing of the tendon fibrocartilage cap in horses with unstable displacement of the SDFT is a plausible explanation of the clinical features of the injury and explains previously unreliable results of reconstructive surgeries. Subtotal resection is a technically demanding technique but appears to offer an improved prognosis.     

Surgical Approach for Removal of Nonarticular Base Sesamoid Fragments of the Proximal Sesamoid Bones in Horses

Objectives— To describe a surgical approach for the removal of nonarticular base sesamoid fragments in performance horses and to report the outcome. Study Design— Retrospective study. Animals— Horses (n=11), 7 months to 10 years of age, with lameness because of nonarticular base sesamoid fragments. Methods— Lameness was localized to the metacarpophalangeal/metatarsophalangeal region by clinical examination or response to diagnostic local anesthesia. Radiographs confirmed the diagnosis of a nonarticular base sesamoid fragment. Surgical removal was performed with an incision over the base of the affected sesamoid through the digital flexor tendon sheath. After identifying the fragment with the aid of needles, a small vertical incision was made in the straight distal sesamoidean ligament (SDSL) and the fragment was freed from its attachments and removed. Six months convalescence and rehabilitation was prescribed for all horses. Results— Eleven horses had 16 nonarticular fragments of the base of the proximal sesamoid bones. Eleven (69%) fragments occurred in the forelimbs with the right front (82%) and medial sesamoid (73%) more commonly affected. Horses were treated by surgical fragment removal. In horses with follow‐up, 9 of 10 returned to their intended use. Conclusions— Surgical removal of nonarticular base sesamoid fragments can be accomplished through a palmar/plantar approach through the digital flexor tendon sheath and SDSL. This “keyhole” approach minimizes damage to the distal sesamoidean ligament attachments to the sesamoid base and allows some horses to return to their intended use. Clinical Relevance— Surgical removal of nonarticular base sesamoid fragments should be considered in horses with performance‐limiting lameness as a result of the fragment.