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Objective: To determine the short-term effect of plantar fasciotomy and neurectomy (PFN) of the deep branch of the lateral plantar nerve on the proximal suspensory ligament (PSL) cross-sectional area (CSA) in horses with hindlimb proximal suspensory desmopathy (PSD)., Study Design: Analytical, observational, cohort study., Sample Population: Twenty-one horses., Methods: Records of horses with chronic PSD treated by PFN were included if a preoperative ultrasonographic examination was available and at least one postoperative ultrasonographic examination. One masked observer measured the ultrasonographic cross-sectional area (CSA) of the PSL. Intraobserver reliability was determined by repeatedly measuring a subset of ultrasonographic images (n = 127). Two masked observers measured the cross-sectional area of the proximal suspensory ligament (PSL-CSA) on preoperative proton density (PD)-weighted transverse high field magnetic resonance images (n = 19 horses) . Agreements for PSL-CSA between preoperative ultrasonographic and MRI measures and between the two magnetic resonance imaging (MRI) observers were assessed. Follow up considered the horses' ability to return to exercise and their owners' satisfaction., Results: The reliability of the ultrasonographic measurement of the PSL-CSA was excellent. Agreement between ultrasonographic assessment and MRI assessment of PSL-CSA was good. No difference was detected between preoperative (median, interquartile range; oblique-incidence, 2.07, 1.72-2.55; on-incidence, 2.23, 1.98-2.65) and postoperative (oblique-incidence, 2.08, 1.80-2.74; on-incidence, 2.28, 2.01-2.74) PSL-CSAs. At a median of 12 months (4-33 months), 16/20 (80%) owners reported the horse was "better" and 15/20 (75%) functioned at or above preoperative levels., Conclusion: Ultrasonographic measurement of the PSL-CSA was reproducible and in good agreement with MRI measurement. The PSL-CSA was not influenced by PFN., Clinical Significance: The PSL-CSA cannot be used to guide return to function., (© 2021 The Authors. Veterinary Surgery published by Wiley Periodicals LLC on behalf of American College of Veterinary Surgeons.)

Background: Injection of the centrodistal (CD) joint in the horse is a commonly performed procedure for both diagnostic and therapeutic purposes. This procedure can be technically challenging, and while radiographic guidance has been previously used, ultrasound localised injection of the CD joint has not been described., Objectives: The purpose of this study was to explore the feasibility of using ultrasound localisation to increase the accuracy of CD joint injection., Study Design: Experimental method assessment., Methods: One operator performed the ultrasound and injection of 24 CD joints in 12 sedated horses. The joints were injected with iohexol (2 ml), sterile saline (1.5 ml) and amikacin (0.5 ml). Dorsoplantar and dorsomedial plantarolateral radiographic projections were obtained immediately after injection to evaluate the presence of contrast material in the CD joint., Results: The CD joint was successfully injected in 17/24 joints, representing a 70.8% accuracy., Main Limitations: The horses used in this study were from the University research herd, and not clinical cases. One investigator performed all the ultrasonography and CD joint injections., Conclusions: The use of ultrasound localisation could improve success of CD joint injection as well as improve the learning curve of less experienced practitioners learning this procedure., (© 2020 EVJ Ltd.)

Background: Clodronate is prescribed to performance horses with lameness. Despite its clinical popularity, little research has been done to understand the effects of clodronate in the horse., Objectives: Our objective was to determine if a single treatment with clodronate at the clinically approved dose altered bone remodelling, bone cell recruitment or lameness in the horse., Study Design: Twelve university-owned equestrian team competition horses with a history of forelimb lameness due to navicular syndrome were randomised to receive either 1.4 mg/kg clodronate (CLOD n = 6) or an equivalent volume of LRS (CONT; n = 6) in a blinded manner., Methods: Blood was evaluated weekly for 8 weeks before and after drug administration (clodronate or placebo) for bone turnover markers CTX-I and osteocalcin. Lameness evaluations were performed to assess for change in lameness 1 week before and 1, 2, 3 and 8 weeks after drug administration. Coach questionnaires were performed to assess for change in ridden performance 1, 2, 3 and 8 weeks after drug administration. Bone cell recruitment was evaluated in vitro 2 weeks before and after drug administration., Results: There were no differences in in vitro bone cell recruitment from whole bone marrow or in bone turnover markers CTX-I or osteocalcin. A small but significant decrease in forelimb lameness was detected in CLOD treated horses 1 week after treatment (P = 0.005). There were no significant differences in hindlimb lameness. Coaches identified an improvement in performance significantly more often in CLOD vs. CONT (P = 0.01) at week 8., Main Limitations: Two CONT horses received intra-articular anti-inflammatory medication after treatment, which may have altered lameness results., Conclusions: A single dose of clodronate appears to reduce lameness without producing detectable effects on bone turnover markers. Due to the long half-life of a bisphosphonate drug, the effect of multiple doses on bone remodelling and lameness should be investigated. The Summary is available in Portuguese - see Supporting Information., (© 2018 EVJ Ltd.)

Objective: To evaluate the effects of a new microfracture and ligament splitting procedure on ligament healing and to examine the usefulness of magnetic resonance (MR) imaging for monitoring ligament healing over time using a collagenase model of hind limb proximal suspensory desmitis., Study Design: Experimental in vivo study., Animals: Healthy adult horses (n=6)., Methods: Horses were free of lameness with normal hind limb proximal suspensory ligaments (PSL). The origin of both hind limb PSL was injected with collagenase and underwent MR imaging 2 weeks later, followed by the microfracture and ligament splitting procedure on 1 limb, with the opposite limb serving as the sham-operated control. Serial lameness and MR examinations were performed. Horses were euthanatized 210 days after surgery, the PSL harvested, and histology, biochemistry, and gene expression performed on both PSL., Results: Collagenase lesions viewed on MR images appeared similar to those seen clinically. Serial MR images demonstrated resolution of abnormal signal intensity and tissue formation in the microfracture sites within the third metatarsal bone. Treated limbs had histologic evidence of connective tissue appearing to originate from the small perforations and blending into the ligament but no statistical differences were identified. Gene expression for cartilage oligomeric matrix protein and decorin were significantly increased in treated compared to control limbs., Conclusion: The microfracture and ligament splitting procedure did incite a tissue response but further clinical investigation is necessary to determine if this tissue remodeling at the bone-ligament interface translates to improved clinical outcome. MR imaging may be useful to follow healing in horses with hind limb proximal suspensory desmitis., (© Copyright 2016 by The American College of Veterinary Surgeons.)

Objective: To describe the location and severity of deep digital flexor tendon (DDFT) lesions diagnosed by means of high-field-strength MRI in horses and to identify variables associated with return to activity following medical treatment., Design: Retrospective case series., Animals: 118 horses., Procedures: Medical records of horses with DDFT injury diagnosed with MRI over a 10-year period (2000-2010) and treated medically (intrasynovial administration of corticosteroids and sodium hyaluronan, rest and rehabilitation, or both) were reviewed. History, signalment, use, results of lameness examination and diagnostic local anesthesia, MRI findings, and treatment details were recorded. Outcome was obtained by telephone interview or follow-up examination. Horses were grouped by predictor variables and analyzed with logistic regression to identify significant effects., Results: Overall, of 97 horses available for follow-up (median time to follow-up, 5 years; range, 1 to 12 years), 59 (61%) returned to activity for a mean duration of 22.6 months (median, 18 months; range, 3 to 72 months), with 25 (26%) still sound at follow-up. Of horses with mild, moderate, and severe injury, 21 of 29 (72%), 20 of 36 (56%), and 18 of 32 (56%), respectively, returned to use. Horses treated with intrasynovial corticosteroid injection and 6 months of rest and rehabilitation returned to use for a significantly longer duration than did horses treated without rest. Western performance horses returned to use for a significantly longer duration than did English performance horses., Conclusions and Clinical Relevance: Results of the present study suggested that outcome for horses with DDFT injuries treated medically depended on injury severity, presence of concurrent injury to other structures in the foot, type of activity, and owner compliance with specific treatment recommendations. Although some horses successfully returned to prior activity, additional treatment options are needed to improve outcome in horses with severe injuries and to improve long-term prognosis.

This study compared in vitro monotonic and cyclic mechanical properties of equine proximal interphalangeal joint arthrodeses stabilized using an open or closed technique combined with axial 4.5 mm narrow limited-contact dynamic compression plate (LC-DCP) or 4.5 mm narrow locking compression plate (LCP). Ten forelimb pairs were randomly assigned to LCP or LC-DCP groups. One limb in each pair was assigned to either open or closed technique. Limbs were tested for cyclic fatigue at 20 000 cycles and then single-cycle to failure under 3-point dorsopalmar bending. There was no significant difference in stiffness of constructs during cyclic fatigue testing or on force or stiffness at failure in single cycle to failure testing between open and closed techniques or between plate types. Both implants, surgical technique, or combinations thereof are suitable for clinical use. More work is necessary to define the interaction between implant type and surgical technique.

Background: The impact of cervical pathology on performance is of great importance to the horse industry. Accurate diagnosis of cervical disease with imaging modalities, including computed tomography (CT) and magnetic resonance imaging (MRI), requires thorough appreciation of normal cervical anatomy., Objectives: (1) To describe in detail the anatomy of the equine cervical spine by comparing anatomical sections with corresponding MR and contrast-enhanced CT images in the sagittal, dorsal, and transverse plane. (2) To discuss the ability of MR and contrast-enhanced CT imaging to visualize anatomical structures in the cervical spine., Animals and Methods: Three cervical spines of young adults (3-8 years), collected immediately after humane euthanasia, were used. The spine was stabilized on a frame in a natural flexed position with an angle of 20°. MR and contrast-enhanced CT imaging was performed within six hours after euthanasia. Anatomical sections of 1 cm were made in the sagittal, dorsal, and transverse plane and compared with corresponding CT and MR images. The intervertebral disk thickness, facet joint angle, sagittal dural space diameter and ventromedial facet joint projection were quantified., Results: The anatomic location of clinically important structures including the facet joints, spinal cord, cervical nerve roots and intervertebral disks were reliably identified in the anatomical sections and their corresponding MR images. Contrast-enhanced CT images depicted all osseous borders, whereas MR images were superior for soft tissue structures., Conclusion and Clinical Importance: This study enhances our understanding of normal cervical spine anatomy and the diagnostic usefulness of cervical MRI and contrast-enhanced CT in the horse.

Objective: To define a method for the basilar sesamoidean approach (BSA) to the digital flexor tendon sheath (DFTS) in horses and compare it with the axial sesamoidean approach (ASA) for DFTS synoviocentesis and injection., Design: Evaluation study., Animals: 12 healthy adult mares without evidence of abnormalities related to the lower limbs., Procedures: Each horse had 1 forelimb and 1 hind limb assigned to each DFTS approach (basilar vs axial, relative to the proximal sesamoid bones) in a Latin square design. The order of horses and of limb injection for each horse was randomly selected. All procedures were performed in standing sedated horses. The number of attempts to place a needle in the DFTS, presence of synovial fluid in the needle hub, time for DFTS injection, and number of accurate injections of sterile contrast material into the DFTS (evaluated by means of radiography) were compared between methods., Results: Median time for injection was significantly shorter for the BSA, compared with the ASA. The median number of times the needle was redirected was also significantly less for the BSA. Odds of obtaining synovial fluid via the BSA were 5.7 times as great as for the ASA (95% confidence interval, 1.2 to 278). Successful injection of contrast material into the DFTS did not differ significantly between the BSA (24/24 limbs) and ASA (23/24)., Conclusions and Clinical Relevance: The BSA was a useful method for DFTS synoviocentesis in the forelimbs and hind limbs of standing sedated horses and was superior to the ASA in most aspects. This approach to the DFTS should be considered when DFTS injection or synovial fluid retrieval is desired, particularly in horses with minimal DFTS effusion.

Two hundred and thirty-two horses with lameness localized to the metacarpo(tarso)phalangeal (MCP/MTP) region without a radiographic diagnosis were evaluated. All horses had high-field magnetic resonance (MR) imaging of the MCP/MTP region performed for the lame limb and the contralateral limb for comparison. There were 46 horses that had bilateral abnormalities in the forelimbs; 27 of these horses were not lame in the contralateral limb at the time of examination. Bilateral hind limb abnormalities were observed in 37 horses; 22 horses were not lame in the contralateral limb. Soft tissue abnormalities alone were observed in 218 limbs (162 horses). Subchondral bone and articular cartilage abnormalities alone were observed in 43 limbs (34 horses). A combination of soft tissue, subchondral bone, and cartilage abnormalities were observed in 64 limbs (36 horses). The distribution of primary abnormalities was as follows; oblique distal sesamoidean ligament desmitis (73 limbs in 56 horses), straight distal sesamoidean ligament desmitis (44 limbs in 38 horses), chronic subchondral bone injuries (15 limbs in 12 horses), suspensory ligament branch desmitis (14 limbs in 12 horses), collateral ligament desmitis (12 limbs in 12 horses), tendonitis of the superficial and deep digital flexor tendons (10 limbs in 10 horses), osteochondral defects greater than 1 cm (nine limbs in six horses), osteochondral defects less than 1 cm (eight limbs in seven horses), bone marrow lesions (six limbs in five horses), intersesamoidean ligament desmitis (five limbs in four horses). MR imaging is useful in diagnosing bone and soft tissue injuries when radiographs and ultrasound fail to yield a diagnosis., (© 2012 Veterinary Radiology & Ultrasound.)

Objective: To determine treatment outcome on the basis of pathological changes identified on MRI and lameness duration in horses with navicular syndrome that underwent injection of corticosteroid and hyaluronan into the navicular bursa., Design: Retrospective case series., Animals: 101 horses with navicular syndrome., Procedures: Medical records of horses with signs of navicular syndrome evaluated between January 2000 and December 2008 were reviewed. Data on signalment, use of the horse, history, affected limbs, duration of lameness, findings on lameness examination, radiographic findings, MRI findings, treatment, and outcome were collected from the medical records. Follow-up information was obtained a minimum of 10 months after navicular bursa injection., Results: Following navicular bursa injection, 76 of 101 (75%) horses returned to their intended use for a mean of 9.66 months, and 35 (35%) were sound at follow-up. Horses that had been lame for < 6 months before treatment were significantly more likely to return to their intended use, have a longer positive response to treatment, and be sound at follow-up, compared with horses that had a longer lameness history. Horses with primary deep digital flexor (DDF) tendonitis responded best to navicular bursa injection with rest and rehabilitation, followed by horses with navicular bursitis and horses with DDF tendonitis and adhesions to the collateral sesamoidean ligament of the distal sesamoid (navicular) bone. Horses with scar tissue in the proximal portion of the navicular bursa, adhesions from the navicular bone to the DDF tendon, or multiple abnormalities did not respond as well to treatment., Conclusions and Clinical Relevance: Response to navicular bursa injection with corticosteroid and hyaluronan in horses with navicular syndrome was dependent on the disease process detected on MRI and duration of lameness.

Objective: To report outcome after desmotomy of the accessory ligament of the deep digital flexor tendon (ALDDFT) in adult horses (≥2 years) for treatment of desmitis of the ALDDFT or flexural deformity of the distal interphalangeal joint (FDDIJ)., Study Design: Case series., Animals: Horses with desmitis of the ALDDFT (n=9) and FDDIJ (n=15)., Methods: Records (April 1996-July 2008) of 24 adult horses (mean age, 6.7 years) that had ALDDFT desmotomy were reviewed. Follow-up data was obtained 12-120 months after desmotomy., Results: Outcome was available for 22 horses; 18 (82%; 6 of 8 horses with desmitis of the ALDDFT and 12 of 14 with FDDIJ) returned to their intended use within 6-24 months (mean, 12 months)., Conclusion: In mature horses, ALDDFT desmotomy resulted in successful return to intended use in most horses with ALDDFT desmitis (75%) or FDDIJ (86%)., (© Copyright 2011 by The American College of Veterinary Surgeons.)

Objective: To evaluate: (1) an arthroscopic technique for transection of the collateral sesamoidean ligament (CSL); and (2) the healing response using magnetic resonance (MR) and microscopic examination., Study Design: Experimental study., Animals: Adult horses (n=6)., Methods: Six sound horses with normal front foot radiographic and MR examinations were used. Lameness examination was performed before surgery and monthly for 12 months. Front foot radiography was performed at 180 and 360 days after surgery. Front foot MR was performed before, and at 7, 90, 180, and 360 days after surgery. Arthroscopic CSL desmotomy was performed on 1 forelimb. Gross and microscopic examination was performed on the CSL from both forelimbs at 360 days after surgery. Lameness scores were compared over time using the nonparametric Friedman's test for paired groups. CSL measurements were compared using paired t-tests with a 2-tailed significance level of P<.05., Results: Radiographs remained normal throughout study period. Surgery resulted in lameness on the operated limb for up to 2 months, after which all horses returned to soundness. CSL transection was confirmed during arthroscopy and with MR examination 7 days after surgery. Gross and microscopic evaluation confirmed ligament healing., Conclusions: CSL desmotomy resulted in short-term lameness after surgery followed by healing of the CSL confirmed by gross and microscopic analysis., (© Copyright 2010 by The American College of Veterinary Surgeons.)

Seventy-two horses with recent onset of navicular syndrome and normal radiographs were assessed. Horses underwent magnetic resonance (MR) imaging of both front feet. All abnormalities were characterized and the most severe abnormality identified, if possible. Abnormal signal intensity in the navicular bone was the most severe abnormality in 24 (33%) horses. Pathologic change in the deep digital flexor tendon was the most severe abnormality in 13 (18%) horses. Pathologic change in the collateral sesamoidean ligament was the most severe abnormality in 11 (15%) horses. Pathologic change in the distal sesamoidean impar ligament was the most severe abnormality in seven (10%) horses. Multiple abnormalities were observed in 13 (18%) horses in which an abnormality that was more severe than the others could not be determined. Abnormalities were not observed in the navicular bone or its supporting soft tissues in four (5%) horses. Fifty-six horses had abnormalities that were most severe in one limb; in 52 (93%) horses, the most severe abnormalities were in the foot of the most lame limb. In 7% (4/56) of horses, the most severe findings were in the opposite limb, and in 16 horses, the findings on both limbs were similar. MR imaging is a useful technique for evaluating horses with navicular syndrome and can differentiate between multiple abnormalities. This provides a more specific diagnosis which affects further treatment of the horse. Pathologic changes in different locations in the foot can cause similar clinical signs that, before MR imaging, were categorized as one syndrome.

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.

Magnetic resonance (MR) imaging abnormalities in horses with lameness localized to the proximal metacarpal or metatarsal region have not been described. To accomplish that, the medical records of 45 horses evaluated with MR imaging that had lameness localized to either the proximal metacarpal or metatarsal region were reviewed. Abnormalities observed in the proximal suspensory ligament or the accessory ligament of the deep digital flexor tendon included abnormal high signal, enlargement, or alteration in shape. Twenty-three horses had proximal suspensory ligament desmitis (13 hindlimb, 10 forelimb). Sixteen horses had desmitis of the accessory ligament of the deep digital flexor tendon. One horse had desmitis of the proximal suspensory ligament and the accessory ligament of the deep digital flexor tendon on the same limb and one horse had desmitis of the proximal suspensory ligament on one forelimb and desmitis of the accessory ligament of the deep digital flexor tendon on the other forelimb. Four horses did not have abnormalities in the proximal suspensory ligament or accessory ligament of the deep digital flexor tendon. Eighty percent of horses with forelimb proximal suspensory ligament desmitis and 69% of horses with hindlimb proximal suspensory ligament desmitis returned to their intended use. Sixty-three percent of horses with desmitis of the accessory ligament of the deep digital flexor tendon were able to return to their intended use. MR imaging is a valuable diagnostic modality that allows diagnosis of injury in horses with lameness localized to the proximal metacarpal and metatarsal regions. The ability to accurately diagnose the source of lameness is important in selecting treatment that will maximize the chance to return to performance.

Injury to the oblique and straight distal sesamoidean ligaments is becoming recognized as a more common cause of lameness in horses than was previously thought. The purpose of this study was to review the magnetic resonance (MR) imaging findings of 27 horses affected with desmitis of the oblique and/or straight distal sesamoidean ligament and determine long-term prognosis for horses with this diagnosis. Imaging was performed with horses in right lateral recumbency in a high-field 1 T magnet. All horses had lameness localized to the digit or metacarpophalangeal/metatarsophalangeal joint region with diagnostic local anesthetic blocks. Ten horses had forelimb lameness and 17 horses had hind limb lameness. MR imaging revealed abnormalities in the oblique distal sesamoidean ligaments in 18 horses, in the straight distal sesamoidean ligament in three horses, and in both the oblique and straight distal sesamoidean ligament in six horses. Treatment consisted of a 6-month rest and rehabilitation program in all horses. The digital flexor tendon sheath was injected with methylprednisolone acetate and hyaluronic acid in 22 horses to decrease inflammation in the injured ligaments before starting the rest and rehabilitation program. Two horses had ligament splitting performed, one in the oblique distal sesamoidean ligament and one in the straight distal sesamoidean ligament. MR imaging is an effective method for diagnosing injury to the oblique and straight distal sesamoidean ligaments in horses. Treatment, primarily a 6-month rest and rehabilitation program, allowed 76% of the horses to successfully resume performance.

Case Description: A 5-year-old Appaloosa mare was examined for severe left forelimb lameness of 4 months' duration., Clinical Findings: Lameness was evident at the walk and trot and was exacerbated when the horse circled to the left. Signs of pain were elicited in response to hoof testers placed over the frog of the left front hoof, and a palmar digital nerve block eliminated the lameness. Radiographs revealed no abnormalities, but magnetic resonance imaging (MRI) revealed increased bone density in the medullary cavity of the distal sesamoid (navicular) bone in the proton density and T2-weighted images and a defect in the fibrocartilage and subchondral bone of the flexor cortex., Treatment and Outcome: Because of the absence of improvement after 4 months and the poor prognosis for return to soundness, the mare was euthanatized. An adhesion between the deep digital flexor tendon and the flexor cortex defect on the navicular bone was grossly evident, and histologic evaluation revealed diffuse replacement of marrow trabecular bone with compact lamellar bone. Changes were consistent with blunt traumatic injury to the navicular bone that resulted in bone proliferation in the medullary cavity., Clinical Relevance: Use of MRI enabled detection of changes that were not radiographically evident and enabled accurate diagnosis of the cause of lameness. Navicular bone injury may occur without fracture and should be considered as a differential diagnosis in horses with an acute onset of severe unilateral forelimb lameness originating from the heel portion of the foot.

CASE DESCRIPTION-A 4-year-old Quarter Horse stallion was evaluated because of a 10-month history of moderate (grade 3/5) left forelimb lameness (detectable during trotting over a smooth, hard surface). CLINICAL FINDINGS-No abnormalities were detected in either forelimb via palpation or application of hoof testers; however, lameness was eliminated after administration of a palmar digital nerve block in the left forelimb. Whereas radiography and ultrasonography did not identify any left forelimb foot abnormalities, magnetic resonance (MR) imaging revealed a circumscribed soft tissue mass in the distal aspect of the digital flexor tendon sheath (DFTS) dorsal to the lateral aspect of the deep digital flexor tendon. Subsequently, the left forelimb DFTS was injected with local anesthetic, which resulted in 90% improvement of the horse's lameness. TREATMENT AND OUTCOME-The distal aspect of the left forelimb DFTS was evaluated tenoscopically. The mass was removed under tenoscopic guidance, after which the distal digital annular ligament was transected. The horse received phenylbutazone orally for 10 days, and the left forelimb DFTS was injected with hyaluronic acid and methylprednisolone acetate 7 days after the surgery. Following a rehabilitation program, the horse was returned to full training at 6 months after surgery and competed successfully during a 2-year follow-up period. CLINICAL RELEVANCE-Use of MR imaging should be considered in all lame horses for which a definitive diagnosis cannot be made via radiography, ultrasonography, or other imaging techniques, especially when the lameness has been localized to a specific anatomic region by use of diagnostic anesthesia.

We evaluated the relationships of heart score (HS) and echocardiographic measures to maximal oxygen consumption (VO2max), maximal cardiac output (Qmax), and maximal stroke volume (SVmax). Six fit, mature Thoroughbred horses weighing (mean +/- s.e.) 487 +/- 11 kg were run 4 times on an inclined (10%) treadmill. Each run consisted of a 3 min warm-up at 4 m/s followed by completion of an incremental exercise test in which each horse ran until VO2max was reached. Arterial and mixed venous blood was collected to determine arteriovenous oxygen content difference C(a-v)O2[ in the last 15 s of exercise. An ATL HDI 3000 ultrasound system and a 3.5 MHz phased array transducer were used to make echocardiographic measurements before and within 2 min of run completion. Guided M-mode echocardiographic measurements of left ventricular diameter (LVD), interventricular septal thickness (IVS) and left ventricular free wall thickness (LVFW) during diastole (D) and systole (S) were made from the right parasternal short axis view at the level of the chordae, and VO2 and C(a-v)O2 were measured as the appropriate M-mode view was recorded. Maximum heart rate (HRmax) was determined using a cardiotachometer, and HS was calculated on nonexercise days using the established technique. Maximum cardiac output and SVmax were calculated from the Fick equation and HRmax. Backward stepwise regression analysis was used to relate pre- and post exercise echocardiographic measurements and HS to VO2, Q, and SV at the time of measurement, and to VO2max, Qmax, and SVmax. Pre- and post exercise LVDD appeared to be the most important variable in these equations. Mean pre-exercise HR at the time of measurement was 54.7 +/- 1.9 beats/min, while the mean post exercise rate was 111.7 +/- 2.6 beats/min. The mean +/- s.e. VO2max was 150.4 +/- 13.2 ml/(kg.min). Heart score was not correlated with VO2max, Qmax, or SVmax. There was no significant difference between pre- and post exercise measurements of LVD, IVSS, and LVFWS.

Eight mature mares were exercised for 20 min at 60% VO2max and to fatigue at 95% VO2max. Plasma beta-endorphin (EN) concentrations were determined before exercise, after a 10 min warm-up, and at the end of each exercise test. Mean +/- s.e. beta-endorphin concentrations were significantly (P < 0.05) higher following work at 95% VO2max when compared to that at 60% VO2max (420.0 +/- 102.7 vs. 269.9 +/- 30.69 pg/ml). Pre-exercise samples were collected between 1000 and 1500 h. In order to evaluate whether any cyclic changes in EN secretion effects may have influenced results, a subsequent study was completed using 12 horses to assess diurnal fluctuations in EN concentrations, by measuring EN concentration every 2 h for a 24 h period. There was no statistical difference in mean values at any time between 0800 and 2000 h. Whether individual differences in EN concentrations reflected varying degrees of stress associated with the exercise could not be determined. Any possible link between EN concentration and exercise stress in exercising horses awaits clarification.

When blood is collected into sodium citrate in the proportion of 9 parts blood:1 part sodium citrate, the concentration of plasma sodium citrate in the sample will depend on the packed cell volume (PCV) of the blood sample. This difference in plasma sodium citrate concentration secondary to alterations in PCV significantly affects human platelet aggregation responses. Since horses attain a high PCV in response to high-intensity exercise we investigated the effect of differences in sample plasma sodium citrate concentration on equine platelet aggregability. In addition, low molecular weight heparin (LMWH) was evaluated as an alternative anticoagulant for assessment of platelet aggregability during strenuous exercise in horses. Blood samples were collected pre-exercise and at fatigue after supramaximal treadmill exercise into either 3.8% sodium citrate (9 parts blood:1 part sodium citrate) or 20 u LMWH/ml of blood. Platelet aggregation responses to 1.25 mumol/l adenosine diphosphate (ADP) were measured via optical aggregometry. For samples collected into sodium citrate, aggregability was significantly less than pre-exercise values in samples collected at fatigue and in pre-exercise samples in which sodium citrate concentrations were adjusted to equal those in fatigue samples. However, samples collected into LMWH showed significantly increased platelet aggregability in samples collected at fatigue when compared to pre-exercise samples. In conclusion, higher plasma sodium citrate concentration had a marked inhibitory effect on equine platelet aggregation responses. Low molecular weight heparin was a good alternative anticoagulant for assessment of equine platelet function and results indicate that equine platelet aggregability was enhanced in response to supramaximal exercise.