Imaging and Gross Pathological Appearance of Changes in the Parasagittal Grooves of Thoroughbred Racehorses.

(1) Background: Parasagittal groove (PSG) changes are often present on advanced imaging of racing Thoroughbred fetlocks and have been suggested to indicate increased fracture risk. Currently, there is limited evidence differentiating the imaging appearance of prodromal changes in horses at risk of fracture from horses with normal adaptive modelling in response to galloping. This study aims to investigate imaging and gross PSG findings in racing Thoroughbreds and the comparative utility of different imaging modalities to detect PSG changes. (2) Methods: Cadaver limbs were collected from twenty deceased racing/training Thoroughbreds. All fetlocks of each horse were examined with radiography, low-field magnetic resonance imaging (MRI), computed tomography (CT), contrast arthrography and gross pathology. (3) Results: Horses with fetlock fracture were more likely to have lateromedial PSG sclerosis asymmetry and/or lateral PSG lysis. PSG lysis was not readily detected using MRI. PSG subchondral bone defects were difficult to differentiate from cartilage defects on MRI and were not associated with fractures. The clinical relevance of PSG STIR hyperintensity remains unclear. Overall, radiography was poor for detecting PSG changes. (4) Conclusions: Some PSG changes in Thoroughbred racehorses are common; however, certain findings are more prevalent in horses with fractures, possibly indicating microdamage accumulation. Bilateral advanced imaging is recommended in racehorses with suspected fetlock pathology.

Does the Low-Field MRI Appearance of Intraosseous STIR Hyperintensity in Equine Cadaver Limbs Change when Subjected to a Freeze-Thaw Process?

Equine advanced imaging research involving racehorse fetlock pathology commonly uses cadaver limbs and a freeze-thaw process. The presence of short tau inversion recovery (STIR) signal intensity in the distal third metacarpal/metatarsal bone is of particular interest and may be clinically relevant in the diagnosis of horses at risk of fracture. However, little is known about the effect of the freeze-thaw process on the MRI appearance of STIR hyperintensity in these bones. This study compares the low-field MRI appearance of the distal third metacarpal/metatarsal bone from cadaver limbs of Thoroughbreds in race training before and after a freeze-thaw protocol. Blinded and unblinded comparisons were made using objective SNR values and subjective grading. Fifteen cadaver limbs with STIR hyperintensity in the distal third metacarpal/metatarsal bone were included. No overall clinical or statistical significance was detected in STIR signal intensity and distribution after freeze-thaw. Three limbs from one horse had individual changes in STIR hyperintensity that were hypothesized to be attributable to ante-mortem haemodynamic abnormalities caused by anaesthesia. These results indicate that the distribution and intensity of STIR hyperintensity in freeze-thawed cadaver fetlocks can be considered representative of the appearance of pathology in the recently euthanized horse. However, care should be taken with horse selection and handling of the cadaver limbs to ensure reliable appearance of STIR signal after freeze-thaw.

Antimicrobial susceptibility of bacterial isolates from 33 thoroughbred horses with arytenoid chondropathy (2005-2019).

OBJECTIVE: To describe the prevalence and antimicrobial susceptibility of bacterial isolates cultured from surgical specimens of infected arytenoid cartilage and granulomas. STUDY DESIGN: Retrospective cohort study. ANIMALS: Thirty-three thoroughbred horses. METHODS: Hospital records were retrieved for all horses admitted to a referral hospital for arytenoid chondropathy surgery that had samples submitted for culture and sensitivity between 2005 and 2019. Descriptive analyses were performed. RESULTS: In total, 56 bacterial isolates were obtained. Gram-positive bacteria (58%), Gram-negative bacteria (54%), and anaerobes (33%) were cultured from samples. Fifty-eight percent of horses had multiple bacteria isolated. Streptococcus spp were the most common (32%), followed by Enterobacteriaceae (13%). Bacterial isolates were sensitive to ceftiofur (83%), followed by ampicillin (64%), tetracycline (48%), enrofloxacin (45%), trimethoprim-sulfamethoxazole (41%), and gentamicin (18%). Multidrug resistance (MDR) was present in 44% of bacterial isolates. CONCLUSION: A wide variety of bacteria was cultured, providing evidence that secondary opportunistic infection by common respiratory bacteria is likely a factor in arytenoid chondropathy. Multidrug resistance was higher than what has been previously reported in equine respiratory samples. Trimethoprim-sulfamethoxazole had low effectiveness. CLINICAL SIGNIFICANCE: Because culture and sensitivity testing is not available in the diagnosis of mild to moderate arytenoid chondropathy, the information from this study may allow for more targeted broad-spectrum antimicrobial treatment to limit disease progression when the disease is first identified. The antimicrobial susceptibilities and MDR found in this study emphasize the importance of following current antimicrobial guidelines and highlight the requirement for surgical intervention rather than continued medical treatment in cases that do not resolve with initial antimicrobial therapy.

Evaluation of the inflammatory response to two intra-articular hyaluronic acid formulations in normal equine joints.

Intra-articular (IA) hyaluronic acid (HA) is commonly used to treat equine arthritis. Inflammatory response or "joint flare" is a recognized potential side effect. However, the incidence and severity of inflammation following IA HA injection in horses is not well documented. This study compared the effects of two IA HA formulations of different molecular weight (MW) and a saline control on clinical signs and synovial fluid markers of inflammation in normal equine joints. Eight adult horses each had three healthy fetlock joints randomly assigned to treatment with either 1.4 mega Dalton HA, 0.8 mega Dalton HA or saline control once weekly for three weeks. Clinical evaluation and synovial fluid analysis were performed by blinded assessors. Outcomes of interest were lameness score, joint effusion score and synovial fluid white cell count and differential, total protein, viscosity and serum amyloid A. Joints injected with HA developed significant mild-to-moderate inflammatory responses often associated with lameness and joint effusion compared with saline control joints. The higher MW HA formulation elicited a significantly greater inflammatory response than the lower MW HA after the first injection. In HA injected joints, viscosity remained poor for the entire study. Both IA HA formulations in this study induced an inflammatory response in healthy equine joints. This may have implications for the use of HA in equine joints. The findings in this study are limited to the two HA formulations used. Further investigation of different HA formulations and the use of HA in normal and arthritic equine joints is warranted.