Subchondral bone sequestrum formation in the proximal intra-articular and osteochondral region of the third metatarsal bone of an Appaloosa mare treated for septic arthritis.

OBJECTIVE: To raise awareness of the potential for intra-articular subchondral bone sequestrum formation secondary to a traumatic or septic process to enable more rapid identification of this uncommon but possible outcome in future cases. ANIMAL: A client-owned 12-year-old Appaloosa mare. CLINICAL PRESENTATION, PROGRESSION, AND PROCEDURES: The mare had a wound to the lateral aspect of the fourth metatarsal bone (MT4) that communicated with the distal tarsal joints. Radiographs revealed a displaced, comminuted fracture of MT4. TREATMENT AND OUTCOME: The horse underwent aggressive debridement of the wound and MT4 as well as, on 2 occasions, needle joint lavage. Systemic, regional, and IA antibiotic therapy was also performed together with a bone graft from the tuber coxae. The horse's comfort improved, and the wound appeared to be healing. Five weeks following discharge, the horse re-presented with a non-weight-bearing lameness and radiographs revealed marked osteomyelitis of the tarsometatarsal and distal intertarsal joints. Postmortem examination of the limb identified a sequestrum within the proximal articular surface of the third metatarsal bone. CLINICAL RELEVANCE: The present report highlights the importance of arthroscopic lavage to visualize the cartilage surface and the benefits of advanced imaging to detect associated changes within the bone earlier than conventional radiographs. To our knowledge, no reports exist of intra-articular subchondral bone sequestra in the tarsometatarsal joint in horses.

Hoof Unevenness in Juvenile Quarter Horses During First 6 Months of Training.

The role of hoof morphology is increasingly recognized as a factor associated with lameness incidence in performance horses. The primary objective was to evaluate effect of training initiation on hoof unevenness in Quarter Horses (n = 42; 29 2-year-olds, 13 3-year-olds) over 6-months (m) in training (m0, m2, m4, and m6). Horses were objectively assessed for lameness (inertial sensor system) and photographs and radiographs of feet were taken. Hoof measurements were taken (palmar/plantar angles, frog base width/length, toe length/angle, heel length/angle, heel/foot width, wall height/angle), and analyzed with regards to laterality. Front and hindfoot pairs were determined even if toe angles were within 1.5°. Statistical analyses were performed (Fisher's exact test, mixed-model linear regression, P < .05). There were no differences in distal phalanx palmar/plantar angle between lame/nonlame forelimbs (P = .54) or hindlimbs (P = .20). Unevenness between front feet was seen in toe angle m6 (P < .001), heel length m6 (P = .01) and heel angle over time (P = .006). Unevenness between hind feet was seen at m6 in toe angle (P < .001), heel length (P = .009) and heel angle (P = .02). Lameness incidence did not differ between even and uneven footed horses in forelimbs (P = .64) or hindlimbs (P = .09). In uneven feet, there was no difference in lameness between high versus low foot in forelimbs (P = .34) or hindlimbs (P = .29). Limitations include lack of control group not entering training, lack of consistency in timing data collection to previous trimming, and small sample size. In summary, differences in foot measurements and laterality were noted over time following training initiation in juvenile Western performance horses.

Effect of age at training initiation on hoof morphology and lameness in juvenile American Quarter Horses.

BACKGROUND: Lameness, discipline, training intensity, environmental variability, and shoeing are all factors demonstrated to affect hoof loading and therefore act as adaptive stimuli to alter hoof morphology. OBJECTIVES: To evaluate the effect of age at training initiation on hoof morphology and lameness incidence and determine if specific hoof morphology measurements correlate with lameness in juvenile American Quarter Horses. STUDY DESIGN: Prospective cohort study. METHODS: American Quarter Horses (n = 42; 29 two-year-olds, 13 three-year-olds) entering training were monitored for hoof morphology and lameness over 6 months (months 0, 2, 4, and 6). Hoof measurements (palmar/plantar angles, frog base width/length, toe length/angle, heel length/angle, heel and foot width, wall height/angle) from radiographs and photographs were recorded. Lameness was graded subjectively and objectively (Lameness locator®). Statistical analyses were performed with Fisher's exact test and repeated measures ANOVA with p < 0.05. RESULTS: 25/42 horses developed subclinical lameness (16/42 forelimb, 19/42 hindlimb), with 3-year-olds developing lameness more frequently compared to 2-year-olds overall (p = 0.04; 84.6 vs. 48.3%) and in forelimbs (p = 0.05; 61.5% vs. 27.6%); no difference was noted between 2- versus 3-year-olds in hindlimbs (p = 0.2; 61.5% vs. 37.9%). In lame versus sound forelimbs, 3-year-olds had decreased foot width (p = 0.03; 11.48 cm [CI 10.68-12.28] vs. 12.21 cm [CI 11.99-12.42]), decreased toe length (p = 0.03; 6.02 cm [CI 5.69-6.36] vs. 6.45 cm [CI 6.32-6.58]), shorter lateral wall height (p = 0.03; 4.64 cm [CI 4.31-4.96] vs. 5.11 cm [CI 5.03-5.2]), and shorter medial wall height (p = 0.02; 4.58 cm [CI 4.06-5.10] vs. 5.15 cm [CI 4.99-5.30]). In lame versus sound hindlimbs, horses overall (p = 0.05; 3.74, CI 3.53-3.96 vs. 3.55, CI 3.48-3.61) and 3-year-olds had longer heels p = 0.01; 3.90 cm (CI 3.5-4.3) vs. 3.50 cm (CI 3.39-3.61). MAIN LIMITATIONS: Small sample size, lack of control group not entering training. CONCLUSIONS: Three-year-old American Quarter Horses entering training were more likely to develop forelimb lameness than 2-year-olds. This subclinical lameness was associated with specific hoof morphology characteristics (decreased foot width, toe length, heel length, and lateral/medial wall height; greater toe angle).

INTRODUCTION/CONTEXTE: Les boiterie, discipline, intensité d'entraînement, variabilité environnementale et ferrage ont tous été établis comme facteurs affectant le port de poids au niveau du sabot. Ils contribuent aux stimuli adaptatifs qui peuvent altérer la morphologie du sabot. OBJECTIFS: Évaluer l'effet de l'âge en début d'entraînement sur la morphologie du sabot, l'incidence de boiterie et déterminer si des mesures spécifiques de morphologie du sabot pourraient être corrélées avec une boiterie chez les chevaux Quarter Horse Américains. TYPE D'ÉTUDE: Étude de cohorte prospective. MÉTHODES: Des Quarter Horse Américains (n = 42; 29 2 ans, 13 3 ans) en début d'entraînement ont été suivi pour la présence de boiterie et la conformation de leur sabot sur une période de 6 mois (mois 0, 2, 4, 6). Des mesures de sabot (angles palmaires/plantaires, largeur/longueur de la base de la fourchette, longueur/angle de la pince, longueur/angle des talons, largeur du pied et des talons, hauteur/angle de la muraille) à partir de radiographies et de photographies ont été recueillies. Les boiteries ont été gradées subjectivement et objectivement (Lameness locator®). Des analyses statistiques ont été effectuées avec la méthode exacte de Fisher et ANOVA pour mesures répétées avec un p < 0.05. RÉSULTATS: 25/42 chevaux ont développé une boiterie sous-clinique (16/42 membre antérieur, 19/42 membre postérieur). Les chevaux âgés de 3 ans ont développé une boiterie de façon plus fréquente comparativement aux 2 ans (p = 0.04; 84.6 vs. 48.3%) et aux membres antérieurs (p = 0.05; 61.5% vs. 27.6%); il n'y avait pas de différence au niveau des membres postérieurs entre les 2 et 3 ans. En comparant les chevaux boiteux des antérieurs avec ceux qui ne boitaient pas, les 3 ans avaient une largeur de sabot diminuée (p = 0.03; 11.48 cm [IC 10.68-12.28] vs. 12.21 cm [IC 11.99-12.42]), une longueur de pince plus courte (p = 0.03; 6.02 cm [IC 5.69-6.36] vs. 6.45 cm [IC 6.32-6.58]), une hauteur de muraille latérale plus courte (p = 0.032; 4.64 cm [IC 4.31-4.96] vs. 5.11 cm [IC 5.03-5.2]) et une hauteur de muraille médiale plus courte également (p = 0.024; 4.58 cm [IC 4.06-5.10] vs. 5.15 cm [IC 4.99-5.30]). En comparant les chevaux boiteux des postérieurs avec ceux qui ne boitaient pas, chevaux dans l'ensemble (p = 0.05; 3.74, CI 3.53-3.96 vs. 3.55, CI 3.48-3.61) et les 3 ans avaient des talons plus long (p = 0.01; 3.90 cm [IC 3.5-4.3] vs. 3.50 cm [IC 3.39-3.61]). LIMITES PRINCIPALES: Petite taille d'échantillon, aucun groupe contrôle n'ayant pas commencé l'entraînement. CONCLUSIONS: Les Quarter Horse Américains âgés de 3 ans qui débutent l'entraînement sont plus à risque de développer une boiterie des antérieurs comparativement aux chevaux de 2 ans. Une boiterie sous-clinique était associée à des caractéristiques morphologiques spécifiques au sabot (Largeur du sabot, longueur de la pince, longueur des talons et hauteur des murailles latérales et médiales toutes diminuées; angle de la pince augmenté).

Evaluation of Intra-Articular Amikacin Administration in an Equine Non-inflammatory Joint Model to Identify Effective Bactericidal Concentrations While Minimizing Cytotoxicity.

Septic arthritis causes significant morbidity and mortality in veterinary and human clinical practice and is increasingly complicated by multidrug-resistant infections. Intra-articular (IA) antibiotic administration achieves high local drug concentrations but is considered off-label usage, and appropriate doses have not been defined. Using an equine joint model, we investigated the effects of amikacin injected at three different doses (500, 125, and 31.25 mg) on the immune and cartilage responses in tibiotarsal joints. Synovial fluid (SF) was sampled at multiple time points over 24 h, the cell counts determined, and amikacin concentrations measured by liquid chromatography-mass spectrometry. Cytokine concentrations and collagen degradation products in SF were measured by ELISA and multiplex immunoassays. The mean amikacin concentrations in SF were greater than or equal to the minimum inhibitory concentration (MIC) (0.004 mg/ml) for most common equine joint pathogens at all time points tested to 24 h for all three amikacin doses evaluated. The inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1ß) increased significantly in SF in the highest amikacin dose group, despite the fact that increases in SF cell counts were not observed. Similarly, the biomarkers of cartilage type II collagen cleavage (C2C and C12C) were increased in SF following amikacin injection. Mechanistically, we further demonstrated using in vitro studies that chondrocytes and synoviocytes killed by exposure to amikacin underwent apoptotic cell death and were phagocytosed by macrophages in a non-inflammatory process resembling efferocytosis. Neutrophils and T cells were susceptible to amikacin cytotoxicity at clinically relevant doses, which may result in blunting of cellular inflammatory responses in SF and account for the lack of increase in total nucleated cell counts following amikacin injection. In summary, decisions on whether to inject cytotoxic antibiotics such as aminoglycosides intra-articularly and what doses to use should take into account the potential harm that antibiotics may cause and consider lower doses than those previously reported in equine practice.

Use of in vitro assays to identify antibiotics that are cytotoxic to normal equine chondrocytes and synovial cells.

BACKGROUND: Intra-articular (IA) antibiotic usage is prevalent in equine practice. However, recent emergence of antimicrobial resistance prompts re-evaluation of antibiotic selection, particularly when used prophylactically. Furthermore, many commonly used antibiotics exert direct cytotoxicity to equine cells, and appropriate IA doses have not been defined. OBJECTIVES: To screen antibiotics in vitro as an initial assessment of cytotoxicity against normal equine joint cells in monolayer culture and explant tissues. STUDY DESIGN: In vitro experimental study. METHODS: Chondrocytes and synovial cells were harvested from three horses and plated on 24-well plates (100 000 cells/wells in triplicate) for 48 hours prior to addition of antibiotics. Joint cells were exposed to antibiotics (n = 15) at various doses (25-0.39 mg/mL in complete DMEM media) for 24 hours and viability was assessed by trypan blue dye exclusion. The half maximal inhibitory concentration (IC50) was determined for each antibiotic. Cartilage explants were obtained from 3 horses, minced and exposed to antibiotics (n = 5) for 72 hours. Live/dead staining was performed, and fluorescence was visualised using Olympus IX83 spinning disk confocal microscope. Percentage of live vs dead cells was quantified. RESULTS: Antibiotics from different antimicrobial classes expressed dose-dependent but variable cytotoxicity to equine joint cells in vitro. Aminoglycosides and doxycycline had the lowest IC50 (most toxic). Ampicillin sulbactam, imipenem, tobramycin, ceftiofur sodium and amoxicillin had IC50 > 25 mg/mL for at least one cell line, representing potentially less cytotoxic alternatives. MAIN LIMITATIONS: Further studies are necessary to extrapolate these in vitro data results to the in vivo joint environment. CONCLUSIONS: Targeted IA antibiotic therapy would involve selection of the safest antibiotics (highest IC50) with efficacy based on bacterial culture/sensitivity. Antimicrobial selection and evidence-based dosing may minimise damage to native articular cartilage and synovial cells and development of antimicrobial resistance when IA antibiotics are used in equine practice.