Septic arthritis is an important disease in horses, necessitating aggressive and prolonged therapy. In order to guide therapy, reliable methods of detecting the eradication of infection are needed. Therefore, the objective of this study was to investigate detection of eradication of infection in an experimental model of equine septic arthritis using standard diagnostic techniques. For this purpose, 17 adult horses were assigned to 3 experimental groups. The middle carpal joint of each horse was injected with Escherichia coli (Septic group, n = 8), lipopolysaccharide (LPS) (LPS group, n = 6), or sterile saline (Control group, n = 3) at day 0. Contralateral joints were not injected. Standard therapy was applied to all joints except non-injected joints in the Control group at day 1. Sequential samples of synovial fluid (SF) were collected for bacterial culture using 3 culture media [Columbia blood agar (CBA), brain heart infusion broth (BHI), and Signal blood culture medium] and for cytological evaluation [percentage neutrophils (PN), total nucleated cell count (TNCC), and total protein (TP)]. Escherichia coli-specific polymerase chain reaction (PCR) was carried out to detect E. coli DNA in synovial fluid. Culture and PCR were positive for E. coli in all joints injected with E. coli at day 1 and 1 joint was positive on BHI at day 4. Based on the results of bacterial culture, PCR, and TNCC, the elimination of infection in our experimental model occurred by day 4 post-infection in 6 out of 7 cases. Total protein (TP) and PN remained elevated at clinical threshold used for diagnosis of septic arthritis until day 14. In our experimental model of E. coli-induced arthritis, we conclude that TP and PN may not be good indicators for detecting the eradication of bacterial infection caused by E. coli from infected and subsequently treated joints.

OBJECTIVE To determine whether therapeutic concentrations (> 0.5 to 1.0 μg/mL) of polymyxin B (PB) were achieved in the tarsocrural joint of horses when the drug was administered by IV regional limb perfusion (IV-RLP) via a saphenous vein at doses of 25, 50, and 300 mg and to describe any adverse systemic or local effects associated with such administration. ANIMALS 9 healthy adult horses. PROCEDURES In the first of 2 experiments, 6 horses each received 25 and 50 mg of PB by IV-RLP via a saphenous vein with at least 2 weeks between treatments. For each treatment, a tourniquet was placed at the midmetatarsus and another was placed midway between the stifle joint and tarsus. Both tourniquets were removed 30 minutes after the assigned dose was administered. Blood and tarsocrural joint fluid samples were collected for determination of PB concentration before and at predetermined times after drug administration. In experiment 2, 4 horses were administered 300 mg of PB by IV-RLP in 1 randomly selected pelvic limb in a manner identical to that used in experiment 1. RESULTS For all 3 doses, the mean synovial fluid PB concentration was > 10 times the therapeutic concentration and below the level of quantification at 30 and 1,440 minutes after drug administration, respectively. No adverse systemic or local effects were observed following PB administration. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that IV-RLP of PB might be a viable alternative for treatment of horses with synovial infections caused by gram-negative bacteria.

OBJECTIVE To assess whether IV regional limb perfusion (IVRLP) and intraosseous regional limb perfusion (IORLP) of ceftiofur sodium resulted in clinically relevant drug concentrations in the synovial fluid of the tibiotarsal-tarsometatarsal joint of chickens (ie, an avian model) and to determine whether one of those techniques was superior to the other. ANIMALS 12 healthy adult hens. PROCEDURES Birds were randomly assigned to receive ceftiofur sodium (2 mg/kg) by the IVRLP (n = 4), IORLP (4), or IM (control; 4) route once daily for 6 consecutive days. Blood and tibiotarsal-tarsometatarsal synovial fluid samples were collected 15 minutes after ceftiofur administration on predetermined days for quantification of ceftiofur concentration. Plasma and synovial fluid ceftiofur concentrations were compared among the 3 groups. RESULTS All 4 birds in the IVRLP group developed mild to moderate bruising around the injection site, but this bruising did not prohibit completion of the prescribed treatment regimen. No adverse effects were observed in any of the other birds. The mean plasma and synovial fluid ceftiofur concentrations exceeded the therapeutic threshold for most common bacterial pathogens (> 1.0 μg/mL) at all sample acquisition times for all 3 groups. The mean synovial fluid ceftiofur concentration for the IVRLP group was significantly greater than that for the IORLP and control groups at all sample acquisition times. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that IVRLP may be a safe and effective technique for antimicrobial administration to birds with joint infections, contaminated wounds, pododermatitis, and other musculoskeletal infections of the distal aspect of a limb.

OBJECTIVE To evaluate lameness and morphological changes associated with an osteochondral fragment–groove procedure as a means of experimental induction of metacarpophalangeal (MCP) joint osteoarthritis within an 11-week period in horses. ANIMALS 6 nonlame adult warmbloods. PROCEDURES The right MCP joint of each horse underwent an osteochondral fragment–groove procedure (day 0). After 1 week of stall rest (ie, starting day 7), each horse was trained daily on a treadmill. Weekly, horses underwent visual and inertial sensor-based assessments of lameness. Both MCP joints were assessed radiographically on days 0 (before surgery), 1, 35, and 77. A synovial fluid sample was collected from the right MCP joint on days 0 (before surgery), 35, 36, 49, 63, and 77 for cytologic and biomarker analyses. On day 77, each horse was euthanized; both MCP joints were evaluated macroscopically and histologically. RESULTS Right forelimb lameness was detected visually and by the inertial sensor system when horses were moving on a straight line after distal forelimb flexion or circling left on days 14 to 77. Compared with presurgical values, synovial fluid interleukin-6, prostaglandin E2, hyaluronic acid, and interleukin-1 receptor antagonist protein concentrations were increased at 2 or 3 time points, whereas tumor necrosis factor-α and interleukin-10 concentrations were decreased at 1 time point. Gross examination of all right MCP joints revealed synovitis and wear lines; synovitis was confirmed histologically. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that a combined osteochondral fragment–groove procedure can be used to induce clinically and grossly observable early MCP joint osteoarthritis during an 11-week period in horses.

OBJECTIVE To determine whether differences existed in the viscoelastic properties of synovial fluid samples from the metacarpophalangeal, intercarpal, and distal interphalangeal joints of orthopedically normal athletic horses. ANIMALS 45 warmblood horses and 30 Thoroughbreds (age range, 4 to 16 years). PROCEDURES Synovial fluid samples were aseptically obtained via arthrocentesis from 1 metacarpophalangeal, intercarpal, and distal interphalangeal joint of each horse, and nucleated cell counts were performed. A commercial ELISA was used to measure sample hyaluronic acid concentrations, and full rheological characterization of samples was performed to measure the elastic or storage modulus G' and viscous or loss modulus G“ at 37.5°C (representing the body temperature of horses). Findings were compared among joints and between breed groups by means of ANOVA. RESULTS Significant differences in synovial fluid G' and G“ values were identified between Thoroughbreds and warmblood horses for the metacarpophalangeal joint, between the metacarpophalangeal and intercarpal joints of Thoroughbreds, and between the metacarpophalangeal and distal interphalangeal joints and intercarpal and distal interphalangeal joints of warmblood horses. No significant differences were identified between breed groups or among joints in synovial fluid hyaluronic concentrations or nucleated cell counts. CONCLUSIONS AND CLINICAL RELEVANCE Viscoelastic properties of the forelimb joints of orthopedically normal Thoroughbreds and warmblood horses differed within and between these 2 groups, mainly as a function of the evaluated joint. To the authors' knowledge, this was the first study of its kind, and additional research is warranted to better understand the viscoelastic properties of synovial fluid in horses to optimize their locomotive function.