EQUINE VETERINARY EDUCATION / AE / APRIL 2018
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Peripheral blood analysis of mature horses with septic
arthritis might show elevated levels of fibrinogen, total protein and WBC count with neutrophilia. However, horses with acute septic arthritis unrelated to systemic disease often have normal complete blood counts. The peripheral blood changes observed in the present case were probably related to both septic conditions (arthritis and thrombophlebitis). Serum amyloid A (SAA), the major acute phase protein in horses, increases in serum and synovial fluid in horses with septic arthritis. Therefore, synovial SAA is a useful adjunct in diagnosis and evaluation of clinical progression of septic arthritis in horses (Ludwig et al. 2016; Sanchez-Teran et al. 2016). Blood culture should be employed when haematogenous spread is suspected and synovial fluid analysis, cytology and culture are paramount in establishing a diagnosis (Carstanjen et al. 2010). Septic synovial fluid is characterised by lowered viscosity
(length of strand between fingers <2.5 cm; normal 2.5–5 cm), pH (<7.3; normal 7.3) and glucose (<400 mg/L, or less than half the serum glucose concentration), and elevated level of total protein (>40 g/L; normal <20 g/L) and lactate (>4.9 mmol/L; normal <3.9 mmol/L) (Tulamo et al. 1989; Carstanjen et al. 2010). The number of total nucleated cells is elevated (>30 9 109 cells/L; normal <0.2 9 109 cells/L), and can often approach and exceed 100 9 109 cells/L (Morton 2005; Carstanjen et al. 2010). Significant and persistent neutrophilia in synovial fluid is one of the earliest hallmarks of infected equine joints and the neutrophils may have toxic changes but are often healthy in appearance (Tulamo et al. 1989; Morton 2005). Intracellular bacteria may be identified in cytological examinations but are only reported to be observed in 25% of cases (Morton 2005). Culture of synovial fluid should be attempted but bacteria
may not always be recovered using conventional culture techniques (Tulamo et al. 1989; Morton 2005; Carstanjen et al. 2010). Aerobic and anaerobic culture using blood culture medium may increase the chance of obtaining a positive result (Morton 2005; Carstanjen et al. 2010). Synovial membrane biopsies can also be used for microbial culture and submitting both synovial fluid and synovial membrane increases the likelihood of identification of the causative micro-organism (Morton 2005). Radiographic examination does not contribute to
detection of a septic process in a joint directly but could provide additional information such as soft tissue swelling or evidence of bone involvement/osteomyelitis that dramatically reduces the prognosis for future soundness. Ultrasonography can be used to detect distension of the joint as well as echogenic particles floating in the synovial fluid (Carstanjen et al. 2010). The technique is also useful to guide centesis for collection of synovial fluid from complex joints, synovial bursas and tendon sheaths (Morton 2005). Other imaging modalities include magnetic resonance imaging and nuclear scintigraphy when soft tissues are affected, and computed tomography when there is suspicion of bone involvement (Carstanjen et al. 2010). Treatment is aimed at rapid elimination of the infection
and removal of debris and inflammatory products from the joint cavity to minimise damage to articular cartilage (Schneider et al. 1992b; Meijer et al. 2000). Nonsteroidal anti- inflammatory drugs should be administered to decrease pain thereby preventing serious pain related complications, such as laminitis and caecal impaction (Morton 2005). Anti-
inflammatory drugs will also reduce synovial inflammation thereby decreasing prostaglandin-E2 production and associated collagen destruction. A combination of systemic broad spectrum antibiotics
should be used during the early stages of the disease and if an anaerobic micro-organism is suspected, metronidazole may also be included (Morton 2005; Carstanjen et al. 2010). Direct intra-articular administration of antimicrobials can
be performed daily to eliminate the offending organism as quickly as possible. Injection of gentamicin into equine joints has been reported to cause mild, transient inflammation but this is much less detrimental than the septic process itself (Schneider et al. 1992b). In the present case, 1 g of ceftiofur was injected daily into the left joint over 8 days without noticeable side effects. Regional i.v. and intraosseous limb perfusions are also effective methods for delivering higher concentrations of antibiotics to synovial tissues (Morton 2005). In the present case, i.v. regional limb perfusion using 500 mg of meropenem diluted in 50 mL of saline was performed six times on alternative days without any side effects. Many surgical techniques have been described for the
physical removal of bacteria, inflammatory products and devitalised tissues from the joints. Arthroscopic debridement and lavage have been shown to improve survival rate and prevent loss of use in horses with infected joints (Carstanjen et al. 2010). Through-and-through lavage can be performed in standing, sedated horses with fair to even good results (Meijer et al. 2000). In horses with chronic or recurring septic arthritis, open drainage by arthrotomy is indicated (Schneider et al. 1992b). In most cases, multiple therapies are used simultaneously until clinical signs and synovial parameters have normalised (Schneider et al. 1992b; Morton 2005). In the present case, arthroscopic exploration and lavage was not enough to control the septic problem in the left joint. Subsequently, we repeated several through-and-through joint lavages until we achieved a significant reduction in the WBC count (10.35 9 109 cells/L) (Meijer et al. 2000). A possible explanation for the slow normalisation of synovial fluid total protein and nucleated cell count values in this case might have been the direct effects of the repeated through-and-through joint lavage in synovial fluid (Sanchez-Teran et al. 2016). Horses with marked pannus, osteochondral pathology or
osteomyelitis are less likely to survive. The main causes of failure include an inability to eliminate the causative agent and disruption of the destructive inflammatory cycle (Meijer et al. 2000; Morton 2005). However, with early intervention and implementation of an aggressive surgical approach, the prognosis for septic arthritis in the mature horse is fair to very good (Meijer et al. 2000; Morton 2005). Once the infection and synovitis have resolved, the horse should be subjected to 2– 4 months of stable confinement in combination with controlled exercise and physical therapy (Meijer et al. 2000; Morton 2005). Treatment of septic arthritis that is secondary to
haematogenous invasion of bacteria from another focus of infection appears to be more complex. In such cases, it is of paramount importance that remote sites of primary infection are treated in order to eliminate them as the source of pathogens in the joint (Meijer et al. 2000). Fortunately, such cases are rare in mature horses (Meijer et al. 2000). In one of those reported cases spread came from a ventral midline incision infection while in another case spread was from a previous soft tissue injury (Schneider et al. 1992a). We describe here an atypical case where a mature horse
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