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been shown to be more sensitive at detecting both osseous and soft tissue pathology of the infraspinatus bursa (Whitcomb et al. 2006).


Synoviocentesis


Synoviocentesis of the proximal limb is technically demanding, in particular the intertubercular and infraspinatus bursae. Radiographic and ultrasonographic guidance can help in guiding needle placement (Schumacher et al. 2007; Schneeweiss et al. 2012). A recent study by Cole et al. reported a modified technique for synoviocentesis of the intertubercular bursa, which may be of help to the reader. The technique reported using a spinal needle introduced through the bicipital tendon with the limb flexed so that the radius is parallel with the ground. This produces a potential space deep to the biceps tendon where synovial fluid collects allowing for more successful aspiration without the need for diagnostic imaging (Cole et al. 2014). O’Sullivan et al. (2015) found that abduction of the limb


during infraspinatus bursoscopy was helpful as it unloaded the infraspinatus tendon reducing its compressive force on the bursa. This technique in combination with ultrasonographic guidance may help in successful infraspinatus synoviocentesis. The laboratory results in the study by O’Sullivan et al. (2015)


are clearly indicative of marked synovial inflammation suggestive of infection. Normal synovial fluid has a low white blood cell count (<5 × 109 cells/l) with <10% neutrophils and low total protein (<25 g/l) (Steel 2008).


Synovial sepsis following haematogenous spread in a mature horse


The case report by O’Sullivan et al. (2015) in this month’s issue of EVE describes an unusual case of synovial sepsis raising interesting points on synovial infection in general and more specifically the implication of haematogenous spread of bacteria from a remote site in a mature horse. The authors make the valid point, that with no history of a penetrating wound, blunt trauma or intrasynovial medication, haematogenous spread would seem most likely despite occurring rarely in mature horses (Martens et al. 1986; Schneider et al. 1992). Haematogenous spread of infection to synovial structures more commonly affects foals (Firth 1983). Synovial sepsis following haematogenous spread more


commonly affects only one synovial structure (Firth 1983). The close anatomical location of the 2 affected synovial structures in the case reported by O’Sullivan et al. (2015) is interesting and suggestive of a predisposing factor. Although not clinically apparent in this case, local trauma with haemorrhage may in the presence of bacteraemia, have predisposed this horse to bacterial colonisation.


Bacteria spp. isolated


As the authors mention, it is unusual to isolate staphylococcal spp. from a synovial cavity following presumed haematogenous spread from a sub-solar abscess. Staphylococcal spp. (including intermedius) are commensal bacteria of the skin and mucosal surfaces of domestic animals. Antimicrobial resistance of


Staphylococus


intermedius is uncommon in the nonhospitalised equine population (Vengust et al. 2006). Due to the environment the equine foot finds itself in, coliformand anaerobic bacteria are a more likely cause of sub-solar abscessation. The most


common genera of bacteria isolated from primary septic synovial structures of mature horses according to one report were (in decreasing prevalence) Enterobacteriacaea, Streptococcus and Staphylococcus (Moore et al. 1992), while in a separate study staphylococcal spp. accounted for the majority (34%) of isolates (Taylor et al. 2010). The most common genera of bacteria isolated from a


septic synovial structure secondary to haematogenous spread are Gram-negative, while staphylococcal spp. infections are rare (Firth 1983). In contrast, staphylococcal spp. are the most frequently identified pathogen following iatrogenic sepsis (Lapointe et al. 1992).


Antimicrobial selection


Wherever possible, antimicrobial selection should be based on the results of bacterial culture and antimicrobial sensitivity. However, in the clinical setting, this is commonly not immediately available and a broad-spectrum antimicrobial regime should be selected. Following the results of culture and sensitivity, a case should be reviewed. If good clinical progress has been made despite laboratory results suggesting ineffectual antimicrobials, there is a strong argument to continue with the same antimicrobial regime. One must bear in mind that effectiveness of antimicrobials in vitro does not always mimic the in vivo environment. In addition, the in vitro setting does not routinely allow for the synergistic behaviour of combinations of antimicrobials (for example penicillin and gentamicin) to be assessed, emphasising the importance of monitoring clinical progress (Watanakunakorn 1971; Watanakunakorm and Glotzbecker 1974). In the case described by O’Sullivan et al. (2015), the


authors acted promptly on culture and sensitivity results in combination with a poor clinical response and changed systemic antimicrobials to intravenous enrofloxacin. It is unclear from the report whether other antimicrobials were also effective against the bacteria isolated. Enrofloxacin is from the fluroquinalone group of antimicrobials and is bactericidal, exhibiting concentration-dependent killing and may exhibit a prolonged in vivo post antimicrobial effect on certain bacteria (Giguere and Dowling 2013). One would question the selection of nondilute intrasynovial administration of enrofloxacin as it has been shown to be highly inflammatory to mucosal and synovial surfaces (Kelmer et al. 2012; Richardson and Ahern 2012). Less inflammatory drugs such as cefquinome or ceftiofur (both commonly effective against staphylococcal spp.) alone or in combination with an aminoglycoside may have been appropriate alternatives for intrasynovial medication post lavage. This case was successfully managed with surgical lavage


and debridement of fibrinocellular conglomerate (pannus). The latter considered critical in the successful management of chronic synovial sepsis. Failure to remove pannus from within a synovial structure will result in a nidus for bacteria to survive despite antimicrobial therapy (Wright et al. 2003; McIlwraith et al. 2014).


Conclusion


O’Sullivan et al. (2015) report an uncommon case of multicentric synovial sepsis following haematogenous spread from a sub-solar abscess. It is of concern that despite the horse presenting from the general population with no history of previous hospitalisation the bacteria species identified was


© 2015 EVJ Ltd


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