Osteomyelitis and sepsis Flashcards

Question

Normal vs septic arthritis vs P or E septic arthritis - synovial fluid analysis

Answer 1

Normal - clear yellow & viscous - WBC: <0.5x10^9 cells/L - diff WBC: <50-60% - TP: <25g/L Septic arthritis - turbid yellow to orange - WBC: >20x10^9 cells/L - diff WBC: >85% neutrophils - TP: >30-50g/L Suggestive of type P or E septic arthritis - from slightly unclear to opaque - WBC: 2-15x10^9cells/L - diff WBC: 75-90% neutrophils - TP: >25g/L

Answer 2

- confirms a septic process and/or systemic sepsis - knowledge of the bacteria involved - guides antimicrobial therapy

Answer 3

- standard biochem, haem and blood gas analysis further establish the degree of general systemic disease - in addition to the diagnosis of sepsis, blood work is critical in order to diagnose and monitor clinical or subclinical organ involvement, nutritional and immune status, and electrolyte and acid-base status - serum SAA can differentiate septic from non-septic joint processes in adults, so presumably is similar in foals - plasma fibrinogen concentrations higher than 9g/L have been suggested to be an indicator of physical or epiphyseal osteomyelitis in foals

Answer 4

- for S- and E-types, synovial effusion and joint distension will be the earliest findings, which can be identified on radiographs, US, CT or MRI - for P-type, early imaging findings include irregularity of the physical margin and/or widening of the physis that progresses to lysis of the metaphyseal and epiphyseal trabecular bone - later, imaging findings include irregular regions of bone loss with a distribution depending on type and location - often the regions of bone loss will be surrounded by sclerosis and an irregular periosteal reaction will also likely appear if they're located superficially

Answer 5

- radiographic sensitivity for bone loss is relatively low, requiring a 30-50% reduction in bone density for it to be radiographically visible - the appearance of S-type lesions varies depending on severity, with joint swelling becoming detectable when effusion becomes moderate - E-type lesions in noncomplex joints can be detected along the chondral surface and appear as poorly defined or irregularly shaped regions of lysis that may, or may not, communicate with the articular surface of the subchondral bone - for complex joints, alternative radiographic projections, including flexed and skyline views, may be required to better assess the articular margins - P-type pathology has a similar appearance to E- type with irregular regions of lysis, but they communicate with the physeal margin instead of the articular margin - P-type lesions can be associated with abscessation of the regional tissues, which radiographically can be visible as focal soft tissue swelling in the region of osseous change

Answer 6

- allows for assessment of the articular cartilage and can show early sites of erosion or cartilage loss -- this is especially true for the tarsocrural and femoropatellar joints, because of the ability to see a large portion of the articular margin - it can't identify lesions along the weightbearing surfaces of most bones, particularly the cuboidal bones of the carpus and tarsus - ultrasonographic appearance of S- and E-type SAPO typically includes synovial thickening and effusion with variable echogenicity of the synovial fluid -- this is particularly useful when effusions are in locations where they are more difficult to inspect and palpate -- the synovial surface may appear irregular and fibrillated -- depending on the location of osseous lesions, they can be visualised as irregularity of the bone surface and a change in the echogenicity of the overlying articular cartilage -- the articular cartilage can also have an altered thickness depending on the stage of the disease process - P-type lesions are difficult to identify on ultrasound, though periphyseal abscessation can be imaged and typically appears as a thick-walled structure with echogenic fluid centrally. - note that an irregular physeal margin is not always associated with SAPO -- consequently, any ultrasonographic changes must be interpreted with caution and correlated with the overall clinical picture - particularly in less accessible joints, ultrasound guidance can be helpful for aspiration of SF, but for most joints, synoviocentesis is straightforward and ultrasound guidance unnecessary - the use of intraoperative ultrasound guidance is largely beneficial for direction of surgical instruments to the affected portion of the physis, thereby limiting damage to unaffected regions

Answer 7

- gold standard for identifying changes associated with SAPO - S-type SAPO manifests as thickening of the synovial structures with increased volume of joint effusion -- if cartilage irregularities occur with disease progression, intra-articular contrast allows for clearer visualisation of cartilage changes as well as better definition of degree of thickening of the synovium - E-type lesions, the subchondral bone becomes irregular and lytic, with eventual progression to irregular regions of lysis of compact and trabecular subchondral bone -- sometimes, the lysis will expand within the trabecular bone leaving a shelf of compact bone along the joint margin -- this can lead to collapse of the subchondral compact bone and permanent irregularities of the articular margin - P-type SAPO changes include physeal lysis with irregularity and widening of the physeal margin, at times with formation of minor sequestra within the lytic area -- as the disease progresses, physeal abscesses can become visible as fluid-filled, thick-walled structures at the level of the physis

Answer 8

- fluid-specific sequences, such as short tau inversion recovery (STIR), can identify regions of bone remodelling/inflammation that may not be delineated on CT and thus could, in theory, identify regions of ‘active’ infection - however, subtle bone loss is poorly defined, particularly on low-field MRI - furthermore, MRI scan times are often longer (1- 2 h) and therefore might be considered suboptimal in systemically ill foals, particularly if the anaesthesia time is going to be prolonged further by surgery immediately following imaging

Answer 9

- in normal foals, the physes often have moderate radioisotope uptake, which may inhibit detection of disease (physitis) in these regions - additionally, NS has poor anatomical localisation, particularly in foals due to their small size - there are potentially also interpretational challenges based on the high variability in activity levels (recumbent vs. active ambulation) and growth rates of foals (bone growth can be minimal or stopped in sick foals and bone resorption may even occur, while healthy foals will have active bone growth) - furthermore, any foal undergoing nuclear scintigraphy will be radioactive following the procedure, which may further complicate handling and delay treatment, consequently rendering NS irrelevant for diagnosis of SAPO in foals for the time being

Answer 10

- radiography is the most common diagnostic imaging modality, but due to its poor sensitivity to minor changes in bone density, radiography might not be able to identify E- and P-type infections early in the course of disease - due to a much higher sensitivity for minor changes of bone density and lack of superimposition, CT or high-field MRI, when available, should in our opinion be considered the gold standard for diagnostic imaging of at least challenging SAPO cases

Answer 11

- removal of infectious material (bacteria, necrotic tissue, inflammatory cells) will allow the administered antimicrobials to be more effective as many antimicrobials have limited penetration into necrotic tissues and into cells, and some also have reduced action in purulent and acidic environments - the removal of infectious material can shorten the time needed to treat with antimicrobials and attenuate the ongoing inflammatory response, which is deleterious to the joint - in addition to reducing the time needed for the foal’s own macrophages to debride the infected area, the removal of infectious and inflammatory debris will also reduce the amount of inflammatory mediators and catabolic enzymes in the joint, and therefore speed up recovery and convalescence of the foal

Answer 12

- should be guided by the results of culture and sensitivity analysis - until these results are available, choice of systemic antimicrobial therapy should be based on empirical knowledge - as SAPO can be caused by Gram- positive and Gram-negative bacteria, and there is no reliable way to determine the infectious agent until culture results become available, it is safest to initially choose broad-spectrum antimicrobial coverage

Answer 13

Distribution in bone and synovial structures - most antimicrobials penetrate well into bone and joint tissues, exceeding the minimum inhibitory concentrations (MIC) values of common bone and joint pathogens - penicillin and metronidazole, however, have shown a lower than optimum penetration into bones - furthermore, the presence of conditions limiting blood flow to the joint, such as ischaemia, may affect the extent of diffusion into the tissues. Activity of the antimicrobial agent in a septic environment - in vitro sensitivity does not necessarily equal in vivo sensitivity - e.g. TMPS not work well in purulent material - e.g. acidic environments markedly decrease MIC values of macrolides and gentamicin Route of admin - several days of intramuscular injections are not ideal, and oral medication might not be possible or reliable in a foal with concurrent gastrointestinal tract infections - although it is a common belief that oral antimicrobials are inferior to intravenous antimicrobials, literature does not support this for bone and joint infections Potential toxicity - in foals, the main toxicity concerns include nephrotoxicity and arthropathy - the fluoroquinolone class has been associated with arthropathy, especially enrofloxacin - however, a recent study has failed to induce arthropathy following enrofloxacin administration in foals, and anecdotally clinicians have used marbofloxacin without development of musculoskeletal problems - nephrotoxicity is mainly caused by antimicrobials from the aminoglycoside class, but also oxytetracycline has been reported to cause nephrotoxicity in a foals - moreover, several other antimicrobials have been described to cause nephrotoxicity in humans, such as polymyxin B, sulfonamides, fluoroquinolones and some cephalosporins AMS - use of critical antimicrobials should be restricted to cases that demonstrate resistance to noncritical groups based on C&ST - correct dosage and timing intervals should be respected, and unnecessarily long treatments should be avoided

Answer 14

In cases of ‘S- type only’ infections, joint lavage with or without arthroscopic visualisation and debridement is generally sufficient and carries a good prognosis for short- and long-term survival. The most simple form of lavage is ‘through-and-through’ lavage, which should be performed with the foal sedated or lightly anaesthetised in recumbency - lavage can be further facilitated by predistending the joint with mepivacaine (post-sampling since mepivacaine has antimicrobial potency - large gauge needles (14-16 gauge) are preferable, and should be placed as far apart as possible to ensure lavage of the entire joint - ideally, the lavage fluid should flow from dorsal/cranial to palmar/plantar/caudal compartments to ensure flushing of the narrow regions of the joint between the two opposing articular surfaces - lavage is often performed with 0.5-2 L of isotonic, physiological crystalloid fluids under aseptic conditions - flexible extensions can be placed on the needle in order to avoid movement or potential withdrawal of the needle in case of unintended movement of the patient (or veterinarian) - at the end of the procedure, it is advisable to evacuate as much fluid as possible and to inject local antibiotics, analgesics and opioids followed by application of a sterile bandage - needle lavage has the obvious advantage of low cost, but due to the relatively small size of the needles, large conglomerates of pus, fibrin or other debris might not be removed from the joint. Arthroscopic lavage is considered gold standard - correctly placed portals on different sides of the joint will allow for thorough lavage and manual and/or motorised debridement of infectious and inflammatory debris - arthroscopic lavage allows for better evaluation of all accessible articular margins, providing information about prognosis and possible identification of additional infectious nidi to be debrided - arthroscopic visualisation will also allow for guided placement of intra- articular catheters for continuous delivery of antimicrobial agents Extensive motorised debridement of the synovial membrane is not advised, since the trauma created and subsequent bleeding may generate an environment favouring bacterial regrowth

Answer 15

Osteolysis and destruction of the physis are common sequela if E- and P-type infections are not detected and treated properly, which can often lead to deleterious consequences for the patient - in addition to joint lavage and systemic broad-spectrum antibiotics, E- and P-type infections require a more aggressive approach with debridement of lytic and infected bone and/or cartilage at the specific site of infection this can be performed with various methods depending on the type and location of the lesion - E-type lesions can be approached either directly from the joint cavity, if there is already lysis of the adjacent cartilage and subchondral bone, or from the physis without going through the articular cartilage - the latter can be facilitated by use of preoperative radiography or, preferably, CT and intraoperative ultrasonography) - due to the potential damage to the articular cartilage, the necessity of, and approach to, debridement should be evaluated carefully - with P-type lesions, the affected region can be identified preoperatively with radiography or CT and further localised with intraoperative ultrasonography - when the specific affected region is identified, needles are placed in the physis, a stab incision is made through the skin, and the soft infectious and necrotic material is carefully debrided using small size curettes - the physis of a foal is relatively soft, and debridement should only include the infected, inflamed and necrotic tissue which is softer and more grey than normal physeal tissue - after debridement, the curetted area is flushed, the skin is closed for primary healing with a monofilament nonabsorbable suture material in a simple interrupted pattern, and a sterile bandage is applied - some vet prefer placement of dialkylcarbamoyl chloride- coated dressings (DACC dressings/Sorbact") as a primary layer followed by an absorbent secondary layer - DACC dressings form a bacterial binding barrier between the surgical portal and the bandage, decreasing the likelihood of recontamination and have shown to be particularly useful in the prevention of surgical site infections in humans - placement of antimicrobial beads or a small subcutaneous catheter to allow for repeated antimicrobial injections can be considered

Answer 16

Foals with SAPO show various degrees of lameness, stiffness and depression due to pain, fever and inflammation, therefore all foals with SAPO should receive systemic treatment with NSAIDs for their analgesic and anti-inflammatory properties - admittedly, successful treatment of the infection should lead to reduced pain, lameness and fever; however, until this effect is fully accomplished, administration of NSAIDs ensures that the foal is comfortable, allowing ambulation and nursing, thus avoiding a negative energy balance and a catabolic state - in very young foals of 0- 1 days old, maintaining normal nursing activity is needed to support passive transfer of immunity - considering the higher risk of side effects of NSAIDs (nephro- and GI toxicity) in compromised neonates NSAID treatment dose and duration should be judicious and renal function should be monitored carefully with prolonged treatment - furthermore, COX-selective drugs, such as meloxicam, should be used - healthy foals tolerate meloxicam well, and in contrast to findings for other NSAIDs, foals appeared more resilient to the renal and gastrointestinal adverse effects of this drug at repeated dosing and high dosages than observed in adult horses - bute should not be used in foals due to the increased risk of side effects - morphine can be administrated intra-articularly together with local antimicrobials at the end of any joint lavage or sampling - LA can also be administered at the end of an arthroscopic procedure -- Mepivacaine is the drug of choice, since lidocaine and bupivacaine are more likely to cause articular cartilage damage -- LA also have some antimicrobial effects - no studies have evaluated potential negative effects of combining gentamicin or amikacin with morphine and mepivacaine - in human medicine, it is common practice to use corticosteroid treatment for septic arthritis -- currently no data for this use in SAPO in foals

Answer 17

In addition to antimicrobial and analgesic treatments, foals with SAPO require monitoring for nutritional and immune status - FPT is common in foals with SAPO, and reduced milk intake, inadequate levels of immunoglobulins or increased usage of immunoglobulins due to infection can place them at risk for developing additional or more severe disease and delay recovery - measuring IgG concentrations is therefore warranted - increased recumbency can easily cause decubital ulcers, and increased recumbency times and reduced ambulation or reduced use of a single limb can lead to muscle atrophy, or laxity or contraction in tendons -- this may ultimately compromise musculoskeletal function and development - thick and clean bedding and close monitoring of the skin is therefore warranted -- however, too thick bedding, especially with straw, can unwillingly complicate and restrict the foals’ movements in the stall - it is worth noting that systemic compromise can increase the risks of complications and death during GA for surgical lavage options and treatment may need to be delayed until the foal is stable (cardiovascular and respiratory) -- therefore, a modified treatment plan may be necessary including less ideal treatment plans in the initial phase (e.g. initial needle lavage under short sedation, or only antimicrobial treatment without lavage), followed at a later stage by more thorough arthroscopic treatments

Answer 18

Careful and close clinical assessment (vital parameters, lameness, swelling) remains key to evaluation of the treatment progress. Although the infection may have subsided, residual lameness can still be present due to unhealed damage to joint surfaces, physis and/or other soft tissue trauma instituted by the disease itself or as sequelae to the treatments. However, the contrary is also valid, and even with unresolved infection, overt lameness may still be absent. Also, some foals that have experienced pain in the affected limb will avoid proper use for some time after resolution until they unlearn this behaviour. Use of serial synovial fluid (SF) analysis has been suggested to evaluate local response to treatment. Synovial total protein and neutrophil percentage may not be good indicators for detecting eradication of bacterial infection as they remained elevated on average 10 days after eradication of infection caused by E. coli from infected and subsequently treated joints in adult horses. Synovial SAA concentrations have shown promise in monitoring response to lavage in adult horses. Synoviocentesis itself, however, increases the risk of recontamination of the joint, and careful consideration should be taken to avoid iatrogenic sepsis in treated cases. On a systemic level, accurate follow-up of WBC count, fibrinogen and SAA concentrations in blood in comparison with earlier concentrations can be used to monitor resolution of infectious and inflammatory processes. There is currently no literature in foals with SAPO, but serial measurements of plasma SAA were found to be a valid tool for monitoring treatment response in otherwise healthy horses presented with injuries penetrating synovial structures, thus avoiding the risk associated with serial synoviocentesis. Even though scientific data are lacking on SAA in foals with SAPO, it is the authors’ clinical experience and impression that serial evaluation of blood SAA concentrations are helpful in monitoring treatment progress and disease development, including spread of infectious foci to other parts of the body in SAPO foals. Follow-up imaging is typically not indicated in foals that are improving clinically. However, repeat radiographs or CT are certainly indicated in patients that suffer from persistent clinical signs (lameness, joint effusion or fever) and a continued elevated SAA concentrations despite treatment. Repeat imaging may help to identify progression of previously identified lesions or identify new lesions (e.g. development of osteomyelitis in foals previously diagnosed with septic arthritis; an E- or P-type lesion could have been mistaken for an S-type lesion). Interpretation of follow-up images should be correlated with any surgical debridement that has been performed, keeping in mind that regions of surgical debridement should have well-defined, smoothly marginated borders and that regions of poorly defined lysis are indicative of new or ongoing infection.

Answer 19

Studies have reported short-term survival of foals with SAPO between 42 and 84%. Of those foals, long-term survival has been reported to be up to 92%, and euthanasia after discharge was often unrelated to the SAPO diagnosis. Early initiation of treatment in foals with SAPO is positively correlated with survival. A study showed that after 24 h, the time to initiation of treatment after onset of clinical signs was not significantly different between survivors and nonsurvivors, suggesting that the first 24 h after onset of clinical signs is the critical time frame. Several other prognostic factors for lower survival in foals with SAPO have been identified including <30 days of age at time of diagnosis, critically ill foals and involvement of multiple bones or joints . Degenerated neutrophils or high SF neutrophil count were also negatively associated with short-term survival, while fibrinogen concentration was positively associated with survival in septic arthritis with a 25% increase of probability of survival to discharge for every 1 g/L increase in plasma fibrinogen concentration. Detection of intra-articular Gram-negative bacteria, mixed bacterial infection, or culture of Salmonella from SF are also negative prognostic factors. Sick foals with positive blood cultures (not specifically SAPO foals) have a better outcome when they are started with an empirical antimicrobial therapy that the isolates are sensitive to, highlighting the importance in knowing typical infection patterns in the local patient population. Moreover, adult horses with a positive bacterial culture from a septic synovitis have a poorer prognosis for survival to discharge from hospital and overall long-term return to function than horses that yielded no bacterial growth. It is unknown whether this is translatable to foals.

Answer 20

Depending on type and location, SAPO may lead to destruction of articular cartilage, thickening of the joint capsule, reduced range of motion, and may eventually lead to osteoarthritis, which will decrease the foal’s chance of a future athletic career. In P-type cases, damage to the physis may lead to uneven growth (varus or valgus deformities, impingement of the spinal cord, etc). T-type infections may lead to deformation of the cuboidal bones of the carpus or tarsus. These changes might lead to altered limb conformations which might not be compatible with future athletic performance. Overall, prognostic outcome for full athletic function following septic arthritis in foals has previously been described as guarded. However, a recent study evaluating athletic performance in horses treated for SAPO as foals reported an overall prognosis for entering athletic work to be 62%, comparable to results seen in adult horses treated for septic arthritis). The presence of multiple septic joints, but not multiple bone involvement, had an unfavourable prognosis for racing. In a sport horse population, only 28% of treated foals eventually performed as intended as adults. Those with synovial cell counts at admission exceeding 60,000 WBC/mm3 were significantly less likely to eventually perform .

Osteomyelitis and sepsis Flashcards

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