Equine LA Sx Flashcards
Arthrocentesis in septic arthritis/tenosynovitis: WBC count
- Increased WBC usually >30,000 cells/ µL
Arthrocentesis in septic arthritis/tenosynovitis: % of neutrophils
- > 80% PMN
Arthrocentesis in septic arthritis/tenosynovitis: Total protein
> 3 g/dL
Normal Arthrocentesis value TP
<2.5 g/dL
Normal Arthrocentesis value: WBC count
<300 cells/µL
Normal Arthrocentesis Cell composition
- Mononuclear cells
What three things do you need to do in all suspected cases of septic arthritis?
- ) Physical exam: clean the wound really well and explore it to see if it goes into the joint.
- ) Arthrocentesis and get a cell count/gram stain
- ) Distend the joint and pressurize it to see if it leaks out the wound (diagnostic), but make sure that you aren’t going through a really dirty layer
What is the most common bacteria associated with joint injections or surgery in septic arthritis?
- Staphylococcus
What is the most common bacteria associated with wounds in septic arthritis?
- Enterobacteriaeceae and anaerobes
- Often polymicrobial
What is the most common bacteria associated with foals in septic arthritis?
- Enterobacteriaeceae, followed by E. coli
Will you always get a positive culture from arthrocentesis?
- NO
Treatment for septic arthritis
- Broad spectrum antibiotics based on most likely organisms
- Joint lavage*** (Important to decrease numbers and contamination; also helps reduce inflammation by flushing out neutrophils and any inflammatory mediators)
How long should antibiotics continue post-infection with septic arthritis?
- 2-3 weeks
Hyaluronan post-infection treatment with septic arthritis
- Intra-articular or IV
- Can reduce inflammation and decrease likelihood of DJD
Survival rate of adults with septic arthritis
85%
Prognosis for return to racing in adults with septic arthritis
- 56% of standardbreds and thoroughbreds released returned to racing
Prognosis for survival in foals with septic arthritis
- 45-84% survival to discharge
- Depends on duration, comorbidities, and $$$$
Prognosis for performance in foals with septic arthritis?
- 48% of TB foals that survived raced
- 33% of TB and SB foals
Joint lavage techniques
- Through and through with needles
- Arthroscopy (gold standard; can see what you’re doing)
- Arthrotomy)
Joint lavage fluid type
- sterile balanced electrolyte solution
- LRS is preferred as saline can cause more inflammation
- NEVER add chlorhexidine or iodine (pro-inflammatory)
- No need to put antibiotics in the lavage solution
- DMSO he doesn’t use because it will get everywhere
Antibiotics for septic arthritis
- Very high local concentrations for > 24 hrs (can get a very high concentration)
- Irritating to the joint
- Careful about antibiotic resistance, but less risk due to local nature
Which antibiotic is most often used for joint infections?
- Amikacin
- Also gentamicin, ceftiofur, timentin, methicillin, impipenem-cilastatin
When is open drainage technique indicated?
- Cases of chronic septis or cases that don’t respond to lavage alone
Describe the open drainage technique for septic arthritis
- 3-5 cm arthrotomy
- Drain into a sterile bandage, which is changed aseptically 1-2x day
- When upper joints are involved cross tie to prevent contamination
Regional perfusion antibiotics advantage
- Maximizes tissue penetration of the antibiotic around the joint
- Antibiotic levels >55x MIC for gentamicin
- > MIC for 24 hours (MIC will stay the same, but they can get much higher than MIC)
- May require general anesthesia
Antibiotic efficacy - is is concentration dependent or time dependent?
- Concentration dependent
Technique for regional perfusion***
- Tourniquet placed above and in some cases below target site
- Abx injected into a vein distal to the site or into the medullary cavity
- 1 gm gentamicin diluted to 30-60 mL delivered slowly (20 min)
- Often need to be sedatedor need a twitch
Antibiotic impregnated PMMA - what are they?
- Bone cement beads
- Mix up and form a powder/liquid monomer
- Mix up and add antibiotics
- They do not dissolve; antibiotics will diffuse over time
Cautions of antibiotic impregnated PMMA
- Moving joint?
What is the MOA of Antibiotic impregnated PMMA
- Polymethylmethacrylate (PMMA)
- Powdered polymer + liquid monomer
- Elution of antibiotics (antibiotic release is based on diffusion concentration gradients)
- Water enters cracks and pores of cement
How long do surface abx release over?
- 24 hours
How long do antibiotics deeper in the beads release over?
- Lower level sustained release (>24 hrs)
What determines abx diffusion rate with antibiotic impregnated PMMA beads?
- Type of cement
- Antibiotic selection
- Antibiotic concentration
- Size/surface area of implants
- Environment
Antibiotic compatibility factors to consider
- Stable at body temp
- Water soluble
- Heat stable
- Bactericidal
- Low incidence of hypersensitivity reactions
Epiphyseal osteomyelitis definition
- part of the polyarthritis or polyosteomyelitis syndrome in young foals
What is more common: septic metaphysitis or epiphyseal osteomyelitis?
- Epiphyseal osteomyelitis
Pathophysiology of epiphyseal osteomyelitis?
- Pooling of blood in the venous sinusoid at the junction of the epiphyseal bone and cartilage is presumed to furnish conditions similar to those known to occur at the metaphysis
- Sluggish blood flow encourages bacteria to lodge and establish at this site
Diagnosis of epiphyseal osteomyelitis
- Accompanied by septic arthritis of the adjacent joint
- Arthrocentesis (most commonly gram neg)
- Radiographs (repeat in 7 days; not super sensitive in picking up bone infection)
What age of foals do you normally see epiphyseal osteomyelitis in?
- <2 months
Advantage of plain x-ray films
- Inexpensive
- readily available
Disadvantage of plain x-ray films
- 30-50% mineral loss to detect lysis
- Not very sensitive
What findings on x-ray suggest osteomyelitis?
- Deep soft tissue swelling
- Periosteal reaction
- Cortical irregularity
- Demineralization
Advantages of CT
- See changes earlier than plain films
- Esepcially good for areas difficult to image with plain films
- CT is better than x-ray in general
Findings suggestive of osteomyelitis
- Increased marrow density early
- Sclerosis, demineralization, periosteal reaction (chronic)
MRI advantages
- Better than plain films/CT
- More sensitive for bone marrow abnormalities (marrow signal abnormalities on MRI more sensitive than lytic changes on plain films)
- Direct few of intramedullary disorders
- Findings may precede bone scan findings with bone marrow abnormalities
- Multiple slices visualized
- Better soft tissue contrast
- better anatomic definition
Some consequences that can be seen with septic arthritis
- Angular limb deformities
Septic implants impact on prognosis for survival
- Significantly decreases prognosis
Septic implants impact on cost of treatment
- Significantly increases it
What % of implants and screws get infected?
- Approximately 50%
Etiology of infected implants
- Open fractures
- Contamination of the surgery site during open repair
- Contamination through surgical incision (traumatized soft tissue)
Clinical signs of infected implant
- Low grade persistent fever
- Decreased use of limb
- Inflammation or drainage from the incision site
Diagnosis of infected implant
- CBC
- Culture drainage
- Ultrasound
- Radiographs
Treatment of infected implant
- removal of implants needed most often
- Bacteria secrete a glycocalix (slime) that covers and protects them from antibiotics, antiseptics, antibodies, phagocytes, and mechanical removal
- You usually don’t have an opportunity to put in another implant
- They try to manage infection and give a bone callus time to form before taking out the implants
Treatment of infected implants
- Broad spectrum antibiotics until culture results guide selection
- Local abx with PMMA or regional perfusion
Prognosis of infected implants
- Guarded to poor
- Depends on fracture type, age of patient, and virulence of the organism
Dfdx for an acutely non-weight bearing limb that have to do with the foot
- Sole abscess (most often)
- Laminitis (most often >1 limb)
- Fracture (pretty uncommon)
In most lamenesses, where does the pain localize?
- The foot
Sole abscess clinical signs
- VERY sensitive to hoof testers
- Foot will be warm
- Increased digital pulses
- Often quite acute
- SEVERE lameness
How common are sole abscesses?
- VERY SENSITIVE
- Look at the bottom of the foot
What is the definition of a foot abscess AKA sole abscess AKA hoof abscess?
- Accumulation of fluid between the sensitive and insensitive laminae
- Pressure is what will cause the pain
Etiology of sole abscess
- Often unknown
- Sole bruise (hemorrhage between sensitive and insensitive laminae that traps bacteria)
- Penetrating injury
- Farrier will often get blamed for this (if you’re pounding a nail, must stay in the insensitive tissues)
- Most of the time goes from bottom up
Diagnosis of sole abscess
- Based on clinical signs
- Sometimes nerve blocks needed or useful
- Radiographs often not needed initially
- ID of abscess tract
- Hoof testers are helpful (help you localize is, and then you can look for a little black tract)
When to do a radiograph with diagnosing foot lameness?
- If you’re unable to localize it
- If you have a recurrent abscess especially to make sure there isn’t osteomyelitis
- Will most often see a gas pocket
Treatment of a sole abscess
- DRAINAGE
- Important to do enough but not too much
- Follow the tract to its completion, e.g. the pus, blood, or end of the tract
- If you can’t get exposure, pack with a poultice to soak the foot and let it break out on its own
- Soaking with warm water, magnesium sulfate
- Poultice (epsom salts; Mag sulfate)
- Treatment plate (needed with extensive sole resection/undermining of sole, frog)
- Flush tract with iodine or pack small amount of iodine soaked gauze to prevent contamination
- +/- soak clean foot 1-2x daily for 2 days
- Check tetanus status
- anti-inflammatory drugs
What can happen if you make too big of a hole for a sole abscess?
- Don’t want to expose too much solar corium which will prolapse and be a source of pain
- Dig around the perimeter of the white line
- Funnel shaped hole
Are antibiotics typically needed for a foot abscess?
- No
- Not typically for an abscess
- Won’t allow it to break open if it hasn’t already
What is gravel?
- Ascending infection of the white line
- Not a migration of gravel from the white line
What are signs of gravel?
- Lameness, heat, pain, swelling, and drainage at the coronary band
Etiology of gravel?
- Ascending white line infection
- Usually associated with pre-existing pathology of the white line
Diagnosis of gravel
- Lameness, heat, pain, swelling, and drainage at the coronary band
- X-rays are warranted as they often have a keratoma or osteomyelitis
Treatment of gravel
- managed similar to a sole abscess
- Appropriate debridement of the hoof
- Radical hoof wall resection sometimes indicated
- Trying to establish ventral drainage
- He will sometimes do a nerve block and slide a canula down, then try to triangulate and dremel over
What is laminitis?
- Inflammation or edema of the sensitive lamellae –> breakdown and degeneration of the union between the horny and sensitive lamellae
- Pathological changes in hoof anatomy that result in crippling pain
Common sequelae of laminitis
- Rotation of P3
- Sinking of P3
Which legs (front or rear) are most likely to be affected by laminitis?
- Front leg
How common is laminitis?
- Approximately 15% of adult horses will develop it
What % of horses with laminitis develop a chronic debilitating disease that often leads to euthanasia?
- Approximately 75%
Seriousness of laminitis
- Second leading killer of horses after colic
What are the two parts of the lamellae that interdigitate?
- Epidermal lamellae (primary and secondary lamellae to increase the surface area)
- Dermal lamellae
Characteristics of epidermal lamellae -
Avascular and aneural
Characteristics of dermal lamellae
- Very vascular and very well innervated
Basement membrane of the lamellae
- Tough sheet of connective tissue at the interface of the lamellar epidermis and dermis
- Forms the receptor site for growth factors, cytokines, and adhesion molecules
What are the three phases of laminitis?
- Developmental phase
- Acute phase
- Chronic phase
Developmental phase of laminitis
- Precedes appearance of clinical signs
- 24-48 hours period during which laminar separation is triggered
- Often times not recognized
- Usually characterized by increased hoof wall temperature (increased blood flow?)
Example of case of horses that got into grain
- Tubed with mineral oil to knock down the absorption
- Acepromazine to increase circulation?
- NSAIDs to knock down inflammation
Acute phase of laminitis
- First signs of foot pain appear
- Lasts until clinical evidence of P3 displacement within the hoof capsule (rotation or sinking)
Chronic phase - when does it start?
- Begins with displacement of P3 and lasts indefinitely
- Clinical signs range from persistent, mild lameness to continued severe foot pain, to penetration of the sole of the hoof by the distal phalanx
When does the process initiating the destruction of the lamellar apparatus start relative to clinical signs?
- Before first clinical signs of laminitis appear
What are the three theories of laminitis?
- Vascular theory (due to vasoconstriction and ischemic necrosis)
- Enzymatic theory says that there are enzymatic changes in the basement membrane (want to slow down reaction with cold)
- Glucose theory (haven’t talked about)
Etiology of laminitis
- Biomechanical
- Ingestion of excess carbohydrate (grain overload)
- Grazing of lush pastures (ponies)
- Excess exercise and concussion in an unfit horse
- Endotoxemia
- Corticosteroids?
- Systemic disease (colic, pneumonia, colitis, enteritis, retained placenta)