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Septic arthritis
1. Stick a needle in it
Diagnosis and management of septic arthritis
in the ED
Dr Sarah Dawson, May 2014
2. Why septic arthritis?
• Most dangerous and destructive monoarthritis
• Can destroy cartilage within days
• Mortality 7-15 % despite antibiotic use
3. Aims
• To list the main differentials for acute monoarthritis
• To understand the pathogenesis of septic arthritis
• To list the main organisms that cause septic arthritis
• To recognise the symptoms and signs of septic arthritis
• To understand the key risk factors for septic arthritis and
how this affects subsequent investigation
• To describe the anatomy and method for needle aspiration
• To describe empirical antibiotic therapy and approaches
for joint aspiration
8. Organisms
• Can be bacterial, fungal, mycobacterial or viral
• Bacterial divided into gonococcal and nongonococcal
• Gonococcal more common but less morbidity and mortality
• Staphylococcus
• Streptococcus
9. Risk Factors
• Age over 80 (LR 3.5, 95% CI 1.8-7.0)
• DM (LR 2.7, 95% CI 1.0-6.9)
• RA (LR 2.5, 95% CI 2.0-3.1)
• Recent joint surgery (LR 6.9, 95% CI 3.8-12.0)
• Hip or knee prosthesis (LR 3.1, 95% CI 2.0-4.9)
• Skin infection (LR 2.8, 95% CI 1.7-4.5)
• Skin infection + joint prosthesis (LR 15, 95% CI 8.1-28)
• HIV (LR 1.7, 95% CI 1.0-2.8)
• IV drug use
• Alcoholism
• IA steroid injection
10. Symptoms
• Pain in affected joint 85%
• Swelling in affected joint 78%
• Large joint (knee or hip 60%)
• Wrists and ankles also common
• Sweats 27%
• Rigors 19%
• May be subacute- especially TB and
prosthetic joints
• More than 1 joint affected in 22%
cases
• Underlying RA or overwhelming
sepsis
16. Initial Antibiotic choice
• Little evidence comparing different antibiotics
• No RCTs, based on likelihood of which organism
Patient group Antibiotic choice
No RF for atypicals Fluclox 2g qds +/- fusidic acid or gentamicin. If pen
allergic Clindamycin or 2nd/3rg gen cephalosporin
High risk gram –ve sepsis (elderly, frail,
recurrent UTI, recent abdominal surgery)
2nd or 3rd gen cephalosporin eg cefuroxime
MRSA risk Vancomycin plus 2nd or 3rd gen cephalosporin
Suspected gonococcus or meningococcus Ceftriaxone
IV drug users d/w micro
ITU patients d/w micro
17. Duration of therapy
• No controlled trials
• Usually IV abs at least 2 weeks in duration followed by at
least two weeks oral therapy
• May need longer for particular organisms- P. aeruginosa,
Enterobacter spp. or S. Aureus with septicaemia
18. Joint drainage
• Aim to remove pus from joint space- i.e. drain abscess
• Surgically- arthroscopy or arthrotomy
• Closed needle aspiration
• No randomised controlled studies comparing the two,
needle aspiration may be preferable
• If adequate aspiration not possible by needle, surgery
may be necessary
• May be indicated initially for hips, shoulders and
prosthetic joints
• Arthroscopy usually for knee shoulder and wrist- hips
may have arthrotomy
19. Outcomes
• The prognosis of bacterial arthritis has not improved
significantly in the last few decades
• Outcome related to:
• host factors- prior joint disease, old age
• Virulence of infecting organism
• Speed of initiating effective treatment
• Inflammation and destruction of joint may continue even
in sterile joints with effective antimicrobial therapy
• Mortality 10-15% dependent on co-morbidities
20. Summary
• Non gonococcal bacterial arthritis is a dangerous and destructive
form of acute arthritis
• Risk factors include pre-existing joint disease, joint replacement, old
age, immunosuppression and overlying infection or ulceration
• It usually presents as monoarthritis involving a large joint like the
knee
• Because symptoms such as fever may be absent and tests such as
FBC and CRP are non specific, joint aspiration is necessary to
establish the diagnosis- for cell count, microscopy and culture. BC
are also useful
• Staph and strep are the most common pathogens and are usually
treated with flucloxicillin, but older patients, ICU patients, IVDUs
may have gram-ves and given3rd gen cephalosporin
• Joint drainage- by needle aspiration or surgical means should also be
considered
21. References
• www.uptodate.com : Septic arthritis in adults
• Mary E. Margaretten, MD; Jeffrey Kohlwes, MD, MPH; Dan
Moore, PhD; Stephen Bent, MD “Does This Adult Patient Have
Septic Arthritis?” JAMA. 2007; 297(13):1478-1488
• C J Mathews, G Kingsley, M Field, A Jones, V C Weston, M
Phillips, D Walker, G Coakley “Management of septic arthritis: a
systematic review” Ann Rheum Dis 2007;66:440-445
Editor's Notes
Synovial tissue has no basement membrane, so bacteria in synovial membrane spread quickly to the synovial fluid
Neisseria Gonorhoea- gram –ve diplococci
Staph- gram + clusters- most common
Strep- gram +ve chains inc strep pneumoniae
Also meningococcus, gram –ves
Gram –ve- tauma, IVDU, neonates, elderly, underlying immunosuppresion
? Sending synovial fluid in BC bottles may increase yield
Incidence of septic arthritis increases with increasing synovial fluid wcc
May also have low glucose and raised lactate but not of diagnostic utility
Arthrocentesis
INDICATIONS
Arthrocentesis is used to establish the cause of an acute monoarthritis or polyarthritis.
Nongonococcal bacterial arthritis is a “do-not-miss” diagnosis, since a delay in identification and treatment may lead to clinically significant joint destruction and even death.
Other infectious causes include disseminated gonococcal infections, tuberculosis, fungal infections, and Lyme disease.
Crystal arthropathies (gout and pseudogout), rheumatic disorders, osteoarthritis, trauma, and hemarthrosis may also lead to acute joint effusions.
Arthrocentesis is also used as a therapeutic procedure, to drain large effusions or hemarthroses, and to instill corticosteroids or local anesthetic.
CONTRAINDICATIONS
Cellulitis overlying the site of needle entry.
Suspected bacteremia is a relative contraindication to arthrocentesis; if septic arthritis is suspected, however, the procedure should be performed.
The safety of arthrocentesis has not been established for patients with coagulopathy or patients who are receiving anticoagulant medications, and the use of reversal agents or products (e.g., fresh-frozen plasma or platelet concentrates) should be considered on a case-by-case basis.
COMPLICATIONS
Arthrocentesis is a relatively benign procedure, and if properly performed, complications are rare. Potential complications include iatrogenic infection, localized trauma, pain, and reaccumulation of the effusion
PREPARATION
The knee may be tapped from either the medial or the lateral side.
The patient’s knee should be extended or flexed at an angle of 15 to 20 degrees.
The needle will enter the skin 1 cm medial (or lateral) to the superior third of the patella and is directed toward the intracondylar notch.
JOINT ASPIRATION
Explain the procedure to the patient, obtain written informed consent, and then gather the equipment you will need.
Position the patient supine on a stretcher, with his or her knee extended or slightly flexed.
Identify the landmarks and demarcate the entry site with a skin-marking pen, or use another appropriate method.
Prepare the skin with a cleansing agent such as povidone–iodine or chlorhexidine. You may place a sterile drape around the site.
Begin to anesthetize the region by placing a wheal of lidocaine in the epidermis, using a small (25-gauge) needle, and then anesthetize the deeper tissues in the anticipated trajectory of the arthrocentesis needle. Intermittently pull back on the plunger during the injection of the anesthetic to exclude intravascular placement.
Using an 18-gauge needle and large syringe, direct the needle behind the patella and toward the intracondylar notch. Resist the temptation to “walk” the needle along the inferior surface of the patella, since this practice may damage the delicate articular cartilage.
Constantly pull back on the plunger while you advance the needle; you will know when the needle enters the synovial cavity, because fluid will enter the syringe.
You should remove as much fluid as possible. “Milking” the effusion, by gently compressing the suprapatellar region with the opposite hand, may aid in this endeavor. In cases of large effusions, you may need a second syringe to complete the aspiration.
Once the aspiration is completed, remove the needle, cleanse the skin, and apply a bandage. You may apply a woven elastic bandage or knee immobilizer to reduce post procedural swelling and discomfort.
TROUBLESHOOTING
Failure to aspirate synovial fluid results in a “dry tap.” Misdiagnosis of knee effusion, obesity, obstruction of the needle lumen by particulate matter or a plica, or hypertrophy of the synovium (owing to chronic inflammation) may all result in a dry tap. If the medial approach was used initially, a lateral approach should be attempted, since this may overcome difficulties presented by a medial plica or thick medial fat pad.
SYNOVIAL-FLUID ANALYSIS
Collected fluid should immediately be placed into appropriate containers and analyzed expediently. Check with the laboratory regarding specific submission procedures (e.g., the correct tubes and the volume of fluid required for each test). If only minute volumes of synovial fluid are obtained, discussions with laboratory personnel are indicated to prioritize testing. As little as one drop of fluid may be sufficient for crystal analysis, and 1 ml may suffice for a cell count and a differential count.
Gram’s Staining and Culture
Gram’s staining and culture of synovial fluid provide the most definitive evidence of septic arthritis. The sensitivity of these techniques is much higher for nongonococcal infections (50 to 75 percent for Gram’s staining and 75 to 95 percent for culture) than for disseminated gonococcal disease (less than 10 percent and 10 to 50 percent, respectively.) If gonococcus is suspected, cultures of the blood and of urethral, rectal, or oropharyngeal swabs should be considered. To minimize the risk of contamination, the synovial fluid is often submitted for testing in the syringe used for the arthrocentesis.
Cell Count and Differential Count
The cell count and differential count are used to differentiate between non inflammatory effusions (e.g., osteoarthritis and trauma) and inflammatory conditions (e.g., septic and crystal-induced arthritis). A cutoff of 2000 white cells per milliliter and 75 percent polymorphonuclear cells is generally used. It should be emphasized that the cell count and differential count cannot reliably differentiate among various inflammatory entities. For example, up to 33 percent of patients with septic arthritis may have white-cell counts below 50,000 per milliliter, and patients with acute gouty arthritis may have counts exceeding 100,000 per milliliter. Synovial fluid is usually submitted for cell and differential counts in specimen tubes treated with EDTA.
Crystal Analysis
Evaluation of synovial fluid under a polarizing-light microscope may reveal the presence of monosodium urate crystals (seen in gout) or calcium pyrophosphate dihydrate crystals (seen in pseudogout). The sensitivity of crystal analysis is relatively high (80 to 95 percent for gout and 65 to 80 percent for pseudogout). It should be noted that the presence of crystals does not exclude the possibility of septic arthritis, since the two conditions may coexist. Synovial fluid is usually submitted for crystal analysis in a lithium heparin–treated specimen tube.
Other Tests
Although often ordered, biochemical assays such as for glucose, protein, and lactate dehydrogenase have little discriminatory value and should not be included in routine synovial-fluid analysis. Other tests, such as specific stains and cultures for atypical infectious agents and cytologic evaluation for suspected malignant effusions, may be indicated in certain situations.
Adequacy of aspiration assessed by clinical criteria- improving temp, wcc, joint swelling and pain
S aureus 46-50% have poor joint outcome vs strep pneumoniae- 90% have good joint outcome
Polyarticular septic arthritis due to S aureus, or in the presence of RA has particularly high mortality upto 50%