Reprinted from www.antimicrobe.org

Septic Arthritis - Management

               Treatment comprises of three facets: appropriate antibiotic therapy to eradicate the infection, decompression of the joint with evacuation of infected and inflammatory exudate and restoration of stability and function of the joint.

Antimicrobial Agent Therapy

Septic arthritis is frequently a medical and surgical emergency. It is important to withhold antibiotics until operative cultures are obtained, especially if the clinical course is atypical or subacute. After obtaining appropriate cultures of blood and synovial fluid, empiric antibiotic therapy should be started immediately.

Gram stains are important to review. If positive, antibiotic therapy can be more readily targeted toward a specific pathogen. If negative, empiric therapy should almost always include therapy against S. aureus (Table 4). Age is an important consideration for coverage against H. influenza and N. gonorrhoeae (Table 1). The three variables of antimicrobial therapy are selection, route and duration of treatment (Tables 4-5).

Table 1  Microbiology of Bacterial Septic Arthritis Related to Age of Patient.

Organism	Children (6 mo. to 5 yrs.)	Young adult	Adult	Elderly
Staphylococcus aureus	10% - 20%	15% - 20%	60% - 70%	45% - 65%
Streptococci	5% - 10%	1% - 5%	15% - 20%	10% - 15%
Gram-negative bacteria	1% - 5%	Rare	10% - 15%	15% - 35%
Haemophilus influenzae	30% - 50%	1% - 5%	1% - 5%	Rare
Neisseria gonorrhoeae	1% - 5%	60% - 80%	1% - 5%	Rare

Adapted from Gorbach SL et al (Eds), Infectious Diseases, 2^nd Edition, 1998

 

 

Table 4.  Empiric Antibiotic Therapy of Suspected Septic Arthritis

Gram Stain of Synovial Fluid	Antibiotic Therapy
Gram-positive cocci      No risk factors for MRSA        MRSA risk factors or b-lactam allergy	Cefazolin 2 g IV q 8 h     Vancomycin 1 g IV q 12 h   Linezolid 600 mg PO/IV q 12 h   Daptomycin 6mg/kg IV q 24 h
Gram-negative cocci (presumptive Neisseria sp)	Ceftriaxone 1 g IV q 24 h
Gram-negative rods	Cefepime 2 g IV q 8 h or piperacillin/tazobactam 4.5 g IV q 6 h
No organisms on gram stain     Previously healthy, low MRSA risk       MRSA risks present	Cefazolin 2 g IV q 8 h     Vancomycin 1 g IV q 12 h plus cefepime, 2 g IV q 8 h or piperacillin – tazobactam 4.5 g IV q 6 h

MRSA = methicillin-resistant Staphylococcus aureus

 

 

Table 5.   Antibiotic Therapy for Specific Pathogens

Microorganism	Antimicrobial agent	Alternative	Duration
Streptococcus species	Penicillin or ampicillin	Clindamycin or first-generation cephalosporin Vancomycin	2 – 4 weeks or longer
Methicillin-sensitive Staph. aureus	Nafcillin or first-generation cephalosporin	Vancomycin, Quinupristin/Dalfopristin, Linezolid	3 – 4 weeks or longer
Methicillin-resistant Staph. aureus	Vancomycin	Daptomycin Quinupristin/Dalfopristin, Linezolid	3 – 4 weeks or longer
N. gonorrheae	Ceftriaxone	Fluoroquinolone	2 – 3 weeks or longer
Gram-negative bacilli other than Pseudomonas aeruginosa	Third-generation cephalosporins	Extended spectrum penicillin, Fluoroquinolone, TMP/Sulfa	3 – 4 weeks or longer
Pseudomonas aeruginosa	Pipercillin plus aminoglycoside	Cefepime plus aminoglycosides Ciprofloxacin, Levofloxacin	3 – 4 weeks or longer

Adjunctive Therapy

               Joint decompression may be accomplished by several methods and often debated between medical and surgical specialists. However, there are no randomized controlled studies comparing different forms of drainage. In the order of invasiveness, cost and effectiveness in the drainage procedure, the methods include needle aspiration, tidal irrigation, arthroscopy and arthrotomy as outlined in Table 6. If the joint is easily accessible and if the infected material be easily removed, patients may be treated at the bed side with repeated aspirations. Tidal irrigation can also be performed at the bed side and is reported as effective as arthroscopy. Arthroscopic lavage is being used increasingly in the management of septic arthritis including hips. Surgeons tend to prefer open drainage which allows rapid decompression, complete removal of accumulated debris including polymorphonuclear byproducts and bacterial toxins. In addition, this procedure allows for lysis of adhesions, removal of thick exudate, clot and fibrin. Arthrotomy is often recommended in cases where joint needs to be decompressed urgently. The role of synovectomy in acute septic arthritis is unclear. It is an essential part of persistent or chronic infection.

               Rehabilitation of the joint begins at the time of diagnosis. Initially the joint should be immobilized in a position of function. Active and passive range of motion should begin as soon as the acute symptoms subside or soon after the drains are removed and the drain-sites are sealed.

The Gram Stain

               The Gram stain is an empirical method of differentiating bacterial species into two large groups (Gram-positive and Gram-negative) based on the chemical and physical properties of their cell walls. The method is named after its inventor, the Danish scientist Hans Christian Joachim Gram (1853 – 1938), who formatted the technique in 1884.

               Gram-positive bacteria have a thick mesh-like cell wall made of peptidoglycan (50-90% of cell wall), which stain purple and Gram-negative bacteria have a thinner layer (10% of cell wall), which stain pink.

               Gram-negative bacteria also have an additional outer membrane which contains lipids, and is separated from the cell wall by the periplasmic space. There are four basic steps of the Gram stain, which include applying a primary stain crystal violet to a heat-fixed smear of a bacterial culture or specimen, followed by the addition of a mordant (Gram's iodine), rapid decolorization with alcohol or acetone and counterstaining with safranin. The Gram stain is the most common staining procedure in clinical microbiology. This tool can aid the physician in determining if infection is present, a possible etiology and a guide to choosing the appropriate antibiotic in just 15 minutes.

The Gram Positive Cell Wall

              The Gram positive cell wall The Gram positive cell wall is characterized by the presence of a very thick peptidoglycan layer, which is responsible for the retention of the crystal violet dyes during the Gram staining procedure. Imbedded in the Gram positive cell wall are polyalcohols called teichoic acids which are lipid-linked to form lipoteichoic acids. Because lipoteichoic acids are covalently linked to lipids within the cytoplasmic membrane they are responsible for linking the peptidoglycan to the cytoplasmic membrane. Teichoic acids give the Gram positive cell wall an overall negative charge due to the presence of phosphodiester bonds between teichoic acids monomers.

The Gram Negative Cell Wall

              The Gram negative cell wall Unlike the Gram positive cell wall, the Gram negative cell wall contains a thin peptidoglycan layer adjacent to the cytoplasmic membrane, which is responsible for the cell wall's inability to retain the crystal violet stain upon decolorization with ethanol during Gram staining. In addition to the peptidoglycan layer, the Gram negative cell wall also contains an additional outer membrane composed by phospholipids and lipopolysaccharides.

Gram Staining Tips

By Jack D. Rihs

1. Slide preparation

               Purulent material should be selected whenever possible.

               Apply the sample evenly and thinly to the slide. Smears that are too thick will be difficult to decolorize and imposable to read.

               Do not cover the entire slide with the sample. This will make handling difficult and areas may be missed during decolorization. An area the size of a nickel usually is adequate.

2. Slide fixation

               The material must be fixed to the slide to prevent it from washing off during staining. This can be done by quickly passing the slide over a gentle flame (the slide should not become to hot to touch) or on a slide warmer. Overheating may alter cell morphology or cause organisms to decolorize more quickly.

               An alternative and superior method of fixation is to flood the slide with methanol for 1 minute. Methanol fixation prevents liquid specimens from washing off the slide better than heat fixing, preserves blood cell morphology and results in a clearer background.

3. Staining

               Flood the entire slide when crystal violet, iodine and safranin are applied. This will ensure that all areas are stained evenly.

4. Decolorization

               The critical step of the Gram staining procedure is the decolorization step. Hold the slide in a tilted downward position and allow the decolorizer to flow over the smear. Be careful not to miss any portion of the smear. Usually a few seconds will suffice.

               95% ethanol will decolorize slower than acetone/alcohol, than does acetone.

5. Reading the Gram stain

               Begin reviewing the slide using the 10x objective. This will allow you to focus quickly and to look for areas of purulence. The 100x oil immersion lens is essential for viewing individual bacteria.

               When reviewing a Gram stain, look at many microscopic fields and in different areas of the slide.

               The presence of many squamous epithelial cells in the smear usually indicates a poorly collected sample that will contain normal flora, whereas, the presence of polymorphonuclear leukocytes and no squamous epithelial cells indicates a good sample and an inflammatory process.

               Some specimens on preparation will have areas on the slide that are thicker than others. This can result in areas that are under decolorized, thus organisms that are truly Gram-negative will appear Gram-positive. Microscopic fields that contain crystal violet precipitant, or PMNs, macrophages or epithelial cells that are staining purple are areas that are under decolorized.

               Gram positive bacteria will usually stand out easily against the pinkish background. Gram negative organisms because of their lower contrast can be missed, particularly in thicker smears. Haemophilus, Bacteroides and Fusobacterium are Gram-negative bacteria that are often overlooked due to their size, pleomorphic morphology or faintly staining qualities.