Septic arthritis

Septic (infectious) arthritis is a bacterial infection of the joint space. Contamination occurs either via the bloodstream, iatrogenically, or by local extension (e.g., penetrating trauma). Patients with damaged (e.g., patients with rheumatoid arthritis) or prosthetic joints have an increased risk. Patients usually present with an acutely swollen, painful joint, limited range of motion, and a fever. Suspected infectious arthritis requires prompt arthrocentesis for diagnosis. In addition to the immediate broad-spectrum antibiotic therapy, surgical drainage and debridement may be necessary to prevent cartilage destruction and sepsis.

• Mechanism of infection
  • Hematogenous spread (most common)
    • From a distant site (e.g., abscesses, wound infection, septicemia)
    • Disseminated infection (e.g., gonorrhea)
  • Direct contamination
    • Iatrogenic (e.g., joint injection, arthrocentesis , arthroscopy ) ^[1]
    • Trauma (e.g., open wounds around the joint, penetrating trauma)
  • Contiguous spread (e.g., septic bursitis, osteomyelitis)
• Risk factors
  • Prosthetic implant
  • Interventions (e.g., intra-articular injections)
  • Underlying joint disease, especially rheumatoid arthritis
  • Immunosuppressed state
  • Diabetes mellitus
  • Age > 80 years
  • Chronic skin infections
  • IV drug use
• Causative organisms
  • Staphylococcus aureus
    • Most common in adults and children > 2 years
    • Frequently found in patients with arthritis following invasive joint procedures ^[2]
  • Streptococci
  • N. gonorrhea
  • Gram-negative rods esp. E. coli and P. aeruginosa
  • S. epidermidis
  • H. influenzae
  • M. tuberculosis and atypical mycobacteria
  • B. burgdorferi (Lyme disease)

• Acute onset
• Classical triad of fever, joint pain, and restricted range of motion
• Arthritis
  • Usually monoarticular
  • Most commonly affected joints: knees (followed by hip, wrists, shoulders, and ankles)
  • Joints are swollen, red, warm, and painful.

Prosthetic joint infection ^[3][4]

• Etiology
  • Early onset (< 3 months of placement): most commonly S. aureus
  • Delayed onset (3–12 months of placement); : coagulase-negative staphylococci, particularly S. epidermidis
  • Late onset (> 12 months of placement): most commonly S. aureus
• Clinical features
  • Usually prolonged, low-grade course
  • Minimal swelling, with or without a sinus that drains pus
  • Can present acutely (see “Clinical features” above)
• Diagnostics
  • Conventional x-ray: loosening of the prosthesis, periosteal reactions
  • For other diagnostic tests, see “Diagnostics” below.
• Therapy
  • Removal of the prosthesis and administration of IV antibiotics for 6–8 weeks
  • Reimplantation of the prosthesis following antibiotic treatment

In order to avoid infection, strict sterile techniques should be ensured in any procedure that involves penetration of the joint space.

Bacterial coxitis (septic arthritis of the hip) ^[5]

• Description: a rare condition that requires urgent treatment to avoid destruction of the joint
• Etiology: S. aureus and group A streptococcus account for the majority of cases
• Clinical findings
  • Joint pain (may be referred to the groin or knee)
  • Patient's hip is often flexed and externally rotated (this decreases intraarticular pressure and alleviates pain)
  • See “Clinical features” above
• Diagnostics: For diagnostics and therapy, see respective sections below.

Bacterial coxitis is an orthopedic emergency!

Gonococcal arthritis

• Gonococcal arthritis is the most common form of arthritis in sexually active young adults.
• See “Purulent gonococcal arthritis” and “Arthritis-dermatitis syndrome.”

In a young, sexually active adult presenting with classic symptoms of septic arthritis, gonococcal infection must be ruled out.

Lyme disease

• See “Lyme arthritis.”

Approach

• If septic arthritis is suspected, arthrocentesis should be conducted for synovial fluid analysis.
• Definitive diagnosis requires detection of bacteria in the synovial fluid, therefore, synovial fluid obtained is to be sent for analysis (culture and gram staining).
• Imaging (e.g., x-ray, MRI) may be indicated to assess potential underlying diseases or differential diagnoses.

Modalities ^[6][7]

• Arthrocentesis: a diagnostic and/or therapeutic procedure in which synovial fluid from a joint is aspirated using a sterile needle to determine the etiology of joint effusions and/or to relieve pressure from a joint
  • Ultrasound-guided arthrocentesis: Definitive diagnosis requires detection of bacteria in the synovial fluid.
    • Indication: to conduct synovial fluid analysis, gram stain, and culture
    • Findings
      • ↑ WBC and dominance of polymorphonuclear (PMN) cells ^[6]
      • Cell count: > 50,000 WBC/μl (neutrophil predominant) points to septic arthritis (can be as low as > 10,000 in early disease).
      • Fluid can be yellowish-green and turbid
• Culture and gram staining
  • Synovial fluid culture and gram stain are positive in most patients with bacterial arthritis.
  • Blood culture: at least 2 sets of blood cultures to rule out a bacteremic origin
• Laboratory tests: ↑ CRP, ESR, and leukocyte count (nonspecific, but may be useful for monitoring response to treatment) ^[8]
• Imaging: to look for signs of underlying osteomyelitis and concurrent joint disease and rule out possible differential diagnoses (see “Differential diagnosis” below)
  • Ultrasound
    • Effusion, edema of the surrounding soft tissue
    • Possible empyema
  • X-ray
    • Unremarkable early in the course of septic arthritis
    • Osteolysis usually becomes visible after 2–3 weeks.
  • MRI or scintigraphy for early detection
    • MRI provides early evidence of infectious involvement of the surrounding soft tissue
    • Scintigraphy is used for detection or exclusion of polyarticular involvement

Suspected septic arthritis requires aspiration of synovial fluid for analysis.

Differential diagnosis based on synovial fluid analysis findings

• Synovial fluid analysis: comprises a group of tests that examine joint fluid (synovial fluid) to aid in definitively establishing specific types of arthritis.

• See “Differential diagnoses of inflammatory arthritis” in “Rheumatoid arthritis.”

Further differential diagnoses to consider

Viral arthritis

• Etiology: parvovirus B19, hepatitis B virus, hepatitis C virus, rubella virus, HIV
• Pathophysiology
  • Direct invasion of the virus (e.g., rubella, enteroviruses)
  • Immune complex formation (e.g., hepatitis B, hepatitis C, parvovirus)
• Clinical features
  • Symmetric involvement of multiple small joints
  • Sudden onset
  • Possibly accompanied by rash and fever
  • Usually no destruction of the joint
• Diagnostics
  • History and clinical findings are the mainstays of establishing a diagnosis
  • Serology: antibodies against the suspected virus
  • Synovial joint analysis
    • Very variable (can be normal or inflammatory)
    • Not routinely used since viral isolation is usually not successful
  • For other diagnostic tests, see “Diagnostics” above.
• Therapy
  • Supportive treatment only (usually self-limited)
  • See “Hepatitis B”, “Hepatitis C“, “Rubella“, and “Parvovirus B19-associated arthritis.“

Fungal arthritis ^[9]

• Etiology: Histoplasma species, Sporothrix schenckii, Blastomyces species, Coccidioides species
• Clinical features
  • Very variable with acute and chronic courses
  • Often with symptoms of disseminated infection (e.g., pulmonary symptoms)
• Diagnostics
  • Synovial fluid analysis may show normal, inflammatory, or septic findings
  • Synovial fluid culture
  • Possibly serologic studies: positive antibodies against the pathogen (e.g., in coccidioidal arthritis)

See “Overview of fungal infections” in the “General mycology.”

Other

• Legg-Calvé-Perthes disease in children

The differential diagnoses listed here are not exhaustive.

Initial management

Following arthrocentesis and culture, simultaneous empiric antibiotic therapy (based on gram stain) and evacuation of purulent material should be performed. ^[8]

• Empiric antibiotic regimens ^[8]
  • Gram-positive cocci: vancomycin
  • Gram-negative cocci: ceftriaxone
  • Gram-negative bacilli: 3^rd generation cephalosporin (e.g., ceftazidime), cefepime, piperacillin-tazobactam, OR carbapenem
  • Suspected pseudomonas infection (e.g., IV drug users): IV ceftazidime PLUS IV aminoglycoside (e.g., gentamicin)
  • No organism on gram stain but strong suspicion for bacterial septic arthritis: IV vancomycin PLUS either ceftazidime, cefepime, OR aminoglycoside
• Start serial drainage with lavage
• Sometimes debridement (arthroscopic or open approach) is necessary ^[8]

Further management

• Tailor antibiotics to gram stain, culture, and susceptibility results when available (see table below)
• Continue antibiotic therapy for at least ≥ 2 weeks ^[10][11]
• Continue serial drainage as needed
• Immobilization and NSAIDs for pain relief and to reduce inflammation
• Follow-up: Physiotherapy should be initiated early to prevent contracture of both the joint and its capsule.

Treatment of adults after culture has returned ^[8][12]

Treatment of children ^[11]

• ≤ 3 months of age: oxacillin PLUS gentamicin
  • If high risk of MRSA (i.e., prolonged ICU stay): replace oxacillin with vancomycin
• > 3 months of age: nafcillin PLUS cefazolin
  • If high risk of MRSA and signs of sepsis: replace nafcillin with vancomycin
  • If high risk of MRSA without signs of sepsis: replace nafcillin with clindamycin

• Joint destruction ^[13]
• Osteomyelitis
• Sepsis
• Children: growth arrest

We list the most important complications. The selection is not exhaustive.

1. Goldman L, Schafer AI. Goldman-Cecil Medicine, 25th Edition. Elsevier ; 2016
2. Chun KC, Kim KM, Chun CH. Infection following total knee arthroplasty.. Knee surgery & related research. 2013; 25 (3): p.93-9. doi: 10.5792/ksrr.2013.25.3.93 . | Open in Read by QxMD
3. Margaretten ME, Kohlwes J, Moore D, Bent S. Does this adult patient have septic arthritis?. JAMA. 2007; 297 (13): p.1478-1488.
4. Betts RF, Penn RL, Chapman SW. Reese and Betts' a Practical Approach to Infectious Diseases. Lippincott Williams & Wilkins ; 2003
5. Horowitz DL, Katzap E, Horowitz S, Barilla-LaBarca ML. Approach to Septic Arthritis. Am Fam Physician. 2011; 84 (6): p.653-660.
6. Mathews CJ, Kingsley G, Field M et al. Management of septic arthritis: a systematic review. Ann Rheum Dis. 2007; 66 (4): p.440-445. doi: 10.1136/ard.2006.058909 . | Open in Read by QxMD
7. Liu C, Bayer A, Cosgrove SE et al. Clinical Practice Guidelines by the Infectious Diseases Society of America for the Treatment of Methicillin-Resistant Staphylococcus Aureus Infections in Adults and Children. Clin Infect Dis. 2011; 52 (3): p.e18-55. doi: 10.1093/cid/ciq146 . | Open in Read by QxMD
8. Septic Arthritis/Infection Native Joints. https://www.infectiousdiseaseadvisor.com/infectious-diseases/septic-arthritisinfection-native-joints/article/609472/. Updated: January 1, 2018. Accessed: January 20, 2019.
9. Mabille C, El Samad Y, Joseph C, et al. Medical versus surgical treatment in native hip and knee septic arthritis. Med Mal Infect. 2020 . doi: 10.1016/j.medmal.2020.04.019 . | Open in Read by QxMD
10. Bennett JE, Dolin R, Blaser MJ. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. Elsevier Saunders ; 2015
11. Tande AJ, Patel R. Prosthetic joint infection. Clin Microbiol Rev. 2014; 27 (2): p.302-345. doi: 10.1128/CMR.00111-13 . | Open in Read by QxMD
12. Betts RF, Chapman SW, Penn RL. Reese and Betts' A Practical Approach to Infectious Diseases. Lippincott Williams & Wilkins ; 2002
13. Berry DJ, Lieberman J, Keeney J. Surgery of the Hip. Elsevier Saunders ; 2013