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Septic Arthritis

Bone & Joint

Source: IDMP View on spectrum chart →
Patient + scenario modifiers
Patient
Clinical scenario / source

Annotations only — chart still shows the full chemistry of each drug.

1. Clinical Syndrome

Acute infection of a native joint, classically presenting as acute monoarticular pain, swelling, warmth, and restricted range of motion. Knee involved in ~50%, followed by hip, shoulder, ankle, wrist.

Subtypes:

  • Non-gonococcal native joint — S. aureus dominates (~50%); streptococci + GNR fill in. Hematogenous seeding most common; older / immunocompromised / IVDU / RA on biologics highest risk.
  • Disseminated gonococcal infection (DGI) / GC arthritis — young, sexually active, often with tenosynovitis + dermatitis. Knee, wrist, hand most common.
  • Prosthetic joint infection (PJI) — separate workflow; CoNS + S. aureus dominate; biofilm-mediated; surgical management critical. Briefly summarized in directed-therapy block.

Excludes: crystal arthropathy (gout/pseudogout — can coexist), reactive arthritis (sterile, post-infectious), Lyme arthritis (oligo/poly-articular, distinct workflow), TB / fungal joint infection (chronic, separate workup).

2. Pathogens

Consider the patient: Age + sexual activity (DGI vs S. aureus dominant), immunocompromise (broaden to GNR + fungi), IVDU (S. aureus, Pseudomonas, polymicrobial), prosthetic joint (CoNS + S. aureus + Cutibacterium acnes for shoulder), recent procedure / steroid injection (S. aureus, MRSA).

Consider the case: Mono vs poly-articular (poly → DGI, viral, reactive). Risk factors for MRSA (healthcare exposure, prior MRSA, severe disease) drive empiric vanc inclusion. Tenosynovitis + pustular rash + young patient = DGI until proven otherwise.

Common

Less common

3. Empiric Therapy

TierFirst choiceAlternativesDurationComments
Admitted to ward
  • load + AUC-guided · — · IV · Empiric MRSA coverage
  • 2 g · q24h · IV · Empiric GNR + strep + GC coverage
  • Vanc + cefepime — · — · IV

    Use cefepime instead of CTX if Pseudomonas risk (IVDU, immunocompromised, healthcare-associated).

2 weeks IV minimum (uncomplicated S. aureus); 3–4 weeks total. Step down to oral when stable + susceptibilities known.**Adult, non-prosthetic, no recent surgery.** Vanc covers MRSA + CoNS. CTX covers MSSA, strep, GC, most enteric GNR. Joint must be **aspirated and drained** — antibiotics alone fail. Repeat arthrocentesis often required for serial drainage.
Outpatient
  • 1 g · q24h · IM/IV · Until 24–48 h after symptom resolution, then PO transition
  • 100 mg · PO BID · PO · 7 days for chlamydia co-treatment

    Add for empiric chlamydia coverage in DGI until NAAT excludes.

  • 1 g · PO × 1 · PO

    Single-dose alternative for chlamydia if doxy contraindicated. Not for GC monotherapy.

CTX × 7 days IV/IM, then PO cefixime to complete 7–14 days total**Disseminated gonococcal infection (DGI) / GC arthritis** — young, sexually active patient with tenosynovitis + dermatitis + monoarticular arthritis. Joint drainage may still be needed. Test/treat partners. HIV + syphilis testing mandatory.
ICU — Pseudomonas risk
  • load + AUC-guided · — · IV
  • 2 g · q8h · IV
  • 1 g · q8h · IV

    ESBL risk or healthcare-associated severe disease.

2–4 weeks IV (longer if bacteremic). Tailor to cultures + clinical course.**Sepsis / IVDU / immunocompromised / sternoclavicular or sacroiliac joint.** Covers MRSA + Pseudomonas + Enterobacterales. Surgical evaluation urgent.

Add coverage if:

MRSA coverage
  • Known MRSA colonization
  • Recent healthcare exposure
  • Severe disease / sepsis
  • IVDU

Add:

  • load + AUC-guided · — · IV
Pseudomonas coverage
  • IVDU
  • Penetrating injury through shoe
  • Immunocompromised
  • Sternoclavicular / sacroiliac joint

Add:

  • 2 g · q8h · IV

    Or pip-tazo / meropenem.

Gonococcus coverage
  • Young, sexually active
  • Tenosynovitis + dermatitis
  • Polyarthralgia evolving to monoarticular

Add:

  • 1 g · q24h · IV/IM
  • 100 mg · PO BID · PO · 7 days

    Empiric chlamydia co-treatment until NAAT excludes.

4. Directed Therapy

Joint drainage is the cornerstone — therapeutic arthrocentesis (often repeated daily until pus stops re-accumulating) or arthroscopic / open washout. Hip and shoulder usually need OR drainage.

Once organism + susceptibilities back:

  • MSSA: cefazolin 2 g IV q8h × 4 weeks (preferred over nafcillin — equivalent efficacy, better tolerated). PO step-down reasonable after 2 weeks.
  • MRSA: vancomycin AUC-guided × 4 weeks. Daptomycin 6 mg/kg or linezolid 600 mg q12h if vanc intolerance.
  • Streptococci: ceftriaxone or PCN-G × 2–4 weeks.
  • Gonococcus: CTX 1 g IV/IM daily × 7 days, then PO cefixime 400 mg BID to complete 7–14 days. Doxy 100 BID × 7 d empiric chlamydia.
  • Pseudomonas: anti-pseudomonal β-lactam (cefepime / pip-tazo / meropenem) × 4–6 weeks. Source control critical.
  • Enterobacterales: ceftriaxone or FQ × 2–4 weeks based on susceptibility.

Prosthetic joint infection (PJI) — brief framework (separate IDSA workflow):

  • DAIR (Debridement, Antibiotics, Implant Retention) for acute (<3 wks post-op or <3 wks symptoms) + susceptible organism + well-fixed implant.
  • One- or two-stage exchange for chronic / loose / resistant infections.
  • Empiric: vancomycin + cefepime or pip-tazo. Add rifampin 300 mg PO BID for staphylococcal PJI with retained hardware (anti-biofilm).
  • Total course typically 4–6 weeks of IV/IV-equivalent, then chronic suppression in some cases.

5. Monitoring

Resolution: fever, pain, swelling, ROM. Serial synovial fluid analysis if pus continues — should clear by 1 week. WBC trend, ESR/CRP (slow normalization, weeks).

Imaging: MRI if no improvement at 5–7 days — adjacent osteomyelitis, abscess, septic joint complication. Repeat aspiration if effusion recurs.

Toxicity: vanc AUC + Cr q48h; cefepime mental status in AKI; rifampin (PJI use) → orange secretions, drug interactions, hepatotoxicity.

Pearls

Aspirate before antibiotics — synovial fluid Gram stain, culture, cell count (typically >50K WBC, >75% PMN). S. aureus > 50% of non-gonococcal cases. Cefazolin = nafcillin for MSSA bone/joint infection — equivalent efficacy, better tolerated. DGI in a young patient with tenosynovitis + pustular rash — don't miss. NAAT > culture for GC. Sternoclavicular / sacroiliac joints in IVDU → think Pseudomonas. PJI is its own beast — early ID + ortho consult, never start empirics until cultures are obtained.

References