Septic Arthritis, Periprosthetic Joint Infection, Spinal Osteomyelitis

Septic Arthritis of Native Joints

Routes: hematogenous seeding (80%), direct inoculation, contiguous spread
Acute: S. aureus, streptococci, enterococci, gram-negatives, Neisseria, Candida
Subacute/chronic: CoNS, C. acnes, Lyme, Syphilis, TB, NTM, Brucella, Whipple’s, Blasto, Crypto
Risk factors: pre-existing joint disease, IVDU, immunosuppression, joint instrumentation, dental infection
DDx: gout, reactive arthritis

Pain, swelling, warmth, restricted ROM, fever; signs may be subtle in subacute/chronic arthritis
Knee most common; axial joints (sternoclavicular, sacroiliac) suggest IVDU, polyarticular suggests hematogenous dissemination (endocarditis)

X-rays (ortho will require them to ensure no fracture/trauma), make NPO and hold AC should they need to be urgently brought to OR, URGENT ortho consult specifically for needle aspiration
Arthrocentesis (before abx): Gram stain, Cx, cell count/differential, crystals
- WBC >50,000 (PMN-predominant) strongly suggests septic arthritis
BCxs, ESR/CRP, TTE if c/f endocarditis, Lyme serologies if tick exposure or travel to northeast, endemic areas

Empiric Abx: Vanc + CTX (Cefe if high PsA risk) AND drainage with Ortho AND ID consult
Abx by organism:
- MSSA: nafcillin/cefazolin (3–6 weeks)
- MRSA: vancomycin (3–6 weeks)
- GNR: cefepime/pip-tazo (3–4 weeks)
- Gonococcal: CTX (1-2 weeks)
Early stepdown to orals should be considered

Biofilm formation on implant means refractory to abx, needs surgery
Routes: perioperative inoculation (most common), hematogenous seeding, contiguous spread
CoNS > S. aureus > Streptococcus > Enterococcus > Cutibacterium > GNRs

Joint pain, erythema, swelling, warmth, +/- fever, sinus tract, prosthetic loosening

X-rays (ortho will require them to ensure no fracture/trauma), make NPO and hold AC should they need to be urgently brought to OR, URGENT ortho consult specifically for needle aspiration
ESR, CRP, +/- BCxs
Arthrocentesis: cell count/differential, aerobic/anaerobic/mycobacterial/fungal Cxs
Intraoperative: tissue cultures, histopath; sonication of explanted prosthesis if possible

ID consult and ortho consult early
Surgical Options: DAIR (“debridement and implant retention”: for acute symptoms and stable prosthesis), 1-stage exchange, 2-stage exchange, resection arthroplasty, amputation (last resort)
Antimicrobials (hold abx if HDS):
- Empiric: after cultures if stable, Vanc + CTX
- MSSA: nafcillin/cefazolin + rifampin × 2–6W IV → rifampin + Cefadroxil × 3-6M
- MRSA: Vanc + rifampin (consider orals after >2W IV)
- GNR: CTX → orals (per sensitivities)
- E faecalis: Amp
- E faecium: dapto vs linezolid

Hematogenous seeding of avascular disc space vs inoculation from instrumentation
- Hematogenous organisms: S. aureus, GNRs, strep, enterococci, Candida
- Inoculation organisms: S. aureus, CoNS, Strep, Candida
- Subacute organisms (highly endemic, requires appropriate exposure): Brucella, TB/Potts, Histo, Cocci, Blasto, Aspergillus
Risk factors: IVDU, HD, immunosuppression, DM, indwelling catheters, hardware

Back/neck pain, fever, elevated ESR/CRP +/- neuro deficits from cord injury; if recent back surgery may see wound dehiscence or
Neurologic deficits (LE weakness or anesthesia, bowel/bladder incontinence) are surgical emergency, call ACUTE CORD (equivalent of stroke code, gets spine surgery to bedside STAT and immediate MRI to eval for cord compression)

Early ID and Spine Consult
- Surgery for neurologic deficits, spinal instability, progressive deformity, persistent bacteremia
Empiric Abx: Vanc + CTX
Organism-directed Abx (~6W, may vary based on organism, hardware):

Organism	First-line	Alternative
MSSA	Cefazolin	Nafcillin, Vanc, dapto, linezolid
MRSA	Vanc	Dapto, linezolid
Streptococci	PCN G or CTX	Vanc
Enterococci	Amp Susceptible: Ampicillin	Vanc, dapto, linezolid
	Amp Resistant: Vanc	Dapto, Linezolid
Enterobacteriaceae	CTX, Cefe, Carbapenem (per sensis)	Per sensis
PsA	Cefe	FQ, Aztreonam, Carbapenem
Salmonella	Cipro	CTX
Brucella	Doxy + rifampin ×3M	Doxy + streptomycin ×3M