Eduovisual
Multisystem Processes & Disorders
Septic arthritis: diagnosis and management
— Incidence ~2–10/100,000/year; rises to 30–70/100,000 in patients with rheumatoid arthritis (RA) or prosthetic joints.
— Knee is involved in ~50% of native joint cases; hip more common in children; sternoclavicular/sacroiliac joints suggest IV drug use.
— Hematogenous seeding (most common in adults) > contiguous spread (cellulitis, osteomyelitis) > direct inoculation (injection, surgery, trauma, bite).
— Synovium is highly vascular and lacks a basement membrane, making it vulnerable to bloodstream pathogens.
— Acute (<2 weeks) monoarticular hot, swollen, painful joint with restricted active and passive ROM.
— Fever in only ~50%; absence of fever does not rule out septic arthritis.
— Underlying joint disease (RA, OA, gout, prior surgery) — pre-existing damage is the single strongest risk factor.
— Bacteremia source: endocarditis, UTI, pneumonia, skin/soft tissue infection, indwelling lines.
Step 3 management: Any acutely inflamed joint in an adult is septic until proven otherwise — the correct first move in both clinic and ED is urgent arthrocentesis before antibiotics, unless the patient is in septic shock requiring empiric coverage first.
Board pearl: A "flare" of gout or RA in a single joint with fever should still trigger tap — crystals and infection coexist in ~5% of cases.
— 1–2 week history of progressive monoarticular pain, warmth, swelling, and inability to bear weight or move the joint.
— Fever, rigors, malaise; in elderly or immunocompromised, may present only as confusion or failure to thrive.
— Young, sexually active adult; triad of migratory polyarthralgia, tenosynovitis (wrist/ankle/fingers), and pustular/vesicular skin lesions on extremities.
— May progress to true purulent monoarthritis of knee/wrist; ask about new partners, dysuria, urethral/vaginal discharge.
— RA patients, immunosuppressed, or those with overwhelming sepsis/endocarditis — S. aureus most common.
— Mortality up to 30% — a red flag for occult endocarditis; get blood cultures and TTE.
— Early (<3 months): virulent organisms (S. aureus, GNRs).
— Delayed (3–24 months): indolent — coagulase-negative staph, Cutibacterium acnes (shoulder).
— Late (>24 months): hematogenous seeding.
— Recent dental work, GU instrumentation, IV drug use, tick exposure (Lyme), unpasteurized dairy (Brucella), TB exposure, cat/dog bite (Pasteurella), rose thorn (Sporothrix), saltwater (Vibrio), freshwater (Aeromonas).
— Sexual history for gonococcus; travel history for endemic mycoses.
— Immunosuppressants, recent intra-articular injection (steroid, hyaluronate).
Key distinction: Migratory polyarthralgia + tenosynovitis + pustules = gonococcal; abrupt monoarticular knee with fever and no skin findings = non-gonococcal (S. aureus). These two phenotypes drive different empiric antibiotic choices.
Board pearl: Lyme arthritis presents as intermittent, large-joint (knee) effusion with surprisingly preserved function — a key contrast to true pyogenic septic arthritis.
— Erythema, swelling, joint held in position of maximal capsular volume (knee in slight flexion, hip in flexion/abduction/external rotation, shoulder adducted/internally rotated).
— Look for portals of entry: skin breaks, cellulitis, puncture wounds, surgical scars, IVDU track marks.
— Pustular or vesiculopustular skin lesions on distal extremities → think DGI.
— Warmth and tenderness over the joint line (not just periarticular).
— Severe pain with minimal passive ROM is the most specific bedside finding; periarticular processes (bursitis, cellulitis) allow gentle passive ROM.
— Effusion: ballottement of patella, fluctuance.
— Hip: log-roll test — pain with internal/external rotation in supine; child may refuse to walk.
— Sacroiliac: FABER, direct SI tenderness; consider in IVDU with buttock/back pain and fever.
— Sternoclavicular: localized swelling/erythema over SC joint in IVDU — get CT to rule out mediastinal extension.
— Vital signs: tachycardia, fever, hypotension → screen for sepsis using qSOFA/SIRS.
— Cardiac: new murmur (endocarditis), especially with polyarticular disease or S. aureus bacteremia.
— Skin: Janeway lesions, Osler nodes, splinter hemorrhages, IVDU stigmata.
— Lymphadenopathy, hepatosplenomegaly.
— MAP <65, lactate >2, AMS, or oliguria triggers sepsis bundle: fluids 30 mL/kg, blood cultures ×2, broad-spectrum antibiotics within 1 hour, source control via arthrocentesis.
CCS pearl: On CCS, after focused MSK exam, immediately order vitals q1h, blood cultures ×2, CBC, CMP, lactate, ESR/CRP, peripheral IV, NPO, then move the clock forward to arthrocentesis — do not start antibiotics before tap unless hemodynamically unstable.
Board pearl: A child refusing to bear weight with fever and hip held in flexion-abduction-ER → septic hip until imaging and arthrocentesis prove otherwise.
— Aspirate as much fluid as possible; send for:
— Cell count with differential
— Gram stain and culture (aerobic + anaerobic)
— Crystal analysis (polarized microscopy)
— Glucose, protein, lactate (lower yield)
— If gonococcal suspected: also send urethral/cervical/pharyngeal/rectal NAAT.
— WBC >50,000/μL with >75% PMNs → highly suspicious for septic arthritis (sensitivity ~60%, specificity ~85%).
— WBC 2,000–50,000 → inflammatory (gout, RA, reactive); still tap and culture.
— Prosthetic joints: lower threshold — WBC >1,100 with >64% PMNs is suggestive after >6 weeks postop.
— Gram stain positive in only 30–50% — a negative Gram stain does not exclude septic arthritis.
— Culture is gold standard; gonococcus grows poorly — only ~50% positive synovial cultures.
— CBC: leukocytosis (~50% sensitive).
— ESR and CRP: elevated in >90%; CRP trends faster for monitoring response.
— Procalcitonin elevated supports bacterial etiology but is not diagnostic alone.
— Blood cultures ×2 before antibiotics — positive in 25–50% of non-gonococcal cases; rule out concurrent bacteremia/endocarditis.
— Lactate, BMP, LFTs for sepsis workup and antibiotic dosing.
— Uric acid: poor discriminator; don't rely on it.
— Plain radiographs of joint: baseline for soft tissue swelling, effusion, osteomyelitis, gas, chondrocalcinosis — usually unrevealing early.
— Ultrasound: confirms effusion, guides aspiration of hip/shoulder.
— MRI: most sensitive — detects osteomyelitis, abscess, especially for SI joint, sternoclavicular, spine.
Board pearl: Synovial lactate >10 mmol/L is highly specific for septic arthritis but not yet a standard order — Gram stain + culture + cell count remain the diagnostic triad.
Step 3 management: Do not delay arthrocentesis for imaging in an accessible joint like the knee.
— Indicated if persistent fever, worsening effusion, or rising inflammatory markers despite 48–72 h of appropriate antibiotics — assess for need for surgical drainage.
— Compare cell counts; drop in WBC and PMN% supports response.
— MRI with contrast — gold standard for axial joints (SI, sternoclavicular, spine, hip) and to rule out adjacent osteomyelitis (which extends antibiotic course from ~2 to ≥6 weeks).
— CT — useful for sternoclavicular joint (mediastinal extension), prevertebral abscess, or guiding aspiration of deep joints.
— Three-phase bone scan / tagged WBC scan — when MRI contraindicated or for prosthetic joint workup.
— PET/CT — emerging role for PJI evaluation.
— Synovial fluid NAAT for N. gonorrhoeae, Borrelia burgdorferi, M. tuberculosis, Kingella kingae (children).
— 16S rRNA PCR of synovial fluid when cultures are negative but suspicion remains high (esp. after empiric antibiotics).
— Fungal cultures and mycobacterial AFB stain/culture for chronic monoarthritis or immunocompromised patients.
— Hold antibiotics ≥2 weeks before aspiration if clinically safe to maximize culture yield.
— Alpha-defensin synovial assay — high sensitivity/specificity for PJI.
— Send multiple intraoperative tissue cultures (5–6 sites) plus sonication of explanted hardware.
Key distinction: Reactive arthritis (post-Chlamydia, Shigella, Salmonella, Yersinia, Campylobacter) has sterile synovial fluid with high WBC but negative Gram stain/culture and resolves with NSAIDs — do not treat with prolonged antibiotics.
Board pearl: Prosthetic shoulder with indolent pain and negative routine cultures → request prolonged anaerobic culture (14 days) for Cutibacterium acnes.
— Hemodynamics: septic shock vs. stable.
— Host: immunocompromised, prosthetic joint, IVDU, age >65.
— Joint: native peripheral vs. axial (hip, SI, SC) vs. prosthetic.
— Pathogen risk: MRSA prevalence locally, gonococcal exposure.
— Two large-bore IVs, IVF resuscitation if septic, continuous monitoring.
— Blood cultures ×2 → arthrocentesis → empiric IV antibiotics → orthopedic surgery consultation same day.
— Pain control with acetaminophen ± short-acting opioid; avoid NSAIDs initially if AKI or sepsis.
— NPO in case of OR.
— Native joint: serial closed-needle aspirations, arthroscopic washout, or open arthrotomy — choice depends on joint and surgeon preference.
— Hip and shoulder typically require operative drainage (deep, difficult to aspirate repeatedly).
— Knee — arthroscopic lavage usually preferred; serial aspirations acceptable if responding.
— Prosthetic joint: DAIR (debridement, antibiotics, implant retention) if acute (<3 weeks symptoms) and stable implant; otherwise 1- or 2-stage revision.
— Healthy, gram stain (+) cocci in clusters → MRSA coverage (vancomycin).
— Gram stain (+) cocci in chains → consider streptococci, continue vanc until speciated.
— Gram stain (-) rods → add antipseudomonal beta-lactam (cefepime/piperacillin-tazobactam).
— Sexually active adult with tenosynovitis/pustules → IV ceftriaxone.
— Negative Gram stain but high suspicion → cover broadly: vancomycin + ceftriaxone.
Step 3 management: Sequence in CCS = blood cultures → arthrocentesis → empiric IV antibiotics → orthopedic consult → admit. Skipping source control delays cure regardless of antibiotic choice.
CCS pearl: Move the clock 24–48 h; reassess fever curve, repeat CRP, examine joint, document trending improvement — if not improving, repeat tap and re-consult ortho for further drainage.
— Vancomycin 15–20 mg/kg IV q8–12h (trough 15–20 or AUC 400–600) — covers MRSA, MSSA, streptococci.
— Add ceftriaxone 2 g IV daily if gonococcal suspicion or gram-negative coverage needed.
— Use cefepime 2 g q8h or piperacillin-tazobactam 4.5 g q6–8h instead of ceftriaxone if immunocompromised, IVDU, or Pseudomonas risk.
— Penicillin allergy: aztreonam + vancomycin; verify allergy history.
— MSSA → nafcillin 2 g IV q4h or cefazolin 2 g IV q8h (preferred over vancomycin for MSSA — better outcomes).
— MRSA → vancomycin; alternatives: daptomycin 6–8 mg/kg/day, linezolid, ceftaroline.
— Streptococci → ceftriaxone or penicillin G.
— Gonococcus → ceftriaxone 1 g IV/IM daily ×7 days + single-dose azithromycin/doxycycline for Chlamydia.
— Pseudomonas → cefepime + tobramycin or ciprofloxacin, especially in IVDU.
— Gram-negative enterics (E. coli, etc.) → ceftriaxone or ertapenem.
— Lyme arthritis → oral doxycycline 100 mg BID ×28 days (not septic per se, but tested).
— Anaerobes (bite wounds) → ampicillin-sulbactam.
— Native joint, gonococcal: 7–14 days total.
— Native joint, non-gonococcal: 2 weeks IV, then 2 weeks oral, total ~4 weeks (some 3–4 weeks IV depending on organism and response).
— With osteomyelitis: ≥6 weeks.
— Prosthetic joint with DAIR: 6 weeks IV + chronic oral suppression for many.
Board pearl: Cefazolin or nafcillin beats vancomycin for MSSA — switch promptly once susceptibilities return. Don't reflexively continue vancomycin.
Step 3 management: Always reconcile renal dosing for vancomycin/cefepime and arrange OPAT (outpatient parenteral antibiotic therapy) follow-up before discharge.
— Serial needle aspiration: acceptable for accessible joints (knee), repeat daily until effusion resolves; document declining cell counts.
— Arthroscopic lavage: preferred for knee, shoulder, ankle; allows debridement and synovectomy; shorter hospital stay.
— Open arthrotomy: hip (especially pediatric), loculated infections, failed arthroscopy, immunocompromised, or extensive joint destruction.
— 48–72 h after initial drainage and antibiotics: clinical exam, repeat CRP, repeat aspirate if effusion persists.
— Lack of improvement → repeat OR washout; do not just "wait it out."
— DAIR (debridement, antibiotics, implant retention): symptoms <3 weeks, stable implant, susceptible organism, intact soft tissue. Exchange modular components (liner, head).
— One-stage revision: select cases with known organism, good bone stock, no sinus tract.
— Two-stage revision: gold standard for chronic PJI — explant + antibiotic spacer × 6 weeks IV abx → reimplant after markers normalize.
— Resection arthroplasty / arthrodesis / amputation: salvage in failed multiple revisions.
— Continuous joint immobilization initially for pain, then early passive ROM by day 2–3 to prevent stiffness.
— Avoid weight-bearing on infected hip/knee until cleared.
— Physical therapy referral once infection controlled.
— Sternoclavicular: often requires resection if mediastinitis or abscess.
— Spine: surgical drainage if neurologic deficit, instability, or epidural abscess.
CCS pearl: On a CCS case, after arthrocentesis confirms septic arthritis, the next single most important order is "consult orthopedic surgery — urgent washout". Antibiotics and consult run in parallel.
Board pearl: Early ROM (within 48–72 h of source control) prevents adhesions and improves functional outcome — immobilization is for analgesia, not therapy.
— Atypical presentation: low-grade fever, confusion, falls, anorexia; classic triad in <50%.
— Higher prevalence of underlying OA, RA, prosthetic joints, diabetes — all risk factors.
— Higher mortality (up to 15–20%) and worse functional recovery.
— Beware polypharmacy: anticoagulants complicate aspiration timing — hold/reverse if INR supratherapeutic or DOAC within 24–48 h, but do not delay tap in unstable patient (use ultrasound guidance, pressure dressing).
— Screen for occult bacteremia source: indwelling Foley, pressure ulcers, endocarditis.
— Renal dose vancomycin by AUC monitoring; trough levels q48–72h if CrCl <30.
— Cefepime — reduce dose to avoid neurotoxicity (encephalopathy, myoclonus, NCSE) — especially in elderly with CKD.
— Avoid aminoglycosides when possible; if needed, single daily dose with levels.
— Daptomycin: dose q48h if CrCl <30; monitor CK weekly (myopathy).
— Dialysis patients have high S. aureus carriage → empiric vanc + cover GNRs.
— Linezolid: monitor for thrombocytopenia, lactic acidosis; limit to 28 days.
— Avoid tigecycline (mortality signal).
— Adjust clindamycin in severe hepatic dysfunction.
— Arthrocentesis is generally safe on therapeutic warfarin (INR <3.5) or DOACs per ACR/EULAR — bleeding risk low; do not withhold tap.
— Hold antiplatelets only if elective and clinically allows.
Step 3 management: In an elderly patient with prosthetic knee, AKI, and septic shock, choose vancomycin (AUC-dosed) + cefepime (renally dosed), get urgent ortho washout, and consult ID and pharmacy for OPAT planning.
Board pearl: Cefepime neurotoxicity in CKD presents as encephalopathy and myoclonus that resolves within 48–72 h of stopping the drug — a frequent test scenario.
— Rare but high-stakes; gonococcal arthritis disproportionately affects pregnant patients due to immune modulation.
— Safe antibiotics: ceftriaxone, cefazolin, nafcillin, vancomycin, azithromycin.
— Avoid: doxycycline (after 2nd trimester teeth), fluoroquinolones, aminoglycosides (relative), TMP-SMX in 1st/3rd trimester.
— Imaging: MRI without gadolinium preferred; ultrasound is first-line for hip aspiration.
— Coordinate with OB; treat partners for STIs.
— Kingella kingae in children 6 months–4 years — fastidious, grows in blood culture bottles; PCR of synovial fluid most sensitive.
— S. aureus (including MRSA) most common overall; Salmonella in sickle cell disease.
— Kocher criteria for septic hip vs. transient synovitis: fever >38.5°C, non-weight-bearing, ESR >40, WBC >12,000 — 4/4 → ~99% probability.
— Hip and shoulder — usually require operative drainage.
— Empiric: cefazolin or vancomycin (if MRSA risk) ± ceftriaxone.
— Duration: 2–4 weeks; early IV-to-oral switch is well-supported.
— Consider fungal (Candida, Cryptococcus), mycobacterial, atypical organisms.
— Tap and send AFB, fungal cultures, and broad bacterial.
Board pearl: A toddler refusing to walk, febrile, with hip held in flexion-abduction-ER → ultrasound of hip and urgent orthopedic aspiration/drainage in the OR, not the ED.
Key distinction: Transient synovitis = afebrile, ambulates, normal labs, resolves with NSAIDs; septic hip = the opposite — Kocher score guides decision-making.
— Cartilage destruction within 8 hours of bacterial inoculation — irreversible chondrolysis from PMN proteases.
— Osteomyelitis (contiguous spread) — extends antibiotic course to ≥6 weeks.
— Joint ankylosis, contracture, chronic instability.
— Avascular necrosis, especially femoral head in septic hip.
— Growth plate damage in pediatric hip → limb length discrepancy.
— Recurrent infection or chronic sinus tract (esp. prosthetic).
— Bacteremia → septic shock, multi-organ dysfunction.
— Endocarditis in 5–10% of S. aureus septic arthritis — get TTE; TEE if persistent bacteremia.
— Metastatic abscesses (psoas, paraspinal, epidural, splenic).
— DVT/PE from immobility and inflammation.
— Toxic shock syndrome (rare).
— Native joint: 7–15%; rises with polyarticular disease, age, immunocompromise, S. aureus bacteremia.
— Polyarticular septic arthritis: up to 30%.
— PJI: 2–7%, with high reoperation/morbidity.
— ~40% with permanent joint dysfunction.
— Delay to drainage and inadequate source control are strongest predictors of poor outcome.
— Vancomycin nephrotoxicity (AKI in ~15%, especially with concurrent piperacillin-tazobactam or contrast).
— C. difficile colitis with prolonged broad-spectrum antibiotics — clindamycin, fluoroquinolones, cephalosporins highest risk.
— Catheter-related bloodstream infection (CRBSI) from prolonged PICC for OPAT.
— Daptomycin myopathy; linezolid thrombocytopenia and serotonin syndrome.
Step 3 management: During OPAT, weekly CBC, CMP, CRP, and vancomycin trough/AUC are standard; document line site exam and re-evaluate need for continued IV access.
Board pearl: Persistent fever or rising CRP at 72 hours of appropriate antibiotics = inadequate source control — re-tap, re-image, re-operate. Don't blame the bug.
— Orthopedic surgery — same-day for drainage/washout.
— Infectious disease — empiric and targeted regimen, OPAT planning, source workup.
— Rheumatology — when crystal arthropathy or autoimmune flare coexists, or when diagnosis remains unclear.
— Cardiology — if endocarditis suspected (new murmur, S. aureus bacteremia, polyarticular).
— Septic shock: MAP <65 despite 30 mL/kg IVF or lactate >4 → vasopressors, central line, ICU.
— Respiratory failure, AMS, severe AKI requiring CRRT.
— Bacteremia with hemodynamic instability awaiting source control in OR.
— Mediastinal extension from SC joint infection or epidural abscess with neurologic compromise.
— Hemodynamically stable, source controlled, on appropriate IV antibiotics with declining markers.
— Telemetry not routinely required unless endocarditis or sepsis-related arrhythmia.
— Afebrile ≥48 h, tolerating PO, declining CRP, definitive drainage achieved, oral or OPAT plan with reliable follow-up, pain controlled.
— Functional status sufficient for safe transition (home with services vs. SNF for IV antibiotics and PT).
— Prosthetic joint infection requiring revision arthroplasty.
— Pediatric septic hip without pediatric ortho on site.
— Complex multidrug-resistant organisms requiring infectious-disease expertise.
CCS pearl: On CCS, the correct admission order set includes "admit to medicine, telemetry/floor, NPO until OR, IV antibiotics, IVF, DVT prophylaxis, PT/OT consult, orthopedic surgery consult, infectious disease consult, blood cultures, repeat labs in 24 h."
Board pearl: Concurrent S. aureus bacteremia in septic arthritis triggers TTE, repeat blood cultures q48h until clearance, and minimum 4 weeks IV antibiotics — manage as if it were endocarditis until proven otherwise.
— Gout: monosodium urate, negatively birefringent needle-shaped crystals; first MTP (podagra), midfoot, knee. Often presents identical to septic — same workup applies.
— Pseudogout (CPPD): rhomboid, positively birefringent crystals; knee, wrist; chondrocalcinosis on XR.
— Critical caveat: Crystals and infection can coexist in ~5% — Gram stain and culture every tap regardless of crystal result.
— Post-GI (Salmonella, Shigella, Campylobacter, Yersinia) or post-GU (Chlamydia trachomatis) infection.
— Asymmetric oligoarthritis lower extremities, enthesitis, dactylitis, conjunctivitis, urethritis ("can't see, can't pee, can't climb a tree").
— Synovial fluid is inflammatory but sterile; HLA-B27 association.
— Treat with NSAIDs; antibiotics only for active Chlamydia.
— Late disseminated Lyme — recurrent large-joint (knee) effusions, surprisingly well-preserved function.
— Serology with confirmatory immunoblot; synovial PCR.
— Doxycycline 100 mg BID ×28 days; refractory → ceftriaxone IV.
— Parvovirus B19, hepatitis B/C, HIV seroconversion, chikungunya — symmetric polyarthritis, often hands/wrists.
— Self-limited; supportive care.
— Indolent monoarthritis in immunocompromised or endemic exposure; AFB and fungal cultures on synovial fluid.
— TB arthritis often hip or knee with adjacent osteomyelitis.
Key distinction: Migratory arthritis differential = rheumatic fever (post-strep, JONES), DGI, Lyme, SBE, SLE — context distinguishes.
Board pearl: A patient with established gout who develops fever + monoarticular flare not responding to colchicine/NSAIDs/steroids deserves a repeat tap to rule out superimposed septic arthritis.
— Cellulitis / erysipelas — erythema and warmth over joint but preserved passive ROM; no effusion on US.
— Bursitis (prepatellar, olecranon) — septic vs. aseptic; aspirate the bursa, not the joint; S. aureus most common in septic bursitis.
— Tenosynovitis — Kanavel signs in flexor tenosynovitis (fusiform swelling, semi-flexed digit, tenderness along sheath, pain with passive extension) — hand surgery emergency.
— Septic flexor tenosynovitis — IV antibiotics + surgical drainage.
— Abscess — fluctuant, focal; needs I&D.
— Hemarthrosis — anticoagulation, hemophilia, ACL tear; bloody aspirate, low WBC.
— Fracture / occult fracture — radiograph, MRI if suspicion high.
— Meniscal tear / loose body — mechanical symptoms, no systemic features.
— RA flare — polyarticular, symmetric, morning stiffness, anti-CCP/RF positive; risk factor for septic arthritis — keep low threshold to tap.
— Spondyloarthropathy — psoriatic arthritis, AS — pattern recognition.
— SLE — non-erosive arthritis, multisystem features.
— Adult-onset Still's disease — quotidian fevers, salmon rash, ferritin extremely elevated.
— DVT — calf swelling, US-confirmed; can mimic knee process.
— Avascular necrosis of femoral head — subacute groin pain, history of steroids/EtOH/sickle cell.
— Metastatic disease / primary bone tumor — focal bone pain, weight loss, plain film/MRI findings.
— PVNS / synovial chondromatosis — chronic monoarticular swelling, MRI shows characteristic findings.
Step 3 management: In an anticoagulated patient with a hot swollen joint, still tap — bloody fluid with low WBC supports hemarthrosis; do not assume without aspiration.
Board pearl: Olecranon bursitis fluid with WBC >2,000–5,000/μL or Gram-positive cocci → septic bursitis; outpatient oral antibiotics often suffice if systemically well.
— Most native joint cases: total 3–4 weeks therapy; first 2 weeks IV (longer for S. aureus bacteremia, osteomyelitis, immunocompromised).
— Transition to oral once afebrile, declining CRP, susceptibilities known, reliable oral absorption: high-bioavailability options include levofloxacin, linezolid, TMP-SMX, clindamycin, doxycycline.
— Prosthetic joint with retention: chronic oral suppression (months to lifelong) — typically doxycycline, TMP-SMX, cephalexin, or rifampin combinations (rifampin always paired to prevent resistance).
— Requires reliable patient, home health/infusion services, PICC line, weekly labs (CBC, CMP, CRP, drug levels), ID follow-up.
— Counsel on PICC care, signs of line infection, DVT.
— Endocarditis: 4–6 weeks IV; valve surgery if indicated.
— Dental, skin, GU sources: address definitively (dental clearance, ulcer care, urology workup).
— STI screening (HIV, syphilis, hepatitis B/C) in DGI cases; partner notification and treatment.
— Diabetes optimization (HbA1c <8%), nutritional support, smoking cessation, alcohol reduction.
— Address IV drug use: harm-reduction counseling, MAT (buprenorphine/methadone), naloxone prescription, SW referral.
— Optimize RA control while balancing immunosuppression timing post-infection (hold biologics during active infection; restart after clearance with rheumatology guidance).
— Pneumococcal (PCV20 or PCV15+PPSV23), influenza, COVID-19, RSV per age guidelines — especially in elderly and immunocompromised.
Step 3 management: Before discharge, confirm: antibiotic plan written, OPAT arranged, ID and orthopedic follow-up scheduled within 1–2 weeks, PT plan in place, weekly lab orders sent, primary care notified.
Board pearl: Prophylactic antibiotics before dental procedures in prosthetic joint patients is not routinely recommended by ADA/AAOS — exceptions for high-risk patients only.
— Orthopedic surgery: 1–2 weeks post-discharge, then 4–6 weeks, then 3 months.
— Infectious disease: weekly during IV course, then 2 weeks after antibiotic completion.
— Primary care: 1–2 weeks post-discharge for medication reconciliation, comorbidity check.
— Weekly CBC, CMP, CRP (and ESR less often).
— Vancomycin AUC or trough q5–7 days when stable; more often with renal change.
— LFTs if on linezolid, rifampin, or hepatotoxic combinations.
— CK weekly on daptomycin.
— C. difficile PCR if new diarrhea.
— Plain films at 6 weeks and 3 months to assess for osteomyelitis or joint destruction.
— MRI if persistent pain or markers not normalizing.
— Echo follow-up if endocarditis was diagnosed.
— Early passive ROM (within 48–72 h of source control) to prevent contractures.
— Progressive active ROM and strengthening once infection controlled (~1–2 weeks).
— Weight-bearing as tolerated per orthopedic guidance.
— Formal PT/OT referral; consider home PT for elderly or post-op.
— Functional reassessment at 6 weeks and 3 months.
— Warning signs: recurrent fever, increasing pain, new effusion, drainage from incision → immediate return.
— Adherence to full antibiotic course even after symptom resolution.
— Activity modification; gradual return to work/sports based on joint recovery.
— Mental health: chronic pain, depression after prolonged hospitalization, especially in elderly.
Step 3 management: A patient 2 weeks post-discharge with rising CRP, increasing joint pain, and a new effusion → arrange repeat arthrocentesis and orthopedic re-evaluation same day; do not extend antibiotics empirically without re-imaging or re-tapping.
Board pearl: Normalization of CRP is the most reliable single marker of treatment success — persistent elevation at 4 weeks is a red flag for inadequate source control or osteomyelitis.
— Document risks (bleeding, infection introduction, neurovascular injury) and alternatives.
— In emergent septic shock, two-physician documentation of implied consent if patient lacks capacity and no surrogate is reachable.
— Decisional capacity assessment for patients refusing tap or drainage — particularly relevant in altered mentation from sepsis or substance use.
— Gonococcal infection is reportable to public health in all US jurisdictions; ensure partner notification (Expedited Partner Therapy where legal).
— TB arthritis: reportable.
— IVDU-related infections: not reportable per se, but addiction counseling and referral are standard of care; harm-reduction approach.
— Discharge with PICC and OPAT: leading cause of readmission is line complication or incomplete antibiotic plan. Use structured handoff (e.g., I-PASS) to ID and primary care.
— Medication reconciliation: ensure DVT prophylaxis decision, pain plan with opioid stewardship (PDMP check, naloxone co-prescribing).
— Confirm follow-up appointments are scheduled before discharge, not "patient to call."
— Wrong-site surgery: time-out, joint marking; particularly with bilateral pathology.
— Vancomycin/piperacillin-tazobactam combination AKI — choose alternatives when possible.
— Anticoagulation reversal decisions documented; arthrocentesis can proceed on therapeutic anticoagulation in most cases.
— IVDU stigma may delay diagnosis; treat with same urgency.
— Insurance and OPAT: some patients need SNF placement because home infusion isn't covered — engage social work early.
Step 3 management: Always perform a formal discharge medication reconciliation, confirm follow-up appointments in writing, and use teach-back to verify patient understanding of OPAT protocol — these reduce 30-day readmission, a value-based metric.
Board pearl: A patient with septic arthritis from IVDU who leaves AMA mid-treatment requires capacity assessment, harm reduction counseling, oral antibiotic bridge, and clear documentation — not abandonment.
— S. aureus — most common overall, all ages.
— N. gonorrhoeae — sexually active young adults, DGI triad.
— Streptococcus pneumoniae — splenectomy, sickle cell, alcoholism.
— Salmonella — sickle cell disease.
— Pseudomonas aeruginosa — IV drug use, puncture through shoe.
— Pasteurella multocida — cat/dog bite.
— Eikenella corrodens — human bite, "fight bite."
— Capnocytophaga — dog bite in asplenic.
— Sporothrix schenckii — rose thorn injury, gardener.
— Mycobacterium marinum — fish tank, aquarium.
— Brucella — unpasteurized dairy, livestock exposure.
— Borrelia burgdorferi — late Lyme, knee.
— Kingella kingae — toddlers, fastidious, blood culture bottles.
— Cutibacterium acnes — shoulder prosthesis.
— Sternoclavicular / sacroiliac → IV drug use.
— Knee → most common overall.
— Hip → children, intra-abdominal source spread.
— Prosthetic shoulder → C. acnes.
— Hand small joints → DGI or gout flare.
— Synovial WBC >50,000 + >75% PMNs → septic likely.
— Gram stain sensitivity only ~30–50%.
— Synovial glucose <50% serum suggestive but nonspecific.
— CRP > ESR for monitoring response.
— MSSA → cefazolin/nafcillin > vancomycin.
— DGI → ceftriaxone + treat for Chlamydia.
— Lyme arthritis → doxycycline 28 days oral.
— Rifampin combo for staph PJI with retained hardware.
— Cefepime causes encephalopathy in CKD.
Board pearl: "Fever + monoarticular hot joint + crystals present" does not rule out septic arthritis. Always culture.
Key distinction: Migratory polyarthralgia + tenosynovitis + pustules = DGI; abrupt fixed monoarthritis = non-gonococcal S. aureus.
— 65-year-old with RA on methotrexate presents with 3-day swollen, hot left knee, fever 38.7°C, refuses to bend knee. Synovial WBC 78,000 with 92% PMNs, Gram stain shows GPCs in clusters.
— Answer: Arthrocentesis already done → empiric vancomycin + ceftriaxone, urgent ortho consult for arthroscopic washout.
— 24-year-old sexually active woman with 1-week migratory wrist/ankle pain, vesicopustular rash on fingers, tenosynovitis of right wrist.
— Answer: Blood/synovial/urethral NAAT for gonococcus; IV ceftriaxone 1 g daily + single dose azithromycin/doxycycline for Chlamydia; partner notification.
— 32-year-old with IV heroin use, fever, sternoclavicular swelling, tender to palpation.
— Answer: CT chest to evaluate mediastinal extension; vancomycin + cefepime; ortho/CT surgery consult; HIV/HCV/HBV testing; addiction medicine referral.
— 3-year-old with fever, refusal to walk, hip held in flexion-abduction-ER; ESR 60, WBC 16,000.
— Answer: Kocher 4/4 → urgent OR drainage; cover S. aureus and Kingella with cefazolin or vancomycin.
— 70-year-old 6 months post TKA with 4 weeks of pain, sinus tract drainage. Synovial WBC 4,500 with 70% PMNs, culture-negative.
— Answer: Chronic PJI → two-stage revision arthroplasty; hold antibiotics before re-aspiration if safe; consider alpha-defensin and prolonged anaerobic cultures.
— Known gout patient with knee flare, fever, synovial WBC 60,000 with positive crystals and Gram stain showing GPCs.
— Answer: Treat both — antibiotics + drainage plus anti-inflammatory for crystals.
Step 3 management: When the stem includes "what is the next best step" in a hot joint scenario, the answer is almost always arthrocentesis unless the patient is in shock — then it's antibiotics + IVF + simultaneous arrangement of tap.
Board pearl: "Polyarticular septic arthritis" stem = check TTE for endocarditis.
Septic arthritis is a joint-and-life-threatening emergency in which urgent arthrocentesis, prompt empiric IV antibiotics tailored to host and Gram stain, and definitive surgical drainage — not antibiotics alone — determine outcome.
Board pearl: When in doubt — tap the joint, culture the blood, call ortho, start vanc + ceftriaxone.