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Acute Joint Pain

The hot swollen joint is septic until drained otherwise.

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Your objective: explain the approach, recognize important warning signs, then test your recall.

Abbreviations explained
ACS
Acute coronary syndrome
OMI
Occlusion myocardial infarction
ECG
Electrocardiogram
PE
Pulmonary embolism
POCUS
Point-of-care ultrasound
QTc
QT interval corrected for heart rate
LBBB
Left bundle branch block
RBBB
Right bundle branch block
hs-cTn
High-sensitivity cardiac troponin
CTA
Computed tomography angiography
ICU
Intensive care unit
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The jobThe hot swollen joint is septic until drained otherwise.

  1. A single hot joint is septic until the tap says otherwise.
  2. Aspirate before antibiotics when safe: Gram stain, culture, crystals, cell count.
  3. Crystals do not exclude infection.
  4. Prosthetic joints belong to orthopedics — do not tap through cellulitis.

A single hot, swollen joint is septic arthritis until aspiration proves otherwise — delay costs cartilage.

Then split the rest: crystal, trauma, degenerative, inflammatory. Multiple joints suggest systemic disease (gout flare, rheumatic, reactive, viral, gonococcal).

Septic arthritis Critical

Key: Fever + hot joint (or an immunosuppressed/diabetic patient without fever) — aspirate before antibiotics when safe; IV therapy + washout. Synovial WBC >50,000/µL is suggestive, not diagnostic; gonococcal and immunocompromised septic joints are often well below that.

Prosthetic joint infection Critical

Key: Any prosthesis + joint symptoms — urgent orthopedics. They perform the aspiration; do not tap through overlying cellulitis.

Fracture / osteomyelitis Critical

Key: Trauma, diabetic foot, sickle cell — X-ray first; MRI for deep infection.

Hemarthrosis (anticoagulated, hemophilia) Emergent

Key: Tense painful joint — reverse coagulopathy / factor replacement + ortho. Do not inject steroids into an uncultured joint.

Lyme arthritis Emergent

Key: Endemic area, often a large knee effusion weeks to months after the tick — serology per regional pathway.

Gout / pseudogout flare Common

Key: First MTP or knee; negatively birefringent needles = MSU (gout). Crystals do not exclude coexistent infection.

Reactive / viral / gonococcal arthritis Common

Key: Migratory polyarthralgia; pustules and tenosynovitis suggest disseminated gonococcus — culture/NAAT mucosa, not just the joint.

Traumatic effusion / OA flare Common

Key: Mechanical history, chronic pattern — image and conservative care.

Tick what your patient has — the banner updates as you go.

Onset speed

minutes (trauma), hours–days (septic, crystal), weeks (inflammatory, Lyme)

Fever, chills, immunosuppression, diabetes, IVDU (septic risk)

Prior similar episodes and crystal disease; alcohol/diuretics (gout)

Prosthetic joint? Recent procedures or wounds?

Travel/ticks (Lyme), sexual history (gonococcal, reactive)

Single vs multiple joints; hot, swollen, painful range of motion (all three = septic until excluded)

Skin over the joint

entry wounds, cellulitis, pustules (gonococcal)

Systemic

rash, psoriasis plaques, urethritis, conjunctivitis

Weight-bearing ability; neurovascular status

Bedside

  • Joint aspiration before antibiotics when possible: Gram stain, culture, crystals, cell count with differential
  • POCUS to confirm effusion and guide the tap

Labs

  • CBC, ESR/CRP, blood cultures; uric acid is unreliable in the acute flare
  • Gonococcal NAAT (urine/cervix/throat/rectum as exposed); Lyme serology in endemic regions

Imaging

  • X-ray for fracture, gas, chondrocalcinosis
  • MRI for osteomyelitis; US for effusion and guided aspiration
Medication safety reminder

Use this as a first-pass prompt; verify all medications, doses, concentrations, contraindications, weight, pregnancy status, and local protocols before administration.

Check indication, allergy, route, renal/hepatic risk, interactions, monitoring, and local formulary.

Discharge

  • Crystal-proven flare responding to NSAIDs/colchicine/steroids, non-septic pattern, functioning follow-up. Never inject intra-articular steroid until infection is excluded.

Admit

  • Septic arthritis on IV antibiotics + washout plan, polyarticular systemic disease, uncertain diagnosis needing serial exams.

Emergency aspiration/washout + ortho

  • Purulent joint, prosthetic infection, hemarthrosis with coagulopathy.

Use objective reassessment and the local pathway.

Before the next decision · reassess and hand over

Use these learning prompts with the presentation’s pathway. They are not discharge criteria.

  1. Reassess: compare symptoms, observations and examination with the initial assessment and response to treatment.
  2. Warning signs for Acute Joint Pain:
    • Fever with a hot swollen joint
    • Prosthetic joint involved
    • Immunosuppression, diabetes, or IVDU
    • Inability to bear weight or move the joint
    • Overlying skin breaks or pustules
    • Synovial fluid that is purulent or Gram-stain positive (WBC >50,000/µL supports but does not prove infection)
  3. Reconsider: check unresolved findings and alternative explanations, including the pitfalls below.
  4. Escalate: communicate deterioration, uncertainty or needs beyond the current setting.
  5. Plan the transition: identify outstanding results, responsibility for follow-up, patient understanding and specific return advice.
Review this presentation’s disposition pathway →Practice a handover →

Clinical Pearls

  • A single hot joint is septic until the tap says otherwise — aspirate before antibiotics when safe.
  • Crystals do not exclude infection; gout and septic arthritis coexist.
  • Synovial WBC >50,000/µL is suggestive, not diagnostic — gonococcal and immunocompromised joints run lower.
  • Do not tap a prosthesis through cellulitis; that aspiration belongs to orthopedics.

Pitfalls

  • Antibiotics before aspiration can sterilize the culture — tap first when safe.
  • Gout and septic arthritis coexist — crystals do not exclude infection.
  • Gonococcal arthritis is often a migratory tenosynovitis with skin lesions and a modest synovial WBC.
  • The immunosuppressed patient with a “mildly” swollen joint can have a septic one — and a synovial WBC well under 50,000.
  • Elderly gout often strikes the knee or midfoot, not the big toe.
  • Do not tap a prosthetic joint through cellulitis; call ortho.
PRACTICE REFRESHER

Rapid recall

Test your first action and the dangerous diagnoses before revealing the answer.

01 · First move

Before you scroll, what needs to happen first?

02 · Immediate threats

Name at least two diagnoses that cannot wait.

PRIVATE TO THIS DEVICE

Your learning note

Capture a weak point, a teaching pearl, or a question to take to your next shift.

Review schedule starts when marked reviewed
Fever & SepsisLow Back Pain

Selected guidance · source check 2026-09-07. These 1 source links support selected teaching points, not a complete review of this topic. Check population, setting and local protocol before applying a recommendation.

  • Rosen’s Emergency Medicine, 10th ed. (2023) — arthritis & joint infection
  • IDSA guidance on native and prosthetic joint infection
  • EULAR crystal arthritis recommendations; Tintinalli’s 9th ed. — musculoskeletal emergencies
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