Monoarticular arthritis

Revision as of 23:26, 20 March 2026 by Danbot (talk | contribs) (Expanded with EM-focused content: septic arthritis red flags, arthrocentesis guidance, synovial fluid analysis, management, disposition)

Background

  • Monoarticular arthritis (monoarthritis) refers to inflammation of a single joint
  • The critical EM question is: Is this septic arthritis?
  • Septic arthritis is a joint emergency requiring urgent drainage — delay increases risk of joint destruction
  • Other common causes include crystal arthropathy (gout, pseudogout) and traumatic hemarthrosis
  • Arthrocentesis is the key diagnostic procedure and should be performed on any hot, swollen joint without clear alternative diagnosis

Clinical Features

History

  • Onset (acute vs. subacute), joint involved, trauma history
  • Prior episodes (recurrent suggests crystal disease)
  • Fever, chills, constitutional symptoms
  • Recent infection, skin break, surgery, or injection
  • Sexual history (disseminated gonococcal infection)
  • History of gout, pseudogout, or autoimmune disease
  • Immunosuppression, IV drug use, prosthetic joint

Physical Exam

  • Joint warmth, erythema, effusion, decreased range of motion
  • Pain with passive range of motion (highly suggestive of intra-articular process)
  • Overlying skin: cellulitis, track marks, surgical scars, tophi
  • Assess for signs of systemic infection
  • Examine other joints (polyarticular process may present initially as monoarticular)

Red Flags for Septic Arthritis

  • Fever with acute monoarthritis
  • Recent bacteremia, skin infection, or surgical procedure
  • Prosthetic joint with new pain/swelling
  • Immunosuppressed patient
  • IV drug use
  • Non-weight-bearing or unable to flex joint

Differential Diagnosis

Monoarticular arthritis

Algorithm for Monoarticular arthralgia

Septic Arthritis

Crystal-Induced Monoarthritis

Traumatic

Ischemic

Hemorrhagic

Neoplastic

  • Metastases
  • Osteochondroma
  • Osteoid osteoma
  • Pigmented villonodular synovitis

Systemic Disease

Periarticular (Non-Articular)

Evaluation

Arthrocentesis (Key Diagnostic Study)

  • Perform arthrocentesis on any acute hot, swollen joint unless clear alternative diagnosis
  • Do not delay arthrocentesis for imaging
  • Overlying cellulitis is a relative contraindication — consult orthopedics

Synovial Fluid Analysis

Arthrocentesis of synoval fluid

Synovium Normal Noninflammatory Inflammatory Septic
Clarity Transparent Transparent Cloudy Cloudy
Color Clear Yellow Yellow Yellow
WBC <200 <200-2000 200-50,000

>1,100 (prosthetic joint)

>25,000; LR=2.9

>50,000; LR=7.7

>100,000; LR=28

PMN <25% <25% >50%

>64% (prosthetic joint)

>90%

Culture Neg Neg Neg >50% positive
Lactate <5.6 mmol/L <5.6 mmol/L <5.6 mmol/L >5.6 mmol/L
LDH <250 <250 <250 >250
Crystals None None Multiple or none None
  • Viscosity of synovial fluid may actually be decreased in inflammatory or infectious etiologies, as hyaluronic acid concentrations decrease
  • The presence of crystals does not rule out septic arthritis; however, the diagnosis is highly unlikely with synovial WBC < 50,000[1]
  • WBC >50,000/mm³ with >90% PMNs: highly suggestive of septic arthritis
  • Crystals: negatively birefringent (gout), positively birefringent (pseudogout)
  • Note: crystals and infection can coexist — always send culture even if crystals present
  • Gram stain: positive in ~50% of non-gonococcal septic arthritis
  • Culture: gold standard; also send blood cultures

Laboratory

  • CBC with differential, ESR, CRP
  • Blood cultures (positive in ~50% of septic arthritis)
  • Uric acid (may be normal during acute gout flare)
  • GC/CT NAAT if disseminated gonococcal infection suspected

Imaging

  • X-ray of affected joint: chondrocalcinosis (pseudogout), fracture, joint destruction
  • Ultrasound: confirm effusion, guide arthrocentesis
  • MRI if osteomyelitis or periarticular abscess suspected

Management

Septic Arthritis

  • Emergent orthopedic consultation for surgical drainage/washout
  • Empiric IV antibiotics after arthrocentesis:
  • Prosthetic joint infection: orthopedic consultation for operative management

Crystal Arthropathy

Traumatic

  • Splinting, pain management
  • Orthopedic follow-up for hemarthrosis or fracture

Disposition

Admit

  • Septic arthritis (for surgical drainage and IV antibiotics)
  • Prosthetic joint infection
  • Sepsis from joint source
  • Unable to rule out septic arthritis with pending cultures in high-risk patient

Discharge

  • Crystal arthropathy with adequate pain control
  • Traumatic arthritis/hemarthrosis with orthopedic follow-up arranged
  • Provide return precautions: fever, worsening pain/swelling, inability to bear weight
  • Primary care or rheumatology follow-up for gout/pseudogout management

See Also

External Links

References

  1. ↑ Shah K, Spear J, Nathanson LA, Mccauley J, Edlow JA. Does the presence of crystal arthritis rule out septic arthritis?. J Emerg Med. 2007;32(1):23-6.
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