Monoarthritis

Monoarthritis is pain and swelling affecting a single joint. Causes are diverse and include infection, crystal deposition disease, osteoarthritis, and trauma. The most common causes of acute monoarthritis are gout and septic arthritis. Clinical evaluation involves a focused history and physical examination to assess for risk factors for specific causes, onset and duration of symptoms, pain characteristics, and evaluation for joint effusion and extra-articular symptoms. Diagnosis is based on the suspected condition, but septic arthritis should be considered even in the absence of fever. Initial workup includes laboratory studies (e.g., CBC, inflammatory markers), synovial fluid analysis, and imaging (e.g., x-rays) of affected joints. Additional studies and specialist referral may be considered based on clinical suspicion. Management is based on the underlying cause and may include symptomatic treatment (e.g., analgesia), glucocorticoids, and/or antimicrobials.

Causes can be stratified by symptom acuity and the typical size of the affected joint, though overlap may occur.

Polyarticular or oligoarticular conditions (e.g., rheumatoid arthritis, reactive arthritis, seronegative spondyloarthropathies) can initially manifest as monoarthritis. ^[1][3]

Focused history ^[1][2][3]

• Joint symptoms
  • Onset and duration ^[3]
    • Acute: < 6 weeks
    • Chronic: ≥ 6 weeks
  • Affected joints
    • Small (e.g., distal interphalangeal joints) vs. large (e.g., knees, ankles, shoulders)
    • Peripheral vs. axial skeleton involvement: See also “Seronegative spondyloarthropathies.”
  • Mechanism of traumatic injury, if applicable
  • Inflammatory features: morning stiffness, gelling, symptoms of synovitis (e.g., warmth, erythema, swelling, tenderness)
  • Previous episodes with similar symptoms (typical of gout, osteoarthritis)
• Extra-articular and/or systemic symptoms (e.g., fever, rash, uveitis, urethral discharge)
• Past medical history
  • Risk factors for septic arthritis (e.g., prosthetic joint implant, recent joint surgery or injection, diabetes mellitus, chronic skin infection)
  • Risk factors for gout (e.g., kidney disease, hypertension)
  • Infectious diseases (e.g., features of gonococcal infection, tuberculosis)
  • Joint trauma
  • Diagnosed articular conditions
  • Medications, e.g.:
    • Glucocorticoids (risk factor for avascular necrosis)
    • Diuretics (risk factor for gout)
    • Anticoagulants (risk factor for hemarthrosis)
  • Alcohol intake (risk factor for gout and avascular necrosis)
  • Cancer
• Family history: autoimmune conditions (e.g., rheumatoid arthritis, seronegative spondyloarthropathies)
• Social history: occupation, intravenous drug use, STIs, exposures (e.g., tick bites, recent travel)

Patients with underlying articular conditions (e.g., rheumatoid arthritis, seronegative spondyloarthropathies) are at increased risk for septic arthritis. ^[2][3]

Fever may be present in acute gout, acute CPPD disease, septic arthritis, and flares of typically polyarticular conditions (e.g., rheumatoid arthritis).

Focused examination ^[1][2][3][4]

Joint examination

Findings should always be compared with the contralateral joint. See also “Orthopedic examination” for details on specific joints (e.g., hip joint examination, knee joint examination).

• Inspection
  • Swelling
  • Erythema
  • Muscle atrophy
  • Ecchymosis
  • Limb deformity
• Palpation
  • Warmth
  • Tenderness or pain (e.g., at the joint line or entheses)
  • Joint effusion
  • Neurovascular examination: especially if joint trauma or injury is suspected
• Range of motion (active and passive)
  • Degree of reduction
  • Pain with movement

Obtain urgent specialist consultation (e.g., orthopedic surgeon, neurologist) if neurovascular compromise is suspected.

Extra-articular examination

• Skin: rashes, nodules, vesicles or pustules, desquamation, tophi
• Eyes: conjunctival injection, signs of uveitis (e.g., ciliary flush, photophobia)
• Oropharynx: ulcers
• Neck: lymphadenopathy
• Neurological: motor function examination, focused sensory examination
• Genitourinary: urethral or vaginal discharge

The presence of extra-articular or systemic symptoms may be suggestive of a monoarticular presentation of rheumatoid arthritis or seronegative spondyloarthropathies. ^[1][3]

General principles ^[1][2][3]

• In most patients with monoarthritis, a presumptive diagnosis is identified during clinical evaluation.
  • Consider the diagnosis of septic arthritis in all patients with monoarthritis.
  • Obtain synovial fluid analysis for any unexplained acute joint effusion.
  • Tailor the diagnostic approach to the suspected condition (e.g., diagnostics for osteoarthritis).
  • Obtain initial laboratory and imaging studies if no specific cause is suspected.
• Monitor the patient closely; monoarthritis may resolve spontaneously or progress to oligoarthritis or polyarthritis.
• Consider early specialist referral (e.g., rheumatology, infectious diseases, orthopedics) if symptoms are present for ≥ 6 weeks or the diagnosis is unclear after an initial evaluation.

Consider septic arthritis in all patients with acute monoarthritis, even if fever is absent. ^[1][2]

Initial studies ^[1][4][5]

Synovial fluid analysis and culture ^[1][6]

• Indication: suspected septic arthritis, joint effusion of unknown cause
• Procedure: See “Arthrocentesis steps.”
• Findings
  • Increased WBC count (e.g., in septic arthritis, acute gout, rheumatoid arthritis)
  • Identification of crystals: in gout, CPPD disease
  • Positive Gram stain and/or culture: in septic arthritis
  • See also “Interpretation of synovial fluid analysis.”
• Additional considerations
  • Consider specialist (e.g., cardiology, hematology) input before arthrocentesis in patients receiving anticoagulants.
  • Consider inoculating synovial fluid into blood culture bottles to improve the sensitivity of cultures. ^[7]

Do not delay synovial fluid analysis in suspected septic arthritis; early detection and treatment are imperative to prevent permanent joint damage. ^[7]

Laboratory studies ^[1][3]

• CBC: may show leukocytosis associated with infectious conditions, acute gout, or acute CPPD disease
• Inflammatory markers (nonspecific study): may be elevated in infectious conditions, acute gout, or acute CPPD disease; usually normal in osteoarthritis
• Serum uric acid: usually elevated in acute gout

Normal or low levels of serum uric acid do not exclude an acute gout attack, and high levels may occur in patients with other causes of monoarthritis. ^[1][2]

X-rays ^[3]

• Bilateral x-rays may be useful for comparison (e.g., in osteoarthritis).
• Findings vary based on the underlying cause of monoarthritis.
  • See “Radiological signs of osteoarthritis.”
  • See “Imaging” in “Gout and hyperuricemia.”
  • See “Imaging” in “Calcium pyrophosphate deposition disease.”
• Other findings include occult fracture, avascular necrosis, and juxta-articular bone tumor.

X-rays are indicated if there is localized bone pain or recent trauma, or if monoarthritis persists for ≥ 6 weeks. ^[1][3]

Additional studies ^[1][4][5]

Obtain additional studies based on initial findings and the suspected cause.

• Laboratory studies, e.g.:
  • Blood cultures: suspected infectious cause (e.g., septic arthritis)
  • Autoantibodies (e.g., rheumatoid factor, ACPA): may be considered if symptoms persist for ≥ 6 weeks or if a monoarticular presentation of rheumatoid arthritis is suspected ^[3]
  • Lyme disease serology
  • Culture and/or NAAT for Neisseria gonorrhoeae ^[8]
  • See “Diagnostic workup of bleeding disorders” and “Diagnosis of hemophilia.”
• Imaging studies, e.g.:
  • Joint ultrasound (e.g., of the first MTP joint): if synovial fluid analysis is unequivocal, or if a subclinical effusion is suspected ^[1][2][9]
  • MRI of affected joints: if osteomyelitis or chronic causes of septic arthritis are suspected (e.g., fungal arthritis, Lyme arthritis) ^[3]
  • Arthroscopy: may be indicated for certain types of traumatic joint lesions (e.g., meniscus tear)