Final Year MBBS • Musculoskeletal Module
TOPIC 2. ACUTE MONOARTHRITIS AND INFECTIVE ARTHRITIS
Connect the causes, diagnostic clues and treatment decisions for rapid revision.
1. THE TOPIC IN ONE CONNECTED FLOW
Monoarthritis is a clinical pattern with several possible causes. Infection, crystals, trauma and immune inflammation can produce similar joint symptoms, but their urgency and treatment differ. This flow connects the initiating process to joint dysfunction, diagnostic evidence and intervention, with particular attention to bacterial and tuberculous disease of the hip and knee in adults and children.
Bacterial entry or tuberculosis → infection.
Crystal deposition, injury, bleeding or immune activity → noninfective inflammation.
Pyogenic bacteria → acute neutrophilic inflammation.
Mycobacteria → slower granulomatous inflammation; crystals or injury → inflammation through a different trigger.
Synovial swelling and fluid accumulation → capsular distension and restricted movement.
Uncontrolled infection → cartilage or bone damage; chronic tuberculosis → progressive erosions and deformity.
Rapid severe pain, warmth and systemic illness → urgent concern for bacterial disease.
Persistent swelling and stiffness → assess chronic causes, including tuberculosis; childhood limb nonuse → assess pain as well as weakness.
Joint fluid → cell count, Gram stain, culture and crystals.
Imaging → effusion, structural injury or adjacent infection; suspected tuberculosis → mycobacterial testing and tissue histology when needed.
Bacterial disease → systemic antibiotics plus drainage.
Tuberculosis → combination antituberculous therapy, with surgery for selected complications; noninfective causes → appropriate anti-inflammatory, injury or bleeding care.
Effective treatment → reduced inflammation → guided movement and functional recovery.
Delayed control → stiffness, joint destruction or deformity; childhood infection may also disturb growth.
2. KEY CLINICAL CONNECTIONS
Similar swelling, different treatment targets
Crystals in fluid → crystal-triggered inflammation → anti-inflammatory treatment after assessing for infection; a traumatic bloody effusion → bleeding or structural injury → address the underlying cause.
Localized periarticular tenderness with relatively preserved passive movement → consider tendon or bursal disease → distinguish it from inflammation inside the joint.
Childhood presentation changes the assessment
Hip disease → referred knee pain → examine the hip when the knee findings do not explain the symptoms; painful limb nonuse in an infant → pseudoparalysis → investigate a joint or bone source.
A well child with an improving postviral limp → supportive care with review; persistent sterile inflammation → consider juvenile idiopathic arthritis → pediatric rheumatology assessment.
Tuberculosis needs joint-specific evidence
Periarticular osteopenia + marginal erosions + gradual joint-space narrowing → support chronic destructive disease; caseating granulomas → support tuberculosis → seek microbiological confirmation.
Normal chest imaging or negative acid-fast staining → limited exclusion value → continue joint assessment when suspicion persists; a positive immune-based TB test → evidence of infection, not proof of active arthritis.
3. AIM HIGH-YIELD INTEGRATION REVIEW
- ⭐ Clinical urgency → antibiotic timing: A stable patient with prompt access to aspiration → obtain samples before antibiotics; sepsis or shock → resuscitate and treat immediately without waiting for joint sampling.
- ⭐ Negative findings → cautious interpretation: No fever, normal blood markers, a negative Gram stain or a lower synovial cell count → infection may still be present → interpret the whole clinical picture.
- Imaging finding → diagnostic limit: Ultrasound detects fluid but does not establish its cause → combine it with clinical assessment and sampling; concern for adjacent osteomyelitis or an abscess → MRI can define the extent.
- Organism and host context → treatment selection: Staphylococcus aureus is a key adult pathogen; Kingella kingae can produce subtle illness in young children → age and resistance risks guide empirical coverage, followed by culture-directed treatment.
- Persistent illness → reassess source control: Worsening pain, ongoing fever or rising inflammatory markers during treatment → consider residual pus, adjacent infection or ineffective antibiotics → reassess drainage and therapy.
- Tuberculosis response → continued treatment: Early pain relief does not establish eradication → complete the prescribed combination regimen; an abscess or disabling residual destruction → assess the appropriate surgical role.
- Functional loss → planned rehabilitation: Infection control and improving pain → progressive mobilization and strengthening → reduced stiffness and better independence; growth-plate injury in children → monitor growth and alignment.
- Anti-inflammatory benefit → infection caution: NSAIDs reduce symptoms but do not eradicate bacteria → use as supportive or cause-specific therapy; suspected joint infection → defer intra-articular corticosteroids until adequately investigated.
Crystals identified → a crystal process is present, but bacterial infection can coexist → assess cultures and clinical findings before attributing the entire episode to gout or calcium pyrophosphate disease.