Student Memory Support
TOPIC 2. ACUTE MONOARTHRITIS AND INFECTIVE ARTHRITIS
Final Year MBBS • Musculoskeletal Module
High-yield recall, clinical associations and last-minute revision.
1. High-Yield Flashcards
Tap each question to reveal the answer.
What does monoarthritis mean?
Inflammation affecting one joint.
Which diagnosis needs urgent exclusion in an acutely hot, swollen joint?
Septic arthritis, because delayed treatment can cause rapid joint destruction.
Which bacterium is a leading cause of adult native-joint infection?
Staphylococcus aureus.
Which organism can cause relatively subtle bacterial arthritis in young children?
Kingella kingae; fever and inflammatory-marker elevation may be modest.
What are the core tests on aspirated synovial fluid?
Cell count with differential, Gram stain, bacterial culture and crystal analysis.
Does a negative Gram stain rule out bacterial arthritis?
No. Its sensitivity is limited; culture and the clinical findings remain important.
What does ultrasound contribute in a painful hip?
It detects an effusion and can guide aspiration; fluid detection alone does not establish infection.
When is MRI particularly useful in suspected joint infection?
When assessing adjacent osteomyelitis, a deep abscess or the extent of infection.
Why might an infant with joint infection appear to have a paralysed limb?
Pain causes avoidance of movement: pseudoparalysis.
Why should the hip be examined in a child with unexplained knee pain?
Hip disease can refer pain to the knee.
What is Phemister’s triad in tuberculous arthritis?
Periarticular osteopenia, marginal erosions and gradual joint-space narrowing.
Which tissue finding supports tuberculous arthritis?
Caseating granulomatous inflammation, interpreted with microbiological testing and clinical findings.
Why can acid-fast staining be negative in joint tuberculosis?
The infection may be paucibacillary, meaning few organisms are present in the specimen.
What are the two central treatment components for bacterial arthritis?
Systemic antibiotics and adequate drainage of the infected joint.
When may surgery be needed in tuberculous arthritis?
For selected abscesses, persistent disease or major structural damage; it complements antituberculous treatment.
What supports transient synovitis rather than an aggressive infection?
A well child with a mild postviral limp and preserved weight-bearing; progression or red flags require reassessment.
2. Mnemonics
Mnemonic Title: Major cause groups of monoarthritis
Mnemonic Word: I-CTIB
Meaning: Infection • Crystals • Trauma • Immune inflammation • Bleeding.
Mnemonic Title: Radiographic clues in joint tuberculosis
Mnemonic Word: O-E-N
Meaning: Periarticular Osteopenia • Marginal Erosions • Gradual joint-space Narrowing.
Mnemonic Title: Initial drugs for drug-susceptible joint tuberculosis
Mnemonic Word: HRZE
Meaning: H—Isoniazid • R—Rifampicin • Z—Pyrazinamide • E—Ethambutol.
3. Memory Tables
Pyogenic versus tuberculous arthritis
| Feature | Pyogenic bacterial disease | Tuberculous disease |
|---|---|---|
| Course | Rapid: hours to days | Indolent: weeks to months |
| Tissue response | Neutrophilic, suppurative | Granulomatous, potentially caseating |
| Presentation | Severe pain; fever may occur | Persistent swelling and stiffness |
| Diagnostic evidence | Joint-fluid bacterial testing | Mycobacterial testing ± tissue histology |
| Treatment principle | Antibiotics plus drainage | Combination therapy ± selected surgery |
Childhood limp: septic arthritis versus transient synovitis
| Feature | Septic arthritis | Transient synovitis |
|---|---|---|
| General condition | May be febrile or unwell | Generally well; may follow viral illness |
| Weight-bearing | Refusal is a concerning clue | Often retained, with a limp |
| Hip effusion | May be present | May be present |
| Management | Urgent assessment and infection treatment | Rest, analgesia and reassessment |
These patterns guide assessment; no single feature reliably excludes infection.
4. Rapid Revision Points — Last-Minute Revision
Must Remember:
- Painful restriction of passive movement supports an intra-articular problem.
- Immunosuppression can blunt fever and the synovial inflammatory response.
- Crystals and bacterial infection can coexist in the same joint.
- A normal serum urate during an attack does not exclude gout.
- Early septic arthritis can have normal plain radiographs.
- Blood cultures can identify a bloodstream source of joint infection.
- Normal chest imaging does not exclude osteoarticular tuberculosis.
- A positive immune-based TB test does not establish active joint disease.
- Persistent fever, worsening pain or rising markers during treatment require reassessment.
- After infection control, progressive mobilization helps limit stiffness and disability.
5. Clinical Memory Hooks
Clinical Hook: Fever + refusal to bear weight → urgent assessment for joint or bone infection.
Clinical Hook: Bloody effusion + bleeding tendency → consider haemarthrosis and assess the underlying cause.
Clinical Hook: Months of hip or knee swelling + wasting or weight loss → investigate tuberculous arthritis.
Clinical Hook: Persistent sterile childhood joint swelling + morning stiffness → consider juvenile idiopathic arthritis.
Clinical Hook: Tense infected hip effusion → compromised femoral-head perfusion → risk of avascular necrosis.
6. Starred High-Yield Exam Points
High-Yield Points:
- ⭐ Suspected septic arthritis is a joint-threatening emergency: antibiotics and adequate source control are central.
- ⭐ Stable patient with prompt sampling available: collect joint fluid before antibiotics to preserve culture yield.
- ⭐ Sepsis or shock: do not delay resuscitation and antibiotics while waiting for aspiration.
- ⭐ No fever, normal C-reactive protein or a low synovial cell count does not reliably rule out infection.
- ⭐ Defer intra-articular corticosteroids while a possible joint infection is being investigated.
- ⭐ Early improvement in joint tuberculosis does not mean eradication: complete the prescribed combination treatment.