Instructions
You are a medical student on placement on the general medical ward. Joanna Dela Cruz, 79, is on day 3 of an admission with pneumonia. Overnight her right knee became hot, swollen and painful; this morning her temperature is 37.9 and her CRP has risen from 74 to 132 mg/L. The registrar has aspirated the knee.
Interpret the results provided
Outline to the examiner:
- Your most likely diagnosis and differentials
- You do not need to take a history or examine the patient
- The examiner will ask you one question at the end
Background
Chronic kidney disease (eGFR about 45); heart failure; high blood pressure; osteoarthritis of both knees. No joint replacements; no previous hot or swollen joints.
Medicines
Furosemide 40 mg daily, amlodipine 5 mg daily, paracetamol as needed. Since admission: IV benzylpenicillin 1.2 g 6-hourly, oral doxycycline 100 mg 12-hourly, enoxaparin 40 mg subcut daily.
Registrar's examination
Right knee hot and tender with a large effusion; movement very limited by pain. No skin break or spreading redness. Left knee: crepitus on movement, no effusion. Other joints normal.
Right knee synovial fluid, aspirated 7.30 am today
| Item | Value | Reference range |
|---|---|---|
| Volume | 35 mL | - |
| Appearance | Turbid, yellow; not blood-stained | Clear, straw-coloured |
| White cell count | 42000 x10^6/L | <200 x10^6/L |
| Neutrophils | 90% | <25% |
| Crystals (compensated polarised light) | Rhomboid and rod-shaped crystals, weakly positively birefringent; some inside neutrophils | None seen |
| Gram stain | No organisms seen; many neutrophils | - |
| Culture | Pending; final result expected in 48 hours | - |
Right knee X-ray, AP and lateral, this morning
| Item | Value | Reference range |
|---|---|---|
| Projection and adequacy | AP and lateral, taken lying; adequate | - |
| Bones and alignment | Mild osteopenia; no fracture, erosion, periosteal reaction or bone destruction | - |
| Joint spaces | Patellofemoral space narrowed with small osteophytes; tibiofemoral spaces mildly narrowed | - |
| Menisci and cartilage | Fine linear calcification within the medial and lateral menisci, running parallel to the joint surfaces | - |
| Soft tissues | Large suprapatellar effusion; no gas in the soft tissues | - |