60 Year old presents systemically unwell with a ankle effusion.
The above ankle aspirate shows turbid fluid with a markedly raised white cell count, with a predominate neutrophilia. There is a small amount of RBC, with no crystal or bacteria seen. In this clinical context, the most likely diagnosis would be septic arthritis, but other differentials diagnosis need to be considered. See bleow:
| Cause | Fluid | WCC | PMN | Crystals | Bacteria |
| Noninflammatory | |||||
| OA or Traumatic Arthritis | Straw coloured, clear | <3000 | <25% | Nil | Nil |
| Inflammatory | |||||
| RA | Straw coloured, cloudy | 3000-20000 | <75% | Nil | Nil |
| Gout | Straw coloured, cloudy | 3000-20000 | <75% | Negative Birefringence | Nil |
| Pseudogout | Straw coloured, cloudy | 3000-20000 | <75% | Positive Birefringence | Nil |
| Infective | Yellow and turbid | >50 000 (92% Specificity)
(If >25000 has a 70% specificity |
>90% | Nil | <25% positive in gonococcal infection
50-75% positive in non gonococcal infection |
Ankle Aspiration:
Indication – to investigate cause of ankle effusion with no history of trauma. Usually to diagnose septic arthritis
Contraindications – overlying cellulitis, coagulopathy (relative in patients taking oral anticoagulants)
Process – identify the following landmarks – tibialis anterior, extensor hallucis longus, extensor digitorum longus, medial and lateral malleoli. Areas for aspiration – between medial malleolus and TA, or between TA and EHL, or between lateral malleolus and EDL. Use sterile technique, and LA. Use a 18 to 20G needle and 20ml syringe. Remove as much flid as possible. Use EDTA blood tube for cell count, and urine specimen jar for MCS. Send to lab for WCC, MCS and crystals.
Complications – infection, bleeding, pain, damage to bone and cartilage.