Trial OSCE exam: 'Practice' by Victoria

You are taking part in a trial exam created by Victoria. There are 18 OSCEs in this exam (180 minutes).
 

You have 3 minutes reading time. This OSCE will run for a maximum of 7 minutes.

Scenario:

John is a 54 year old male who presents to ED with an isolated warm inflamed knee joint on the right.

Please teach the junior registrar how to do a knee joint aspiration & interpret the joint aspirate results.

Instructions for the candidate

Please teach the junior registrar how to do a knee joint aspiration. Interpret the synovial fluid analysis provided.

Domains being examined

  • Medical Expertise
  • Teamwork and Collaboration
  • Scholarship and Teaching
 
The candidate has 3 minutes reading time. This OSCE is expected to run for a maximum of 7 minutes.

For the actor

For the examiner

Do not interact with candidate.

Domains Assessment Objectives

Medical Expertise

Teamwork and Collaboration

Scholarship and Teaching

Other Assessment Notes

Synovial fluid analysis for Interpretation:
Appearance- cloudy

WCC 45,000 mm3

Polymorphs 92%

Crystals- positively bifringent

Gram stain- negative

Culture pending

Knee joint aspiration
Indications
Diagnostic- to Ix for septic arthritis
Therapeutic- relieve the pain of a large, tense traumatic effusion

C/I
Overlying skin infection
Known bacteremia (rel C/I)
Prosthetic joint
Haemophilia (until clotting factors given)
Warfarin- value of reversing INR up to 4.5 not proven (risk of iatrogenic haemarthrosis low)

Cx rare
Skin bacteria introduced into joint space- 1/10,000
Haemarthrosis if bleeding diathesis
Allergy to LA

Technique
In general- puncture site should avoid tendons, major vessels & nerves
Pt position- Knee flexed 20 degrees (towel under popliteal region) [or knee fully extended]
Want quadriceps to be relaxed.

Assistant- compression of suprapatellar region

PPE, aseptic technique
Puncture site- Anteromedial approach. Superior portion or midpoint of patella, btn posterior surface of patella & intercondylar femoral notch. [Alternative- anterolateral approach]

18G needle or cannula, 3 way stop-cock, 60ml syringe
Keep needle & syringe parallel to bed.
Try to remove as much fluid as possible

Ix Gram stain, culture, cell count & differential, polarising microscopy
+/- glucose & protein & LDH (poor differentiators of infectious VS non-infectious cause)

Interpretation of above knee aspirate: DDx Septic arthritis or gout. Refer to ortho to consider washout then iv AB. Depending on patient's risk factors (eg immunosuppression, diabetes) and vital signs (eg fever, tachycardia), may start empiric iv AB prior to Ortho review.