Emergency Medicine

KNEE ASPIRATION

Practical Procedures 493

TECHNIQUE

1 Explain the procedure to the patient and position the patient comfortably on
the bed, with the affected joint fully exposed.

2 Use a strict aseptic technique. Clean the skin with chlorhexidine and inject
2% lignocaine (lidocaine) 2–3 mL into the skin, subcutaneous tissue and
synovium.

3 Insert a large-bore, 14-gauge cannula at the mid-point of the superior
portion of the patella 1 cm lateral to the anterolateral edge (see Fig. 18.8).

4 Aim the cannula between the posterior surface of the patella and the inter-
condylar femoral notch.

5 Diagnostic tap
(i) Aspirate 15–20 mL fluid from the joint, and then withdraw the
syringe and needle.
(ii) Transfer 5 mL of fluid into each of the three sterile containers,
and label for biochemical testing including polarizing light
microscopy, microbiology and cytology.

6 Therapeutic tap
(i) Withdraw the needle and attach a 20 mL syringe with three-way
tap to the remaining catheter.
(ii) Do not apply too great a negative pressure on the syringe, as it
will cause the local tissues to occlude the cannula.

Figure 18.8 Knee aspiration.