Author: Kehinde Sunmboye
Indications, contraindications and potential complications are summarized in Table 124.1. If you are not familiar with joint aspiration, ask the help of a rheumatologist or orthopaedic surgeon.
- Confirm the indications for joint aspiration. Explain the procedure to the patient and obtain consent. Verbal consent is sufficient.
- The patient should lie down with the knee slightly flexed. The knee joint can be aspirated from the medial or lateral side. The needle should pass from a skin entry point 1 cm medial or lateral to the superior, middle or inferior third of the patella (see Figure 124.1). Points marked with X medially and laterally are the preferred entry sites due to the proximity to the suprapatellar pouch where effusions usually accumulate. Check the bony landmarks and mark the skin entry point with the tip of the needle cover.
- Put on gloves. Prepare the skin with chlorhexidine or povidone-iodine. Anaesthetize the skin with 2 mL of lidocaine 1% using a 25 G (orange) needle. Then infiltrate a further 5 mL of lidocaine along the planned needle path.
- Give the local anaesthetic time to work. Mount a 21 G (green) needle on a 20 mL syringe and then advance along the anaesthetized path, directing the needle perpendicularly behind the patella. Aspirate as you advance.
- When you enter the effusion, hold the needle steady and aspirate to dryness (two syringes may be needed if the effusion is large). Remove the needle and place a small dressing over the puncture site. Send samples of the effusion for analysis: ethylene diaminetetra-acetic acid (EDTA) tube for white cell count; plain sterile container for Gram stain and culture; plain sterile container for microscopy for crystals.
- Clear up and dispose of sharps safely. Write a note of the procedure in the patient's record: approach/appearance of synovial fluid/volume aspirated/samples sent. Ensure the samples are sent promptly for analysis.
Troubleshooting
Dry tap
- This may be due to misdiagnosis of effusion, or obesity with resulting difficulty in accurately identifying the bony landmarks.
- Try again from the lateral approach if the medial approach was used, and vice versa.
- If you still cannot obtain fluid, and septic arthritis needs to be excluded, use ultrasound to confirm the presence of the effusion and identify the appropriate puncture site and depth of needle insertion.
See Table 124.2.