Knee Arthrocentesis: Removing Fluid from the Knee

I Have Fluid on My Knee — Does It Need to Be Drained?

Knee arthrocentesis is a medical procedure that involves removing fluid from the knee.

It plays a key role in relieving pain, diagnosing joint conditions and improving joint function.

Understanding the importance of the procedure, the process itself and post-procedure care is essential for patients and healthcare professionals alike.

The Importance of Arthrocentesis

• Pain Relief: Arthrocentesis is often performed to relieve the pain associated with joint effusions (knee swelling), such as those caused by traumatic injuries, arthritis or other inflammatory conditions.
• Accurate Diagnosis: By removing a sample of synovial fluid from the joint, your knee surgeon can accurately diagnose the underlying cause of the effusion. This is important for guiding treatment.
• Improved Joint Function: Reducing excess synovial fluid can significantly improve the range of movement and joint function, contributing to rehabilitation.

The Arthrocentesis Procedure

• Preparation: The patient is positioned comfortably and the knee is sterilised. A local anaesthetic is sometimes used to minimise discomfort during the procedure.
• Inserting the Needle: A needle is carefully inserted into the knee joint to aspirate the synovial fluid. In some cases, ultrasound may be used to guide the insertion of the needle.
• Aspirating the Fluid: The synovial fluid is aspirated. The volume removed can vary depending on the amount of fluid present and the purpose of the procedure.
• Sending for Analysis: The synovial fluid sample is sent for laboratory analysis to determine the presence of cells, crystals, bacteria or other substances that may aid the diagnosis.

Post-Arthrocentesis Care

• Rest and Elevation: After the procedure, it is advisable to rest and elevate the leg to help reduce any residual swelling.
• Monitoring the Arthrocentesis Site: The area where the needle was inserted should be monitored for signs of infection, such as redness, swelling or pain.
• Restricted Activity: Avoid strenuous physical activity involving the knee for a short period — 24 to 48 hours is common — to allow for proper recovery.
• Medical Follow-Up: The patient should follow the knee surgeon's post-procedure instructions and attend follow-up appointments to ensure proper recovery.

Conclusion

Knee arthrocentesis plays a crucial role in managing joint pain and accurately diagnosing joint conditions.

This minimally invasive procedure offers immediate relief and valuable information to guide subsequent treatment.

With appropriate post-arthrocentesis care, patients can expect an effective recovery and improved joint function.

Ongoing dialogue between the patient and their knee surgeon is essential to optimise outcomes and ensure satisfaction.

Text Reviewed in January 2026

Nuno Camelo Knee Surgery