Joint Aspiration

The joint puncture, also called arthrocentesis, is a diagnostic or therapeutic procedure in which fluid is removed from a joint. The removed synovial fluid is examined in the laboratory to diagnose diseases or inflammations in the joint. In dogs, joint puncture is frequently used when the cause of swelling, pain or movement restrictions in the joints needs to be clarified.

Joint aspiration is usually performed on large joints such as the elbow, knee or hip joints.

When is joint aspiration performed in dogs?

A joint aspiration is indicated if there is a suspicion of a joint disease or an inflammation and the exact cause needs to be determined. The most common areas of application include:

• Arthritis (joint inflammation): If infectious or non-infectious arthritis is suspected, joint aspiration is used to find inflammatory cells, bacteria or other signs of infection in the joint fluid.
• Autoimmune diseases: Diseases such as rheumatoid arthritis or lupus affect the joints and can be diagnosed by analysing the synovial fluid.
• Injuries: If a dog has suffered an acute injury to the joint, for example due to an accident or overexertion, arthrocentesis can be used to check whether there is bleeding or inflammation in the joint.
• Degenerative joint diseases: In chronic conditions such as osteoarthritis (joint wear and tear), examination of the synovial fluid can provide clues about the degree of inflammation and possible changes in the joint.
• Infections: Arthrocentesis is performed to check whether a bacterial infection is affecting the joint (septic arthritis).

Procedure for arthrocentesis in dogs

The joint aspiration is performed under local anaesthesia or light sedation, so that the dog remains calm and does not feel pain.

Preparation

• The dog’s joint is shaved and disinfected to minimise the risk of infection.
• In some cases, the dog is lightly sedated or locally anaesthetised to make the procedure as stress-free as possible.

Inserting the needle

A sterile needle is inserted into the joint space. It penetrates through the skin and surrounding tissue into the joint.

Withdrawal of synovial fluid

A small amount of synovial fluid is withdrawn from the joint with a syringe and then sent to the laboratory for analysis.

Conclusion

After the fluid has been removed, the puncture site is disinfected and bandaged in some cases. The dog can usually go home shortly after the procedure.

Analysis of synovial fluid

The withdrawn joint fluid is examined in the laboratory for various parameters to determine the cause of the joint problems:

• Colour and consistency: Normal synovial fluid is clear and viscous. Cloudy or reddish fluid may indicate inflammation, infection or bleeding.
• Cell count: The number and type of cells in the fluid are counted. High levels of white blood cells indicate inflammation or infection.
• Bacterial examination: The fluid can be tested for bacteria to determine whether septic arthritis (bacterial joint inflammation) is present.
• Crystals: In rare cases, crystals can be detected in the synovial fluid, which may indicate gout or similar conditions.

Risks and complications of arthrocentesis

A joint aspiration is considered a safe procedure. However, as with any medical intervention, there are some risks:

• Infections: Although the needle is sterile and the procedure takes place under hygienic conditions, there is a slight risk that bacteria may enter the joint and cause an infection.
• Bleeding: In rare cases, minor bleeding may occur in the joint or at the puncture site after the procedure.
• Pain or swelling: Some dogs experience pain, swelling or stiffness in the affected joint after arthrocentesis. Such symptoms usually subside on their own.
• Injuries: There is a very slight risk that tissue, ligaments or cartilage in the joint may be injured by the needle.

Aftercare following arthrocentesis

After the procedure, the dog should be kept calm for a few hours. In most cases, dogs can walk normally again on the same day, but intensive activities should be avoided for a few days. The vet may prescribe a painkiller if the dog has pain after the aspiration.

When is arthrocentesis not suitable?

There are situations in which a joint aspiration may not be suitable or should only be carried out with caution:

• Severe joint deformities: In dogs with advanced joint damage, it can be difficult to insert the needle safely without damaging tissue.
• Blood clotting disorders: In dogs with blood clotting disorders or those taking blood thinners, there is an increased risk of bleeding after the procedure.