What Is Joint Aspiration?

Overview

Your joints are like a well-oiled machine. Allowing muscle and bone to move smoothly in order for their effective and efficient functioning, the joints are an integral part of our system. like the lubricating oil that allows the gears of a machine to glide effortlessly against each other, the spaces around joints are filled with synovial fluid. Synovial fluid minimises friction and prevents the wear and tear of bones connected in a joint. Additionally it plays a role in shock absorption reducing external damage to the joint socket and its contents.¹

Joint Aspiration, also referred to as ‘Arthrocentesis’, is a procedure wherein this synovial fluid is extracted from the joint. This may be done either for diagnostic purposes or as a method to treat certain conditions.²

In the following article we will discuss the procedure more in-depth and look into why, how, and towards what end, the procedure may be conducted.

What is Joint Aspiration?

Joint Aspiration or Arthrocentesis is a procedure conducted in order to collect synovial fluid - the lubricating, shock-absorbing liquid present in the spaces around the joints - from a joint capsule for either diagnostic or therapeutic purposes.³

When do I need a Joint Aspiration?

Joint aspiration may be necessary in the diagnosis of conditions like 

• Arthritis- different types of arthritis show signs that can be observed in the synovial fluid of affected individuals
• Infections such as septic arthritis may be caused by the presence of infective bacteria in and around the joints. In such a case, analysis of the synovial fluid would reveal the presence of these microbes^3,4
• Gout - this is a relatively common condition in which uric acid accumulates, forms into crystals and deposits in the joint capsule causing inflammation.⁵ Joint aspiration may therefore be prescribed in order to test the synovial fluid for presence of these crystals⁶

Joint aspiration may also be recommended for the treatment of certain conditions. The accumulation of fluid in the joint capsule may cause you an immense amount of pain, not to mention swelling and inflammation, leading to restricted movement. Joint aspiration may then be carried out to remove the excess fluid, reducing the pressure in your joint, relieving the pain.³

Lastly, in some cases, when a treatment for a joint disorder must be injected directly into the synovial cavity, joint aspiration may be needed in order to remove some fluid to make space for the medicine being injected in.⁷

More detail regarding the aims and objectives of a joint aspiration procedure can be read here.

The Procedure

Arthrocentesis involves the use of a hollow needle, inserted into the joint capsule, and extraction using a syringe, via the inserted needle. The extracted fluid is collected and sent for analysis.

Prior to the procedure your healthcare provider will ask you to sign a consent form. Following this you will be asked for:

• Your medical history - including allergies
• Current and previous medication, 
• Whether you have had bleeding/clotting disorders in the past, 
• Whether you are, or suspect that you may be pregnant. 

Answering these questions to the best of your ability allows your healthcare provider to ensure all necessary preparations and precautions are taken

 If you want to know what to expect during a Joint Aspiration, you will find below a step-by-step description of the process:

1. Your doctor will first identify the sites of fluid build-up, examining the joint by hand. Alternatively, ultrasound may be used in order to scan for fluid if necessary.
2. The appropriate site of injection is determined and the skin of the surrounding area is swabbed with antiseptic to sterilise the region.
3. After the skin is dry, you will first be injected with local anaesthesia in order to numb the region. 
4. Following this, a larger needle and syringe are used. The needle is inserted all the way into the joint capsule. Due to the anaesthetic, this will not be a painful process - in fact, apart from slight pressure, you won't feel it at all! 
5. Your doctor will then remove as much of the accumulated synovial fluid/blood from the joint. If lots of fluid remains, multiple syringes may be used in order to completely drain the joint of fluid.^2,3

Finally, the extracted fluid is sealed in sterile tubes and sent to the lab for analysis. The puncture site is bandaged and the procedure is concluded.

Conditions Diagnosed or Treated with Joint Aspiration

Joint Aspiration is conducted in order to remove or collect the synovial fluid filling the joint cavity. This fluid is involved in lubrication of the joint, allowing for seamless motion of bones, while reducing friction and preventing wear and tear. Additionally the fluid acts as a shock-absorber, minimising damage to the bones and bathing them, as well as the other members of the joint capsule, in nutrients and molecules necessary for normal functioning. 

This exchange of molecules, and its presence in the joint capsule means that analysis of the synovial fluid can assist in the diagnosis of various joint-related conditions.

Removal of the fluid can serve to reduce pressure, mitigating pain in affected patients. In case of septic and hemorrhagic arthritis especially, arthrocentesis is a necessary part of treating the affected joint.

Synovial fluid analysis reveals conditions based on the categorization of synovial fluid extracted. This categorization is based on parameters such as the cellular, physical  and chemical composition of the fluid:

1. Normal synovial fluid: clear/straw coloured fluid in which the white blood cell count is at a relatively normal level (less than 2000 WBCs per microliter).² This type of synovial fluid indicates non-inflammatory forms of arthritis like osteoarthritis.⁸
2. Inflammatory synovial fluid: yellow synovial fluid with signs of inflammation.² This may be due to infection, which could lead to an increase in WBCs (2000-20,000 WBCs per uL). Inflammatory synovial fluid is also an indicator of Rheumatoid Arthritis, which is characterised by chronic inflammation.⁹ 
3. Inflammatory Synovial fluid with crystals: as mentioned above, gout is a disorder in which excess uric acid deposits in the joint socket as urate crystals. The synovial fluid extracted through arthrocentesis therefore reveals the presence of these crystals.⁹ 
4. Septic synovial fluid: Septic synovial fluid is opaque/cloudy with a high WBC count at 20,000-200,000 WBCs per uL.² This occurs with severe infection of the synovial fluid, causing septic arthritis. The infection can reach the joints through the bloodstream, and may have begun at another part of the body. Such infections include skin infections like staphylococcus, respiratory infections like streptococcus or even STDs like gonorrhoea.¹⁰ Early diagnosis of septic arthritis is essential as the disease is severe and progresses quickly. If diagnosed with septic arthritis, your Joint Aspiration procedure will involve the complete draining of synovial fluid from the affected joint/s.³
5. Hemorrhagic synovial fluid: analysis may reveal an opaque synovial fluid also containing blood.² This is called hemarthrosis or joint bleeding and occurs due to trauma or bleeding disorders such as haemophilia.¹¹ the entry of blood into the joint also leads to swelling and pain. Thus through joint aspiration the excess fluid, including all the blood, is drained from the joint capsule.

Complications

Joint aspiration comes with risks, however these complications are very rare. The inadvertent effects of a joint aspiration are as follows:

• Infection: Like all procedures involving needles or the opening of skin, there exists the risk of infection. However this only occurs if proper aseptic protocols are not correctly in place.² In a medical setting, this is extremely rare. Injection through infected regions of skin is notably avoided to minimise risk.
• Bleeding: the risk of bleeding is why your doctor may ask you about any history of blood disorders. Individuals with bleeding diathesis or with problems in clotting, have a risk of hemarthrosis - the entry of blood into the synovial cavity/fluid.² Stable injection of the needle minimises this risk
• Allergy: patients who suffer allergic reactions with local anaesthesia should avoid this procedure²

By determining all possible risks prior to your procedure - through questioning, examination and investigation of your medical history - your healthcare provider will account for all risks.

Aftercare and Recovery

Arthrocentesis is a generally safe, quick procedure with relatively quick recovery time. In some patients, normal activity can be conducted immediately following completion of the procedure, while others may be asked to rest and recover for 4-24 hours.¹² Healing from the procedure can be accelerated following the RICE method:¹³

• Rest - reducing physical activity as much as possible
• Ice - applying ice/cold packs around the joint using a cloth
• Compression - your physician would have appropriately bandaged and wrapped the joint
• Elevation - elevating the treated joint above heart-level

The joint which underwent the procedure will likely remain sore for a day or two. If you think it may be necessary, speak to your doctor about pain or anti-inflammatory medication. Consult your doctor before taking any medication as drugs like aspirin may increase the risk of bleeding.³

Following the procedure, if any of the following inadvertent effects occur, inform your healthcare provider:

• Fever over 100.4° F or 38° C
• Bleeding or fluid secretion from injection site
• Severe increase in pain at the site of joint aspiration

If any additional treatment is required as a result of these, your healthcare provider will guide you as necessary.

SUMMARY

Joint Aspiration, also called Arthrocentesis is a low-risk procedure involving the removal of some or all the fluid from the joint socket, also termed synovial fluid. The procedure involves insertion of a needle into the synovial cavity and draining of the synovial fluid. Joint aspiration may be conducted in order to collect synovial fluid for diagnosis of various joint disorders, or it may be to remove all of the infected/bloody synovial fluid from the joint of an affected individual. The procedure is recommended for the diagnosis of various forms of arthritis like osteoarthritis, and rheumatoid arthritis, as well as for infections of the joint. It is also necessitated in the case of severe conditions like septic or hemorrhagic arthritis, in which the synovial fluid abnormally consists of infectious bacteria or blood respectively. While the risk is low, poor care may lead to complications like bleeding, infection or allergic reaction. Generally, however, joint aspiration is a safe and quick procedure, provided accurate information is given to your doctor. It has shown good success rates and a quick recovery time.