Arthritis And Rheumatism

Joint Aspiration and Injection

Introduction: Joint aspirations and injections are common medical procedures used in the diagnosis and treatment of many different arthritic conditions. Known by the medical term "arthrocentesis, " aspiration of fluid from a joint usually involves placing a needle into a joint space and withdrawing fluid into a syringe or collecting device. The fluid that is removed from the joint, known as "synovial fluid, " can be sent for testing to determine if the joint is infected, inflamed, or filled with blood from trauma. Removal of fluid from joint spaces may also remove inflammatory cells and byproducts that can further damage a joint.[1] Finally, medications can be locally administered through a needle into a joint in order to reduce pain and inflammation at that site. [2, 3]

Understanding the Anatomy: Most, but not all joints in the human body can move. Those that do move are often lined by a fibrous capsule and ligaments that maintain the structural integrity of the joint. The joint space itself is defined by a thin layer of cells within the inner lining of the joint capsule known as the synovial membrane, and it secretes synovial fluid into the joint itself to lubricate and nourish its surface. Under normal conditions, most joints contain less than a few milliliters of clear, viscous, and acellular synovial fluid. However, with certain infectious, inflammatory, and traumatic disease processes, the volume and character of the joint fluid can change, and these changes can be detected in the fluid that is withdrawn from an affected joint. The most commonly aspirated joints include the knees, ankles, elbows, shoulders, wrists, and occasionally small joints of the hands and feet. Aspiration and injection of the hip is more complicated and usually accomplished with xray guidance.

What is involved in a joint injection?

• The specific procedure and anatomy of the joint will determine the size of both the needle and syringe involved. Most of the time, the procedure can be performed in a doctor's office or at a hospital patient's bedside. Aspiration or injection of hips is more complicated and usually attempted with radiographic guidance.
• The needle is hooked up to a syringe and the injection site marked.
• An antiseptic agent, such as iodine or isopropyl alcohol, is applied to the skin before the needle is inserted.
• To minimize discomfort, local anesthesia is used in some cases. This could be injected under the skin or applied as a cold, topical spray.
• A trained medical professional uses sterile technique to insert a needle into the joint space.
• For joint aspirations, fluid is drawn back into an empty syringe and sent to the laboratory for further analysis. For injections, a syringe is loaded with one or more medicines and then inserted into the joint space. In some cases where both an aspiration and injection are warranted, both the aspiration and injection syringes can be exchanged over the same needle while it is still located within the joint space, thereby minimizing the number of needle sticks.
• A simple bandage may be applied to the injection site once the procedure is completed.
• Many doctors generally recommended "resting" a joint for up to 12-24 hours after the procedure, which usually means limiting heavy use of that affected joint.

What are the Reasons to do Joint Aspiration? The most common reason that a doctor may recommend aspirating a joint is to make sure that it is not infected. [1, 2] Common signs of an infected joint include rapid onset of extreme pain with or without use of the joint, redness, warmth, and swelling. An infected joint is a medical emergency, and prompt diagnosis is required by aspirating fluid and sending it for analysis and culture.[1, 4] Other conditions that can cause similar symptoms include gout and rheumatoid arthritis, and examination of aspirated fluid can help aid the diagnosis of these conditions as well.

Indications for Joint Aspiration:

• Diagnosis of acute arthritis in one or more joints
• Remove fluid and relieve intra-articular pressure
• Serial aspiration of infected fluid from a joint

What are the Reasons to do a Joint Injection? In many instances, joint injections provide a safe, effective, and rapid means to treat local symptoms of pain and inflammation [4] without many of the side effects encountered with medications taken orally. They can also provide additional therapeutic benefits to those patients whose symptoms of pain and inflammation have not been completely relieved with oral anti-inflammatory and pain relieving medications. Frequently, the medication that is injected contains a cocktail of two different agents. One is usually a local anesthetic, and the other is an intra-articular preparation of a cortisone-type medicine (called a corticosteroid). The anesthetic rapidly relieves pain associated with the acute or chronic arthritis, however its effect usually lasts only for a few hours. The corticosteroid reduces pain and inflammation in the joint, and begins to take effect within a day or two, with effects lasting up to several months. [2] It is generally not recommended to inject the same joint more than once every three months.

• Treatment of pain and inflammation caused by crystal-induced diseases such as gout and pseudogout.
• Reducing pain and inflammation from rheumatic diseases such as, but not limited to, rheumatoid arthritis, psoriatic arthritis, reactive arthritis, and ankylosing spondylitis.
• Relief of pain resulting from osteoarthritis. For a subset of patients with osteoarthritis of the knee who do not respond to this therapy, a series of "viscosupplementation" injections may be prescribed. These agents are thick viscous substances that are thought to lubricate the joint surface and reduce pain.

Interpretation and Analysis of Joint Fluid: So what happens to that fluid once it is aspirated into the syringe? Usually, it is sent for several types of tests to determine if the fluid is infected, inflamed, bloody (usually from a traumatic process), or otherwise bland. Depending upon the results of these tests, the synovial (joint) fluid can be categorized into one three classes that help the doctor determine the cause for the joint problem: non-inflammatory, inflammatory, or infected (see table below). A fourth class of joint fluid, hemorrhagic, may be encountered when blood is aspirated from a joint.

First, the different types of leukocytes (white blood cells) are counted to determine if the fluid is inflammatory or non-inflammatory, with inflamed and infected joints having higher numbers of white blood cells in their fluid. [5] Next, the fluid can be sent for culture to determine if it is infected. If infected, the organism(s) can usually be identified and tested for susceptibility to various antibiotics. Finally, the fluid can be visualized under a polarized microscope to determine if there are any crystals present. The diagnosis of gout, for example, can frequently be made by identifying needle shaped uric acid crystals in joint fluid that is visualized by polarized microscopy.

Classes of Synovial Fluid

Class I Class II Class III

Non-Inflammatory Inflammatory Infected

Color Clear/Yellow Yellow/White Yellow/White

Clarity Transparent Slightly Opaque Opaque

Viscosity High Medium Low

White Blood Cell Count 50-100, 000

(WBC's per microliter)

Types of WBC's 50% >90%

(% of Neutrophils)

Culture Negative Negative Positive

Some Side Effects and Complications: Most of these side effects and complications are rarely encountered in normal clinical practice, but should be understood and recognized. [1-4]

• Infection of the joint: A very rare complication whereby bacteria are introduced from the skin into the joint space. Studies estimate that this occurs in roughly 1:80, 000 joint injections.
• Atrophy of the skin overlying the injection site: This can occur especially with shallow injections of joints and soft tissues. Some of the fat underneath the skin can disappear and cause dimpling or divots.
• Atrophy and rupture of tendons: A very unusual complication that may or may not be related to a previous corticosteroid injection.
• De-pigmentation (loss or lightening of skin color): Can happen at the site of injection, especially with shallower injections.
• Post-injection flares of pain and inflammation: An acute worsening of arthritis can occur as a reaction to crystals contained in the corticosteroid preparation. Onset of these symptoms usually occurs within 24-36 hours of the injection [3] and is usually self-limited, causing no lasting effects.
• Post injection flushing
• Bleeding into the joint

Selected References:

1. Imboden J., Hellmann D., and Stone J. Current Diagnosis and Treatment in Rheumatology 2007. 2nd edition. McGraw Hill
2. Courtney P and Doherty M. Joint Aspiration and Injection. Best Practice & Research Clinical Rheumatology 2005; 19:345-369.
3. Cardone D and Tallia A. Joint and Soft Tissue Injection. American Family Physician 2002; 66:283-288.
4. Dooley P and Martin R. Corticosteroid Injections and Arthrocentesis. Canadian Family Physician 2002; 48:285-292.
5. Shmerling RH, Trentham DE, et al. Synovial Fluid Tests. What Should be Ordered? JAMA 1990; 264:1009-1014.

Other Recent Academic Articles of Interest

1. McGillicuddy D, Edlow J, et al. How Sensitive is the Synovial Fluid White Blood Cell Count in Diagnosing Septic Arthritis? American Journal of Emergency Medicine 2007; 25:749-752.
2. Li S, Torres J, et al. Diagnostic Utility of Laboratory Tests in Septic Arthritis. Emergency Med J. 2007; 24:75-77.

Websites with Useful Information

1. American College of Rheumatology

http://www.rheumatology.org/public/factsheets/injection_new.asp?aud=pat

2. American Academy of Family Physicians

http://www.aafp.org/afp/20020715/290ph.html

3. American Academy of Orthopedic Surgeons Fact Sheet: Viscosupplementation for Osteoarthritis

http://orthoinfo.aaos.org/topic.cfm?topic=A00217&return_link=0