Synovial Biopsy - Clinical Significance, Indications and Contraindications

Introduction

In the human body, there are various joints between the bones that enable or disable humans to move different body parts in different ways. Based on their histological structure, the joints are classified into three main types:

1. Fibrous Joints - Immovable joints.

2. Cartilaginous Joints - Slightly movable joints.

3. Synovial Joints - Movable joints.

When exercised for laboratory studies, the synovial tissue helps to understand what leads to the onset or progression of a disease condition and further helps to develop new treatment measures for the disease condition.

What Is a Synovial Joint?

A synovial joint has a synovial cavity between the articulating surfaces of the bones. At the joint, the surfaces of the bones are covered with a thin layer of strong, smooth articular cartilage (hyaline cartilage), which reduces friction and helps to absorb shock during movement.

A synovial membrane (synovium) encloses the joint like a capsule and produces synovial fluid, a thick, clear fluid that provides lubrication and nourishment to the joint. The synovial membrane is a thin specialized connective tissue and is an important component that forms an integrated joint along with bone, articular cartilage, tendon, ligament, and fibrous capsule. Synovial joints are classified into six types based on the movements they permit. The classification is as follows:

• Hinge Joint - Knee.

• Saddle Joint - Thumb.

• Planar Joint - Knuckle.

• Pivot Joint - Neck.

• Condyloid Joint - Wrist.

• Ball and Socket Joint - Shoulder.

All synovial joints allow for movement and are susceptible to arthritis.

What Is a Synovial Biopsy?

A synovial biopsy is a medical procedure involving the removal of a small tissue sample from the synovial membrane.

When Is Synovial Biopsy Indicated?

• Synovitis - Inflammation of the synovial membrane due to an infection which could be bacterial, viral, or fungal.

• Autoimmune Diseases - Such as rheumatoid arthritis (a disease condition that causes painful joints), and systemic lupus erythematosus (a disease condition that causes skin rashes and painful joints).

• Metabolic and Inherited Disorders - Such as Wilson’s disease (a disease condition causing copper accumulation), hemophilia (a disease condition where the blood fails to clot).

• Diseases - Such as gout (a disease condition that affects toes and fingers with uric acid crystal deposition), cancer of the synovium (a covering of the joints such as that of the knee).

• Evaluation of Treatment - To assess the effectiveness of a treatment that was initiated for disease management.

When Is Synovial Biopsy Contraindicated?

In individuals with skin infections, systemic infections, or presence of any coagulation abnormalities or clotting disorder conditions, a synovial biopsy cannot be performed. For the procedure to be performed with ease, the individuals need to cooperate well, even though synovial biopsy is noninvasive and does not involve many risks.

How Is a Synovial Biopsy Done?

The procedure is performed by using a needle or arthroscopy, a minimally invasive surgical technique that involves inserting a small camera and surgical instruments through small incisions in the skin. The steps for a synovial biopsy are as follows:

1. Anesthesia (a general, regional, or local anesthesia is given depending on the condition of the individual and the joint involved for synovial biopsy).

2. A small incision is made on the skin of the involved joint.

3. Through this incision, a surgical instrument with a three-sided cutting point enclosed in a tube which is called a trocar is inserted into the joint. A small light-enabled camera may also be used for better visibility into the joint.

4. A biopsy grasper is inserted through the trocar to remove a small piece of the synovial tissue membrane.

5. The biopsy grasper along with the excised tissue is removed.

6. Every instrument and aid is removed from the incision and the incision is closed using sutures.

7. The excised tissue sample is sent to the laboratory for examination. The sample of synovial tissue is then examined under a microscope to look for signs of inflammation, infection, or other abnormalities.

A synovial biopsy can also be done using an ultrasound-guided needle biopsy. In this procedure, an ultrasound scan is performed at the joint involved. A biopsy needle is inserted through a needle-sized trocar inserted at the joint after anesthetizing the area to excise a small-sized tissue. Multiple tissues can be excised in this procedure. Once all the needles and instruments are removed, the area does not require stitches and heals faster with just a bandage. The appropriate synovial biopsy procedure depends on the site involved and the cooperation of the individual.

What Is the Clinical Significance of Synovial Biopsy?

A synovial biopsy is a valuable diagnostic tool in the evaluation of joint diseases and can provide important information that cannot be obtained through other diagnostic methods. The clinical significance of synovial biopsy includes:

• Diagnosis of Arthritis - Synovial biopsy can help to identify the cause of joint inflammation and swelling, which can be due to a variety of conditions such as rheumatoid arthritis, osteoarthritis, infectious arthritis, and gout. The biopsy may also help in understanding the severity and activity of the disease, which in turn can help with the treatment measures.
• Decide Treatment - Based on the synovial biopsy result, the doctor can decide on appropriate treatment options or medications that can be prescribed to the individual. For example, if the biopsy shows evidence of an infection, antibiotics may be prescribed, whereas if the biopsy shows evidence of an autoimmune disease then the individual requires immunosuppressive drugs or disease-modifying immunomodulating drugs (DMARDs).
• Disease Outcome - The results of a synovial biopsy can help to predict the course of the disease and the response of the individual to treatments for rheumatic diseases. The presence of certain types of inflammatory cells (for example in acute bacterial infections, the presence of many polymorphonuclear leukocytes) in the synovium may indicate a poor prognosis of the disease.
• Research - Synovial biopsy can be used to increase the knowledge and study the pathophysiology of joint diseases and to develop new therapies. It can also help predict the treatment response of an individual. Biopsy samples can be analyzed using various techniques to identify specific proteins, genes, and other molecules that may be involved in the disease process and help discover new therapeutic targets.

What Are the Risks of Synovial Biopsy?

A synovial biopsy is generally considered a safe and minimally invasive procedure, but like any medical procedure, it carries some risks, such as bleeding, infection, and damage to surrounding tissues. The risks are outweighed by the benefits before doing the procedure.

However, more serious complications may arise as a result of damage to a blood vessel, which causes bleeding into the joint space and may cause stiffness or damage to the joint. During the biopsy procedure, the breaking of the needle instrument is another possible complication.

Conclusion

Recent advancements in synovial tissue research have been significant. This tissue is crucial in evaluating different rheumatic and non-rheumatic diseases, as it provides vital information on infections, cancer, and other disorders. Obtaining good quality synovial tissue samples from both large and small joints through safe and affordable methods is now possible and desired. Therefore, including synovial biopsy in clinical practice may play a vital part in managing diseases and making treatment decisions.