Synovial Fluid Analysis- An Overview

Introduction

Synovial fluid is a collection of fluid that is contained in a joint space. Synovial fluid is physiologic and serves as a joint space lubricant of articular cartilage as well as a nutrition supply for surrounding tissues such as cartilage, meniscus, labrum, and so on. Synovial fluid is predominantly composed of hyaluronan, lubricin, proteinases, collagenases, and prostaglandins and is formed as an ultrafiltrate of blood plasma. Synovial fluid is produced by fibroblast-like type B synovial cells. Trauma, inflammation and bacterial, fungal, or viral penetration all cause physiological alterations in the volume and composition of the synovial fluid. When patients arrive with intensely painful joints and suspicion of infection, inflammation, non-inflammatory causes of effusion, or aspiration, an examination of synovial fluid is critical to help in diagnosing and directing therapeutic methods.

The traditional routine synovial fluid (SF) examination includes a total and differential white blood cell (WBC) count as well as a detection for monosodium urate and calcium pyrophosphate crystals. Once basic calcium phosphate crystals are detected, alizarin red staining is done, whereas microbiological investigations are conducted in situations of suspected septic arthritis.

How Is the Synovial Fluid Sample Collected?

• In the presence of joint effusion, unclear cause of joint discomfort, or anticipated infection inside a joint area, arthrocentesis can help in identification. When considering intra-articular injection, aspiration should be done initially as the aspirated fluid should be evaluated for the presence of any gross abnormalities or evidence of gross infection.

• Arthrocentesis can also be used therapeutically to relieve pain in a painful joint if an effusion or hemarthrosis (bleeding in the joints) is impeding the complete range of motion of the afflicted joint. In order to reduce the danger of infection and contamination of the aspirate, aspiration should be conducted by a skilled physician following sterile procedural protocol.

What Are the Procedures for Synovial Fluid Collection?

• Arthrocentesis is the procedure of collecting synovial fluid by aspiration into the joint space. This technique should be conducted in sterile settings by a physician with a solid understanding of the associated anatomy. Sterility is required not just to avoid transmission of infection but also to ensure proper fluid analysis. Although ultrasound technology can help ensure proper needle insertion, it is frequently unneeded.

• Fluoroscopy and CT-guided arthrocentesis can also be useful for deeper joints such as the shoulder and hip. After arthrocentesis indications are satisfied, an aspiration site is chosen and marked. The literature extensively details the safe entrance ports for the shoulder, elbow, wrist, hip, knee, and ankle.

• The area is subsequently treated and wrapped in the standard sterile manner, using antiseptics such as alcohol, Betadine, and Chlorhexidine. For local pain relief, a cutaneous or subcutaneous wheel can be created using local anesthetic. Following that, a large gauge, sharp needle, generally 18 gauge (or less if aspirating a smaller joint), is introduced into the joint and connected to a minimum 10 cc syringe.

• A spinal needle may be an alternative for deeper joints or people with difficult anatomy due to obesity. After gaining access to the joint, maintain negative pressure in the syringe till an appropriate volume of synovial fluid is collected.

• After that, the fluid should be deposited into a sterile specimen collecting cup and sealed before being sent to the laboratory for examination. The syringe may be frequently emptied and reattached to the indwelling needle, reducing needle entrance sites.

• After the treatment, the antiseptic should be washed off the skin, dried, applied pressure, and covered with a soft dressing for local hemostasis. In the absence of additional disease, no adjustments in activity or weight-bearing status are required following the surgery. Compressive ace bandage dressings are frequently used to help avoid fluid reaccumulation.

What Are the Indications?

Indications for synovial fluid aspiration and analysis include:

• Acute painful joint with warmth or redness surrounding the joint.

• The belief of septic arthritis.

• Doubt of subacute or chronic infection in the periprosthetic joint.

• Acute exacerbation of chronic knee pain from osteoarthritis.

• Non-inflammatory arthritis.

• Acute trauma with painful effusion.

With the clinical appearance of a damaged knee, arthrocentesis for hemarthrosis can often be therapeutic and give considerable pain relief. Effusions from chronic inflammatory arthritis can be aspirated for pain relief. Aspiration is also indicated by a clear diagnosis of gout or pseudogout. It should be noted that infection and gout can occur in the same joint region. Effusions of uncertain cause should be aspirated and analyzed.

What Are the Normal and Critical Findings?

It is crucial to note that cell count criteria differ in joints that have previously had the hardware, such as post-traumatic fixation with hardware or prior joint replacement.

1. Analyses of Native Adult Joint Synovial Fluid: Guidelines from the American Rheumatological Association are given below.

• Non-inflammatory less than 200 to 2000 WBC cells/mm3.

• Inflammatory more than 2000 to 50,000 WBC cells/mm3.

• Infectious more than 50,000 WBCcells/mm3.

2. Differential With Polymorphic Nuclear Cells (PMNs): More than 75 percent of PMNs are suggestive of bacterial joint infection.

3. Gout and Pseudogout Crystal Analysis:

• The presence of monosodium urate crystals implies gout.

• The presence of calcium pyrophosphate dihydrate crystals implies a pseudogout diagnosis.

4. Gram Stain and Bacterial Culture: To assess the existence of infection, the synovial fluid aspirate is examined for gram stain and aerobic and anaerobic culture; the existence of any organism suggests aberrant results.

What Are the Factors That Interfere With Aspiration?

Many reasons can obstruct aspiration and hence synovial fluid analysis. Aspiration failure is prevalent because the synovium might block the needle and interfere with sample collection. The collected fluid may be contaminated if the procedure is not sterile. It is vital to note that several etiologies might coexist; for example, the presence of gout does not rule out the existence of a concurrent infection.

What Are the Potential Diagnosis?

The following are possible diagnoses based on synovial fluid aspiration and analysis:

• Non-Inflammatory Arthritis: Involve effusion from osteoarthritis or meniscal tears, or inflammatory arthritis, which includes gout, pseudogout, infection, or spondyloarthritis.

• Septic Arthropathy: Acute septic arthropathy, subacute or chronic septic arthropathy, or periprosthetic infection of the joints.

• Hemorrhagic: Traumatic damage to a tendon, meniscus, or ligament or spondyloarthritis.

What Are the Complications?

Problems from arthrocentesis are uncommon, and those that do arise are usually minor. Potential complications include: creating a cutaneous infection inside the joint; causing damage to the cartilage from needle placement (rare); causing persistent pain at the arthrocentesis site or local ecchymosis (discoloration caused by bleeding below the skin); causing bleeding and iatrogenic hemarthrosis; and causing a skin reaction to antiseptics or soft bandage adhesive. Reaccumulation of the joint effusion is the most common problem documented.

Conclusion

Aspiration and analysis of the synovial fluid are important therapeutic and diagnostic methods for relieving pain caused by a joint effusion and diagnosing potentially significant joint diseases. It is a low-cost, extremely effective method of pain relief and diagnostics that may be performed rapidly at the bedside without the use of general anesthesia. Arthrocentesis does not necessitate the use of a specialized surgeon, which boosts its value in terms of rapid therapy and diagnosis.