General clinical analysis of synovial fluid

A general clinical examination (analysis) of joint fluid includes determination of the physicochemical properties of the fluid and microscopic examination of cellular elements.

Macroscopic characteristics of synovial fluid (color, turbidity, and viscosity) are assessed in transmitted light. Viscosity is assessed by the length of the mucin thread: the length of the thread formed by a drop released from a syringe should normally be more than 3 cm. During inflammation, viscosity decreases, and the length of the thread decreases accordingly.

The manipulation is performed with the patient in a sitting position with the arm lowered along the body and lying on the knee. The needle is inserted from the front, its end is directed slightly downwards and laterally, towards the coracoid process of the scapula; the needle is advanced backwards, towards the articular surface of the scapula. Puncture of the shoulder joint through the posterior approach is also possible.

The patient bends the arm at the elbow joint at an angle of 60°, the wrist is in a pronated position. The needle insertion point is located on the lateral surface of the joint, between the lateral epicondyle of the humerus and the radius.

The knee joint and its periarticular bags can be punctured with the patient lying on his back, with the lower limb extended at the knee joint. The needle, usually 0.8 mm in diameter, is inserted from the lateral side directly under the caudal edge of the patella. Alternatively, the needle can be inserted from the medial side, also under the caudal edge of the patella.

Macroscopic characteristics allow in many cases to differentiate between non-inflammatory, inflammatory and infectious effusions. In addition, the presence of blood in the joint fluid is possible. The type of effusion allows to assume a certain disease. So-called non-inflammatory effusions actually correspond to pathological processes characterized by mild or moderate inflammation, such as osteoarthritis.

Laboratory studies of the synovial fluid include cell counting and assessment of their qualitative composition, microbiological examination (if an infectious process is suspected), and microscopic examination of a native preparation to detect various cells and crystals. However, the choice of a specific study depends on the suspected diagnosis.

Reference values (normal) of synovial fluid

Indicator	Characteristic
Color	Colorless
Transparency	Transparent
Protein	No
Leukocytes, in 1 µl	<200
Neutrophils,%	<25

The study of synovial fluid plays an important role in determining the nature of the process in the affected joint.

Indications for joint puncture: monoarthritis of unclear etiology, discomfort in the affected joint (with an established diagnosis), the need to monitor the effectiveness of treatment for infectious arthritis, for differential diagnosis of arthritis and arthrosis, since the choice of a program for further examination and treatment of the patient depends on this.

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