General clinical analysis of synovial fluid

A general clinical study (analysis) of fluid from the joint involves the determination of the physico-chemical properties of the fluid and the microscopic examination of cellular elements.

The macroscopic characteristics of the synovial fluid (color, degree of turbidity and viscosity) are evaluated in transmitted light. The viscosity is estimated by the length of the mucinic filament: the length of the filament formed by the droplet released from the syringe should normally be more than 3 cm. In inflammation, the viscosity decreases, so the length of the filament decreases.

Manipulation is performed in the patient's position while sitting with a hand lowered along the trunk and lying on the knee. The needle is inserted from the front, its end pointing slightly downwards and laterally, towards the coracoid process of the scapula; The needle advances posteriorly, towards the articular surface of the scapula. It is also possible to puncture the shoulder joint through the rear access.

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

The knee joint and its periarticular bags can be punctured in the position of the patient on the back, with the lower limb unbent in 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 distinguish between effusions of non-inflammatory, inflammatory and infectious. In addition, the presence of blood in the joint fluid is possible. The type of exudation allows to presume a certain disease. The so-called non-inflammatory effusions actually correspond to pathological processes characterized by mild or moderate inflammation, for example, osteoarthrosis.

Laboratory examinations of intraarticular fluid include cell counting and evaluation of their qualitative composition, microbiological examination (with suspicion of an infectious process), and microscopic examination of the native preparation for the detection of various cells and crystals. Nevertheless, the choice of a particular study depends on the alleged diagnosis.

Reference parameters (normal) of synovial fluid

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

Investigation of synovial fluid plays an important role in elucidating the nature of the process in the affected joint.

Indications for joint puncture: monoarthritis of unclear etiology, unpleasant sensations in the affected joint (with established diagnosis), the need to monitor the effectiveness of treatment for infectious arthritis, for the differential diagnosis of arthritis and arthrosis, as this determines the choice of the program for further examination and treatment of the patient.

[1], [2], [3], [4]