Joint aspiration

Overview & Definition

Picture the three-year-old who will not walk, carried into the emergency department with a flexed hip and a face that says pain, or the eight-year-old with a knee swollen tight and hot after a fever. In both, the question the team must answer quickly is whether there is infection in the joint, because septic arthritis dissolves articular cartilage within hours and the only way to answer the question with certainty is to aspirate the synovial fluid and analyse it. That is the territory this page owns. [5] [10]

A joint aspiration (arthrocentesis) is the percutaneous passage of a hollow needle through skin, subcutaneous tissue and the joint capsule into the synovial cavity, to withdraw synovial fluid for diagnostic analysis, to decompress a tense effusion or haemarthrosis, or to instil a drug such as a corticosteroid. The core diagnostic use is the child with a possible septic joint, where the cell count, Gram stain and culture of the fluid settle the diagnosis that no blood test or imaging can settle alone. The therapeutic uses are drainage of a painful effusion, washout of a septic joint in concert with the orthopaedic team, and the intra-articular corticosteroid injection that is a mainstay of juvenile idiopathic arthritis care. [12] [11]

What makes paediatric arthrocentesis a distinct skill from the adult procedure is the child who cannot hold still, the joints that are small and superficial or deep and inaccessible, and the clinical decision that dominates everything else — separating septic arthritis from the common and benign transient synovitis of the hip. The fellowship skill being tested is reading the limping child, applying the prediction rules to decide who crosses the threshold to aspiration, choosing the right joint and the right guidance, and performing a calm single-pass sterile procedure that yields diagnostic fluid without harm. [1] [10]