Objective: To describe or determine reference values for the intracapsular cavity and its joint recess of the hip, knee and joints of the hand and for the tendon sheaths of fingers, examined with B-mode gray-scale ultrasonography (US) and power Doppler (PD) in healthy children.
Methods: Sixty healthy children (31 boys and 29 girls; age range 2-16 years) were examined bilaterally with gray-scale and PD US (after obtaining the informed consent), using a standardized technique. The maximum distance from bone surface to the outer margin of the capsule (namely, intracapsular cavity) and its joint recess of hip, knee, wrist, non-thumb metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints of the hand were measured with US. Mean values +/- 2 SD (standard deviation) were indicated as reference values.
Results: None of the children showed joint hip fluid. In 5% of the children younger than 5 years an intra-capsular PD flow signal was detected in the posterior layer of the hip capsule. Fluid was detected in 60 % of the suprapatellar recesses. A small amount of fluid was detected within synovial recesses of the fingers, most commonly in the 2 MCP and PIP joints. Less frequently, a hypoechoic rim was detected around the finger flexor tendons on the palmar surface of the metacarpal bone.
Conclusion: High-resolution US evidences a normal small amount of fluid located at the MCP and IFP joint recesses and/or the flexor tendon sheaths without any PD flow signal in healthy children, that is relevant for interpreting ultrasonographic findings in children with inflammatory diseases.