Sonographic appearance of fluid in peripheral joints and bursae of healthy asymptomatic Chinese population.

Background: High frequency ultrasound is often used to measure the thickness of fluid in peripheral joints and bursae of healthy asymptomatic populations. Two major steps critical to this procedure are obtaining the detection rates and analyzing the relevant factors.

Methods: Healthy Chinese adult volunteers with no history of arthritis, past trauma or surgery and joint pain were enrolled in this study. Ultrasonography was performed on the bilateral shoulders, elbows, wrists, metacarpophalangeal joints (MCP) 1-5, proximal interphalangeal joints (PIP) 1-5, distal interphalangeal joints (DIP) 2-5, suprapatellar knees, ankles, metatarsophalangeal joints (MTP) 1-5, subacromial and subdeltoid bursae, deep infrapatellar bursae, retrocalcaneal bursae and long biceps tendons in B mode. Average size of fluid thickness and detection rate were calculated and correlated with demographic parameters. Mean + 1.64 SD was defined as the upper limit of the 95% reference range.

Results: One hundred and fifty-two volunteers (71 males and 81 females) with mean age of 48.0±14.1 years were enrolled. Both the highest detection rate and the thickest fluid were found in the suprapatellar knee (82.9%, 3.7±1.7 mm). There was no significant difference between the left and right side of the same structure in the detection rate and the fluid thickness. Females had a higher detection rate and fluid thickness than males in most examined structures, especially in the upper-limb joints. The greatest number of examined structures was found to be affected by age, and all of the correlations were positive (r from 0.118 to 0.510, P<0.05). Positive correlations were found in the long biceps tendon and MTP1 between detection rate and body mass index (BMI) (r=0.251 and 0.123, respectively, P<0.05), and in the long biceps tendon between effusion thickness and BMI (r=0.228, P<0.05). The upper limits of the 95% reference range for peripheral joints and bursae were determined.

Conclusions: Fluid in certain peripheral joints of healthy asymptomatic populations can be associated with gender, age or BMI. This study provided reference values for future comparisons with pathological conditions among Chinese populations.