Age-related vascularization and ossification of joints in children: an international pilot study to test multi-observer ultrasound reliability.

Objective To determine the intra- and interobserver reliability of ultrasound (US)-detected age-related joint vascularization and ossification grading in healthy children. Methods Following standardized image acquisition and machine setting protocols, 10 international US experts examined 4 joints (wrist, second metacarpophalangeal joint, knee, and ankle) in 12 healthy children (divided into 4 age groups: 2-4, 5-8, 9-12, and 13-16 years). Gray-scale was used to detect the ossification grade, and power Doppler ultrasound (PDUS) was used to detect physiologic vascularization. Ossification was graded from 0 (no ossification) to 3 (complete ossification). A positive PDUS signal was defined as any PDUS signal inside the joint. Kappa statistics were applied for intra- and interobserver reliability. Results According to the specific joint and age, up to 4 solitary PDUS signals (mean 1.5) were detected within each joint area with predominant localization of the physiologic vascularization in specific anatomic positions: fat pad, epiphysis, physis, and short bone cartilage. The kappa values for ossification grading were 0.87 (range 0.85-0.91) and 0.58 for intra- and interobserver reliability, respectively. The bias-adjusted kappa values for intra- and interobserver reliability were 0.71 (range 0.44-1.00) and 0.69, respectively. Conclusion Detection of normal findings (i.e., grading of physiologic ossification during skeletal maturation and identification of physiologic vessels) can be highly reliable by using clear definitions and a standardized acquisition protocol. These data will permit development of a reliable and standardized US approach for evaluating pediatric joint pathologies.