Precision of sonographic measurement of articular cartilage: Inter- and intraobserver analysis

Objective. To establish the precision of sonographic measurement of the thickness of the articular cartilage of the hip and knee in children. Design. The precision was assessed by evaluating the intra- and interobserver variations in sonographic measurements. Patients. A total of 65 healthy children were in the study. The articular cartilage of the right hip and knee of 40 subjects (mean age 10.3 years, range 4-16.9 years) was evaluated in masked fashion by two observers to assess the interobserver variability. The articular cartilage of the right hip and knee of 25 children (mean age 10.1 years, range 6.2-15.5 years) was examined twice by the same observer to assess the intraobserver variability. Results and conclusions. Discrepancies between repeated measurements were expressed as data differences. The ''limits of agreement'' of data differences, i.e. the mean +2 SD and the mean -2 SD, ranged from -0.26 to +0.22 mm and from -0.56 to +0.48 mm for the interobserver analysis of the femoral head cartilage (FHC) and femoral condylar cartilage (FCC), respectively. The ''limits of agreement'' for the intraobserver analysis ranged from -0.16 to +0.15 mm and from -0.51 to +0.41 mm for the FHC and the FCC, respectively. The overall precision of the sonographic measurements was satisfactory. When used for determination of skeletal age, sonographic assessment of FHC thickness resulted in under/overestimation of skeletal age by about 7.5 months. In conclusion, sonographic measurement of articular cartilage is precise enough to be used in clinical practice.