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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 10.4 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.

Fifty-seven subjects aged 1.5-14 years (mean: 6.5; standard deviation: 3.3) complaining of hip pain and/or limp underwent clinical, US and radiologic examinations on admission and after variable time intervals. Twenty-eight of them were found to be affected with transient synovitis, 2 with rheumatic fever, 2 with slipped capital femoral epiphysis and 5 with Legg-Calvè-Perthes disease. The extant 20 subjects with normal US and X-ray findings were diagnosed as having irritable hip without effusion. No false-negative results were obtained from US (100% sensitivity), whereas X-ray provided false-negative results in 28 of 37 patients with hip disorders other than irritable hip without effusion (24.3% sensitivity). No significant difference in the extent of hip joint effusion was found at US between the various groups. In the transient synovitis group, joint effusion was apparent on X-ray image in 3 of 28 patients, in whom the effusion was significantly more severe than in the extant 25 patients. Capsular joint effusion resolved more rapidly in transient synovitis than in Legg-Calvè-Perthes disease. The patients with both rheumatic fever and transient synovitis exhibited the most rapid onset of symptoms. On the basis of our results, we suggest that each patient complaining of hip pain and/or limp should undergo US first and that X-rays be performed second, in selected cases only.