This study evaluated the intraobserver and interobserver reliability of cross sectional areas of the supraspinatus (SSP) and the infraspinatus (ISP) by ultra sound images. We examined fourteen shoulders of seven men (average age: twenty-seven years old). The same ultra sound system (Toshiba Echo Camera SSA340-A Toshiba, Co, Japan) was used for all measurements. According to the method of Katayose, the cross sectional area of the SSP was measured at midpoint of the spina scapula at an angle of 40°. That of the ISP was measured at the point of the glenohumeral joint of the spina scapula at an angle of 80°. Three observers measured three times each muscle. The mean of each area were recorded. After one week, measurements were repeated. Data were analyzed using a one-factor ANOVA and paired t-test. The areas of the SSP were 7.6±0.7, 7.5±0.9, and,7.6±0.9cm2on the right and 7.4±0.6, 7.4±0.9, and 7.5±0.9 cm2on the lef. Those of the ISP were 5.4±O.5, 5.2±0.5, and 4.6±0.9 cm2on the right and 5.1±O.5, 4.8±0.6, and 4.4±0.9 cm2on the left. The reliability of the interobserver of the ISP was low (P<0.05). It was difficult to measure the area of the ISP by ultra sound images because the border between the ISP and the teres minor was not clear. More acurate visualization of the border would increase the reliability.
