Tendon cross-sectional area

The cross-sectional area of the patellar tendon was measured using an ultrasonic apparatus (SSD-6500, Aloka, Tokyo, Japan) at 50% of the patellar tendon length. Subjects remained in a supine position with the knee joint flexed at an angle of 90° (full extension=0°) and the muscles relaxed. An outline of the tendon was traced from the axial image, and the traced image was transferred to a computer in order to calculate the tendon CSA using open-source image analysis software (Image J, NIH, Bethesda, MD).

The repeatability of the measurement of tendon cross-sectional area was investigated on 2 separate days in a preliminary study with 7 young males. No significant differences were observed between the test and retest values of the tendon cross-sectional area. The intraclass correlation coefficient (ICC) and coefficient of variation (CV) were 0.92 and 2.7%, respectively.