In Vivo Measurement of the Cyclic Creep of Human Patellar Tendons Using Ultrasonography

The cyclic creep of patellar tendons was in vivo evaluated in five male subjects. The cyclic stress (0-10 MPa) was applied to the patellar tendons by isometric knee extension contractions. The force in the patellar tendons was determined from the knee moment and the deformation of the patellar tendons was measured using ultrasonography. Stress was calculated by dividing the patellar tendon force by the patellar tendon cross-sectional area measured using ultrasonography. Strain was determined from dividing the patellar tendon deformation by the initial patellar tendon length. From these data, the stress-strain relations were obtained. The strain at the stress of 10 MPa increased from 5.9 % to 7.6 % with the cyclic loading until 10 cycles and thereafter was almost constant. The tangent modulus decreased from 322 MPa to 242 MPa with the cyclic loading until 10 cycles and thereafter was almost constant.