Figure 1. A schematic illustration of the condylar surface showing the location selected for indentation (A) and a block diagram of the dynamic indentation machine with a schematic representation of the relationship between stress and strain of a viscoelastic material during a sinusoidal oscillating strain (, angular velocity) (B). (A) The articular fibrocartilage was divided into 4 regions; anteromedial, anterolateral, posteromedial, and posterolateral. For each region, the center of the crosspoint, as illustrated in the anteromedial region, was selected for indentation. (B) The sinusoidal strain was produced by a tension control motor in the driver, and the stress and strain were measured by means of load and displacement detectors and transmitted to a data processor. In a viscoelastic material, the phase difference between stress and strain is somewhere between (0 < < /2), and the complex modulus E* is resolved into two components: the storage modulus E' and the loss modulus E'', shown in vector format. The tangent of the phase angle () between stress and strain is a measure of the ratio of energy loss to energy stored during cyclic deformation.