Pressure on the Tibial Plateau when Standing from a Seated Position.

Abstract

The object of this study was to estimate changes in pressure on the tibial plateau as a person stands up from being seated in a chair. Eight young men and eight young women performed this task while being photographed by a video camera from the left side in such a way that movements of individual segments of the body in the sagittal plane could easily be determined. All subjects used the same chair, which had a seat height of 40 cm. Myoelectric activity was recorded from the left rectus femoris during the task as well. Pressure on the tibial plateau was calculated on the basis of a rigid-body link model and of published data on area of contact between the femur and the tibia at different angles of knee flexion. Pressure estimated in this manner was highest at the onset of the task and decreased in a fairly uniform fashion over angular displacement of the knee into full extension. Because the peak pressure was at the very beginning of the task, adjusting height of the chair to height of the subject became a more critical variable than we had originally anticipated. Also, because we used the same values for area of joint contact for all subjects, we found that adjusting the magnitude of the area of contact to the size the subject was another consideration worthy of further investigation.