A technique for the in vitro measurement of principal strains in the human tibia

An experimental technique employing strain-gauge rosettes is described for the in vitro study of principal strains in the tibia as they are affected by various modes of loading on the knee joint. The experimental procedure, based around a Hewlett-Packard 9830A desk-top computer and an HP 3495A 80-channel scanner, is described in detail. The linearity of strain versus load up to 150 kg is shown in the "normally" loaded knee-joint. In these studies, the angle between the principal compressive strain and the vertical axis of the left tibia is reported to vary between 2.2 degrees and -60.2 degrees (Mean -16.5 degrees +/- 16.2 degrees), depending upon the position on the bone. Due to the gross variation of strain at a given point with respect to the angle of measurement, it is essential that strain-gauge rosettes be used to obtain meaningful data in any study of the strain distribution in the tibia.