Effects of compression and cyclical loading on fracture healing—A quantitative biomechanical study

Abstract

Under standardized operative techniques, the tibial shafts of 24 adult female rabbits were osteotomized. With a specially constructed spring calibrated clamp, a 20N compressive load was applied to both tibias. During the subsequent healing time, 7d per week, 4hr per day, a cyclical compression loading of 20 additional N at 55 cycles per min was applied to one of the paired tibias. The animals were suspended during the entire experiment so that external forces from activity were eliminated. X-rays of the healing bones were taken in two planes at weekly intervals. Animals were sacrificed at periods of three, four, six, seven and eight weeks and the bones tested in a dynamic torsion testing machine. Torque, angle, energy absorption to failure and stiffness were measured from the torque-angle curves. These four quantitated variables of bone “strength” were then studied as a function of time for the two loading patterns. In these experiments, the “strength” of the healing bone was not preferentially enhanced by either constant compression, or cyclic compression superimposed on constant compression.