Stress shielding by rigid fixation studied in osteotomized rabbit tibiae.

In 48 rabbits the bone-formation rates and strength in the tibial shaft, osteotomized and treated with rigid internal plate fixation, were compared with contralateral bones, which were treated with plate fixation without osteotomy. The plate fixation alone induced a 35 percent decrease in torsional strength after 12 weeks. The healing of the osteotomy counteracted the decrease in strength induced by stress protection of the rigid plate at 6 weeks, but this effect subsided within 12 weeks. The osteotomy also induced a 2-3-fold increase in the synthesis of bone matrix and mineral accretion of the bone underlying the plate at 6 and 9 weeks when compared with the contralateral side, which was plated but not osteotomized. The bone-formation levels returned to normal within 12 weeks; and the bone underlying the plate became subject to atrophy, resulting in decreased mechanical strength.