ABSTRACT
-The mechanism underlying hypertrophy of experimentally vascularized bone grafts was
studied in 15-week-old rats. The segmental ulna was grafted to the tibial defect with
an external fixator. In experiment 1, 24 rats were classified into four groups to
evaluate conventional (non-vascularized), cuff (periosteum-encased, non-vascularized),
and vascularized bone grafts, and vascularized segmental grafts with fracture. In
experiment 2, 12 rats were classified into two groups according to the presence of
mechanical loading. This involved vascularized bone grafts with external fixators,
and vascularized bone grafts with external fixators removed after bone union. The
bone dynamics of the grafts were investigated by several methods, including roentgenographic
analysis, histologic studies, and fluorochrome labeling.
In experiment 1, a slight bone formation was recognized in the conventional bone graft,
while irregular bone formation with creeping substitution was observed in the cuff
graft. The vascularized bone graft showed significant hypertrophy; hypertrophy of
the vascularized bone with fracture was greater than that without fracture. In experiment
2, markedly circumferential bone formation was observed after removal of the external
fixator, while slight new bone formation was observed during the late postoperative
period in bone with an external fixator.
These results suggest that hypertrophy can be promoted by artificial fracture of the
grafted bone, and that mechanical loading is an important factor for remodeling of
grafted bone.
