To determine if stem cells transplanted directly into a bone defect of rabbit tibias have osteogenic induction potential.

Immature white New Zealand rabbits underwent tibial osteotomies, and were divided into three groups according to the implant material used: stem cells embedded in agar (group 1); agar alone (group 2); nothing (group 3). For all rabbits, radiographs were taken weekly for 8 weeks, and histological studies of the newly formed-bone were performed. CM-Dil was used to label the stem cells prior to transplantation to ascertain whether or not the newly formed bone was derived from the transplanted stem cells.

Fibroblasts and osteoblasts (osteoid matrix-forming cells) derived from the stem cells were identified by electron microscopy. Interspersed enchondral ossification (probably induced by osteogenic cells from the remaining periosteum and marrow) and pure osteoids (created directly from the osteoblasts originating from the transplanted stem cells) were identified. Fluorescent-labeled cells were conspicuous in the new bones until 6 weeks after surgery, which indicates that the new bones were induced by the stem cells.

The osteogenic induction potential of the undifferentiated stem cell has promise for therapeutic application, which may be used for the treatment of bone defects in the future.