Lengthened callus activated by axial shortening. Histological and cytomorphometrical analysis.

The tibiae of rabbits were lengthened by 10 mm in 2 weeks, then approximately one half of the limbs were shortened by 2 mm in 3 days, and left for 3 days. Histological and cytomorphometrical findings of the calluses in both groups were compared. In the shortened callus, marked histologic changes were observed in the central mesenchymal cell layer where the number of the osteoblasts increased 4 fold, and massive primitive fiber bone formation took place. Cartilaginous tissue did not seem to respond to the axial shortening stress.