CALLUS FORMATION AFTER RE-INJURY TO EXPERIMENTAL BONE DEFECT

Osteochondrogenic callus formation after delayed re-injury at differen t time intervals was evaluated. Twenty young rats were operated, and a standard bone defect reaching the medulla was sawn into the left hind leg. The rats were divided into two groups and the defect was re-crea ted after 4 or 12 days. The rats were killed 7 or 14 days after the se cond operation. The developing new bone was revealed with a triple flu orochrome labelling system. The areas of bone and cartilage were measu red histomorphometrically, The results suggested that an external fact or, re-trauma, could increase both external and internal primary osteo genic callus formation. The optimum time to potentiate bone formation in the defects was found to be earlier than identified in previous fra cture studies. After a 4-day delay the external callus was significant ly larger than after the 12-day delay. Cartilage formation was not enh anced despite the sudden increase in osteogenic callus formation.