1. Clinical studies in humans have indicated that a delay of one to three weeks in the open reduction of a fracture decreases the incidence of delayed union and non-union.

2. Studies in cats indicate that a delay of two weeks before open reduction causes a different repair mechanism from that following immediate operation.

3. Repair after delayed operation is characterised by increased periosteal new bone formation and more rapid endochondral bone formation. After immediate operation periosteal new bone is slow to develop; much more fibrous tissue and cartilage develop, followed by slow endochondral bone formation.