Clinical reviews of fracture treatment have almost uniformly suggested that a period of delay of 1 to 2 weeks prior to internal fixation of a fracture enhances the chance of union and speeds the rate of union. The mechanisms whereby delayed internal fixation operates to enhance fracture healing is not known. Substantive experimental evidence to support the clinical impression that a delay in internal fixation is beneficial is lacking. It is proposed to compare an osteotomy in the same dog fixed immediately with an osteotomy fixed after a 2-week delay. An effect of delayed fixation will be studied by morphologic, physiologic (morphometric) and bioengineering methods. A morphologic determination of osteotomy union will be determined by x-ray, with special attention to any difference in the time to union. Physiologic or morphometric evaluation will be accomplished by the use of a tetracycline labeling method employing 4 different labels. In this fashion, the response of bone to immediate and delayed fixation can be quantified in relation to the time of fixation. Bioengineering studies will be performed to describe load deflection and torque rotation curves for bones treated by immediate and delayed fixation.