Experimental healing of distraction osteogenesis comparing metaphyseal with diaphyseal sites. 
Distraction osteogenesis was performed on 32 adult dogs to compare bone healing at metaphyseal and diaphyseal sites.  Sixteen dogs underwent proximal metaphyseal corticotomy and 16 dogs underwent middiaphyseal corticotomy of the left tibiae for gradual lengthening.  Each major group was then divided into four subgroups of four dogs each on the basis of zero-, seven-, 14- and 21-day latency periods.  The standard radiograph, quantitative computer tomography density, and bone-healing index were used to evaluate new bone formation and consolidation.  A distraction rate of 1 mm per day for four weeks created an average elongation of 23.9 +/- 3.7 mm in the metaphyseal groups and 23.8 +/- 2.0 mm in the diaphyseal groups, excluding nine premature consolidations.  In the 16 metaphyseal lengthenings, there were six premature consolidations (37.5%): four with a 21-day latency, two with a 14-day latency, and one nonunion (6.2%).  In the 16 diaphyseal lengthenings, three fused prematurely (18.7%), two with a 21-day latency and one incomplete corticotomy with a seven-day latency.  Three lengthenings of the diaphyseal group resulted in nonunion (18.7%).  All animals, metaphyseal and diaphyseal, successfully bridged the distraction gap after a zero-day latency.  The bone-healing index showed that new bone consolidation was best with a zero-day latency in metaphyseal (22 +/- 7.6 days/cm) and diaphyseal lengthening (26.5 +/- 6.5 days/cm).  Comparing the minimum quantitative computer tomography density ratio of the experimental side with the contralateral side indicated a significant difference at the end of distraction (p = 0.001), at fixator removal (p = 0.001), and when the dogs were killed (p = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)