Lengthening osteotomy in the metaphysis and diaphysis. An experimental study in the ovine tibia.

In 20 sheep, aged seven to eight months, a tibial lengthening osteotomy was performed to compare the process of repair of the metaphyseal and diaphyseal regions of the bone. Analogous to clinical lengthening, two frame configurations of a bilateral external fixation device were used to obtain adequate fixation of the bone segments in the metaphyseal and diaphyseal lengthening osteotomies. A daily distraction rate of 1 mm for 4.5 weeks yielded an average length increase of 2.6 cm (12.5%). After death at 4.5 weeks postdistraction, the elongated bones were tested mechanically with the contralateral tibiae as controls. No significant difference in relative torsional strength of the elongated tibiae was found between the two groups. Inferior mechanical stability of the bone segments in metaphyseal compared with diaphyseal lengthening (due to differences in frame rigidity and distribution of muscular moments) influenced healing to such an extent that any superior biologic, osteogenic potential in the metaphyseal bone region was nullified. With the clinical use of two configurations of a given external device necessary for fixation of the bone segments in a metaphyseal or diaphyseal lengthening osteotomy, the empirically accepted idea that metaphyseal healing is superior may not be correct.