Longitudinal overgrowth of bone after osteotomy in young rats: influence of bone stability.

One hundred and five 5-week-old male rats were used to study the influence of the stability of an osteotomy on longitudinal overgrowth of the bone. In 45 rats (Group 1) a transverse diaphyseal osteotomy of the right tibia was made; the left tibia was left untreated. In the second 45 rats (Group 2) the right tibia was osteotomized after applying an external fixator; the left tibia underwent a sham operation without osteotomy. Fifteen further rats (Group 3) were used as a nonoperated control group. After being measured at different periods up to 20 weeks, the osteotomized tibiae of the Group 1 (unstable) were 16-25% longer than those of their nontreated limbs (P < 0.001). The osteotomized tibiae of the Group 2 (stable) were 6-11% longer than those of the sham-operated opposite limbs (P < 0.001). The osteotomized and unstable tibiae were 9-17% longer than the osteotomized and stable tibiae (P < 0. 001) throughout the whole study. Although several factors have been considered to be responsible for longitudinal bone overgrowth after fracture in young animals, this work suggests that bone's stability plays a decisive role in the final outcome.