Introduction and Aims: A previous study showed the inhibitory effect of 30% metaphyseal lengthening on tibial growth (Lee 1993). This study was to investigate the effect of 30% diaphyseal lengthening of tibia on tibial growth plate and growth.

Method: 32 immature rabbits were equally divided into two groups: lengthening and sham. A bilateral external fixator was applied to the tibia and a mid-diaphyseal osteotomy performed. The lengthening group had their tibia distracted on the fifth day after the surgery at a rate of 0.4 mm twice daily until the achievement of 30% lengthening. In each group, half were sacrificed at the end of lengthening and another half after an additional five weeks. Standard radiographs were used to measure the lengths of the tibiae from the most proximal part of the intercondylar eminence to the most distal part of the medial malleollus. The actual length gained was measured by subtracting the pre-operative distance from the lengthened distance using the central points of two middle wires in the tibia as reference points. Specimens from the proximal and distal tibia were sectioned longitudinally in the midcoronal plane and the mean growth plate thickness was calculated from several measurements taken at the middle third of both medial and lateral halves of the section.

Results: In the sham group, the thickness of the growth plates continued to increase with skeletal development showing an increase in total tibial length compared with the contra-lateral control. In contrast, the lengthening group showed no increase in total tibial length compared to the contra-lateral control, suggesting that the stimulation due to the osteotomy may be matched by an inhibitory effect of 30% lengthening.

Conclusion: Thirty percent diaphyseal lengthening of tibia did not change the longitudinal growth of the tibia.