Response of the physis to leg lengthening.

UNLABELLED: The physeal response to limb lengthening by callotasis was investigated in an animal model by measuring 1) the growth rate using an oxytetracycline labelling technique, 2) histomorphological changes, and 3) proliferative cellular activity using bromodeoxyuridine. An osteotomy without lengthening stimulated growth at the physis. At 20% lengthening, regardless of the rate of distraction, no significant changes were detected. However, the growth rate was drastically reduced after 30% or more of lengthening and in 50% of cases there was evidence of premature closure of the distal growth plate. CLINICAL RELEVANCE: Caution should be exercised in carrying out high percentages of lengthening of children's bones.