FACTORS AFFECTING CALLUS DISTRACTION IN LIMB LENGTHENING

Factors affecting the process of callus distraction in limb lengthenin g include the type of osteotomy, timing and rate of distraction, and s tability of fixation. Thirty-two rabbits were studied to evaluate the reliability of transverse osteotomy and delayed distraction and to exa mine the appropriate rates of distraction. Rabbit tibiae were osteotom ized subperiosteally and were subjected to slow distraction using a ri gid monolateral external fixator. There was a ten-day waiting period b efore distraction. The animals were divided into three groups accordin g to the rate of distraction (0.35 mm/12 hours, 0.7 mm/12 hours, 1.4 m m/12 hours). The process of callus formation was monitored by soft x-r av. The reliability of delayed distraction after transverse osteotomy was demonstrated by microangiographic study. Even though intramedullar vessels were interrupted by osteotomy at surgery, blood circulation r ecovered during the waiting period before distraction. Bone lengthenin g was successful when distraction was carried out at rates of 0.35 mm/ 12 hours or 0.7 mm/12 hours. The callus filling a distraction gap show ed a characteristic zone structure, i.e., one central radiolucent zone and two adjacent sclerotic zones. Microangiographic study demonstrate d the continuity of blood vessels, under these rates of distraction. B ased on the results of these experiments and clinical experiences on 1 80 bone lengthenings, the authors believe that a waiting period after osteotomy is more practical than achieving immediate distraction after uncertain corticotomy.