Reliability of radiological measurements of the distraction gap during leg lengthening.

Abstract

The aim of this study was to determine the accuracy of length measurements on plain radiographs during leg lengthening and to evaluate a reliable method of measuring the amount of lengthening suitable for clinical praxis. In an experimental study, a plastic femur was lengthened 40 mm and assessed radiographically in different positions, and the orthoradiographically calculated total length of the femur was compared with the true value. In a clinical study, 96 radiographs encompassing 14 femoral and 2 tibial lengthenings were assessed on a digitized table with a computer program (PROFILE) with regard to the amount of lengthening and the degree of magnification. The radiographic magnification in the experimental study, depending on position of the femur, was 17% (5-25%), and in the clinical material it averaged 16% (0-36%). Radiographs obtained with a radiopaque ruler placed at the same level as the lengthened bone allowed reliable measurements of the distraction gap.