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

Purpose: 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.

Material And Methods: 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.

Results: 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%).

Conclusion: Radiographs obtained with a radiopaque ruler placed at the same level as the lengthened bone allowed reliable measurements of the distraction gap.