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Reliability of radiological measurements of the distraction gap during leg lengthening
B Tjernström1, O Jakobsson, P Pech
1Department of Orthopaedics, University Hospital, Uppsala, Sweden.
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.