Validating loads going through the lower limbs in various positions during a weight-bearing CT scanner

M. Shamsuddin, I. McCarthy, D. Singh, A. Goldberg

Introduction: With the advent of standing CT and MRI scans, there is increasing interest in establishing the role and usefulness of these investigations. When ordering a standing investigation, we assume that 100% of body weight is loaded through the limb, but most machines have handlebars for support and some have seats to allow patients the opportunity to sit. The aim of this study was to evaluate the amount of load going through the lower limbs in various positions supported and unsupported, to explore the range and variation in measurements obtained.

Methods: Following ethics and local IRB approval, 40 healthy volunteers were asked to stand on an electronic weighing scales and be measured for height. They were then asked to stand on an identical electronic weighing scale on the PedCAT standing CT. Their weight was measured single and double leg stance, with the hands supported and unsupported on the side bars. The subjects were then asked to sit with a single and then both legs on the scale.

Results: 40 subjects participated. 28 were female, average BMI 25.8 (4.98). By holding on to the hand rails between 10-20% (2.0) of body weight was removed. Single stance meant 85% (4.0) of body weight went through the single limb and by sitting, with the single limb on the scanner only 8.8% (2.3) of body weight goes through the limb.

Conclusions: Standing CT and MRI are increasing in popularity. We now know that in standing the majority of body weight is transferred to the limbs, but if the subject is holding onto support up to 20% of body weight is removed. If the subject is sitting then only 9% of body weight goes through the single limb. This information will help inform future studies that use weight bearing MRI or CT.