Measurement of leg-length discrepancy using laser-based ultrasound method

Abstract

Background The evidence on the role of leg-length discrepancy (LLD) in low back pain (LBP) is contradictory, possibly due to the diversity of measurement methods. Purpose To assess the reliability of a laser-based ultrasound method and its agreement with the radiographic method. Material and Methods The measurement device consisted of a laser measure fixed to a rod holding the scanning head of the ultrasound and could be moved automatically by a linear actuator. The reliability of the measurement was evaluated using 20 healthy voluntary subjects with no known previous LLD (90% women, mean age 23 years). We assessed the agreement of the ultrasound method with a radiographic LLD measurement using 19 voluntary patients (95% men, mean age 38 years), who had had radiographic LLD measurements taken during the previous year. We used intraclass correlation co-efficients (ICC) and Bland & Altman analysis in the statistical analysis. Results The ICC value for agreement between methods was 0.97 (95% confidence intervals [CI] 0.93–0.99) indicating almost perfect agreement. The ICC values for both raters indicated almost perfect agreement between repeated measurements (ICC 0.996 and 0.994, respectively). In the Bland and Altman analysis, the mean difference was close to zero (0.56 mm and 0.40 mm), indicating minimal systematic error. Conclusion The ultrasound-laser technique is quick and easy to perform. Both reliability and agreement with the radiographic method are excellent. The ultrasound measurement is non-invasive and therefore a potential alternative to radiographic methods in the evaluation of LLD.