title: 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.
  
  
  OBJECTIVE
  To assess the reliability of a laser-based ultrasound method and its agreement with the radiographic method.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Finnish Institute of Occupational Health, Department of Physical and Rehabilitation Medicine, University of Oulu, Finland. satu.rannisto@sarastus.fi
authors.forename: Satu
authors.initials: S
authors.lastname: Rannisto
authors.forename: Niko
authors.initials: N
authors.lastname: Paalanne
authors.forename: Pasi-Heikki
authors.initials: PH
authors.lastname: Rannisto
authors.forename: Arto
authors.initials: A
authors.lastname: Haapanen
authors.forename: Sanna
authors.initials: S
authors.lastname: Oksaoja
authors.forename: Jukka
authors.initials: J
authors.lastname: Uitti
authors.forename: Jaro
authors.initials: J
authors.lastname: Karppinen
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007834:Lasers; D007866:Leg / Q000000981:diagnostic imaging; D007870:Leg Length Inequality / Q000000981:diagnostic imaging*; D008297:Male; D015588:Observer Variation; D011859:Radiography; D015203:Reproducibility of Results; D014463:Ultrasonography; D055815:Young Adult