Validity of derived measurements of leg-length differences obtained by use of a tape measure.

Determining the difference in the length of an individual's legs is often an important component of a musculoskeletal examination. Although measurements are easily obtained with a tape measure, the validity of these measurements is not known. The purpose of this study was to examine the validity of determinations of leg-length differences (LLDs) obtained by use of a specified tape measure method (TMM). Leg-length differences using the TMM and a radiographic technique were determined for 10 subjects who were candidates for clinical leg-length measurements and for 9 healthy control subjects. Validity of the TMM measurements was determined by assessing the degree of agreement between TMM-obtained LLDs and those obtained by the radiographic method. Validity estimates as determined by intraclass correlation coefficients (ICCs) were .770 for patients, .359 for healthy subjects, and .683 for all subjects. When the means of the two values obtained by use of the TMM were compared with the radiographic measurements, the ICCs were .852 for the patient group, .637 for the healthy subjects, and .793 for all subjects. This study suggests that TMM-derived LLD measurements are valid indicators of leg-length inequality and that the estimates of validity are improved by using the average of two determinations rather than a single determination.