Validity of measuring leg length with a tape measure compared to a computed tomography scan.

A frequently used technique to measure leg length (LL) is the supine tape measure method (TMM). However, radiographic imaging, more recently computed tomography (CT) scans, has been considered the most accurate. The purpose of this study was to assess the validity of the TMM for measuring LL compared to CT scans. Additionally, intrarater and interrater reliability of the TMM were assessed. LL measurements of 30 adults (mean  =  38.4 years, SD  =  13.1 years) were obtained by two physical therapists (PT) using the TMM method, anterior superior iliac spine (ASIS) to medial malleoli. Lower extremity CT scans were completed and subsequent LL measurements were obtained. The validity of a single TMM LL compared to CT scan was ICC(2,1) of 0.984 for examiner 1 and 0.978 for examiner 2, while the ICC(2,2) validity of the mean of two measures was 0.992 and 0.990, respectively. Excellent intrarater (ICC3,2 of 0.990 and 0.985) and interrater reliability (ICC2,1 of 0.991) were also found. The supine TMM for measuring LL was shown to have excellent validity when compared to CT scans and excellent intrarater and interrater reliability. These results indicate that the supine TMM is a valid and reliable clinical measurement for PTs when measuring LL.