The reliability of leg circumference assessment: a comparison of spring tape measurements and optoelectronic volumetry.

The purpose of this study was to compare the reliability of repeated spring tape measurements with optoelectronic volumeter measurements for the assessment of lower leg circumferences. The limb circumferences at mid-calf and ankle level of both legs were measured three times using a spring tape measure as well as an optoelectronic volumeter. In all, 30 healthy volunteers participated in the study. Test reliability and repeatability were described through the process-related and between-subject variances and variance-derived parameters such as the reliability coefficient (intraclass correlation coefficient, RC), the relative precision (RP), and the coefficient of repeatability (CR). A higher value for the RC and a lower value for the RP indicate that the test variability is predominantly due to between-subject variance and not to test process-related variance. RCs for both methods, independent of whether measurements were taken at calf or at ankle level, always exceeded 0.95. RPs were in the same order of magnitude for both methods but lower for measurements at calf than at ankle level (range: RPcalf 6.36-8.74%; range: RPankle 12.49-18.56%). CRs for both methods were low and of comparable magnitude (CR range: 4.8-7.7), although slightly smaller for the spring tape. When measurement results from the spring tape and the volumeter were compared, results achieved with the volumeter were significantly longer than those from the spring tape (p<0.05). Results from both methods were linearly in good agreement and there was no proportional bias; differences shown were due to a significant constant bias regarding the volumeter. Circumference measurements taken by spring tape and by optoelectronic volumetry are both characterized by a comparably high reliability. However, these methods cannot be used in an interchangeable way because a constant bias exists for volumetry, resulting in significantly larger circumferences compared with those measured using the spring tape.