Comparison of two methods of lower limb volume measurement Key Words: lymphedema, lower limb volume, perometry, volumeter and optoelectric perometry.

Abstract

Objective: To investigate the agreement between lower limb volume measurements for the vertically orientated perometer and the water displacement method (volumeter). Design: Between methods agreement and test-retest reliability study. Setting: University setting. Participants: Fifteen university students were recruited using convenience sampling with no participant drop outs. Intervention: All participants' dominant lower limb volumes were measured using the vertically oriented perometer and the volumeter. Outcome measures: The Bland-Altman difference plot was used to determine the agreement between the two methods and its 95% confidence interval. Test-retest reliability and the measurement error for both methods was determined using the ICC (3,1) model and within subject standard deviation (sw) respectively. A one sample T-test was used to test the agreement between methods. Results: The Bland-Altman difference plot showed that the perometer method overestimated limb volume by 832ml compared to the water displacement method. A 95% confidence interval of 219ml and 1445ml was observed. The test-retest reliability of the perometer method was ICC (3,1) = 0.99 and the test-retest reliability for the volumeter was ICC(3,1) = 0.99 The measurement error of the perometer was 146ml and 204ml for the volumeter, both clinically acceptable. The one sample t-test score was T (14) = 10.309, P=0.001 with a confidence interval of 95%. Conclusion: There was a lack of agreement between the two methods investigated. Therefore the perometer and volumeter methods are not interchangeable. It is recommended that future validity studies for the perometer are conducted on a clinical population and on the foot