Measurement of lower limb volume: agreement between the vertically oriented perometer and a tape measure method

Abstract

Objective: To investigate the agreement between lower limb volume measurements for the vertically oriented perometer and a tape measure method.

Design: Between-methods agreement and test-retest reliability study.

Setting: University setting.

Participants: Thirty university staff and students were recruited using convenience sampling with no participant drop-outs.

Interventions: All participants' dominant lower limb volumes were measured using the vertically oriented perometer and a tape measure method.

Main outcome measures: The Bland-Altman difference plot was reported for determining the bias between the two methods and its 95% confidence interval. Test-retest reliability and the measurement error for the perometer method were determined using the ICC(2,1) model and within-subject standard deviation (sw) respectively.

Results: There was a lack of agreement between the tape measure and perometer method. The Bland-Altman difference plot showed that the tape measure method overestimated limb volume by 157ml compared to the perometer method. A 95% confidence interval of -834ml to 519ml was observed. The test-retest reliability of the perometer method was ICC(2,1)=0.99. The measurement error of the perometer method was clinically acceptable (sw=121ml).

Conclusions: There was a lack of agreement between the two methods investigated. Therefore the perometer and tape measure methods are not interchangeable. It is recommended that future validity and reliability studies for the vertically oriented perometer are conducted on clinical populations.

Keywords: CV; ICC; Lower extremity; Rehabilitation; Reliability and validity; coefficient of variation; intraclass correlation; s(w); within subject standard deviation (measurement error).