The objective of this study was to investigate the intra-rater (within day & between days) and inter-rater reliability of foot/ankle water volumetry in healthy subjects.
Study design: Repeated measures design with 2 raters.
Background: Physiotherapists more often aim to reduce swelling in the acute phase of soft tissue injury. Reduction in swelling will hasten the healing process. Therefore swelling forms an important outcome measure that is worth studying during the healing process to determine the efficacy of the intervention. Though there are different methods available to measure extremity swelling, water displacement method is widely used in physiotherapy studies. Although water volumetry has been used to assess the reduction in swelling over time, there is paucity of reliability studies that have assessed the between-days reliability.
Methods: Thirty normal subjects with asymptomatic ankles were measured by 2 raters. Three repeated foot volume measurements were performed by each of the rater using water volumetry during a single test session. The same procedure was repeated approximately at the same time on the 3rd day and 5th day following the 1st measurement day by the same raters on the same subjects. The raters were blinded to each other's measurements. The order for rater's volumetric measurement on each subject on each day was determined by a random chart produced by SPSS. The reliability was measured in terms of systematic bias (Paired t test & Bland & Altman's plot), absolute reliability (Limits of Agreement [LOA] & Standard Error of Measurement [SEM]) and relative reliability (Intraclass Correlation Coefficient [ICC]).
Results: There was no systematic bias between any of the trials within day/between days or between raters. The intra-rater reliability within day as calculated by ICC; LOA and SEM were 0.99, ±10ml and ±3.5ml respectively and for between days reliability the values were 0.99 (ICC), ±20ml (LOA) and ±7ml (SEM) and for interrater reliability the values were 0.99 (ICC), ±13ml (LOA) and ±5ml (SEM). The results demonstrated that water volumetry method was highly reliable within day and between days for both the raters; and highly reliable between raters.
Conclusion: Water volumetry is a highly reliable method for measuring foot/ankle volume repeatedly on different days. The random error range in milliliters (ml) as estimated by the absolute reliability indices provides the practical use of this method in a clinical/research setting.
