Perometry measurement of lower limb volume: an investigation of criterion validity.

Abstract

PURPOSE: This study aimed to develop a measurement protocol for the Perometer (400T) and compare it with the tape measure method for the calculation of lower limb volume in healthy individuals. RELEVANCE: A variety of musculoskeletal, vascular and neurological conditions impact on limb volume, therefore its measurement is important in their management. It is frequently measured using geometric calculations from limb circumferences using a tape measure (TM). The Perometer (P) optoelectronic imaging device demonstrates potential to become a gold standard of measurement. However, there is a lack of standardised protocol and research into its validity in the lower limb. PARTICIPANTS: Thirty healthy volunteers participated in the study (22 women, 8 men; mean age 26.0; mean height 67.2 cm; mean weight 171.0 kg). Individuals were excluded if they had relevant specified past medical history. The study was approved by an ethics committee at Queen Margaret University College. METHODS: Pilot work was undertaken to establish a standardised limb position, lower limb landmarks and a percentage of limb length for measurement. Participants were requested to avoid vigorous exercise and alcohol consumption 24 hours prior to testing, and food/fluid intake one hour before. After a 15-minute rest period with the limb elevated to 90 degrees, standardised reference marks were placed to indicate the start and end of TM and P volume calculations. The dominant limb was placed within the P frame in a standardised position. Three P measurements were taken, followed by TM measurements at three-centimetre intervals. Volumes in ml were calculated between the two reference marks using the P computer software and using the TM Disc model method (Man et al, 2004: Clinical Physiology and Functional Imaging. 24: 352- 358). ANALYSIS: Statistical analysis involved testing for normality of distribution before using parametric inferential statistics: an ICC (3,1) was used to assess the correlation, and limits of agreement were calculated to assess the degree of agreement, between P and TM limb volume estimates. RESULTS: Limb volume calculations (mean of 3 readings) were 8560 ml (P) and 8717 ml (TM), with a difference of 157 ml. Data were normally distributed (Shapiro-Wilk: p = 0.268 P; 0.602 TM). While the ICC (3,1) indicated good associations between the two measures (r = 0.952), limits of agreement analysis indicated that 95% of the time P limb volume estimates will be between 519 ml greater, and 834 ml less than TM estimates, indicating 15.67% variation, and poor agreement. CONCLUSIONS: Results indicated poor agreement and therefore measurement methods are not interchangeable. However, results cannot determine the respective accuracy of each method. IMPLICATIONS: This was the first study to calculate limits of agreement between estimates of lower limb volume using the TM method and upright 400T model of Perometer. Further work is needed in relation to different aspects of validity and reliability to determine which method is more accurate and should therefore be used as a gold standard