Perometer (400T) Measurement of lower limb volume: development of a standardised protocol.

Abstract

PURPOSE: This abstract presents a standardised protocol for the measurement of lower limb volume using the Perometer (400T) and evaluation of its test-retest reliability. RELEVANCE: Changes in limb volume result from a variety of musculoskeletal, vascular and neurological conditions. Limb volume measurement is important in monitoring treatment efficacy. Although the Perometer (400T) optoelectronic imaging device can be used to assess limb volume, no protocol has been published to standardise its use. DESCRIPTION: A standardised protocol was developed through multiple pilot studies: 1) The individual to be measured is required to sit with their lower limb elevated for five minutes to allow equilibration of tissue fluid. Pilot work involving one individual compared rest periods of 5, 10 and 15 minutes. Lower limb volume reduced by 0.28%, 0.12% and 0.52% respectively; the maximum reduction of 26.67 mls is likely to be clinically negligible. 2) A standardised endpoint for limb volume calculation is marked at 65% of femur length measured from distal (inferior lateral condyle) to proximal (superior greater trochanter). This proportion of limb length was selected following pilot work with three male and three female participants of different heights. 3) Normally the participant's foot is placed in the middle of the Perometer base-plate. A cylinder of known volume was placed in 16 segments outlined on the base-plate and the most accurate volume estimates were achieved in the central positions. 4) The normal stance for use with the Perometer (400T) requires the individual to stand sideways to the vertical Perometer track. Strict positioning of the lower limb in neutral rotation is not necessary: measurements carried out at increasing degrees of rotation from 0-60 degrees to both right and left demonstrated low coefficients of variation (<0.6%). 5) The Perometer frame is moved vertically up the lower limb to the standardised end-point at an average speed. Pilot work demonstrated higher measurement variability when the frame was moved rapidly compared to average or slow translations, although the coefficient of variation remained below 0.6%. 6) The distance from floor to standardised endpoint on the lower limb is entered into the computer software to calculate the volume of a standardised proportion of the lower limb. EVALUATION: The finalised protocol was repeated nine times on 30 participants by one investigator on two separate occasions. Test-retest reliability was calculated using Limits of Agreement (Bland & Altman, 1986), indicating that 95% of the time lower limb volume calculations will vary between 159.2 mls and -181.04 mls, amounting to 0.0004% variation and excellent test-retest agreement. CONCLUSIONS: Adoption of this standardised protocol for the Perometer (400T) will allow reliability of measurement in clinical practice. Further development and evaluation are needed, including investigation of defined speeds of Perometer frame movement, and reliability and validity of the protocol in different clinical populations. IMPLICATIONS: Standardised protocols are important to enable comparison of data within and between individuals at different clinical sites. This protocol for measuring lower limb volume using the Perometer (400T) will facilitate ongoing multi-site audit and evaluatin of management strategies.