Perometer (400T) measurement of lower limb volume: An investigation of criterion validity Cathy Bulley, Fiona Coutts, Andrew Grainger Queen Margaret University, Edinburgh, UK

Background Various musculoskeletal conditions  limb volume Limb volume – outcome measures  Fluid displacement  Geometric calculations from limb circumferences using tape measure  Perometer – optoelectronic imaging device; limb shape and volume (Pero-System GmbH)

Current Methods Fluid displacement: limb submerged in water, measurement of fluid displaced  inconvenient  unhygienic  poor reliability  no information on shape Geometric calculations from limb circumferences using tape measure  frequently used clinically  non-standard protocols  reliability issues

Circumferential Measurement Limb circumference at specified points on limb – quick, simple Lack of agreement on measurement points – specific anatomical landmarks or regular intervals e.g. 3 or 4 cm (Karges et al, 2003) Geometric formulae to estimate volume of different segments  summed Different formulae used (e.g. disc model, truncated cone model) Reliability issues: e.g. tape measure tension (Brorson, 2000)

Perometer (Pero-System GmbH)  optoelectronic imaging device  limb shape and volume  quick, easy Base plate Frame Track

Perometer estimation of limb volume Positioned every 2.54 mm Positioned every 1.27 mm Diameter measurements every 4.7 mm Summed volume of elliptical discs

Perometer – gold standard? Face validity Lack of standardised protocol and research Criterion Validity: This study compared lower limb volume measured using :  Geometric calculation from limb circumferences (Tape measure Disc model method, Man et al, 2004)  Perometer (400T: upright model) Purpose

Standardised Protocol Development of a standardised protocol  Limb position on the base plate, and degree of rotation  Lower limb landmarks – standardised proportion of the limb for volume measurement Greater trochanter 65% Femur Lateral epicondyle Lateral Malleolus

Validity Study Ethical approval: Physiotherapy Ethics Sub- Committee, QMU. 30 healthy volunteers:  22 F, 8M  mean age: 26  mean height: 67.2 cm  mean weight kg.  Exclusion criteria: relevant past medical history

Protocol 1 Participants requested to avoid vigorous exercise / alcohol consumption 24 hr before testing and avoid food / drink intake 1 hr before testing 15 minute rest period with limb elevated to 90° Standardised limb reference marks

Protocol 2 Standardised limb reference marks Standardised positioning of limb in Perometer frame – use of spirit level Three Perometer measurements Tape measurements at 3 cm intervals Assessor blinded to limb volume

Limb volume estimation Perometer: Volumes in ml calculated between two reference marks in perometer computer software Tape measurements: Disc model method (Man et al, 2004) in ml (1ml = 1 cm 3 ) Σ (C²/4π) x h C = circumference of disc h = height of disc

Statistical Analysis Shapiro-Wilk: Normality of distribution Parametric inferential statistics:  ICC (3,1)  Limits of agreement (Bland & Altman, 1986) between two limb volume estimates

Results Perometer limb volume (x of 3) = 8560 ml Normal distribution p=0.268 Circumferential limb volume = 8717 ml Normal distribution p=0.602 Difference 157 ml ICC (3,1): good association (0.952, p<0.001) Poor agreement 15.67% variation between estimates: 95% of Perometer estimates will be: between 519 ml (6.01%) more and 834 ml (-9.66%) less than circumferential estimates

Conclusions Poor agreement – measurement methods are not interchangeable  Perometer – greater face validity  Circumferential – more clinically feasible Results do not indicate accuracy of either method 21 / 30 data sets – overestimation by circumferential method More work is needed to determine accuracy

Acknowledgements MSc pre registration Physiotherapy students: Nicola Dinsmore Georgina Enderson MaryAnne Geraghty

Sponsors: School of Health Sciences, Queen Margaret University, Edinburgh Centre for Integrated Healthcare Research, Edinburgh THANK YOU

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