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 measuresFluid displacementGeometric 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 displacedinconvenientunhygienicpoor reliabilityno information on

shape

• Geometric calculations from limb circumferences using tape measure frequently used

clinicallynon-standard

protocolsreliability 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 protocolLimb 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, 8Mmean age: 26mean height: 67.2 cmmean weight 171.0 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 cm3)

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

Bland-Altman LOA for Perometer and Cicumferential Measure

-840

-740

-640

-540

-440

-340

-240

-140

-40

60

160

260

360

460

560

660

760

6000 7000 8000 9000 10000 11000 12000

Average limb volumes by Perometer and Circumferential Measure (ml)

Dif

fere

nce

s in

mea

n v

olu

mes

of

Per

om

eter

an

d C

ircu

mfe

ren

tial

M

easu

re (

ml)

Mean + 2 S.D. 519.19 mls

Mean -157.48 mls

Mean - 2 S.D. -834.25 mls

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

References• Bland J, Altman D (1986) Statistical methods for

assessing agreement between two methods of clinical measurement. The Lancet 8: 307-310

• Brorson H (2000) Liposuction gives complete reduction of chronic large arm lymphoedema after breast cancer. Acta Oncologica 39: 407-420

• Karges J, Mark B, Stikeleather S et al (2003) Concurrent validity of upper-extremity volume estimates. Physical Therapy 83: 134-145

• Man I, Markland K, Morrissey M (2004) The validity and reliability of the Perometer in evaluating human knee volume. Clinical Physiology and Functional Imaging 24: 352-358