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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
Track
limb shape and
volume
quick, easy
Frame
Base
plate
Perometer estimation of limb
volume
Positioned every 2.54 mm
Diameter measurements
every 4.7 mm
Positioned every 1.27 mm
Summed volume of
elliptical discs
Purpose
• 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)
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 SubCommittee, QMU.
• 30 healthy volunteers:
22 F, 8M
mean age: 26
mean height: 67.2 cm
mean 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
Difference = 8717 ml
157 ml • Normal distribution
p=0.602
• 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
760
Differences in mean volumes of Perometer and Circumferential
Measure (ml)
660
560
Mean + 2 S.D.
519.19 mls
460
360
260
160
60
-40
6000
7000
8000
9000
10000
11000
-140
12000
Mean
-157.48 mls
-240
-340
-440
-540
-640
-740
Mean - 2 S.D.
-834.25 mls
-840
Average limb volumes by Perometer and Circumferential Measure (ml)
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
THANK YOU
Sponsors:
School of Health Sciences,
Queen Margaret University,
Edinburgh
Centre for Integrated
Healthcare Research,
Edinburgh
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