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