Bouter, L.M.

Elzinga, W.

Essers, A.

Kessels, F.

Koes, B.W.

Mameren, H. van

Verstegen, G.

English

DSpace at VU

REPRODUCIBILITY OF RANGE OF MOTION MEASUREMENTS OF THE SPINE WITH THE CYBEX EDI 320
Bart Koes, Henk v Mameren, Lex Bouter, Alex Essers, Willem Elzinga, Gard Verstegen and
Fons Kessels.
University of Limburg, Department of Epidemiology and Health Care Research, P.O. Box
616, 6200 MD Maastricht, the Netherlands
Range of motion (ROM) measurements of joints are often used in physiotherapy for
diagnosis and for the selection of an appropriate intervention. In addition, it makes it
feasible to quantify the effect of the intervention on the ROM. In this study we
investigate the reproducibility (precision or reliability) of ROM measurements of the
spine with the CYBEX Electronic Digital Inclinometer (EDI) 320. A further aim of the
study is to estimate the minimum effect that can be detected in a clinical trial as a
function of group size. In other words, this article deals with random variability in
ROM measurements of the spine with the EDI 320. As is explained elsewhere in this
volume, lack of random error is one of the main desiderata for an effect parameter
(Bouter et al., 1990). We considered reproducibility as the degree in which repeated
measurements on the same subjects provide the same results. This can be disturbed by
intra-individual variability and measurement error.
METHODS 
Reproducibility is determined by comparing repeated measurements on the same
subjects (test-retest method). Sixteen healthy subjects (physiotherapy students)
participated in the study. ROM measurements were carried out for several spinal
movements (table 1).
*
Table 1: Movements between extremes of the path of motion and position of the
inclinometer
Movement
1 cervical forward flexion
2 cervical lateral flexion
to the left
3 cervical lateral flexion
to the right
4 thoracic forward flexion
5 lumbar forward flexion
position
inclinometer
os nasale
os temporale
proc. zygomaticus
os temporale
proc. zygomaticus
Tl
T12
position
subject
sitting
sitting
sitting
standing
standing
*
movements 4 and 5:from anatomical to extreme position
These movements were chosen because they are part of the research protocol of a clinical
trial which has been conducted recently (Koes et al, 1990). All measurements were
carried out by one physiotherapist who was experienced in the use of the inclinometer.
Special attention was paid to standardisation of the measurement protocol. This meant
that all subjects received the same information concerning the movements to be executed.
Table 2 presents the eight series of measurements which were taken on each subject.
Reproducibility of the measurements was determined for the following time intervals:
consecutive ratings;
on the same day with a time interval of at least one hour;
after two days.
Intervals were chosen because of the considerable degree of intra-individual variability
known in the cervical spine (Mameren, 1988). Furthermore it presents how the
measurements for each time interval were compared. When comparing measurements with one
hour and two days time difference the mean of the measurements which were taken
consecutively is used.
442
Table 2. Comparison of the measurements for each time interval
time interval	 moment	 comparison
day 1
	
day 2
consecutive ratings 	 A	 B	 C	 D
	
for each moment the difference between
X X	 X X	 X X	 X X	 two easurements (X,X) is calculated
1 hour	 A < 	 > B
	
the difference is calculated between the
moments (A and B), and (C and D)
C < 	 > D
2 days	 A <v---7> C
•
••
•
B <L---1> D
The difference is calculated between
(A and C) (A and D), (B and C) and
(B and D)
* At the moments A, B, C and D the two measurements (X,X) were carried out
consecutively. Between the moments on one day (A and B) and (C and D) there was a
time interval of at least one hour.
*•
Between day 1 and day 2 there was a time interval of two days.
RESULTS 
Figure 1 presents the frequency (%) of differences in degrees between the first and
second measurement for each of the three time intervals.
For measurements carried out consecutively it appears that in about 90% of the
measurements the differences are lees than or equal to 10°. What is notable are the
differences in results for the category 0° - 5° of lumbar forward flexion (91%) and
cervical forward flexion (62%). The latter shows a smaller reproducibility.
For measurements carried out on the same day with a time interval of one hour, it
appears that, except for thoracic forward flexion (80%), the differences are less than
or equal to 10°, in about 90% of the measurements. For cervical forward flexion and
thoracic forward flexion 50% of the measurements carried out with one hour difference
fall in the category 0° - 5°. For thoracic forward flexion some differences (4%) were
more than 20°.
For measurements carried out with a time interval of two days, it appears that for
cervical forward flexion and thoracic forward flexion in about 70% of the measurements
the differences are less than or equal to 10°. Differences of more than 20° or more are
found for cervical forward flexion (8%), cervical lateral flexion to the right (3%) and
thoracic forward flexion (3%). For all ROM it appears that, with an interval of two
days, the percentage of measurements with differences less than or equal to 5° is lower
than for smaller time intervals between measurements.
443
Figure 1. Results of the measurements *
*
movements:
I	 : cervical forward flexion
II	 : cervical lateral flexion to the left
III : cervical lateral flexion to the right
IV	 : thoracic forward flexion
: lumbar forward flexion
time intervals:
1	 : consecutive ratings
2	 : minimum of one hour
3	 : two days
frequency (%) of differences between first and second
measurement in categories of 5°:
a	 : 0° - 5°
b	 : 6° - 10°
c	 : 11° - 15°
: 16° - 20°
: more than 20°
Table 3 presents a calculation to determine which difference in ROM is detectable
when comparing groups in a randomized clinical trial (RCT) (Bouter et al, 1990). A
'sample size formula' is used to calculate the minimum number of subjects which are
needed in an RCT to detect a difference between the study groups of a certain magnitude
(Meinert 1986). However, when the size of the study groups is decided in advance (in the
example the experimental group (nt) and the control group (nc) comprise 60 subjects), it
is possible to calculate the magnitude of the treatment minimal difference between the
groups which can be detected in the study. Components necessary for the calculation of
the sample size are:
magnitude of the effect (6 A) in which one is interested.
acceptable level of type I error (a): probability of finding a significant difference
between groups when in reality there is no difference.
acceptable level of type II error (B): probability of not finding a significant
difference when in reality there is a difference.
the variance (o 2 ) of the outcome measure. An approximation for this is the mean
variance calculated over all moments (A, B, C and D). We assume that the variance
(due to random measurement error and intra-individual variability) which occurs in
the hypothetical group of 60 subjects would be the same as among the 16 subjects in
444
our study. Additional variance which could occur because patients may have a
different reaction to therapy or show differences in the natural course of their
complaints, is assumed not to be present. This may lead to an underestimation of the
true variance in an RCT. Results of the calculations must therefore be interpreted
with caution.
Table 3. calculation
*
 of the minimal difference in cervical forward flexion which is
detectable with study groups of 60 subjects.
subject
	 measurement	 mean	 variance
A	 B	 C	 D	 (a2)
1 139 127 123 122 127.8 60.9
2 135 140 140 139 138.5 5.7
3 149 141 142 140 143.0 16.7
4 162 153 162 158 158.8 18.3
5 152 148 141 141 145.5 29.7
6 144 151 145 145 146.3 10.3
7 158 157 154 145 153.5 35.0
8 150 150 142 152 148.5 19.7
9 149 146 145 138 144.5 21.7
10 148 163 165 162 159.5 60.3
11 149 141 140 146 144.0 18.0
12 147 145 129 120 135.3 168.3
13 138 128 165 158 147.3 295.6
14 157 158 153 149 154.3 16.9
15 152 155 140 149 149.0 42.0
16 142 132 129 140 135.8 38.9
sample-size formula
6 A	 = V 2(Z a + Z B ) 2 X 2  02
nt
a
2
= 858/16 = 53.6
a	 = 0.05 (Z a = 1.96)
B	 = 0.1 (Z B = 1.282)
nt	 = 60
thus: 6 A = V 2(1.96 + 1.282) 2 2 X 53.6	 = 6.1°
60
Table 4 presents the minimum difference (in degrees) for each movement which can be
detected in an RCT with two groups of 60 subjects. It appears that differences between
the experimental and the control group of 5° (or more) will be detectable; that is,
(transversal) differences between two study groups (experimental group and control
group).
Table 4. Magnitude of the minimal difference in ROM detectable with study groups of 60
subjects:
cervical forward flexion 	 6°
cervical lateral flexion to the left 	 4°
cervical lateral flexion to the right 	 4°
thoracic forward flexion 	 5°
lumbar forward flexion	 4°
DISCUSSION 
The most important results of our study can be summarised as follows:
1. In about 70% of the measurements (for the three different time intervals studied) the
first and second measurements differ by less than 10°. For nearly all measurements
these differences vary between the 0° and 20°.
445
For all ROM it shows that the longer the time interval the more frequently the
differences between the first and second measurements are larger than 5°.
Cervical forward flexion provides the least reproducible results, while the lumbar
forward flexion measurements are the most reproducible.
4. With sample-size formulas it can be calculated that in an RCT with study groups of 60
subjects differences between the experimental and the control groups of about 5° will
be detectable.
All measurements were carried out on subjects without complaints. Therefore
conclusions about reproducibility of ROM for patients can not be drawn with certainty.
In addition to this, all measurements were carried out by the same physiotherapist who
had practised extensively in advance with the inclinometer. It is not known whether
another physiotherapist would have performed with the same degree of reproducibility.
The longest time interval between the measurements was two days. Strictly speaking it is
not possible to extrapolate our results to longer time intervals (e.g. weeks or months).
The results of this study show that ROM cannot be measured with the same
reproducibility for different movements. The data for cervical forward flexion were less
reproducible than the measurements of the lumbar forward flexion. When measurements were
carried out consecutively, it turned out that differences of more than 5° were found for
cervical forward flexion in 38% of the measurements and in only 9 % of the measurements
of the lumbar forward flexion. The reason for these differences in reproducibility is
that for some movements there is greater opportunity for intra-individual variability
and/or random measurement error. The following determinants of reproducibility are
important.
First, standardization of the measurement protocol of the specific movement is often
difficult to realise, for example, due to problems with the positioning of the
inclinometer on the specific body segment.
Second, variability of some movements might be larger than for others. For cervical
forward flexion this might be the case because motion is possible in more planes than
for movements such as lumbar forward flexion.
Third, when the absolute difference between the first and second measurement was
determined for each movement, we did not take into account the magnitude of the total
ROM of that movement. It is possible that for movements with a larger (total) ROM (for
example 150°), the variance of the measurements will be greater than for movements with
a smaller (total) ROM of 60°.
What conclusions can be drawn from these data for clinical use?
When measurements are taken on individual patients, one needs to consider that the value
which is measured can deviate from the true value because of random measurement error.
When after some time measurements are taken again on the same patient, a difference with
the first rating can be explained by measurement error, intra-individual variability,
the natural course of the disease and a therapeutic effect. In this study with healthy
subjects we found differences which vary in most cases between 0° and 20°. Essentially
these differences can be attributed to 'physiological' intra-individual variability and
random measurement error. So, if we want to draw conclusions for an individual patient
about the effect (increase of ROM) of a therapeutic intervention, the difference between
the two measurements (before and after the intervention) must be at least 20° to be
attributable to the intervention. The assumption is that patients will have at least the
same degree of 'physiological' variability as healthy subjects. However, in our study in
70% of the measurements the differences were less than or equal to 10°. Therefore, with
some caution differences between 10 and 20° can probably be interpreted as an indication
of a therapeutic effect.
When measurements are taken on groups of patients, random measurement error and
intra-individual variability play a role in the interpretation of the results as well.
However, if we want to study the effect of an intervention (increase in ROM) by
comparing an experimental to a control group in an RCT, we can detect differences of
less than 20°. The reason for this is that it is not very likely that all patients in
one group will show differences of 20° solely because of measurement error and/or intra-
individual variability. Furthermore, overestimations and underestimations on the
individual level will (partly) cancel each other out and thus the true mean ROM will be
approximated better by increasing the size of the study groups. In this study we
calculated on the basis of the results from 16 healthy subjects that with study groups
446
of 60 subjects true differences of about 5° would seem to be detectable.
Another issue is the clinical relevance of an effect of such a magnitude. Does a
difference of 5°, 10° or 20° have to be considered relevant? Furthermore, measurement of
maximum ROM does not give any information about the quality or the velocity of the
movement. But these questions go beyond the reproducibility of the ROM as measured by
the EDI 320 and thus fall outside the scope of this article.
References 
Bouter LM, Linden van der S and Koes B (1990), How to assess the effects of
physiotherapy, (in this volume)
Koes BW, Bouter LM, Knipachild PG, Mameren van H, Essers A, Houben JP, Verstegen GMJR
and Hofhuizen DM (1990), The effectiveness of manual therapy, physiotherapy and
treatment by the general practitioner for chronic non-specific back and neck complaints,
(in this volume)
Mameren H van (1988), Motion patterns in the cervical spine, Thesis, University of
Limburg, Maastricht, The Netherlands
Meinert CL (1986), Clinical trials: design, conduct and analysis, Oxford University
Press, New York


How to assess the effects of physiotherapy, (in this volume)

Reproducibility of range of motion measurements of the spine with the Cybex EDI 320

Reproducibility of range of motion measurements of the spine with the Cybex EDI 320

Abstract

Similar works

Full text

Available Versions

DSpace at VU