Upsala J Med Sci 100: 151-160,1995 

A Clinical Method for Measuring the Distribution of 
Segmental Flexion Mobility in the 

Cervico-Thoracic Spine 
Staffan Norlander, RPT,’ Ulnka Aste-Norlander, RPT: Bengt Nordgren, MD, PhD3 

and Bo Sahlstedt, MD, PhD3 
’Research Foundation for Occupational Safety and Health in the Swedish Construction Industry,2 US Fysioterapi, Trosa 

and Departmentv of ‘Rehabilitation Medicine and Diagnostic Radiology, Akademiska Sjukhuset, 
Uppyala Universir): Uppsala, Sweden 

ABSTRACT 

The aim of this study was to evaluate the validity and the repeatability of a new technique to assess 
segmental flexion mobility in the cervico-thoracic spine between segments C7 and T5. The new 
technique is referred to as the Cervico-Thoracic-Ratio (the CTR-technique). The radiological 
evaluation of skin distraction measurements showed that validity was high for the CTR-technique. 
A high correlation between vertebral flexion mobility and skin distraction was recognized individu- 
ally and for the whole group. The evaluation of repeatability was found to be high for intratester and 
fair for intertester repeatability. The CTR-technique may become a valuable complement to other 
method? for assessing segmental flexion mobility in patients suffering from neck-shoulder pain in 
clinical practice. 

INTRODUCTION 

A new technique has been described tomeasure the segmental flexion mobility in thecervico-thoracic 
junction and the upper thoracic spine (7). The measuring technique is referred to as the Cervico- 
Thoracic-Ratio (the CTR-technique). The CTR-technique describes what is defined as relative 
flexion mobility (CTR%). Relative flexion mobility is a calculated ratio based on absolute values of 
skin distraction between C7 - T5. Absoluteflexinn mobility is defined as the measured alteration in 
cm between 3 cm interdistant skin markings marked from C7 down t o T 5  and measured with a tape 
measure after a maximal forward flexion of the trunk and neck from an upright posture. The distance 
of 3 cm marked, in the upright posture, has been used as the definition of one motion segment, as the 
height of one disc and one thoracic vertebral body is approximately 3 cm, according to (5). 

The validity of the CTR-technique is dependent on an individual and strong reiationship bezween 
vertebralflexion mobility and skin distraction in the motion segments between C7 and T5, since the 
method is meant to be used for individual assessment of flexion mobility. Several attempts have been 
made to establish the relationship between spinal mobility and different methods for cliiiical 
examination. According to (2) and (9) clinical examinations and radiographic measurements showed 
high validity for measurement of lumbar curvature during stance and trunk forward flexion. 

151 



According to (1) and (10) different clinical examinations showed poor validity compared with 
measurements from radiographic pictures. I n  conclusion, validity differs for different instruments 
and methods. The CTR-technique has to be evaluated i n  order to become areliable method for clinical 
examination of the segmental flexion mobility. 

Repeatubiliry is defined as the capability to repeat a measurement. Many clinical methods for 
examination of spinal mobility are known to show low repeatability. Different factors affect the 
repeatability, for example if the mobility is tested passively or actively, or how long the time interval 
is between repeated measurernents. According to (3)the best repeatability is obtained if the mobility 
is tested actively and with as short time interval as possible between measurements, the classic " ~ e s  
retest design". In the CTR-technique mobility is tested actively. Repeatability is also known to be 
higher when it is perfomied by one tester, intratester repeutubility, compared with measurements 
done by two testers, intertester repeutuhility. In order to get acceptance of the CTR- technique the 
repeatability also has to be evaluated. The aim of this study is to evaluate the validity a n d  the 
repeatability of the CTR- technique as a method to be used in clinical practice for assessment of the 
segmental flexion mobility between C7 and TS. 

MATERIALS AND METHODS 

Radiological evaluation of validity 

The validity of the CTR-technique is dependent on a n  individual and strong relationship between 
vertebral flexion mobility and skin distraction i n  motion segments between C7 and TS. In order 10 
study the individual relationship six different vertebral angles C7 to TS were evaluated against six 
corresponding skinmarkings for each subject. The analysis of relationship was also evaluated for the 
whole group of 42 different vertebral angles versus 42 corresponding skinmarkings. Seven male 
subjects with pain in the neck-shoulder region, mean age 40.3, (SD16.0) years participated i n  the 
evaluation of validity. The evaluation was only done on male subjects, since previous studies did not 
show any significant differences between female and male subjects with reference to the degree of 
skin distraction, during forward flexion measured according to the CTR-technique(7). 

Procedure. Six small metal markings were glued onto the skin with 3 cm intervals, according to the 
marking procedure described i n  the CTR-technique. The markers were glued with the subject in an 
upright sitting posture and the upper marking p u t  over the most prominent part of the spinous process 
of C7. Lateral radiographs were used to obtain overlay measurements of the alteration of vertebral 
angles and of skin marker (Fig. 1). The first radiograph was taken with the subject i n  an upright sitting 
posture and the second in a maximal flexed sitting posture. Since the spinous processes could not be 
demonstrated in the thoracic region without tomography, the angle between the vertebral endplates 
were used as the independent variable. An aluminium wedge was usedin order to equalize the contrast 
differences and to visualize the metal markers on the skin. The angles between the endplates and the 
distances between the markers were measured on the films with the patient i n  upright position a n d  

152 



i n  maximal forward flexion. The T6-vertebra was used as a reference vertebra, the cumulative angles 
of C7 down to TS were measured with a gauge. The diagonal alteration of metal skin markers M 1 - 
M6 were measured with a pak of compasses and a ruler (Fig. 1). The measurements were done only 
once. 

Figure 1 Lateral radiographs were used Lo obtain overlay measurements of Lhecumulative vertebral angles (c7 - TS) 
and the diagonal alterations of the metal markings (M1 - M6). 

Statistical analysis. The determination of the relationship between skin distraction and vertebral 
flexion mobility was done by deciding the highest regression coefficient for five different regression 
models. Both the relationship for the individual and the whole group was evaluated for each model. 
A computerprogrmi (Quest) calculated the equation for linear (Y=A+B*X), exponential ( Y  =Aiexp 
(B*X)), power (Y=A*XAB), logarithmic (Y=A+B*ln ( X ) )  and polynomial models ( Y = A - B , * X  + 
B,* X2). Vertebral angles were used as the independent variable, and skinmarkers as the dependent 
variable. Breakdowns with one-way anova were also used to describe the mean values of the 
dependent variable skinmarkers as a function of the independent variable vertebral angles. 

Evaluation of repeatability 

The evaluation of repeatability was done for intra- and intertester repeatability. Tests were done by 
two investigators, two trials each. The evaluation was done with a test-retest design on 26 male 
subjects, mean age 41.2, (SD 9.3) years. 

Procedure . On arrival the subject was instructed to sit in a chair. The first investigator put the 
markings on the subject according to the examination procedure described in the CTR-technique, and 
the subject was asked to flex forward as much as possible. The investigator measured and noted all 
the five alterations. After that the markings were erased. The same procedure was repeated by the 
second investigator. Finally a second trial was repeated by both investigators, altogether four trials. 

12-950246 153 



Statistical analysis. In the evaluation of repeatability a sign-test was used to reveal byslernatic errors. 
Random errors were evaluated by calculating t h e  measuring precision and the relative measuring 
error. Both absolute and relative flexion mobility was evaluated. The precision was calculated as the 
pooled standarddeviations of the differences between trialsor investigators, divided by the extracted 
square root of two. The relative measuring error, the coefficient of variation (CV) was calculated as 
the standard deviation divided by the mean, times 100. Breakdown with one way anova was used to 
analyse the degree of conformity between intra- and intertester repeatability expressed as R square 
and p-values. 

RESULTS 

Evaluation of validity 

The results of the analysis of the relationship between vertebral flexion mobiIity and skin distraction 
show that the validity of the CTR-technique was individually very high. (Table 1). The degree of 
relationship vaned between different regression models, which implies an individual variation of 
spinal flexion mobility. The polynomial model showed the highest degree of individual relationship 
in five subjects, the logarithmic model in two subjects and the power model and the linear model 
showed equally high values as the polynomial model in one subject each. The different r2 values 
ranged between 0.68-0.98, which is a very high degree of explanation and all seven subjects showed 
a statistically significant relationship in at least one of the models (Table 1). 

Table 1 Results of individual relationships between dependent variable skin distraction and independent variable 
vertebral angles. 

I Regression models 

0.68 
0.1 1 
0.91 

p-value 

0.08 
0.002 
0.004 
0.003 
0.04 
0.52 
0.004 

Exponential 

0.89 0.006 
0.83 0.13 

0.56 
0.07 
0.97 0.001 

Power i;i--I...I- Logarithmic +- Polynomial - rz p-value .~ 
0.6X 0.04 
0.95 0.002 
0.88 0.007 
0.93 0.003 
0.44 0.14 
0.00 1.0 
0.81 0.04 

0 61 0.07 
0.95 0.002 
0 9 3  0003 
0.96 0.002 
0.56 0.09 
0.01 0.81 
0.70 0.08 

0.68 0.18 
0.96 0.008 
0.92 0.023 
0.94 0.012 
0.82 0.07 
0.91 0.03 
0.98 0.003 

For the whole group the polynomial regression model showed the strongest relationship between 
vertebral flexion mobility arid skin distraction, r2= 0.44 arid p<0.001. (n=42) (Fig. 2). The linear 
model showed r2= 0.39, (p<O.001), (n=42), the exponential model ?= 0.27 (p<O.OOI), (n=42), the 
power model r2= 0.19 (p<0.005), (n=42) and the logarithmic model showed r2 = 0.28 (p<0.001), 
(n=42). Themean cumulativevertebral angleforC7 was 18" and the alteration of the AM1 skinmarker 
was 5.3 cm. The cumulative flexion mobility for TI and AM2 was 13" versus 3.8 cm. T2 and AM3 
was 8.1' versus 3.0 cm. T3 and AM4 was 5.9" versus 2.5 cm. T4 and AM5 was 5 .  I ' versus 2.1 cm. 
T5 and AM6 was 4.6" versus 1.8 cm (Fig. 2). 

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7 -, I 

y = 2 2525 - 0 UO81 x + 0 0078 xi 

6 I 

Figure 2 Regression model describing thc highest relationship between vertebraiangles (C7 - T5) and alteration of 
skin markings (AM1 - AM6) (r = 0.66, p<O.Wl) (n = 32). Mean values (& SD) for studied variable>. 

The breakdowns with one- way anova analysis showed a relationship similar to the polynomial model 
(Table 2) between vertebral angles and skin distraction, r2 was 0.41 and p-value 0.001. Increasing 
vertebral angles showed increasing skin distraction. 

Table 2 Thc breakdown with one-way anova analysis showcd a similar rclationship between vertebral angles and 
alterations of sktnmarkings, rZ = 0.413 and p< 0.001 (n = 42). 

Vertebral ... Skinmarkings (cm) 
angles ( )" X SD Min M a x  
0 -  6 2.335 0.916 0.600 - 3.200 
6 - 12 2.883 1.389 1.300 - 5.800 

12 - 18 3.622 1.645 1.300 - 5.800 
I 8  - 24 5.300 0.781 4.400 - 5.800 
24 - 30 6.700 - 6.700 - 6.700 

-. 

4 Number crf,ioints 17 
12 
9 
3 
1 

Total 3.083 1.546 0.600 - 6.700 42 

Evaluation of repeatability 

Absoliiteflex.xionmobilily. Theresults of theevaluation showed that repeatability was high fc~rabsolute 
flexion mobility, for both intra- and intertester repeatability, which was important, as the values of 
relative flexion mobility exclusively depended on the values of absolute flexion mobility. The 
absolute flexion mobility was measured in cm according to the description of the CTR-technique 
from motion segment C7 down to T5. The inrrutester repeatability showed no systematic error 
between the first and second trial either for tester 1 or tester 2, when absohte flexion mobility was 

155 



evaluated for all motion segments. The sign test did not show any significant differences between 
trials for the two testers (Table 3, I* and 2*).The intertester repeatability, comparing tester 1 with 
tester 2 showed a small, but significant systematic measuring error between testers in both trials and 
in all five motion segments, (Table 3,3* and 4 9 .  Tester 2 systematically measured a 2-3 mm shorter 
absolute flexion mobility for all motion segments, The random errors expressed as measuring 
precision (mm) and as relative measuring error CV showed that repeatability was high for both intra- 
and intertester repeatability (Table 3, 1* and 4*). In general the precision is higher the shorter the 
distance measured , while the CV is greater. The CV for intratester repeatability ranged from 2.1- 
4.8% for tester 1 and from 1.9 - 4.4% for tester 2 for the different motion segments (Table 3, I* and 
2*). The CV for inlertesterrepeatability ranged from 2.4- 5.7% for trial 1 and from 1.8-4.1 % for trial 
2 for the different motion segments (Table 3,3* and4*). The breakdown with one way aiiova analysis 
describing the relationship between repeated trials for absolute flexion mobility showed a very high 
degree of conformity, r2values ranged 0.995 - 0.998 and p-values was p<O.OOI, for both intra- and 
intertester repeatability. 

Table 3 Results Irom evaluation ofrcpedtability of absolute flexion [nobility (n = 26), 1* and 2" = inwitester, 3* 
and 4* = intertester repeatability. 

Absolute flexion 
mobility (cm) 
X SD 

3.8 0.2 
3.6 0.2 
3.8 0.2 
3.6 0.2 

7.3 0.3 
7.1 0.4 
7.3 0.3 
7.1 0.3 

10.6 0.4 
10.5 0.5 
10.6 0.4 
10.4 0.5 

14.0 0.5 
13.8 0.6 
14.0 0.5 
13.7 0.5 

17.4 0.5 
17.1 0.6 
17.3 0.5 
17.1 0.6 

- 

~. 

Motion 
segment Trial Tester 

Random errors Systematic 
Measuring Measuring errors 
precision (mm) error ( C V % )  I Sign test 

.~ 

I *  1.8 4.8 
2* 1.6 
3* 2.1 5.7 
4* 1.5 4.1 

I* 2.7 3.6 
2* 2.4 3.4 11s 
3* 3.1 4.3 ns 
4* 2.5 3.5 4" 0.01 

1* 2.7 2.5 ns 
' 2* 2.5 2.4 2* 11s 

3' 4.2 4.0 :1* ns 
4* 2.8 2.6 J* 0.0 I 

I *  3.1 2.3 ' 1 *  n.: 
2" 3.0 2.2 2* ns 
3* 3.6 2.6 3" 0.05 

4* ns 4* 3.1 2.2 
2.1 I *  ns I *  3.6 

2* 3.3 1.9 2* n s  
3* 4.1 2.4 3* 0.02 

4* ns 4" 3.0 1.8 

~ ~ _ _ _  

__ 

.. 

~~~ 

C 7 - T 1  1 1 
2 2 
3 1 
4 2 

c 7 - T 2  1 1 
2 2 
3 1 
4 2 

C 7 - T 3  1 1 
2 2 
3 1 
4 2 

c 7 - 7 - 4  1 
2 
3 
4 

C 7 - T 5  1 
2 
3 
4 

Total 
1 * lntratestcr 

2* Intratester 

3* Intertester 

4* Intertester 

repeatability tester 1 10.60 4.8 2.8 3. I n b  

repeatability tester 2 10.40 4.8 2.6 2.9 11s 

repeatability trial 1 10.51 4.8 3.4 3.8 0.01 

repeatability trial 2 10.49 4.8 2.6 2.8 0.01 
_ _ _ _  



Relative,flexion mobiliry. Relative flexion mobility expressed as CTR% is based on two values of 
absolute flexion mobility. This makes relative values afflicted with a somewhat greater measuring 
error. The intratester repeatability showed no systematic errors between the first and second trial 
either for tester 1 or tester 2 when relative flexion mobility was evaluated for all motion segments. 
The sign test did not show any significant differences between trials for the two testers (Table 4, 1 * 
and 2*). Theintertesrclrrepeatability, comparing tester 1 with tester 2 ,  showed a significant systematic 
measuring error between testers i n  both trials for motion segment C7-T 1 and T4 - TS (Table 4 , 3 *  and 
4*). The systematic measuring error in absolute flexion mobility between testers resulted i n  a 
calculated CTR value which in average is 0.7% lower for motion segment C7-Tl and 0.4% higher 
for motion segment T4 - T5 for tester 2 compared with tester 1. The random errors expressed as 
measuring precision (%) and as relative measuring error CV showed that repeatability was high for 
intratester repeatability and fair for intertester repeatability (Table 4, 1" and 4*). In general the 
precision is higher in motion segments C7-T1 andT4 - 'I'S arid so is also the CV compared with motion 
segments i n  between. The CV for intratester repeatability ranged from 2.9-3.9%; for tester 1 and from 
2.9 - 4.4% for tester 2 for the different motion segments (Table 4, 1 * and 2*) The CV for intertester 
repeatability ranged from 5.4- 7.7% for trial 1 and from 3.2-7.7% for trial 2 for the different motion 
segments (Table 4, 3" and 4"). 

Table 4 Resultsfromevaluationofrc~catabilitvofrelativeflexionmobilit\;(n=26), I *  m d 2 *  =intriltcster,3* and 
4* = menester repeatability 

I Relative flexion 1 Random error3 
Motion mobilitj ( C I  R % )  Measuring Measuring 

~ 

segment Trial Tester X S D  

C 7 - 1 ' 1  1 1 
2 2 
3 1 
4 2 

1'1 -1'2 1 1 
~~~ 

2 2 
3 1 
4 2 

T 2 - T 3  1 1 
2 2 
3 1 

2 2 
3 1 

2 2 
3 I 
4 2 

2 I .x 1.2 
21.2 1 .0 
22.1 O.Y 
21.3 1.1 
20.0 0.9 
20.4 1.3 
20.0 0.8 
20.0 1.4 
19.3 1 .o 
19.8 I .3 
19.6 1 .o 
19.6 1.7 
19.7 1.6 
19.4 1.5 
19.5 1 .s 
19.3 1.3 
19.3 1.7 
19.3 1 .0 
18.8 1.4 
19.6 1 .0 

Total 
1 * Intratester 

2" Intratester 

'3* Intertester 

4* Intertester 

repeatability tester 1 

repeatability tester 2 

repeatability trial 1 

repeatability trial 2 

20.0 1.5 

20.0 I .3 

20.0 1.2 

20.0 1.3 

precision ('70) error ( C V 7 o )  
I *  0.9 39 
2' 0.8 3.5 
3* 1.3 6.3 
4* 0.7 3.2 
I* 0.6 3.1 
2* 0.9 4.4 
3* 1.1 5.4 
4* 1.3 6.4 
1 *  0.6 2.9 
2* 0.8 3.8 
3* 1 . 1  6.0 
4) 1.5 7.7 
I *  0.7 3.1 
2* 0.7 3.1 
3* 1.5 1.7 
4* 1.3 6.8 
I *  0.7 3.7 
2* 0 6  2.9 
3* 1 4  7 0  
4* I 0  5 1  

0.7 3.5 

0 . X  3.7 

1.3 6.5 

1.2 5.9 

Systematic 
errors 
Sign test 

l x  n b  
2" ns 
3 ,  0.02 
4* 0.01 
I* ns 
2* 11s 
3* ns 
4* ns 
I *  11s 
2* ns 
1* ns 
4" ns 
1 *  ns 
2* 11s 
?* ns 
4* ns 
I* ns 
2* ns 
3* ns 
4* 0.02 

- *  

~~ - 

~ ~~ 

~~~~ ~ 

ns 

ns 

0.01 

0.01 

157 



The breakdown with one way anova analysis, describing the relationship between repeated trials for 
relative flexion mobility, showed a very high degree of conformity. Intratester repeatability showed 
a r  2=0.79 (p<O.001) fortester 1 andar2 =0.68 (p<0.001) fortester 2. Intertesterrepeatability showed 
a r2= 0.38 (p<0.001) for trial 1 and a 1-2= 0.58 (p< 0.001) for trial 2. Not in any motion segment did 
the variation of repeatability significantly exceed the limits for what is defined as ordinary mobility 
i n  the classification model, described by (7), (Fig. 3). 

Mobility Profile 

Motion segment 
~~ 

Figure 3 The resuits or the iiiua- and inrerterrer repcatability evaluation shown in thc mobility prof1 lz. The variation 
betwccn trials and testers is kepi w i t h i n  the limils for ordinary mobility. 

DISCUSSION 

The results of this study have shown that the distribution of segmental flexion mobility i n  the cervico- 
dorsal region can be examined with the CTR-technique. The validity of skin distraction measure- 
ments in the cervico-dorsal spine was found to be individually very high. In this study it was necessary 
to use conventional X-ray technique to evaluate the relationship between skin distraction and 
vertebral motion. It was also necessary to choose the vertebral endplates to study the alteration of 
vertebral angles since the spinous processes could not be clearly identified in this difficult region. 
Great efforts were made tooptimize the technique. The number of subjects was limited to seven, since 
the relationship between individual vertebral flexion mobility and skin distraction was found to be 
convincingly high for our application. The aim with the CTR-technique was assessinent of joint 
flexion mobility, from a clinical point of view. The aim was not to decide the exact vertebral angle 
i n  degrees. Further more the method has shown an important clinical application as an instrument to 
identify dysfunction in the cervico-thoracic junction correlating to neck-shoulder pain (8). The 
evaluation of validity was done on patients suffering from neck-shoulder pain and the evaluation of 
repeatability was done on healthy subjects. This was not a problem, since clinical trial has shown that 

158 



the CTR-method can distinguish between different flexion mobility in individuals with and without 
increased risk for neck-shoulder pain (8). 

The intratester repeatability demonstrated high repeatability and was not impaired by any systematic 
measuring error.The intertester repeatability demonstrated fair repeatability for both absolute and 
relative flexion mobility. The measuring procedure was impaired by a sinall but systematically 
measuring error for both absolute and relative flexion mobility, values between testers showed 
slightly different characteristics. It was most likely that the marking procedure of the 3 cm interdistant 
penmarkings contributed to the systematic measuring error. However, for absolute flexion mobility, 
the relative measuring error must be considered small, only in one trial and for one motion segment 
did the CV exceed 5 %  (Table 3). As tester 2 systematically measured a 2-3 mm shorter absolute 
flexion mobility for all motion segments, the calculation of the CTR resulted in a value which on an 
average was 0.7% lower for motion segment C7-Tl and 0.4% higher for motion segment T4 - TS for 
tester 2 compared with tester 1. This increased CV to 7.7% as the highest for relative flexion mobility. 
This variation in intertester repeatability for relative flexion mobility was, however. not greater than 
i t  was comprised within the limits for what was defined as ordinary mobility in the classification 
model described by (7). Consequently the systematic measuring error for intertesterrepeatability was 
less than what was defined as ordinary variation between individuals. As the CTR was a ratio between 
two absolute flexion mobility values, it was quite obvious that the relative value was impaired by a 
somewhat greater measuring error compared with absolute values. If the precision in absolute values 
could be improved by approximately 1 mm i n  each motion segment, t h e  CV would decline and nor 
exceed the 5% limit for relative calculations. This could most likely be achieved by using an 
instrument with fixed 3 cm interdistances for marking instead of an ordinary tape measure. 

Only a few studies have used the coefficient of variation (CV) of their data to describe repeatability 
and to our knowledge nobody has studied measurements in the thoracic spine according to the C l R -  
technique. The present study was therefore difficult to compare with other studies. However, some 
studies must be commented on. Gill et a1 (4) found that the intratester variation was 1.5% for the low 
backmeasurements using the modified Schober technique, with the subject examined i n  a f u l l y  flexed 
sittingposture. Merittetal(6)founda6.6% intratestervariation with the modified Schobertechnique, 
examined in a fully flexed standing posture. Thus, also other skin distraction methods have shown 
values of coefficient of variation of the same magnitude. 

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Address for offprints: 

Staffan Norlander 
Bygghalsans forskningsstiftelse 
Svardvagen 25 A 
S-182 33 DANDERYD, Sweden 

160