Variations during repeated standing phases of asymptomatic ... · The Kolmogorov-Smirnov-Lilliefors...

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Accepted Manuscript Variations during repeated standing phases of asymptomatic subjects and low back pain patients Hendrik Schmidt, Maxim Bashkuev, Jeronimo Weerts, Friedmar Graichen, Joern Altenscheidt, Christoph Maier, Sandra Reitmaier PII: S0021-9290(17)30313-5 DOI: http://dx.doi.org/10.1016/j.jbiomech.2017.06.016 Reference: BM 8255 To appear in: Journal of Biomechanics Received Date: 5 January 2017 Revised Date: 9 May 2017 Accepted Date: 13 June 2017 Please cite this article as: H. Schmidt, M. Bashkuev, J. Weerts, F. Graichen, J. Altenscheidt, C. Maier, S. Reitmaier, Variations during repeated standing phases of asymptomatic subjects and low back pain patients, Journal of Biomechanics (2017), doi: http://dx.doi.org/10.1016/j.jbiomech.2017.06.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Transcript of Variations during repeated standing phases of asymptomatic ... · The Kolmogorov-Smirnov-Lilliefors...

Page 1: Variations during repeated standing phases of asymptomatic ... · The Kolmogorov-Smirnov-Lilliefors test was applied to evaluate the normal distribution for each investigated group.

Accepted Manuscript

Variations during repeated standing phases of asymptomatic subjects and lowback pain patients

Hendrik Schmidt, Maxim Bashkuev, Jeronimo Weerts, Friedmar Graichen,Joern Altenscheidt, Christoph Maier, Sandra Reitmaier

PII: S0021-9290(17)30313-5DOI: http://dx.doi.org/10.1016/j.jbiomech.2017.06.016Reference: BM 8255

To appear in: Journal of Biomechanics

Received Date: 5 January 2017Revised Date: 9 May 2017Accepted Date: 13 June 2017

Please cite this article as: H. Schmidt, M. Bashkuev, J. Weerts, F. Graichen, J. Altenscheidt, C. Maier, S. Reitmaier,Variations during repeated standing phases of asymptomatic subjects and low back pain patients, Journal ofBiomechanics (2017), doi: http://dx.doi.org/10.1016/j.jbiomech.2017.06.016

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customerswe are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, andreview of the resulting proof before it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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1st revision (Ms. No. BM-D-17-00012)

How do we stand?

Variations during repeated standing phases of asymptomatic subjects and low back pain

patients

Hendrik Schmidt1, Maxim Bashkuev1, Jeronimo Weerts1, Friedmar Graichen1, Joern

Altenscheidt2, Christoph Maier2, Sandra Reitmaier1

1 Julius Wolff Institut, Charité – Universitätsmedizin Berlin, Germany

2 Department of Pain Management, BG-University Hospital Bergmannsheil, Bochum, Germany

Address of corresponding author

Hendrik Schmidt

Julius Wolff Institut

Charité – Universitätsmedizin Berlin

Augustenburger Platz 1

13353 Berlin

Germany

Phone: +49 30 2093 46016

Fax: +49 2093 46001

Email: [email protected]

Word count:

Abstract: 210

Introduction - Discussion: 3540

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Abstract

An irreproducible standing posture can lead to mis-interpretation of radiological measurements, wrong

diagnoses and possibly unnecessary treatment. This study aimed to evaluate the differences in lumbar

lordosis and sacrum orientation in six repetitive upright standing postures of 353 asymptomatic subjects

(including 332 non-athletes and 21 athletes – soccer players) and 83 low back pain (LBP) patients using a

non-invasive back-shape measurement device.

In the standing position, all investigated cohorts displayed a large inter-subject variability in sacrum

orientation (~40°) and lumbar lordosis (~53°). In the asymptomatic cohort (non-athletes), 51% of the

subjects showed variations in lumbar lordosis of 10–20% in six repeated standing phases and 29%

showed variations of even more than 20%. In the sacrum orientation, 53% of all asymptomatic subjects

revealed variations of >20% and 31% of even more than 30%.

It can be concluded that standing is highly individual and poorly reproducible. The reproducibility was

independent of age, gender, body height and weight. LBP patients and athletes showed a similar

variability as the asymptomatic cohort. The number of standing phases performed showed no positive

effect on the reproducibility. Therefore, the variability in standing is not predictable but random, and

thus does not reflect an individual specific behavioral pattern which can be reduced, for example, by

repeated standing phases.

Keywords

Human Posture; Standing; Lumbar Lordosis; Sacrum Orientation; Age; Gender

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Introduction

The degree and progression of spinal disorders is frequently evaluated in full-length sagittal-plane

radiographs of the spine and pelvis in an upright standing position. For standardized capture of the

current state of alignment (Amonoo-Kuofi, 1992; Hammerberg and Wood, 2003) and for a more precise

assignment of patients to appropriate treatments (Lin et al., 1992; Tuzun et al., 1999), different

anatomical parameters have been identified: e.g., pelvic incidence, pelvic tilt (Hansson et al., 1985;

Schwab et al., 2006), vertical plumb line (Gelb et al., 1995; Jackson and McManus, 1994; La Grone, 1988),

lumbar lordosis (Pellet et al., 2011; Troke et al., 2005; Van Herp et al., 2000) and sacrum orientation

(Peleg et al., 2007a; Peleg et al., 2007b). During radiographic examination, patients are requested to

stand relaxed with extended knees and parallel shoulder girdle and pelvis (Stagnara et al., 1982). Despite

these instructions, variations in the adopted posture cannot be avoided. Just a slight pelvic rotation

combined with hip extension was found to markedly shift the anterior-superior corner of the sacrum,

causing a change in the horizontal distance of the plumb line to the S1 vertebra (Gelb et al., 1995;

Jackson and McManus, 1994).

To provide adequate visualization of the spine, the typical diagnostic lateral radiograph is often taken

with the subject’s arm flexed forward (Gelb et al., 1995; Vedantam et al., 1998). The effect of different

arm positions on the segmental and global changes in the sagittal alignment of the spine associated with

two standing radiographic positions (arms forward-flexed to 45° vs. fists-on-clavicles) was examined in

asymptomatic subjects (Aota et al., 2009) and in patients with adolescent idiopathic scoliosis (Faro et al.,

2004). It was attempted to define the most functional standing position for the evaluation of an accurate

sagittal balance. Aota and colleagues (2009) showed that fists-on-clavicles caused less negative shift in

plumb line and less compensatory posterior rotation of the pelvis, and therefore appeared more

appropriate for defining a patient’s functional balance. However, in patients with a previous spinal

fusion, Vedantam et al. (1998) recommended positioning the arms at 30° for a lateral radiograph to

prevent a negative shift in the plumb line and to gain a more functional position.

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Currently, it has not been investigated how sagittal alignment parameters can change under repetitive

upright standing positions. Therefore, the reproducibility of lumbar lordosis and sacrum orientation

among six repetitive upright standing postures of 353 asymptomatic subjects (including 332 non-athletes

and 21 athletes) and 83 low back pain (LBP) patients was evaluated. We postulated the following

hypotheses:

1. The variability in lumbar lordosis and sacrum orientation in repetitive upright standing postures

decreases with the number of standing phases. After an initial adaptation-phase it was expected that

subjects will get more and more familiar with the test set-up and, therefore, the variability will

decrease in repeated standing phases.

2. Age and gender significantly affect the variation in lumbar lordosis and sacrum orientation. Own

previous findings indicated a significant correlation between gender/age and lumbar lordosis/sacrum

orientation (Dreischarf et al., 2014; Pries et al., 2015a).

3. LBP patients show a significantly greater variability in lumbar lordosis and sacrum orientation than

asymptomatic subjects due to pain-related functional adaptation and/ or pain and movement

avoidance behaviour.

4. Athletes with a higher and more uniform fitness level stand more reproducible than non-athletes. The

authors assumed that neuromotoric and muscular adaptations support athletes to have a more stable

and reproducible posture in comparison to the general population and especially to patients.

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Methods

Ethics

The Ethics Committee of the Charité – Universitätsmedizin Berlin for asymptomatic subjects (registry

numbers: EA4/011/10, EA1/162/13) and the Ruhr University Bochum for LBP patients (registry numbers:

4385-2012 (06.07.2012); 4427-12 (20.08.2012); 5233-15 (26.03.2015)) approved this study. All

participants were informed about the study’s procedure and signed a written consent giving their

permission to conduct measurements.

Asymptomatic subjects – non-athletes

This group includes data from 332 subjects (187 females; 145 males) from a previously published cohort

on the measurement of lumbar spinal posture and motion (Consmuller et al., 2012a). These subjects did

not experience pain in the lower back or pelvis in the 6 months prior to the measurements and never

underwent spinal or pelvic surgery. More details are provided in Table 1.

Athletes - Soccer players

This group includes data obtained from 21 men without pain in the lower back or pelvis in the 6 months

prior to the measurements and who had no history of spinal or pelvic surgery. They were recruited from

a professional soccer team and regularly performed seven training sessions á 90 min per day

(10.5 h/week).

LBP patients

This group includes data from 83 patients with chronic LBP of >12 months duration (range: >12 month to

>20 years). Patients with paresis, for example, after nerve-root compression, other acute serious

conditions (e.g., tumor, infection, compression fracture, heart insufficiency) and prior fusion surgery of

more than two segments were excluded.

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Measurement system

The Epionics SPINE system (Epionics Medical GmbH, Potsdam, Germany) was used to assess lumbar

spinal shape as well as sacrum orientation and rotation in the sagittal plane (Fig. 1). The system involves

two flexible sensor strips, each consisting of twelve 2.5-cm-long segments based on differential strain-

gauge elements which provide a sensitive measure of the curvature in each segment. During a

measurement, the sensor strips are inserted into two hollow plasters attached to the back

paravertebrally, 7.5 cm away from the spinal column on each side.

The lower end of each strip was aligned with the spina iliaca posterior superior, which was approximately

in line with the first sacral vertebra. A tri-axial accelerometer was located at this end, allowing the

system to assess sacrum orientation. This acceleration sensor determined the spatial orientation of the

sensor relative to the vertical direction of the earth’s gravitational field. The sensor strips were

connected to a storage unit (size: 12.5 cm × 5.5 cm; mass: 80 g) that collected data with a frequency of

50 Hz. The sensor strips of the system exhibit high accuracy and repeatability (interclass correlation

coefficient, ICC>0.98) with test-retest reliability ICCs of >0.98. Previous studies confirmed the suitability

of the system for assessing lumbar and pelvic motion (Consmuller et al., 2012a, b; Pries et al., 2015b;

Rohlmann et al., 2014; Taylor et al., 2010).

Measurement protocol

All study participants were equipped with the Epionics SPINE system and performed a standardized

choreography consisting of (1st standing) flexion, (2nt

standing) extension, (3rd standing) left and (4th

standing) right

lateral bending as well as (5th

standing) left and (6th

standing) right axial rotation (Fig. 1). Each exercise was

repeated three times before going to the next exercise. Before each exercise, the subjects were explicitly

requested to stand in a relaxed upright position with extended knees for 2 seconds. In these 2 seconds,

the lumbar lordosis and sacrum orientation were recorded in a frequency of 50 Hz and subsequently the

mean value of both was calculated.

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Data analysis

The lumbar angle was individually calculated by summing all Epionics’ segments that were lordotically

curved in the individual volunteer, as shown by the transition from lordosis to kyphosis (change of sign)

during standing, accounting for differences in subjects’ anthropometrics. The corresponding data from

the left and right sensors were averaged. Sacrum orientation was determined from the orientation of the

accelerometer (Pries et al., 2015a). All data were processed using in-house developed MATLAB routines

(MATLAB R2009b, MathWorks, Inc., Natick, MA, US.).

Statistics

The Kolmogorov-Smirnov-Lilliefors test was applied to evaluate the normal distribution for each

investigated group. To detect the presence of outliers, the Grubb’s test was performed. Levene’s test

was used to test for variance homogeneity. For normally distributed data and variance homogeneity,

Student’s t-test was applied to access gender-specific differences and a one-way analysis of variance

(ANOVA) followed by post hoc Scheffé’s test to analyze differences between cohorts. The subjects were

later grouped based on the variability in the sacrum orientation and lumbar lordosis during different

standing phases. Due to small size of the individual sub-groups, the non-parametric Friedman test was

performed to assess the differences between repeated measurements in the subgroups, followed by

post hoc Nemenyi test. Additionally, a regression analyses was applied and the coefficient of

determination (R2) was calculated. P-values of <0.05 were considered statistically significant. The

statistical analyzes were performed with R 3.2.5 (R-Core-Team, 2016).

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Results

In the standing position, all investigated cohorts displayed a large inter-subject variability in sacrum

orientation and lumbar lordosis (Fig. 2). As an example, for asymptomatic subjects, the sacrum

orientation ranged between 1.2° and 38.5° while the lumbar lordosis varied between 7.7° and 59.5°. The

lumbar lordosis in LBP patients did not differ significantly from asymptomatic subjects (p = 0.29);

however, the sacrum orientation was significantly smaller (11.6°, p < 0.001). Moreover, both lumbar

lordosis and sacrum orientation significantly differed between asymptomatic subjects and soccer

players. While the lumbar lordosis of soccer players was larger (39.1°; range: 21.7–59.5°; p < 0.001), the

sacrum orientation was smaller (13.3°; range: 1.9–26.8°; p = 0.003). A significant difference was detected

between LBP patients and soccer players in lumbar lordosis (30.1° vs. 39.1°, p < 0.001), but not in sacrum

orientation (11.6° vs. 13.3°, p = 0.51). After adjusting the data for age and gender, the difference in the

lumbar lordosis remained significant only between asymptomatic subjects and soccer players (p = 0.034).

The sacrum orientation in asymptomatic subjects was still significantly different from both soccer players

(p = 0.002) and LBP patients (p = 0.017).

In six repeated standing phases, 51% of all asymptomatic women and men showed on average variations

in lumbar lordosis between 10% and 20%; 20% between 20% and 30% and 6% between 30% and 40%

(Figs. 3, 4). In the sacrum orientation, 42% of all asymptomatic women and 29% of all asymptomatic men

revealed variations of 10%-20%. Interestingly, 18% of all asymptomatic men showed variations in sacrum

orientation >40%. For variations of 10–20%, sacrum orientation and lumbar lordosis did not show

significant differences between repeated measurements (① and ② in Fig. 3; p=0.34). For variabilities

>50%, the variations in sacrum orientation decreased significantly with the number of repetitions (③ in

Fig. 3, p=0.003 between the first and the last standing phases). Similarly, high variability in the lordosis

demonstrated no significant changes between the repeated measurements (④ in Fig. 3; p=0.34)

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The percentages of subjects of different variability levels did not substantially change between men and

women or between asymptomatic subjects and LBP patients (Fig. 4). However, soccer players displayed a

more uniform distribution in sacrum orientation and lumbar lordosis, with up to 40% variability.

In the absolute values, the majority of study participants showed variations of 2–10° (Fig. 5). However,

2% of the asymptomatic subjects, 5% of LBP patients and 10% of the soccer players displayed variations

of >12°, mostly in sacrum orientation. Maximum values of 16.3° in sacrum orientation and 19.9° in

lumbar lordosis were found for asymptomatic subjects, 13.8° and 23.8°, respectively, for LBP patients

and 10.6° and 14.4°, respectively, for soccer players.

Body height, body weight and age displayed no effect on the variability in sacrum orientation and lumbar

lordosis (R2<0.033; Fig. 6). Similar trends could be observed for LBP patients and soccer players (R2<0.04)

as well as separately for gender sub-cohorts (R2<0.04). Moreover, the time of the day showed also no

effect on the variability of both parameters in all three cohorts (R2<0.012).

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Discussion

An irreproducible standing posture can lead to false radiological measurements, incorrect diagnoses and

possibly unnecessary treatment. For X-ray examination, physicians usually instruct the patient to stand in

a relaxed position, as this is assumed to be the most reproducible posture and allows the best possible

overview of the spinal shape. Furthermore, standing often forms the basis (as an anatomical reference

frame) for motion analyzes in laboratory setup. However, numerous relaxed positions are possible, and

thus inconsistent postures may be taken. Therefore, it is difficult to ensure a reproducible state in this

posture. This work, exploiting data collected in earlier studies, was designed to evaluate the variations in

sacrum orientation and lumbar lordosis in six repetitive upright standing postures of different cohorts:

332 asymptomatic non-athletes (general population), 21 asymptomatic soccer players and 83 LBP

patients. It was demonstrated that sacrum orientation and lumbar lordosis in the standing position are

highly variable (individual). For asymptomatic non-athletes, the lordosis angle varied between 7.7° and

59.5° and the sacrum orientation between 1.2° and 38.5°. Previous studies have also indicated a large

degree of normal variability in the sagittal alignment of the spine in young, healthy subjects (Stagnara et

al., 1982), middle- and older-aged patients (Gelb et al., 1995) and patients with back pain (Jackson and

McManus, 1994; Kumar et al., 2001). It is therefore unreasonable to expect one “normal lordosis” or

“normal sacrum orientation” of subjects/patients in the standing position.

The results further demonstrated a high variability in lumbar lordosis and sacrum orientation between

six repeated standing phases. In the sacrum orientation, for example, 53% of all asymptomatic subjects

displayed variations of >20%, 31% of >30% and 18% of >40%. In absolute values, 2% of the asymptomatic

subjects, 5% of the LBP patients and 10% of the soccer players showed variations of >12°. Maximum

variations of 16.3° in the sacrum orientation for asymptomatic subjects and 23.8° for LBP patients were

found. Several studies have indicated that the sagittal alignment can be accurately measured and that

the measurements were repeatable when the same subject was examined at two different points in time

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(Jackson and Hales, 2000; Jackson et al., 1998). This cannot be supported by the present findings. At this

point it should be mentioned that the measurement device was fixed at the subject’s back once and not

removed and reattached during the measuring session. This prevents additional measurement

inaccuracies (variations in lumbar lordosis and sacrum orientations between different standing phases)

due to an imprecise reattachment of the device.

Contrary to our first hypothesis, the variability in lumbar lordosis and sacrum orientation did not

decrease with the number of standing phases. The authors hypothesized that the greatest variations in

lumbar lordosis and sacrum orientation occur between the first and second standing phase. They

assumed that the first measurement provokes the subjects to think too much about what they are

requested to do and thus take an unusual posture. After the first flexibility measurement (three times

flexion), the subject should be standing more relaxed, and therefore, the variability should diminish with

increased standing phases, which was, however, not supported by the results.

Contrary to our second hypothesis, no influence of gender and age on the variability in standing was

found. LBP patients did not show a greater variability of different standing postures, which disagrees

with our third hypothesis. Therefore, it is important to understand that the variability in standing is not

predictable but random, and thus does not reflect an individual specific behavioral pattern which can be

reduced, for example, by repeated standing phases.

The fourth hypothesis that regularly trained subjects improve the reproducibility of standing postures

was also not supported by the present findings. The authors assumed that their muscular adaptations

support them to have a more stable and therefore a more reproducible posture in comparison to the

general population and especially to patients.

The present results showed no effect of the time of the day on the variability in lumbar lordosis and

sacrum orientation in all three cohorts. This is in contrast to previous measurements on spinal flexibility

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which clearly showed diurnal variations (intra-day variations) in spinal stiffness. A simple flexibility test

by monitoring temporal changes in the fingertip-to-floor distance could potentially indicate the trunk

“stiffness/flexibility” and temporal variations therein with the maximum stiffness occurring early in the

morning after rising (Gifford, 1987). Maximum flexibility occurs late in the evening before going to bed

(Adams and Dolan, 1996). A similar response is seen in the lumbar flexion with the maximum stiffness

early in the morning and the maximum flexibility late in the afternoon (Gifford, 1987; Manire et al.,

2010). This corroborates findings of Adams et al. (1987) who showed that the range of trunk flexion

increased by about 5° during the day. These previous findings would suggest that also the variability in

repeated standing phases is time dependent, which was however not the case in the current analyses.

Given the high impact of a reproducible posture, practical recommendations for patient positioning

during X-ray radiography have been given by different authors. Dewi et al. (2010) suggested a balancing

plate, BalancAid, which consists of a square board with a cylindrical disc at the center point attached at

the center of the bottom. This design should realize a forced balance in the sagittal and frontal planes.

The balancing effect from the device forces the subject to stand balanced and directs the posture in a

specific upright position. The authors showed a greater reproducibility when using BalancAid compared

to standing on the ground by grasping a supporting bar. However, it has to be noted that the position

during standing on such an apparatus is not comparable to naturally relaxed standing. Koreska et al.

(1978) implemented the ‘‘Throne’’ to reproduce the positioning of the patients. However, this device

merely enabled the patient to be imaged in a sitting position, whereas the standardized method for

curvature measurement using X-ray requires standing. Other researchers showed that the arm position

is not only important in having an optimal vertebral visibility in X-ray radiographs but also plays an

important role in the generation of a reliable three-dimensional representation of the spine (Hayashi et

al., 2009; Schmidt and Gassel, 1994; Vialle et al., 2005).

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Given that from one standing posture to the next standing posture, the study participants performed

different exercises (e.g., flexion or extension), it is likely that some of the observed variability was due to

differences in exposures. Such results would highlight the need for the development of protocols capable

of making standing posture more reproducible. The present results showed a tendency towards larger

variability in lumbar lordosis after 3 times flexion (1st exercise) and smaller variability after 3 times

extension (2nd exercise). Although these differences were not significant, the present results support the

development of standardized protocols; the including exercises, however, have to be investigated in

future studies.

In accordance with other non-invasive measurement tools, Epionics SPINE has certain limitations. First, it

should be noted that the Epionics SPINE system measures the back shape and not directly the curvature

of the lumbar spine and the orientation of the sacrum. Recent studies have found a significant

correlation between lumbar lordosis assessed via the back shape and determined radiologically only for

subjects with a body mass index (BMI) <27.0 kg/m² (Adams et al., 1986; Guermazi et al., 2006; Stokes et

al., 1987). In our own validation studies, we could additionally show that the correlation between the

back and spinal shape is poor in overweight and obese persons, which limits this study to normal-weight

subjects (BMI<27.0 kg/m2). Therefore, to ensure a strong correlation between back shape and underlying

spinal structures, only subjects with a BMI <27.0 kg/m² were included in the asymptomatic cohort. For

the LBP patients’ cohort, this criterion could not be fulfilled and therefore, the lumbar lordosis measured

with Epionics cannot be directly transferred to the actual shape of the spine. However, since the study

focused not on the validity of the spinal shape measurements, but on the variability in posture between

repetitive measurements, the authors assumed this a minor limitation. Moreover, the acceleration

sensors estimate the sacrum orientation from the spina iliaca posterior superior. This procedure is in

accordance with other non-invasive measurement approaches (Granata and Sanford, 2000; Maduri et

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al., 2008; Tafazzol et al., 2014), but does not directly reflect clinically relevant sacrum or pelvic

parameters, which can only be obtained from radiographs.

The sensor stripes are seated inside hollow plasters, which are taped along their entire length to the

subject's back and allow the sensors to slide relative to the back's surface. The elastic fibers in the

plasters are aligned longitudinally to allow stretching during flexion and extension of the subject's back.

The plasters are able to elongate by about 50% (24 cm) of its original length which is much more than

the maximum value of 13 cm found in the present study. In the transverse direction (perpendicular to

the subject’s back), the plasters are least compliant to avoid deviations of the stripes in both

perpendicular directions and to ensure that the sensors remain closely attached to the subject's back.

Due to possible relative motion of the sensor stripes inside the hollow plasters and due to the large

stiffness of the sensor stripes in comparison to the skin, the measurement is less sensitive to skin

movements. Therefore, the measured variations in lumbar lordosis and sacrum orientations are assumed

to be due mainly to the inherent irreproducibility and not because of detachment of sensors.

It can be concluded that standing is highly individual and poorly reproducible. The reproducibility was

not affected by age, gender, BMI, body height and body weight. Back pain patients and athletes did not

show a different behavior to asymptomatic non-athletes. The number of standing phases also showed no

positive effect on the reproducibility. Therefore, it should be considered that each examination in

standing and the resulting measurements, for example, the sacrum orientation and lordosis angle, can

greatly vary in subsequent analyses.

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Acknowledgments

This study was partially financed by the Bundesinstitut für Sportwissenschaft, Bonn, Germany

(MiSpExNetwork).

Conflict of Interest

There is no conflict of interest.

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Table and figures caption

Table 1 Data for asymptomatic subjects (non-athletes, soccer players) and low back pain (LBP) patients.

Median and ranges are given for age, body height, body weight and body mass index (BMI).

Figure 1 The Epionics SPINE system affixed to a volunteer’s back in standing. The system consists of two

flexible sensor strips utilizing strain-gauge sensors, tri-axial accelerometers and a storage unit.

Demonstration of the assessment of the total lordosis angle, which is the sum of all lordotically curved

segments during standing (average lordosis range highlighted in green: S1–S6) as well as the orientation

of the sacrum given by ‘α’, with respect to the vertical direction. The measurement protocol consisted of

six standing phases and six exercises. Each exercise was repeated three times before going to the next

exercise. Standing was recorded before the first flexion and after each exercise.

Figure 2: Box plots for sacrum orientation and lumbar lordosis. The upper diagram represents the entire

cohorts, the lower diagram summarizes age- and gender-adjusted data. Box plots are based on the

median of all six standing phases. Dashed lines indicate statistical significances.

Figure 3: Number of asymptomatic subjects classified into groups of different variability ranges in sacrum

orientation and lumbar lordosis in six repeated standing phases. Diagrams ①-④ show the relative

variations of sacrum orientation and lumbar lordosis of six individuals for all standing phases: ① and ②

10–20%, ③ >50% and ④ 40–50%. The bars represent the entire cohort. The dashed lines indicate

significant differences.

Figure 4: Relative number of subjects (with respect to the cohort size) classified into groups of different

variability ranges in sacrum orientation and lumbar lordosis in six repeated standing phases.

Figure 5: Classification of subjects into groups of different variability ranges in sacrum orientation and

lumbar lordosis in six repeated standing phases. In contrast to Fig. 5, absolute values are given on the

horizontal axis.

Figure 6: Scatter plot with variability in sacrum orientation and lumbar lordosis vs. body height, body

weight and age. The median of all six standing phases are shown. The plots are presented for the

asymptomatic cohort, except for the influence of the body weight (second line), where the results of the

LBP patients are also shown because they cover a greater body-weight range.

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Table 1 Data for asymptomatic subjects (non-athletes, soccer players) and low back pain (LBP) patients. Median and ranges are given for age, body height, body weight and body mass index (BMI).

study groups number

women / men

Age

(y)

body height

(cm)

body weight

(kg)

BMI

(kg/m2)

asymptomatic subjects

(non-athletes)

w: 187 36 (20-75) 168 (148-184) 61 (45-88) 22.0 (16.7-26.9)

m: 145 39 (20-74) 180 (159-206) 76 (55-98) 23.4 (17.9-26.9)

soccer players m: 21 23 (19-28) 181 (163-193) 79 (63.3-111) 23.8 (21.4-26.5)

LBP patients w: 45 57 (24-84) 167 (152-189) 75 (52-120) 26.5 (19.8-44.1)

m: 38 54.5 (25-80) 181.5 (164-199) 93 (74-150) 30.0 (21.2-42.4)