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1.  The extent and risk of knee injuries in children aged 9–14 with Generalised Joint Hypermobility and knee joint hypermobility - the CHAMPS-study Denmark 
Generalised Joint Hypermobility (GJH) is suggested as an aetiological factor for knee injuries in adolescents and adults. It is presumed that GJH causes decreased joint stability, thereby increasing the risk of knee injuries during challenging situations like jumping and landing. The aim was to study the extent and risk of knee injuries in children with GJH and knee hypermobility.
In total, 999 children (9–14 years) were tested twice during spring 2012 and 2013 with Beighton´s Tests (BT) for hypermobility, a 0–9 scoring system. GJH was classified with cut-point ≥5/9 on both test rounds. On basis of weekly cell phone surveys of knee pain, children requiring clinical examination were seen. Traumatic and overuse knee injuries were registered by WHO ICD-10 diagnoses. Logistic regression and Poisson regression models with robust standard errors were used to examine the association between GJH and knee injuries, taking into account clustering on school class levels.
Totally, 36 children were classified GJH on both test rounds. Overuse knee injuries were the most frequent injury type (86 %), mainly apophysitis for both groups (61 %), other than patella-femoral pain syndrome for the control group (13 %). For traumatic knee injuries, distortions and contusions were most frequent in both groups (51 % resp. 36 %), besides traumatic lesions of knee tendons and muscles for the control group (5 %). No significant association was found between overuse knee injuries and GJH with/without knee hypermobility (OR 0.69, p = 0.407 resp. OR 0.75, p = 0.576) or traumatic knee injuries and GJH with/without knee hypermobility (OR 1.56, p = 0.495 resp. OR 2.22, p = 0.231).
Apophysitis, distortions and contusions were the most frequent knee injuries. Despite the relatively large study, the number of children with GJH and knee injuries was low, with no significant increased risk for knee injuries for this group. This questions whether GJH is a clinically relevant risk factor for knee injuries in school children aged 9–14 years. A fluctuation in the individual child´s status of GJH between test rounds was observed, suggesting that inter- and intra-tester reproducibility of BT as well as growth may be considered important confounders to future studies of children with GJH.
PMCID: PMC4465013  PMID: 26065679
Knee injuries; Generalised Joint Hypermobility; Children; Beighton tests
2.  Reliability of diagnostic ultrasound in measuring the multifidus muscle 
Ultrasound is frequently used to measure activity in the lumbar multifidus muscle (LMM). However previous reliability studies on diagnostic ultrasound and LMM have included a limited number of subjects and few have used Bland-Altman’s Limits of Agreement (LOA). Further one does not know if activity affects the subjects’ ability to contract the LMM.
From January 2012 to December 2012 an inter- and intra-examiner reliability study was carried out in a clinical setting. It consisted of a total of four experiments with 30 subjects in each study. Two experienced examiners performed all measurements. Ultrasound measurements were made of: 1. the LMM in the resting state, 2. during a contracted state, 3. on subsequent days, and, before and after walking. Reliability and agreement was tested for 1. resting LMM, 2. contracted LMM, and 3. thickness change in the LMM. Mean values of three measurements were used for statistical analysis for each spinal level. The intra-class correlation coefficient (ICC) 3.1 and 3.2 was used to test for reliability, and Bland-Altman’s LOA method to test for agreement.
All of the studies indicate high levels of reliability, but as the LMM thickness increased (increasing contraction) the agreement between examiners was poorer than for low levels of contraction.
The use of diagnostic ultrasound to measure the LMM seems to be reliable in subjects who have little or no change in thickness of the LMM with contraction.
PMCID: PMC4397671  PMID: 25878771
Diagnostic ultrasound; Measurement; Lumbar multifidus; Agreement; Reliability; Limits of agreement; Intraclass correlation coefficient
3.  Back pain in children surveyed with weekly text messages - a 2.5 year prospective school cohort study 
Back pain is reported to occur already in childhood, but its development at that age is not well understood. The aims of this study were to describe BP in children aged 6–12 years, and to investigate any sex and age differences.
Data on back pain (defined as pain in the neck, mid back and/or lower back) were collected once a week from parents replying to automated text-messages over 2.5 school years from 2008 till 2011. The prevalence estimates were presented as percentages and 95% confidence intervals. Differences between estimates were considered significant if confidence intervals did not overlap. A test for trend, using a multi-level mixed-effects logistic regression extended to the longitudinal and multilevel setting, was performed to see whether back pain reporting increased with age.
Depending on the age group, 13-38% children reported back pain at least once per survey year, and 5-23% at least twice per survey year. The average weekly prevalence estimate ranged between 1% and 5%. In the final survey year more girls than boys reported back pain at least twice. The prevalence estimates did not increase monotonically with age but showed a greater increase in children younger than 9/10, after which they remained relatively stable up to the age of 12 years.
We found that back pain was not a common problem in this age group and recommend health professionals be vigilant if a child presents with constant or recurring back pain. Our results need to be supplemented by a better understanding of the severity and consequences of back pain in childhood. It would be productive to study the circumstances surrounding the appearance of back pain in childhood, as well as, how various bio-psycho-social factors affect its onset and later recurrence. Knowledge about the causes of back pain in childhood might allow early prevention.
Electronic supplementary material
The online version of this article (doi:10.1186/s12998-014-0035-6) contains supplementary material, which is available to authorized users.
PMCID: PMC4237741  PMID: 25414789
Children; Back pain; Text messages
4.  Is puberty a risk factor for back pain in the young? a systematic critical literature review 
Back pain is a common condition that starts early in life and seems to increase markedly during puberty. A systematic review was performed in order to investigate the link between puberty and back pain, using some Bradford Hill criteria for causality.
We sought to obtain answers to the following questions: 1) Is there an association between puberty and back pain? If so, how strong is this association? And do the results remain unchanged also when controlling for age and sex? 2) Are the results of the studies consistent? 3) Is there a dose–response, showing a link between the increasing stages of puberty and the subsequent prevalence of back pain? 4) Is there a temporal link between puberty and back pain?
A systematic critical literature review.
Systematic searches were made in March 2014 in PubMed, Embase, CINAHL and PsycINFO including longitudinal or cross-sectional studies on back pain for subjects <19 years, written in French or English. The review process followed the AMSTAR recommendations. Interpretation was made using some of the Bradford-Hill criteria for causality.
Four articles reporting five studies were included, two of which were longitudinal. 1) Some studies show a weak and others a strong positive association between puberty and back pain, which remains after controlling for age and sex; 2) Results were consistent across the studies; 3) There was a linear increase of back pain according to the stage of puberty 4) Temporality has not been sufficiently studied.
All our criteria for causality were fulfilled or somewhat fulfilled indicating the possibility of a causal link between puberty and back pain. Future research should focus on specific hypotheses, for example investigating if there could be a hormonal or a biomechanical aspect to the development of back pain at this time of life.
Electronic supplementary material
The online version of this article (doi:10.1186/s12998-014-0027-6) contains supplementary material, which is available to authorized users.
PMCID: PMC4200222  PMID: 25328668
Back pain; Puberty; Adolescent; Cause; Aetiology; Systematic review
5.  Do extra compulsory physical education lessons mean more physically active children - findings from the childhood health, activity, and motor performance school study Denmark (The CHAMPS-study DK) 
Primarily, this study aims to examine whether children attending sports schools are more active than their counterpart attending normal schools. Secondary, the study aims to examine if physical activity (PA) levels in specific domains differ across school types. Finally, potential modifications by status of overweight/obesity and poor cardio-respiratory fitness are examined.
Participants were from the first part of the CHAMPS-study DK, which included approximately 1200 children attending the 0th – 6th grade. At the sports schools, the mandatory physical education (PE) program was increased from 2 to 6 weekly lessons over a 3-year period. Children attending normal schools were offered the standard 2 PE lessons. PA was assessed at two different occasions with the GT3X ActiGraph accelerometer, once during winter in 2009/10 and once during summer/fall in 2010. Leisure time organized sports participation was quantified by SMS track. Based on baseline values in 2008, we generated a high-BMI and a low-cardio-respiratory fitness for age and sex group variable.
There were no significant differences in PA levels during total time, PE, or recess between children attending sports schools and normal schools, respectively. However, children, especially boys, attending sports schools were more active during school time than children attending normal schools (girls: β=51, p=0.065; boys: β=113, p<0.001). However, in the leisure time during weekdays children who attended sports schools were less active (girls: β=-41, p=0.004; boys: β=-72, p<0.001) and less involved in leisure time organized sports participation (girls: β=-0.4, p=0.016; boys: β=-0.2, p=0.236) than children who attended normal schools. Examination of modification by baseline status of overweight/obesity and low cardio-respiratory fitness indicated that during PE low fit girls in particular were more active at sports schools.
No differences were revealed in overall PA levels between children attending sports schools and normal schools. Sports schools children were more active than normal schools children during school time, but less active during leisure time. In girls, less organized sports participation at least partly explained the observed differences in PA levels during leisure time across school types. Baseline status of cardio-respiratory fitness modified school type differences in PA levels during PE in girls.
Electronic supplementary material
The online version of this article (doi:10.1186/s12966-014-0121-0) contains supplementary material, which is available to authorized users.
PMCID: PMC4180151  PMID: 25248973
Physical activity; Physical education; School-based; Organized sports; Children; Objective monitoring; Accelerometry; CHAMPS-study DK
6.  Field assessment of balance in 10 to 14 year old children, reproducibility and validity of the Nintendo Wii board 
BMC Pediatrics  2014;14:144.
Because body proportions in childhood are different to those in adulthood, children have a relatively higher centre of mass location. This biomechanical difference and the fact that children’s movements have not yet fully matured result in different sway performances in children and adults. When assessing static balance, it is essential to use objective, sensitive tools, and these types of measurement have previously been performed in laboratory settings. However, the emergence of technologies like the Nintendo Wii Board (NWB) might allow balance assessment in field settings. As the NWB has only been validated and tested for reproducibility in adults, the purpose of this study was to examine reproducibility and validity of the NWB in a field setting, in a population of children.
Fifty-four 10–14 year-olds from the CHAMPS-Study DK performed four different balance tests: bilateral stance with eyes open (1), unilateral stance on dominant (2) and non-dominant leg (3) with eyes open, and bilateral stance with eyes closed (4). Three rounds of the four tests were completed with the NWB and with a force platform (AMTI). To assess reproducibility, an intra-day test-retest design was applied with a two-hour break between sessions.
Bland-Altman plots supplemented by Minimum Detectable Change (MDC) and concordance correlation coefficient (CCC) demonstrated satisfactory reproducibility for the NWB and the AMTI (MDC: 26.3-28.2%, CCC: 0.76-0.86) using Centre Of Pressure path Length as measurement parameter. Bland-Altman plots demonstrated satisfactory concurrent validity between the NWB and the AMTI, supplemented by satisfactory CCC in all tests (CCC: 0.74-0.87). The ranges of the limits of agreement in the validity study were comparable to the limits of agreement of the reproducibility study.
Both NWB and AMTI have satisfactory reproducibility for testing static balance in a population of children. Concurrent validity of NWB compared with AMTI was satisfactory. Furthermore, the results from the concurrent validity study were comparable to the reproducibility results of the NWB and the AMTI. Thus, NWB has the potential to replace the AMTI in field settings in studies including children. Future studies are needed to examine intra-subject variability and to test the predictive validity of NWB.
PMCID: PMC4057805  PMID: 24913461
Sway; Children; Nintendo Wii; Reproducibility of results; Validity
7.  Spinal pain in adolescents: prevalence, incidence, and course: a school-based two-year prospective cohort study in 1,300 Danes aged 11–13 
The severity and course of spinal pain is poorly understood in adolescents. The study aimed to determine the prevalence and two-year incidence, as well as the course, frequency, and intensity of pain in the neck, mid back, and low back (spinal pain).
This study was a school-based prospective cohort study. All 5th and 6th grade students (11–13 years) at 14 schools in the Region of Southern Denmark were invited to participate (N = 1,348). Data were collected in 2010 and again two years later, using an e-survey completed during school time.
The lifetime prevalence of spinal pain was 86% and 89% at baseline and follow-up, respectively. A group of 13.6% (95% CI: 11.8, 15.6) at baseline and 19.5% (95% CI: 17.1, 22.0) at follow-up reported that they had pain frequently. The frequency of pain was strongly associated with the intensity of pain, i.e., the majority of the participants reported their pain as relatively infrequent and of low intensity, whereas the participants with frequent pain also experienced pain of higher intensity. The two-year incidence of spinal pain varied between 40% and 60% across the physical locations. Progression of pain from one to more locations and from infrequent to more frequent was common over the two-year period.
Spinal pain is common at the age of 11–15 years, but some have more pain than others. The pain is likely to progress, i.e., to more locations, higher frequency, and higher pain intensity over a two-year period.
PMCID: PMC4045997  PMID: 24885549
Prevalence; Incidence; Frequency; Intensity; Course; Spinal pain; Adolescence
8.  Absence of low back pain in the general population followed fortnightly over one year with automated text messages 
Over one year, the majority of patients with low back pain (LBP) from the secondary care sector could not report a single week without LBP and few could report a non-episode, defined as at least one month without LBP. Presumably, non-episodes would be more common in the general population. The aim of this study was to assess the usefulness of this definition of ´”non-episodes”, by studying their presence over one year in the general population. Specifically, we wanted to: 1) determine the prevalence of non-episodes, 2) identify the proportion of study participants who could be classified as being in a non-episode at the end of the observation period, and 3) estimate the proportion of participants classified as having at least two separate non-episodes.
Danes, aged 49/50, who previously participated in a population-based study on LBP received fortnightly automated text (SMS) messages over one year. Each time, participants reported the number of days with LBP in the preceding fortnight. Fortnights with 0 days of LBP were defined as ‘zero-fortnights’ and two such fortnights in a row (one month) were defined as a ‘non-episode’. Estimates are reported as percentages with their 95% confidence intervals in brackets.
Two hundred and ninety-three people were invited to participate. Of these, 16 declined participation and 16 were excluded because they failed to return their text message at least 20 of the 26 times, leaving 261 in the current analyses. Of these, 11% (2-22) never reported a zero-fortnight. In all, 83% (78-88) had at least one non-episode throughout the study period and the proportion of participants classified as being in a non-episode at the end of the study was 59% (53-65). The percentage of individuals with at least two non-episodes was 52% (46-58).
It is possible to differentiate people from the general population as having or not having episodes of LBP using the definition of absence of LBP over one month as the measure. Non-episodes were far more common in the general population than in the secondary care sector, suggesting it to be a potentially useful definition in research.
PMCID: PMC3892070  PMID: 24405834
Low back pain; General population; Population study; Episodes; Epidemiology; Text messages; Longitudinal; Prospective; Survey
9.  Seasonal variation in musculoskeletal extremity injuries in school children aged 6–12 followed prospectively over 2.5 years: a cohort study 
BMJ Open  2014;4(1):e004165.
The type and level of physical activity in children vary over seasons and might thus influence the injury patterns. However, very little information is available on the distribution of injuries over the calendar year. This study aims to describe and analyse the seasonal variation in extremity injuries in children.
Prospective cohort study.
10 public schools in the municipality of Svendborg, Denmark.
A total of 1259 school children aged 6–12 years participating in the Childhood Health, Activity, and Motor Performance School Study Denmark.
School children were surveyed each week during 2.5 school-years. Musculoskeletal injuries were reported by parents answering automated mobile phone text questions (SMS-Track) on a weekly basis and diagnosed by clinicians. Data were analysed for prevalence and incidence rates over time with adjustments for gender and age.
Injuries in the lower extremities were reported most frequently (n=1049). There was a significant seasonal variation in incidence and prevalence for lower extremity injuries and for lower and upper extremity injuries combined (n=1229). For the upper extremities (n=180), seasonal variation had a significant effect on the risk of prevalence. Analysis showed a 46% increase in injury incidence and a 32% increase in injury prevalence during summer relative to winter for lower and upper extremity injuries combined.
There are clear seasonal differences in the occurrence of musculoskeletal extremity injuries among children with almost twice as high injury incidence and prevalence estimates during autumn, summer and spring compared with winter. This suggests further research into the underlying causes for seasonal variation and calls for preventive strategies to be implemented in order to actively prepare and supervise children before and during high-risk periods.
PMCID: PMC3902503  PMID: 24401728
Public Health; Sports Medicine
10.  Inter-tester reproducibility and inter-method agreement of two variations of the Beighton test for determining Generalised Joint Hypermobility in primary school children 
BMC Pediatrics  2013;13:214.
The assessment of Generalised Joint Hypermobility (GJH) is usually based on the Beighton tests, which consist of a series of nine tests. Possible methodological shortcomings can arise, as the tests do not include detailed descriptions of performance, interpretation nor classification of GJH. The purpose of this study was, among children aged 7-8 and 10-12 years, to evaluate: 1) the inter-tester reproducibility of the tests and criteria for classification of GJH for 2 variations of the Beighton test battery (Methods A and B) with a variation in starting positions and benchmarks between methods, and 2) the inter-method agreement for the two batteries.
A standardised three-phase protocol for clinical reproducibility studies was followed including a training phase, an overall agreement phase and a study phase. The number of participants in the three phases was 10, 70 and 39 respectively. For the inter-method study a total of 103 children participated. Two testers judged each test battery. A score of ≥5 was set as the cut-off level for GJH. Cohen's kappa statistics and McNemar´s test were used to test for agreement and significant differences.
Kappa values for GJH (≥5) were 0.64 (Method A, prevalence 0.42) and 0.59 (Method B, prevalence 0.46), with no difference between testers in Method A (p = 0.45) and B (p = 0.29). Prevalence of GJH in the inter-method study was 31% (A) and 35% (B) with no difference between methods (p = 0.54).
Inter-tester reproducibility of Methods A and B was moderate to substantial, when following a standardised study protocol. Both test batteries can be used in the same children population, as there was no difference in prevalence of GJH at cut point 5, when applying method A and B. However, both methods need to be tested for their predictive validity at higher cut-off levels, e.g. ≥6 and ≥7.
PMCID: PMC3878084  PMID: 24358988
Hypermobility; Beighton tests; Reproducibility; Standardised protocol; Children
11.  Is the development of Modic changes associated with clinical symptoms? A 14-month cohort study with MRI 
European Spine Journal  2012;21(11):2271-2279.
Modic changes (MCs) have been suggested to be a diagnostic subgroup of low back pain (LBP). However, the clinical implications of MCs remain unclear. For this reason, the aims of this study were to investigate how MCs developed over a 14-month period and if changes in the size and/or the pathological type of MCs were associated with changes in clinical symptoms in a cohort of patients with persistent LBP and MCs.
Information on LBP intensity and detailed information from MRI on the presence, type and size of MCs was collected at baseline and follow-up. Changes in type (Type I, II, III and mixed types) and size of MCs were quantified at both time points according to a standardised evaluation protocol. The associations between change in type, change in size and change in LBP intensity were calculated using odds ratios (ORs).
Approximately 40 % of the MCs followed the expected developmental path from Type I (here Type I or I/II) to Type II (here Type II or II/III) or Type I to Type I/II. In general, the bigger the size of the MC at baseline, the more likely it was that it remained unchanged in size after 14 months. Patients who had MC Type I at both baseline and 14-month follow-up were less likely to experience an improvement in their LBP intensity as compared to patients who did not have Type I changes at both time points (OR 7.2, CI 1.3–37). There was no association between change in size of MCs Type I and change in LBP intensity.
The presence of MCs Type I at both baseline and follow-up is associated with a poor outcome in patients with persistent LBP and MCs.
PMCID: PMC3481109  PMID: 22526703
Low back pain; Modic changes; Magnetic resonance imaging; Association
12.  Effect of four additional physical education lessons on body composition in children aged 8–13 years – a prospective study during two school years 
BMC Pediatrics  2013;13:170.
Strategies for combating increasing childhood obesity is called for. School settings have been pointed out as potentially effective settings for prevention. The objective of this paper was to evaluate the effect of four additional Physical Education (PE) lessons/week in primary schools on body composition and weight status in children aged 8–13.
Children attending 2nd to 4th grade (n = 632) in 10 public schools, 6 intervention and 4 control schools, participated in this longitudinal study during 2 school years. Outcome measures: Primary: Body Mass Index (BMI) and Total Body Fat percentage (TBF%) derived from Dual Energy X ray Absorptiometry (DXA). Secondary: the moderating effect of overweight/obesity (OW/OB) and adiposity based on TBF% cut offs for gender.
Intervention effect on BMI and TBF% (BMI: β -0.14, 95% CI: -0.33; 0.04, TBF%: β -0.08, 95% CI:-0.65;0.49) was shown insignificant. However, we found significant beneficial intervention effect on prevalence of OW/OB based on BMI (OR 0.29, 95% CI: 0.11;0.72). The intervention effect on adiposity based on TBF% cut offs was borderline significant (OR 0.64, 95% CI:0. 39; 1.05).
Four additional PE lessons/week at school can significantly improve the prevalence of OW/OB in primary schoolchildren. Mean BMI and TBF% improved in intervention schools, but the difference with controls was not significant. The intervention had a larger effect in children who were OW/OB or adipose at baseline.
PMCID: PMC3853216  PMID: 24131778
School-based intervention; BMI; DXA; Total body fat percentage; Children; Obesity prevention; Longitudinal study
13.  Evidence-based classification of low back pain in the general population: one-year data collected with SMS Track 
It was previously assumed that low back pain (LBP) is a disorder that can be classified as acute, subacute and chronic. Lately, the opinion seems to have veered towards a concept of it being a more recurrent or cyclic condition. Interestingly, a recent review of the literature indicated that LBP in the general population is a rather stable condition, characterized as either being present or absent. However, only one of the reviewed studies had used frequent data collection, which would be necessary when studying detailed course patterns over time. It was the purpose of this study to see, if it was possible to identify whether LBP, when present, is rather episodic or chronic/persistent. Further, we wanted to see if it was possible to describe any specific course profiles of LBP in the general population.
In all, 293 49/50-yr old Danes, who previously participated in a population-based study on LBP were invited to respond to 26 fortnightly text-messages over one year, each time asking them the number of days they had been bothered by LBP in the past two weeks. The course patterns for these individuals were identified through manual analysis, by observing the interplay between non-episodes and episodes of LBP. A non-episode of LBP was defined as a period of at least one month without LBP as proposed by de Vet et al. A fortnight with at least one day of pain was defined as a pain fortnight (FN). At least one pain FN surrounded by a non-episode on each side was defined as an episode of LBP. After some preliminary observations of the spread of data, episodes were further classified as brief (consisting of only one pain FN) or longer (if there were at least 2 pain FNs in a row). An episode of at least 6 pain FNs in a row (i.e. 3 months) was defined as a long-lasting episode.
In all, 261 study subjects were included in the analyses, for which 7 distinct LBP subsets could be identified. These could be grouped into three major clusters; those mainly without LBP (35%), those with episodic LBP (30%) and those with persistent LBP (35%). There was a positive association between number of episodes and their duration.
In this study population, consisting of 50-yr old persons from the general population, LBP, when present, could be classified as either ‘episodic’ or ‘mainly persistent’. About one third was mainly LBP-free throughout the year of study. More information is needed in relation to their relative proportions in various populations and the clinical relevance of these subgroups.
PMCID: PMC3766189  PMID: 24139224
Low back pain; Epidemiology; Trajectories; Subgroups; Episodes; Text-messages
14.  The intensity of physical activity influences bone mineral accrual in childhood: the childhood health, activity and motor performance school (the CHAMPS) study, Denmark 
BMC Pediatrics  2013;13:32.
Studies indicate genetic and lifestyle factors can contribute to optimal bone development. In particular, the intensity level of physical activity may have an impact on bone health. This study aims to assess the relationship between physical activity at different intensities and Bone Mineral Content (BMC), Bone Mineral Density (BMD) and Bone Area (BA) accretion.
This longitudinal study is a part of The CHAMPS study-DK. Whole-body DXA scans were performed at baseline and after two years follows up. BMC, BMD, and BA were measured. The total body less head (TBLH) values were used. Physical activity (PA) was recorded by accelerometers (ActiGraph, model GT3X). Percentages of different PA intensity levels were calculated and log odds of two intensity levels of activity relative to the third level were calculated. Multilevel regression analyses were used to assess the relationship between the categories of physical activity and bone traits.
Of 800 invited children, 742 (93%) accepted to participate. Of these, 682/742 (92%) participated at follow up. Complete datasets were obtained in 602/742 (81%) children. Mean (range) of age was 11.5 years (9.7-13.9). PA at different intensity levels was for boys and girls respectively, sedentary 62% and 64%, low 29% for both genders and moderate to high 9% and 7% of the total time. Mean (range) BMC, BMD, and BA was 1179 g (563–2326), 0.84 g/cm2 (0.64-1.15) and 1393 cm2 (851–2164), respectively. Valid accelerometer data were obtained for a mean of 6.1 days, 13 hours per day.
There 7was a positive relationship between the log odds of moderate to high-level PA versus low level activity and BMC, BMD and BA. Children with an increased proportion of time in moderate to high-level activity as opposed to sedentary and low-level activity achieved positive effects on BMC, BMD and BA.
PMCID: PMC3599700  PMID: 23452342
Dual energy X- ray absorptiometry; Bone health; Physical activity; Accelerometers
15.  Single leg mini squat: an inter-tester reproducibility study of children in the age of 9–10 and 12–14 years presented by various methods of kappa calculation 
Multiple studies suggest that reduced postural orientation is a possible risk factor for both patello-femoral joint pain (PFP) and rupture of the anterior cruciate ligament (ACL). In order to prevent PFP and ACL injuries in adolescent athletes, it is necessary to develop simple and predictive screening tests to identify those at high risk. Single Leg Mini Squat (SLMS) is a functional and dynamic real-time screening test, which has shown good validity and reproducibility in evaluation of postural orientation of the knee in an adult population. The aim of this study was to determine the inter-tester reproducibility of SLMS in the age group of 9–10 and 12–14 years by evaluating postural orientation of the ankle, knee, hip and trunk. Further on, this study exemplify the divergence of kappa values when using different methods of calculating kappa for the same dataset.
A total of 72 non-injured children were included in the study. Postural orientation of the ankle, knee, hip and trunk for both legs was determined by two testers using a four-point scale (ordinal, 0–3). Prevalence, overall agreement as well as four different methods for calculating kappa were evaluated: linear weighted kappa in comparison with un-weighted kappa, prevalence-adjusted bias-adjusted kappa (PABAK) and quadratic weighted kappa.
The linear weighted kappa values ranged between 0.54-0.86 (overall agreement 0.86-0.97), reflecting a moderate to almost perfect agreement. When calculating un-weighted kappa (with and without PABAK) and quadratic weighted kappa, the results spread between 0.46-0.88, 0.50-0.94, and 0.76-0.95, reflecting the various results when using different methods of kappa calculation.
The Single Leg Mini Squat test has moderate to almost perfect reproducibility in children aged 9–10 and 12–14 years when evaluating postural orientation of the ankles, knees, hips and trunk, based on the excellent strength of agreement as presented by linear weighted kappa. The inconsistency in results when using different methods of kappa calculation demonstrated the linear weighted kappa being generally 15% lower than the quadratic weighted values. On average, prevalence-adjusted bias-adjusted kappa increased the un-weighted kappa values by 7% and 12% by children aged 9–10 and 12–14, respectively.
PMCID: PMC3560108  PMID: 23082764
Children; Single Leg Mini Squat; Postural orientation; Reproducibility; Kappa statistics
16.  Occurrence and co-existence of localized musculoskeletal symptoms and findings in work-attending orchestra musicians - an exploratory cross-sectional study 
BMC Research Notes  2012;5:541.
Due to ergonomic exposure musicians are at risk of work-related musculoskeletal disorders in the neck, back, and upper extremities. The literature confirms musculoskeletal problems in these anatomic regions among orchestra musicians.
An explorative cross-sectional study among 441 musicians from six Danish symphony orchestras; 216 underwent a clinical examination constructed for the purpose. Prior to the examination the musicians rated their maximally perceived trouble within the last week on a scheme blinded to the examiner. Accessibility to the clinical examination differed between orchestras.
The aims were to assess the prevalence of 1) perceived symptoms within the previous week in the neck, back and limbs and of 2) clinical findings in the neck, back, and upper extremities, and 3) to investigate the co-existence of the perceived symptoms and clinical findings.
Symptoms and findings were most common in the neck, back, and shoulders. Due to a poor co-existence between self-reported symptoms and clinical findings musicians experiencing bodily trouble could not be identified through this clinical examination. Free accessibility to the examination was of major importance to participation.
In compliance with the purpose, perceived symptoms within the previous week and present clinical findings were assessed. Although both symptoms and findings were most frequent in the neck, back, and shoulders the co-existence of anatomically localized symptoms and findings was generally quite poor in this study.
Discrepancy between symptoms and findings might be caused by the participants currently attending work and therefore being relatively healthy, and the fluctuating nature of musculoskeletal problems. Furthermore from a comparison of different measuring units - self-reported symptoms being period prevalence rates and clinical findings point prevalence rates; a bias which may also be inherent in similar studies combining self-reported questionnaire data and clinical findings.
PMCID: PMC3515426  PMID: 23025290
Musicians; Symphony orchestra; Musculoskeletal symptoms; Musculoskeletal findings; Clinical examination; Pain; Repetitive strain injury; Nordic musculoskeletal questionnaire; Cross-sectional; Exploratory
17.  Gender difference in genetic association between IL1A variant and early lumbar disc degeneration: a three-year follow-up 
The purpose of the present study was to analyze the associations between specific genetic markers and early disc degeneration (DD) or early disc degeneration progression (DDP) defined by magnetic resonance imaging (MRI).
We selected eleven of the most promising single nucleotide polymorphisms (SNP) and compared the distributions of these genetic markers between groups defined by MRI in a Danish adolescent population (N=166) over a three-year follow-up period.
We observed a ten-fold higher annual incidence of endplate changes than previously reported in adults. The gender difference in IL1A rs1800587 association with DD remained significant and another association with DDP emerged in follow-up assessment. Among girls, the rs1800587 T-allele was associated both with DD (OR 2.82 [95% CI 1.29-6.16]) and with DDP (OR 2.45 [95% CI 1.03-5.82]). Among boys, the IL6 rs1800795 genotype G/C was protective in both DD (OR 0.26 [95% CI 0.09-0.72]) and DDP (OR 0.32 [95% CI 0.12-0.88]) with the IL6 rs1800797 genotype G/A was associated with a decreased likelihood of DD (OR 0.27 [95% CI 0.10-0.77]). Gender-genotype interactions were significant for polymorphisms in both IL1A and IL6. Correction for multiple testing weakened the associations for IL6 polymorphisms.
We conclude that gender specific effects in lumbar disc degeneration and its progression are possible. However, further evaluations in larger populations are needed. Our results provide some support to the hypothesis that early disc degeneration is an especially important phase in the cascade of degenerative disc disease.
PMCID: PMC3459213  PMID: 23050050
Disc degeneration; disc degeneration progression; adolescents; genetics; interleukins
18.  Study protocol. The Childhood Health, Activity, and Motor Performance School Study Denmark (The CHAMPS-study DK) 
BMC Pediatrics  2012;12:128.
An increasingly passive life-style in the Western World has led to a rise in life-style related disorders. This is a major concern for all segments of society. The county council of the municipality of Svendborg in Denmark, created six Sport Schools with increased levels of suitable physical activities, which made it possible to study the health outcomes in these children whilst comparing them to children who attended the ‘normal’ schools of the region using the design of a “natural experiment”.
Children from the age of 6 till the age of 10, who accepted to be included in the monitoring process, were surveyed at baseline with questionnaires, physical examinations and physical and biological testing, including DXA scans. The physical examination and testing was repeated during the early stage of the study. Every week over the whole study period, the children will be followed with an automated mobile phone text message (SMS-Track) asking questions on their leisure time sports activities and the presence of any musculoskeletal problems. Children who report any such problems are monitored individually by health care personnel. Data are collected on demography, health habits and attitudes, physical characteristics, physical activity using accelerometers, motor performance, fitness, bone health, life-style disorders, injuries and musculoskeletal problems. Data collection will continue at least once a year until the children reach grade 9.
This project is embedded in a local community, which set up the intervention (The Sport Schools) and thereafter invited researchers to provide documentation and evaluation. Sport schools are well matched with the ‘normal’ schools, making comparisons between these suitable. However, subgroups that would be specifically targeted in lifestyle intervention studies (such as the definitely obese) could be relatively small. Therefore, results specific to minority groups may be diluted. Nonetheless, the many rigorously collected data will make it possible to study, for example, the general effect that different levels of physical activity may have on various health conditions and on proxy measures of life-style conditions. Specifically, it will help answer the question on whether increased physical activity in school has a positive effect on health in children.
PMCID: PMC3483192  PMID: 22906115
19.  Analyzing repeated data collected by mobile phones and frequent text messages. An example of Low back pain measured weekly for 18 weeks 
Repeated data collection is desirable when monitoring fluctuating conditions. Mobile phones can be used to gather such data from large groups of respondents by sending and receiving frequently repeated short questions and answers as text messages.
The analysis of repeated data involves some challenges. Vital issues to consider are the within-subject correlation, the between measurement occasion correlation and the presence of missing values.
The overall aim of this commentary is to describe different methods of analyzing repeated data. It is meant to give an overview for the clinical researcher in order for complex outcome measures to be interpreted in a clinically meaningful way.
A model data set was formed using data from two clinical studies, where patients with low back pain were followed with weekly text messages for 18 weeks. Different research questions and analytic approaches were illustrated and discussed, as well as the handling of missing data. In the applications the weekly outcome “number of days with pain” was analyzed in relation to the patients’ “previous duration of pain” (categorized as more or less than 30 days in the previous year).
Research questions with appropriate analytical methods
1: How many days with pain do patients experience? This question was answered with data summaries.
2: What is the proportion of participants “recovered” at a specific time point? This question was answered using logistic regression analysis.
3: What is the time to recovery? This question was answered using survival analysis, illustrated in Kaplan-Meier curves, Proportional Hazard regression analyses and spline regression analyses.
4: How is the repeatedly measured data associated with baseline (predictor) variables? This question was answered using generalized Estimating Equations, Poisson regression and Mixed linear models analyses.
5: Are there subgroups of patients with similar courses of pain within the studied population? A visual approach and hierarchical cluster analyses revealed different subgroups using subsets of the model data.
We have illustrated several ways of analysing repeated measures with both traditional analytic approaches using standard statistical packages, as well as recently developed statistical methods that will utilize all the vital features inherent in the data.
PMCID: PMC3434072  PMID: 22824413
20.  Rest versus exercise as treatment for patients with low back pain and Modic changes. a randomized controlled clinical trial 
BMC Medicine  2012;10:22.
Clinical experience suggests that many patients with Modic changes have relatively severe and persistent low back pain (LBP), which typically appears to be resistant to treatment. Exercise therapy is the recommended treatment for chronic LBP, however, due to their underlying pathology, Modic changes might be a diagnostic subgroup that does not benefit from exercise. The objective of this study was to compare the current state-of-the art treatment approach (exercise and staying active) with a new approach (load reduction and daily rest) for people with Modic changes using a randomized controlled trial design.
Participants were patients from an outpatient clinic with persistent LBP and Modic changes. They were allocated using minimization to either rest therapy for 10 weeks with a recommendation to rest for two hours daily and the option of using a flexible lumbar belt or exercise therapy once a week for 10 weeks. Follow-up was at 10 weeks after recruitment and 52 weeks after intervention and the clinical outcome measures were pain, disability, general health and global assessment, supplemented by weekly information on low back problems and sick leave measured by short text message (SMS) tracking.
In total, 100 patients were included in the study. Data on 87 patients at 10 weeks and 96 patients at one-year follow-up were available and were used in the intention-to-treat analysis. No statistically significant differences were found between the two intervention groups on any outcome.
No differences were found between the two treatment approaches, 'rest and reduced load' and 'exercise and staying active', in patients with persistent LBP and Modic changes.
Trial Registration NCT00454792
PMCID: PMC3348080  PMID: 22376791
21.  Prevalence and consequences of musculoskeletal symptoms in symphony orchestra musicians vary by gender: a cross-sectional study 
Musculoskeletal symptoms are common in the neck, back, and upper limbs amongst musicians. Playing-related musculoskeletal disorders have been found to range from 32% to 87% with a tendency for female musicians to have more problems than males. Studies of musculoskeletal problems in instrumentalists have generally involved pre-professional musicians or populations comprising musicians of different levels. The objective of this study was therefore to investigate the prevalence, duration and consequences of musculoskeletal symptoms in professional symphony orchestra musicians.
A cross-sectional questionnaire study. The study population comprised of 441 musicians from six Danish symphony orchestras; 342 (78%) completed the questionnaire.
During the last year 97% of the women and 83% of the men experienced symptoms in at least one of nine anatomic regions (neck, upper and lower back, shoulders, elbows, and hands and wrists). 86% of the women and 67% of the men experienced symptoms for more than seven days, while 63% of the women and 49% of the men had symptoms for more than 30 days. Woodwind players had a lower risk for musculoskeletal symptoms and a lower risk for the consequences. Among consequences were changed way of playing, reported by 73% of the musicians, difficulty in daily activities at home, reported by 55%, and difficulty in sleeping, reported by 49%. Their health behaviour included taking paracetamol as the most used analgesic, while physiotherapists and general practitioners were reported as the most consulted health care professionals concerning musculoskeletal problems.
Results regarding symptoms in six anatomic regions were compared to results for a sample of the general Danish workforce. Symptoms were more frequent in musicians and lasted longer than in the general workforce. This applied to both genders.
Within the last year most symphony orchestra musicians experienced musculoskeletal symptoms in the neck, back or upper extremities. The symptoms impacted on their level of function in and outside work and were reflected in their health behaviour. Generally women had a higher risk than men and woodwind players a lower risk than other instrumentalists. Finally, symptoms were more frequent and lasted longer in the musicians than in the general workforce.
PMCID: PMC3221643  PMID: 21978278
22.  Prevalence and tracking of back pain from childhood to adolescence 
It is generally acknowledged that back pain (BP) is a common condition already in childhood. However, the development until early adulthood is not well understood and, in particular, not the individual tracking pattern. The objectives of this paper are to show the prevalence estimates of BP, low back pain (LBP), mid back pain (MBP), neck pain (NP), and care-seeking because of BP at three different ages (9, 13 and15 years) and how the BP reporting tracks over these age groups over three consecutive surveys.
A longitudinal cohort study was carried out from the years of 1997 till 2005, collecting interview data from children who were sampled to be representative of Danish schoolchildren. BP was defined overall and specifically in the three spinal regions as having reported pain within the past month. The prevalence estimates and the various patterns of BP reporting over time are presented as percentages.
Of the 771 children sampled, 62%, 57%, and 58% participated in the three back surveys and 34% participated in all three. The prevalence estimates for children at the ages of 9, 13, and 15, respectively, were for BP 33%, 28%, and 48%; for LBP 4%, 22%, and 36%; for MBP 20%, 13%, and 35%; and for NP 10%, 7%, and 15%. Seeking care for BP increased from 6% and 8% at the two youngest ages to 34% at the oldest. Only 7% of the children who participated in all three surveys reported BP each time and 30% of these always reported no pain. The patterns of development differed for the three spinal regions and between genders. Status at the previous survey predicted status at the next survey, so that those who had pain before were more likely to report pain again and vice versa. This was most pronounced for care-seeking.
It was confirmed that BP starts early in life, but the patterns of onset and development over time vary for different parts of the spine and between genders. Because of these differences, it is recommended to report on BP in youngsters separately for the three spinal regions, and to differentiate in the analyses between the genders and age groups. Although only a small minority reported BP at two or all three surveys, tracking of BP (particularly NP) and care seeking was noted from one survey to the other. On the positive side, individuals without BP at a previous survey were likely to remain pain free at the subsequent survey.
PMCID: PMC3123615  PMID: 21575251
23.  Preventing back pain 
BMJ : British Medical Journal  2008;336(7641):398.
Advice to stay active may not be appropriate for people in manual jobs
PMCID: PMC2249629  PMID: 18244956
24.  Comparison between data obtained through real-time data capture by SMS and a retrospective telephone interview 
The aims of the current study were: a) to quantitatively compare data obtained by Short Message Service (SMS) with data from a telephone interview, b) to investigate whether the respondents had found it acceptable to answer the weekly two SMS questions, c) to explore whether an additional weekly third SMS question would have been acceptable, and d) to calculate the total cost of using the SMS technology.
SMS technology was used each week for 53 weeks to monitor 260 patients with low back pain (LBP) in a clinical study. Each week, these patients were asked the same two questions: "How many days in the past week have you had problems due to LBP?" and "How many days in the past week have you been off work due to LBP problems?" The last 31 patients were also contacted by telephone 53 weeks after recruitment and asked to recall the number of days with LBP problems and days off work for the a) past week, b) past month, and c) past year. The two sets of answers to the same questions for these patients were compared. Patients were also asked whether a third SMS question would have been acceptable. The test-retest reliability was compared for 1-week, 1-month, and 1-year. Bland-Altman limits of agreement were calculated. The two quantitative questions were reported as percentages. Actual costs for the SMS-Track-Questionnaire (SMS-T-Q) were compared with estimated costs for paper version surveys.
There was high agreement between telephone interview and SMS-T-Q responses for the 1-week and 1-month recall. In contrast, the 1-year recall showed very low agreement. A third SMS question would have been acceptable. The SMS system was considerably less costly than a paper-based survey, beyond a certain threshold number of questionnaires.
SMS-T-Q appears to be a cheaper and better method to collect reliable LBP data than paper-based surveys.
PMCID: PMC2883994  PMID: 20500900
25.  Genetic risk factors of disc degeneration among 12-14-year-old Danish children: a population study 
The objective of the present study was to examine the associations between eleven putative predisposing single nucleotide polymorphisms (COL9A3, COL11A2, IL1A, IL1B, IL6 and VDR) and early disc degeneration (DD). The population consisted of 12 to 14-year-old Danish children (N=352). DD was evaluated from magnetic resonance images (MRI). We analysed the association between DD and single nucleotide polymorphisms or haplotypes using logistic regression analyses. Of the 352 children studied, 73 boys and 81 girls had no MRI changes, while 30 boys and 36 girls had lumbar DD. Among girls, IL1A rs1800587 in CT/TT compared to CC resulted in OR 2.85 [1.19-6.83]. In IL6 promoter polymorphism rs1800796, the C-allele was more frequent among the subjects with DD, OR 6.71 [1.71-26.3]. Of the IL6 haplotypes, GCG was associated with DD, OR 6.46 [1.61 – 26.0]. No associations were observed among boys. Our results suggest possible roles for IL1A and IL6 in early DD among girls.
PMCID: PMC3076758  PMID: 21537388
Disc degeneration; children; genetics; interleukins

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