Lower Limb Pain in a Preadolescent Population: Prognosis and Risk Factors for Chronicity—A Prospective 1- and 4-Year Follow-up Study
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《小儿科》
Department of Physical and Rehabilitation Medicine, Rheumatism Foundation Hospital, Heinola, Finland
Tampere School of Public Health, University of Tampere, Tampere, Finland
Department of Physical and Rehabilitation Medicine, University Hospital of Turku, Turku, Finland
Pediatric Research Center, Tampere University Hospital, Tampere, Finland
ABSTRACT
Objective. To determine the short-term and long-term prognosis of preadolescent lower limb pain and to assess factors that contribute to pain persistence at 1-year follow-up and pain recurrence at 4-year follow-up.
Methods. A 1- and 4-year follow-up was conducted of a population-based 10- and 12-year old cohort of schoolchildren with lower limb pain at baseline
Results. Of the baseline students with lower limb pain, 32% reported pain persistence at 1-year follow-up and 31% reported pain recurrence at 4-year follow-up. Vigorous exercise was the only statistically significant predictor of lower limb pain persistence at 1-year follow-up (odds ratio [OR]: 2.43; 95% confidence interval [CI]: 1.16–5.05), whereas at 4-year follow-up (at adolescence), hypermobility was predictive of pain recurrence (OR: 2.93; 95% CI: 1.13–7.70). Traumatic lower extremity pain had a 50% lower risk for pain recurrence compared with nontraumatic pain (OR: 0.48; 95% CI: 0.19–0.92).
Conclusion. Trauma-induced lower extremity pain in preadolescents has a favorable long-term natural course. Children’s involvement in vigorous exercise predicts short-term outcome of lower limb pain, whereas hypermobile children have a worse long-term prognosis.
Key Words: musculoskeletal pain pain prognosis lower limb preadolescents
Abbreviations: CI, confidence interval VO2max, maximal oxygen uptake OR, odds ratio
Lower limb pain is 1 of the most common medical complaints in children, affecting up to 42% of schoolchildren in Western societies.1–4 The annual cumulative incidence of this condition has recently been estimated as 30%.5 Traditionally, the term "growing pains" has been used to describe cases with intermittent nonarticular limb pain that usually occurs late in the day and may awaken the child at night.6 These children are usually 4 to 10 years of age with no abnormal physical signs.7 This condition accounted for most of the cases of lower limb pain, with a prevalence reaching up to 33.6% in children.8 However, during the past half-century, the number of preadults involved in organized athletic programs has increased dramatically in Western countries, reaching 75% of children between 5 and 15 in Britain in the late 1980s.9 This may be putting the children at a higher risk for lower limb trauma and, subsequently, pain. We previously reported that trauma was responsible for 33% of lower limb pain episodes in Finnish preadolescents.10 As more children are involved in athletic activities, the risk for lower limb pain as well as this proportion is expected to increase, given that the lower extremity is the most commonly injured anatomic area in sports.11
The natural course of lower extremity pain in preadults has been described as benign and self-limiting,7,12 although few prognostic studies have been conducted to prove this assumption. Studies on growing pains have shown that there is a gradual decrease in the frequency of pain episodes over a period of 1 to 2 years. However, recurrences have also been reported a few years later.13–16 In another 2- to 8-year follow-up study of female adolescents with idiopathic anterior knee pain, the majority, although with less severity, reported persistence of pain.17
Prognostic studies on traumatic lower limb injury in schoolchildren are scarce and almost exclusively about athletic adolescents. In a large study, 59% of injured young players returned to their full athletic activity within 1 week of injury.18 However, it would not be appropriate to generalize this finding to nonathletic preadults in the general population, given the differences between the 2 groups in the level of physical fitness, type of injury, and other unknown factors related to injury recovery.
The main limitation in the past prognostic studies on lower limb pain in youths lies in their reliance on clinical or athletic settings, which are usually highly selected study populations. Valid data about the natural course of childhood musculoskeletal pain is best obtained from population-based follow-up studies. Another important limitation is that none of these studies has systematically investigated contributing factors for lower limb pain persistence/recurrence. This information is needed to identify children who are at higher risk for chronic pain and might be in need of early preventive interventions.
This is a 1- and 4-year population-based follow-up study of preadolescents with lower limb pain. The purpose of the study was to determine the extent of chronicity of lower limb pain at both follow-up assessments. We also investigated which baseline factors predict persistence/recurrence of this condition during follow-up.
METHODS
The study was started in March 1995, when all primary schools in Lahti, Finland, were asked to take part in a survey to assess pain symptoms in Finnish preadolescents. Lahti is a town of 100000 inhabitants (2002) in southern Finland, with 21 primary schools. The Steiner school, the hospital school, and the schools for physically and mentally disabled were excluded from our survey because some of the methods used in this study were not suitable for their pupils. Two primary schools refused to participate, and all pupils from the third and fifth grades in the remaining 19 schools and present at school on the day of the survey participated in the study.10,19 The parents were informed about the study by letters, and both the children and their parents had the possibility to refuse enrollment in the survey. The final sample consisted of 1756 children, 867 of whom were third-grade (mean age: 9.8 years; SD: 0.4 years) and 889 were fifth-grade (mean age: 11.8 years; SD: 0.4 years) schoolchildren. This sample represented 82.9% of the children of these age groups in Lahti attending normal or special schools. The study was approved by the Ethics Committee of the Health Care Center of the City of Lahti.
Instruments
Pain Questionnaire
A structured pain questionnaire was designed to assess lower limb pain as well as other musculoskeletal pain symptoms (neck, upper limb, chest, upper back, lower back, and buttock) during the previous 3 months. Musculoskeletal pain symptoms were classified according to pain frequency (pain seldom or never, once a month, once a week, more than once a week, or almost daily). The 5-level frequency classification was adopted from the questionnaire used in a nationwide survey on health and health-related behaviors in schoolchildren by the World Health Organization.20 The questionnaire contained a pain drawing. The body area concerned was marked in a picture beside the question to help the child to recognize the named area. Children were also asked whether they had directly traumatized the pain areas that they had drawn (eg, injured when exercising, fallen down, stumbled), and those who had trauma were asked to mark the pain area with a different color on the drawing. The lower extremity area shown in the picture included the area from the level of the anterior superior iliac spine to the toes anteriorly and the area from the gluteal folds to the toes posteriorly.
Psychosomatic symptoms were assessed, and the children were asked to report the frequency with which they had experienced each symptom during the preceding 3 months. These symptoms included headache, abdominal pain, depressive mood, day tiredness, difficulties in falling asleep, and waking up during nights. Each symptom was considered positive when it was present at least once a week.
The questionnaire also assessed disabilities caused by pain. The children were asked to respond dichotomously (yes/no) to the following questions: (1) Do you have difficulties in falling asleep because of your pain, or does your pain disturb your sleep (2) Do you have difficulties while sitting during lessons (3) Do you feel pain if you walk >1 km (4) Do you feel pain during physical exercise class (5) Does your pain disturb your hobbies A subjective disability index (1 point for each, maximum 5) was calculated from answers to these questions. Preadolescents were categorized into 2 groups according to their disability index score (0–2 and 3–5). Absence from school as a result of pain or aches was assessed to ascertain functional limitations. However, this question did not distinguish musculoskeletal pain from other types of pain (eg, headache, abdominal pain). The children were asked about the frequency with which they have exercised to breathlessness, for at least half an hour, during the preceding 3 months and were categorized into 3 groups (0–2, 3–4, and 5–7 times a week). The pain questionnaire also included questions about other diseases and regular use of medications.
During the study design phase, 2 drafts of the questionnaire were tested in 2 different schools in Nastola, a neighboring community of Lahti, Finland, and the final draft was evaluated by repeating the survey after a 1-week interval. The test–retest reliability of the questionnaire in detecting children with pain at least once a week was good ( = .9). The concurrent validity of the pain questionnaire was examined by comparing it with interviews of 31 third- and 25 fifth-grade children. The observed agreement between pain questionnaire and interview technique was 86% (95% confidence interval [CI]: 74–94), and was .67.19
Hypermobility Test
A hypermobility test was conducted only at baseline using Beighton’s method (score 0–9).21 A nurse who was specially trained for the tests tested the children during school lessons. The intra- and interobserver reliabilities were measured earlier, with coefficients of .75 and .78, respectively.19 Of 1756 children at baseline, 1637 (93.2%) were examined for hypermobility. School absence on the examination date was the reason for nonparticipation. Beighton score of 6 was chosen as the cutoff point for hypermobility on the basis of the distribution of the results. This cutoff indicated that 7.8% (95% CI: 6.6–9.2) of all tested children exhibited hypermobility.19
Shuttle Run Test
As with the hypermobility test, the shuttle run test22 was conducted only at baseline. It measures maximal performance indoors and provides a valid and reliable index of cardiorespiratory endurance or maximal oxygen uptake (VO2max).23 It was performed on all of the study subjects except for children with acute musculoskeletal injury, acute respiratory infection, or other diseases that inhibit maximal physical strain. Of 1756 children at baseline, 1603 (91.3%) underwent the test. On the basis of the distribution of the results (median: 51.1 mL/kg per min), children were categorized into 3 groups according to their VO2max measurements: equal to or below average, fair (75th percentile), and high (>75th percentile).
Follow-up
The 1- and 4-year follow-ups were conducted in March 1996 and March 1999, respectively, with the same pain questionnaire as at baseline.
Case Definition of Lower Limb and Other Musculoskeletal Pain Symptoms
Those who reported pain in their lower extremity, with or without reporting traumatizing the pain area, in a frequency of at least once a week during the preceding 3 months fulfilled our case definition of lower limb pain at baseline. The same case definition was used for other musculoskeletal pain symptoms. The case definition at follow-up assessments did not include lower extremity pain caused by a direct trauma.
In this article, the term "pain persistence" is used to describe children who had lower limb pain at baseline and reported pain at 1-year follow-up; the term "pain recurrence" is used to describe the same baseline children who reported pain at 4-year follow-up.
Statistical Methods
Data were summarized using frequency tables, and the most important descriptive values were expressed with 95% CIs. Logistic regression analyses were used to identify predictive factors of 1-year persistence and 4-year recurrence of lower limb pain. Baseline characteristics from a total number of 295 children, found at 1-year follow-up, were used to assess factors that predict pain persistence, whereas data from 228 children, found at 4-year follow-up, were used to assess factors that are associated with pain recurrence. Presence of lower limb pain at each stage was used as the dependent variable. The analysis included the following independent variables: age (below/above 11 years), psychosomatic symptoms (present/absent), disability index score (0–2/3–5), frequency of exercise (0–2/3–4/5–7 times a week), Beighton score of hypermobility (below/above 6), traumatizing the lower limb (yes/no), extent of lower limb pain (regional/combined), frequency of lower limb pain (once a week/more), and VO2max (low/fair/high scores). The logistic models first were fitted with each of these variables separately to estimate the unadjusted odds ratios (ORs) between each factor and persistence/recurrence of lower limb pain, and then a multivariate analysis was conducted using a backward stepwise method. All independent variables were initially included in the regression equation, and elimination of variables, at each step, was based on the likelihood ratio test at 10% level of significance. In all tests, a P < .05 (2 tailed) was considered statistically significant. All statistical analyses were performed using SPSS (for Windows), version 10.0.
RESULTS
At 1-year follow-up, 295 (91.9%) children of the lower limb pain group at baseline filled in the pain questionnaire. Data from these children were used to investigate factors that predict lower limb pain persistence. At 4-year follow-up, 228 (71.0%) children of the lower limb pain group at baseline completed the pain questionnaire again. The numbers and proportions of children who were followed up at each stage in both the lower limb pain and the no lower limb pain groups are shown in Fig 1. Reasons for nonparticipation in the follow-ups included absence from school on the day of testing, changing schools, moving away, and refusing to participate.
A dropout analysis was performed for the children with lower limb pain at baseline, comparing the baseline variables of those who were found at 4-year follow-up with those who were lost to follow-up or had incomplete data. Students who were lost to follow-up evaluation or had incomplete data were similar to those who remained in the study with respect to almost all of the baseline variables (Table 1). Furthermore, a multivariate logistic regression analysis was conducted to assess the effect of various baseline factors on the odds that a child would be lost to follow-up, and none of the baseline variables significantly influenced the rate at which children drop out.
Of our baseline students with lower limb pain, 32.2% reported pain persistence at 1-year follow-up, and 30.7% reported pain recurrence at 4-year follow-up. Of these, 14.5% had lower limb pain at both follow-up evaluations. Compared with preadolescents who did not report lower limb pain at baseline, those with lower limb pain had almost 3-fold risk for occurrence of lower extremity pain at both 1-year follow-up (relative risk: 2.76; 95% CI: 2.21–3.44) and at 4-year follow-up (relative risk: 2.79; 95% CI: 1.16–3.62; Fig 2).
On the other hand, 2 factors were identified as statistically significant predictors of pain recurrence within the univariate logistic models. Hypermobile children with lower limb pain at preadolescence had an increased risk for pain recurrence compared with those with normal joint laxity. Children with nontraumatic lower limb pain at preadolescence were also at significantly higher risk for pain recurrence compared with children with trauma-induced pain (Table 4). In the multivariate analysis, the same 2 factors were the only statistically significant predictors. Having a nontraumatic lower limb pain at preadolescence carried an 50% higher risk for pain recurrence than children with trauma-initiated pain, and hypermobile children had 3-fold the risk for pain recurrence compared with the nonhypermobile group (Table 5).
With additional analysis, pain recurrence was reported by 71.4% of the hypermobile children who had musculoskeletal pain at both baseline and 1-year follow-up (with persistent preadolescent lower limb pain). However, pain recurrence was reported by only 38.5% of nonhypermobile children with persistent preadolescent lower limb pain. The difference in the recurrence proportions between the 2 groups was not statistically significant (P = .12).
DISCUSSION
Our study shows that approximately one third of preadolescents with lower limb pain at baseline had persistent pain at 1-year follow-up, and almost the same proportion reported pain recurrence at 4-year follow-up. We also found that 15% of these children reported lower limb pain at both follow-up assessments. These figures are similar to the persistence/recurrence proportions previously reported for children with low back pain and upper back pain in the same study population,24 yet the short- and long-term prognosis of pain experience in all 3 musculoskeletal locations seemed to be more favorable than preadolescent neck pain. As reported earlier, children with neck pain at baseline had 47% persistence and 52% recurrence proportions.24 The predictive effect of pain location at baseline on subsequent pain persistence in children was documented in a recent longitudinal study.25 To our knowledge, this is the first follow-up study of children with lower limb pain to adolescence. For this reason, it is difficult to compare our persistence/recurrence proportions with those of the very few prospective studies that have investigated the outcome of this condition in preadults, given the differences in age and length of follow-up. In their controlled interventional study, Baxter and Dulberg13 prospectively followed from ages 5 to 14 years and for a period of 18 months children who had growing pains at baseline. Their control group, which was simply reassured of a self-limiting outcome, showed a gradual decline in the average number of pain episodes during this follow-up period, reaching an average of 2 episodes at the 18th month. In another long-term follow-up study of female adolescents with idiopathic anterior knee pain at baseline, defined by the author as knee pain without definitive diagnosis by history, examination, and plain radiographs, Nimon et al26 found that 50% of these girls had persistent knee pain, with at least the same baseline subjective magnitude, at a mean follow-up of 3.8 years. Of these subjects, 27% still complained of knee pain after a mean follow-up period of 16 years. Comparing our results with both of these studies might not be appropriate in light of the previously mentioned differences in the study populations, as well as the differences in case definitions of lower limb pain. However, all of these studies showed that the assumption of a self-limiting, favorable prognosis of lower limb pain in preadults is not always true, but some children continue to experience pain in their lower extremities for many years after their first presentation. This necessitates additional research to help understand the etiologic features of this condition in children.
In the present study, practicing vigorous exercise was the only baseline factor that was predictive of persistent lower limb pain at 1-year follow-up. A positive association has been reported between frequency of physical exercise and lower limb pain in a number of previous studies,27–29 yet no correlation was observed in a recent follow-up study.5 Despite these conflicting results concerning the role of childhood exercise frequency in the development of lower limb pain, limitation of vigorous exercise for children with lower limb pain may be protective, given its prognostic relevance in our study.
In the current study, children with trauma-induced lower extremity pain had a significantly better long-term prognosis compared with children with nontraumatic lower limb pain. We previously reported that children with traumatic lower limb pain experienced significantly more disabilities at baseline compared with the nontraumatic pain group (unpublished data). These findings demonstrate the favorable long-term outcome of the relatively more disabling traumatic lower limb pain. Previous studies on children have shown that their bones and muscles are more elastic30 and heal faster31 than those in adults. Similar findings have been reported earlier in adolescent populations among athletes.18 The difference in the long-term prognosis of traumatic versus nontraumatic lower extremity pain found in our study further proves our previous conclusion, based on our cross-sectional study, that these 2 conditions should be regarded as different entities (unpublished data).
Hypermobility was the only contributing factor of lower limb pain recurrence at 4-year follow-up (at adolescence). Exercise was not an effect modifier for this relationship, ie, the predictive role of hypermobility on pain recurrence was not altered by the frequency of physical exercise practiced by the children. The same finding was observed in our previous study when we used the wide case definition of musculoskeletal pain.24 In both studies, hypermobility did not predict pain persistence of pain at 1-year follow-up but was a statistically significant factor for pain recurrence at 4-year follow-up. One possible explanation for this finding is that there is a group within the hypermobile youths who are more prone to experience musculoskeletal pain from childhood to adolescence, and this can be seen by the differences in the recurrence proportions between hypermobile and nonhypermobile children with persistent preadolescent musculoskeletal pain. We previously reported that of 1637 children who were examined for hypermobility at baseline, only 127 (7.8%) exhibited hypermobility,19 and our present findings are based on only 18 hypermobile children who had lower limb pain at baseline and were found at both follow-ups. This finding requires confirmation in larger studies.
The appropriateness of the terms "persistence" and "recurrence" for describing occurrence of lower limb pain at 1- and 4-year follow-ups, respectively, might be argued. Occurrence of musculoskeletal pain during the 3 months preceding the 1-year follow-up assessment does not necessarily indicate that the child had musculoskeletal pain during the entire preceding year, which might be assumed by using the term "persistence." However, occurrence of musculoskeletal pain at 4-year follow-up might have been persistent musculoskeletal pain if the child had had pain during the whole 4-year follow-up period. We have used the short time scale (3 months) to avoid difficulties of pain recall in children. Recall difficulties have been reported in previous studies that have used a protracted recall time scale in collecting data about pain experience in preadult study populations.32–34
It must be noted that we categorized our baseline children (with lower limb pain) into 2 groups according to whether they have directly traumatized their lower limb area with pain. We did not collect complete data about the traumatic event (eg, injured during playing sports, stumbled) that initiated lower limb pain in the traumatic group. Furthermore, children who might have had overuse injuries that caused their lower limb pain were not included in the traumatic group but rather in the nontraumatic group, as they did not indicate a direct trauma to the lower limb in the pain questionnaire at baseline. The rationale of excluding pain caused by a direct trauma from our case definition of lower limb pain at follow-up assessments is to avoid spurious overestimated persistence/recurrence proportions, as pain initiated by a direct trauma at 1- and 4-year follow-ups most probably was unrelated to the history of lower limb pain at baseline.
Strengths of this prognostic study lay in its population-based design, fairly long follow-up period, and the use of a valid method for assessing the frequency of lower limb pain aided by a diagram. However, we did not evaluate pain intensity and did not gather information about sociodemographic factors. Another limitation of this study is that joint laxity was the only anatomic factor measured by physical examination. Although it was found that various anatomic and misalignment factors were unrelated to the long-term outcome of knee pain in young adults,26 some anatomic/structural factors associated with lower limb pain in our children may have played a role in pain persistence or recurrence.
We have been using the term "psychosomatic symptoms" to refer collectively to the following symptoms: headache, abdominal pain, depressive feelings, waking up during nights, difficulty in falling asleep, and day tiredness. Previous studies have demonstrated that the first 3 symptoms have a psychosomatic origin in most children.35,36 However, it might be argued that the last 3 symptoms were manifestations of lower limb pain rather than an expression of psychological stress.
In conclusion, our study shows that trauma-induced lower extremity pain in preadolescents has a favorable long-term natural course compared with nontraumatic lower limb pain. Furthermore, vigorous exercise predicts short-term outcome of lower limb pain, whereas hypermobility in preadolescence indicates a risk for pain recurrence at adolescence. These results might have implications both for understanding the natural course of this prevalent complaint in schoolchildren and for providing guidance for identifying children who are at high risk for pain persistence for better preventive and curative care.
ACKNOWLEDGMENTS
This study was funded by PATU and EVO Development Projects, the Signe and Ane Gyllenberg Foundation, the Medical Research Funds of the Rheumatism Foundation, and Tampere University hospitals.
We thank Tuija Sulonen, RN, for assistance in collecting the data at follow-up.
FOOTNOTES
Accepted Dec 23, 2004.
No conflict of interest declared.
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El-Metwally A, Salminen JJ, Auvinen A, Kautiainen H, Mikkelsson M. Prognosis of non-specific musculoskeletal pain in preadolescents: a prospective 4-year follow-up study till adolescence. Pain. 2004;110 :550 –559
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Tampere School of Public Health, University of Tampere, Tampere, Finland
Department of Physical and Rehabilitation Medicine, University Hospital of Turku, Turku, Finland
Pediatric Research Center, Tampere University Hospital, Tampere, Finland
ABSTRACT
Objective. To determine the short-term and long-term prognosis of preadolescent lower limb pain and to assess factors that contribute to pain persistence at 1-year follow-up and pain recurrence at 4-year follow-up.
Methods. A 1- and 4-year follow-up was conducted of a population-based 10- and 12-year old cohort of schoolchildren with lower limb pain at baseline
Results. Of the baseline students with lower limb pain, 32% reported pain persistence at 1-year follow-up and 31% reported pain recurrence at 4-year follow-up. Vigorous exercise was the only statistically significant predictor of lower limb pain persistence at 1-year follow-up (odds ratio [OR]: 2.43; 95% confidence interval [CI]: 1.16–5.05), whereas at 4-year follow-up (at adolescence), hypermobility was predictive of pain recurrence (OR: 2.93; 95% CI: 1.13–7.70). Traumatic lower extremity pain had a 50% lower risk for pain recurrence compared with nontraumatic pain (OR: 0.48; 95% CI: 0.19–0.92).
Conclusion. Trauma-induced lower extremity pain in preadolescents has a favorable long-term natural course. Children’s involvement in vigorous exercise predicts short-term outcome of lower limb pain, whereas hypermobile children have a worse long-term prognosis.
Key Words: musculoskeletal pain pain prognosis lower limb preadolescents
Abbreviations: CI, confidence interval VO2max, maximal oxygen uptake OR, odds ratio
Lower limb pain is 1 of the most common medical complaints in children, affecting up to 42% of schoolchildren in Western societies.1–4 The annual cumulative incidence of this condition has recently been estimated as 30%.5 Traditionally, the term "growing pains" has been used to describe cases with intermittent nonarticular limb pain that usually occurs late in the day and may awaken the child at night.6 These children are usually 4 to 10 years of age with no abnormal physical signs.7 This condition accounted for most of the cases of lower limb pain, with a prevalence reaching up to 33.6% in children.8 However, during the past half-century, the number of preadults involved in organized athletic programs has increased dramatically in Western countries, reaching 75% of children between 5 and 15 in Britain in the late 1980s.9 This may be putting the children at a higher risk for lower limb trauma and, subsequently, pain. We previously reported that trauma was responsible for 33% of lower limb pain episodes in Finnish preadolescents.10 As more children are involved in athletic activities, the risk for lower limb pain as well as this proportion is expected to increase, given that the lower extremity is the most commonly injured anatomic area in sports.11
The natural course of lower extremity pain in preadults has been described as benign and self-limiting,7,12 although few prognostic studies have been conducted to prove this assumption. Studies on growing pains have shown that there is a gradual decrease in the frequency of pain episodes over a period of 1 to 2 years. However, recurrences have also been reported a few years later.13–16 In another 2- to 8-year follow-up study of female adolescents with idiopathic anterior knee pain, the majority, although with less severity, reported persistence of pain.17
Prognostic studies on traumatic lower limb injury in schoolchildren are scarce and almost exclusively about athletic adolescents. In a large study, 59% of injured young players returned to their full athletic activity within 1 week of injury.18 However, it would not be appropriate to generalize this finding to nonathletic preadults in the general population, given the differences between the 2 groups in the level of physical fitness, type of injury, and other unknown factors related to injury recovery.
The main limitation in the past prognostic studies on lower limb pain in youths lies in their reliance on clinical or athletic settings, which are usually highly selected study populations. Valid data about the natural course of childhood musculoskeletal pain is best obtained from population-based follow-up studies. Another important limitation is that none of these studies has systematically investigated contributing factors for lower limb pain persistence/recurrence. This information is needed to identify children who are at higher risk for chronic pain and might be in need of early preventive interventions.
This is a 1- and 4-year population-based follow-up study of preadolescents with lower limb pain. The purpose of the study was to determine the extent of chronicity of lower limb pain at both follow-up assessments. We also investigated which baseline factors predict persistence/recurrence of this condition during follow-up.
METHODS
The study was started in March 1995, when all primary schools in Lahti, Finland, were asked to take part in a survey to assess pain symptoms in Finnish preadolescents. Lahti is a town of 100000 inhabitants (2002) in southern Finland, with 21 primary schools. The Steiner school, the hospital school, and the schools for physically and mentally disabled were excluded from our survey because some of the methods used in this study were not suitable for their pupils. Two primary schools refused to participate, and all pupils from the third and fifth grades in the remaining 19 schools and present at school on the day of the survey participated in the study.10,19 The parents were informed about the study by letters, and both the children and their parents had the possibility to refuse enrollment in the survey. The final sample consisted of 1756 children, 867 of whom were third-grade (mean age: 9.8 years; SD: 0.4 years) and 889 were fifth-grade (mean age: 11.8 years; SD: 0.4 years) schoolchildren. This sample represented 82.9% of the children of these age groups in Lahti attending normal or special schools. The study was approved by the Ethics Committee of the Health Care Center of the City of Lahti.
Instruments
Pain Questionnaire
A structured pain questionnaire was designed to assess lower limb pain as well as other musculoskeletal pain symptoms (neck, upper limb, chest, upper back, lower back, and buttock) during the previous 3 months. Musculoskeletal pain symptoms were classified according to pain frequency (pain seldom or never, once a month, once a week, more than once a week, or almost daily). The 5-level frequency classification was adopted from the questionnaire used in a nationwide survey on health and health-related behaviors in schoolchildren by the World Health Organization.20 The questionnaire contained a pain drawing. The body area concerned was marked in a picture beside the question to help the child to recognize the named area. Children were also asked whether they had directly traumatized the pain areas that they had drawn (eg, injured when exercising, fallen down, stumbled), and those who had trauma were asked to mark the pain area with a different color on the drawing. The lower extremity area shown in the picture included the area from the level of the anterior superior iliac spine to the toes anteriorly and the area from the gluteal folds to the toes posteriorly.
Psychosomatic symptoms were assessed, and the children were asked to report the frequency with which they had experienced each symptom during the preceding 3 months. These symptoms included headache, abdominal pain, depressive mood, day tiredness, difficulties in falling asleep, and waking up during nights. Each symptom was considered positive when it was present at least once a week.
The questionnaire also assessed disabilities caused by pain. The children were asked to respond dichotomously (yes/no) to the following questions: (1) Do you have difficulties in falling asleep because of your pain, or does your pain disturb your sleep (2) Do you have difficulties while sitting during lessons (3) Do you feel pain if you walk >1 km (4) Do you feel pain during physical exercise class (5) Does your pain disturb your hobbies A subjective disability index (1 point for each, maximum 5) was calculated from answers to these questions. Preadolescents were categorized into 2 groups according to their disability index score (0–2 and 3–5). Absence from school as a result of pain or aches was assessed to ascertain functional limitations. However, this question did not distinguish musculoskeletal pain from other types of pain (eg, headache, abdominal pain). The children were asked about the frequency with which they have exercised to breathlessness, for at least half an hour, during the preceding 3 months and were categorized into 3 groups (0–2, 3–4, and 5–7 times a week). The pain questionnaire also included questions about other diseases and regular use of medications.
During the study design phase, 2 drafts of the questionnaire were tested in 2 different schools in Nastola, a neighboring community of Lahti, Finland, and the final draft was evaluated by repeating the survey after a 1-week interval. The test–retest reliability of the questionnaire in detecting children with pain at least once a week was good ( = .9). The concurrent validity of the pain questionnaire was examined by comparing it with interviews of 31 third- and 25 fifth-grade children. The observed agreement between pain questionnaire and interview technique was 86% (95% confidence interval [CI]: 74–94), and was .67.19
Hypermobility Test
A hypermobility test was conducted only at baseline using Beighton’s method (score 0–9).21 A nurse who was specially trained for the tests tested the children during school lessons. The intra- and interobserver reliabilities were measured earlier, with coefficients of .75 and .78, respectively.19 Of 1756 children at baseline, 1637 (93.2%) were examined for hypermobility. School absence on the examination date was the reason for nonparticipation. Beighton score of 6 was chosen as the cutoff point for hypermobility on the basis of the distribution of the results. This cutoff indicated that 7.8% (95% CI: 6.6–9.2) of all tested children exhibited hypermobility.19
Shuttle Run Test
As with the hypermobility test, the shuttle run test22 was conducted only at baseline. It measures maximal performance indoors and provides a valid and reliable index of cardiorespiratory endurance or maximal oxygen uptake (VO2max).23 It was performed on all of the study subjects except for children with acute musculoskeletal injury, acute respiratory infection, or other diseases that inhibit maximal physical strain. Of 1756 children at baseline, 1603 (91.3%) underwent the test. On the basis of the distribution of the results (median: 51.1 mL/kg per min), children were categorized into 3 groups according to their VO2max measurements: equal to or below average, fair (75th percentile), and high (>75th percentile).
Follow-up
The 1- and 4-year follow-ups were conducted in March 1996 and March 1999, respectively, with the same pain questionnaire as at baseline.
Case Definition of Lower Limb and Other Musculoskeletal Pain Symptoms
Those who reported pain in their lower extremity, with or without reporting traumatizing the pain area, in a frequency of at least once a week during the preceding 3 months fulfilled our case definition of lower limb pain at baseline. The same case definition was used for other musculoskeletal pain symptoms. The case definition at follow-up assessments did not include lower extremity pain caused by a direct trauma.
In this article, the term "pain persistence" is used to describe children who had lower limb pain at baseline and reported pain at 1-year follow-up; the term "pain recurrence" is used to describe the same baseline children who reported pain at 4-year follow-up.
Statistical Methods
Data were summarized using frequency tables, and the most important descriptive values were expressed with 95% CIs. Logistic regression analyses were used to identify predictive factors of 1-year persistence and 4-year recurrence of lower limb pain. Baseline characteristics from a total number of 295 children, found at 1-year follow-up, were used to assess factors that predict pain persistence, whereas data from 228 children, found at 4-year follow-up, were used to assess factors that are associated with pain recurrence. Presence of lower limb pain at each stage was used as the dependent variable. The analysis included the following independent variables: age (below/above 11 years), psychosomatic symptoms (present/absent), disability index score (0–2/3–5), frequency of exercise (0–2/3–4/5–7 times a week), Beighton score of hypermobility (below/above 6), traumatizing the lower limb (yes/no), extent of lower limb pain (regional/combined), frequency of lower limb pain (once a week/more), and VO2max (low/fair/high scores). The logistic models first were fitted with each of these variables separately to estimate the unadjusted odds ratios (ORs) between each factor and persistence/recurrence of lower limb pain, and then a multivariate analysis was conducted using a backward stepwise method. All independent variables were initially included in the regression equation, and elimination of variables, at each step, was based on the likelihood ratio test at 10% level of significance. In all tests, a P < .05 (2 tailed) was considered statistically significant. All statistical analyses were performed using SPSS (for Windows), version 10.0.
RESULTS
At 1-year follow-up, 295 (91.9%) children of the lower limb pain group at baseline filled in the pain questionnaire. Data from these children were used to investigate factors that predict lower limb pain persistence. At 4-year follow-up, 228 (71.0%) children of the lower limb pain group at baseline completed the pain questionnaire again. The numbers and proportions of children who were followed up at each stage in both the lower limb pain and the no lower limb pain groups are shown in Fig 1. Reasons for nonparticipation in the follow-ups included absence from school on the day of testing, changing schools, moving away, and refusing to participate.
A dropout analysis was performed for the children with lower limb pain at baseline, comparing the baseline variables of those who were found at 4-year follow-up with those who were lost to follow-up or had incomplete data. Students who were lost to follow-up evaluation or had incomplete data were similar to those who remained in the study with respect to almost all of the baseline variables (Table 1). Furthermore, a multivariate logistic regression analysis was conducted to assess the effect of various baseline factors on the odds that a child would be lost to follow-up, and none of the baseline variables significantly influenced the rate at which children drop out.
Of our baseline students with lower limb pain, 32.2% reported pain persistence at 1-year follow-up, and 30.7% reported pain recurrence at 4-year follow-up. Of these, 14.5% had lower limb pain at both follow-up evaluations. Compared with preadolescents who did not report lower limb pain at baseline, those with lower limb pain had almost 3-fold risk for occurrence of lower extremity pain at both 1-year follow-up (relative risk: 2.76; 95% CI: 2.21–3.44) and at 4-year follow-up (relative risk: 2.79; 95% CI: 1.16–3.62; Fig 2).
On the other hand, 2 factors were identified as statistically significant predictors of pain recurrence within the univariate logistic models. Hypermobile children with lower limb pain at preadolescence had an increased risk for pain recurrence compared with those with normal joint laxity. Children with nontraumatic lower limb pain at preadolescence were also at significantly higher risk for pain recurrence compared with children with trauma-induced pain (Table 4). In the multivariate analysis, the same 2 factors were the only statistically significant predictors. Having a nontraumatic lower limb pain at preadolescence carried an 50% higher risk for pain recurrence than children with trauma-initiated pain, and hypermobile children had 3-fold the risk for pain recurrence compared with the nonhypermobile group (Table 5).
With additional analysis, pain recurrence was reported by 71.4% of the hypermobile children who had musculoskeletal pain at both baseline and 1-year follow-up (with persistent preadolescent lower limb pain). However, pain recurrence was reported by only 38.5% of nonhypermobile children with persistent preadolescent lower limb pain. The difference in the recurrence proportions between the 2 groups was not statistically significant (P = .12).
DISCUSSION
Our study shows that approximately one third of preadolescents with lower limb pain at baseline had persistent pain at 1-year follow-up, and almost the same proportion reported pain recurrence at 4-year follow-up. We also found that 15% of these children reported lower limb pain at both follow-up assessments. These figures are similar to the persistence/recurrence proportions previously reported for children with low back pain and upper back pain in the same study population,24 yet the short- and long-term prognosis of pain experience in all 3 musculoskeletal locations seemed to be more favorable than preadolescent neck pain. As reported earlier, children with neck pain at baseline had 47% persistence and 52% recurrence proportions.24 The predictive effect of pain location at baseline on subsequent pain persistence in children was documented in a recent longitudinal study.25 To our knowledge, this is the first follow-up study of children with lower limb pain to adolescence. For this reason, it is difficult to compare our persistence/recurrence proportions with those of the very few prospective studies that have investigated the outcome of this condition in preadults, given the differences in age and length of follow-up. In their controlled interventional study, Baxter and Dulberg13 prospectively followed from ages 5 to 14 years and for a period of 18 months children who had growing pains at baseline. Their control group, which was simply reassured of a self-limiting outcome, showed a gradual decline in the average number of pain episodes during this follow-up period, reaching an average of 2 episodes at the 18th month. In another long-term follow-up study of female adolescents with idiopathic anterior knee pain at baseline, defined by the author as knee pain without definitive diagnosis by history, examination, and plain radiographs, Nimon et al26 found that 50% of these girls had persistent knee pain, with at least the same baseline subjective magnitude, at a mean follow-up of 3.8 years. Of these subjects, 27% still complained of knee pain after a mean follow-up period of 16 years. Comparing our results with both of these studies might not be appropriate in light of the previously mentioned differences in the study populations, as well as the differences in case definitions of lower limb pain. However, all of these studies showed that the assumption of a self-limiting, favorable prognosis of lower limb pain in preadults is not always true, but some children continue to experience pain in their lower extremities for many years after their first presentation. This necessitates additional research to help understand the etiologic features of this condition in children.
In the present study, practicing vigorous exercise was the only baseline factor that was predictive of persistent lower limb pain at 1-year follow-up. A positive association has been reported between frequency of physical exercise and lower limb pain in a number of previous studies,27–29 yet no correlation was observed in a recent follow-up study.5 Despite these conflicting results concerning the role of childhood exercise frequency in the development of lower limb pain, limitation of vigorous exercise for children with lower limb pain may be protective, given its prognostic relevance in our study.
In the current study, children with trauma-induced lower extremity pain had a significantly better long-term prognosis compared with children with nontraumatic lower limb pain. We previously reported that children with traumatic lower limb pain experienced significantly more disabilities at baseline compared with the nontraumatic pain group (unpublished data). These findings demonstrate the favorable long-term outcome of the relatively more disabling traumatic lower limb pain. Previous studies on children have shown that their bones and muscles are more elastic30 and heal faster31 than those in adults. Similar findings have been reported earlier in adolescent populations among athletes.18 The difference in the long-term prognosis of traumatic versus nontraumatic lower extremity pain found in our study further proves our previous conclusion, based on our cross-sectional study, that these 2 conditions should be regarded as different entities (unpublished data).
Hypermobility was the only contributing factor of lower limb pain recurrence at 4-year follow-up (at adolescence). Exercise was not an effect modifier for this relationship, ie, the predictive role of hypermobility on pain recurrence was not altered by the frequency of physical exercise practiced by the children. The same finding was observed in our previous study when we used the wide case definition of musculoskeletal pain.24 In both studies, hypermobility did not predict pain persistence of pain at 1-year follow-up but was a statistically significant factor for pain recurrence at 4-year follow-up. One possible explanation for this finding is that there is a group within the hypermobile youths who are more prone to experience musculoskeletal pain from childhood to adolescence, and this can be seen by the differences in the recurrence proportions between hypermobile and nonhypermobile children with persistent preadolescent musculoskeletal pain. We previously reported that of 1637 children who were examined for hypermobility at baseline, only 127 (7.8%) exhibited hypermobility,19 and our present findings are based on only 18 hypermobile children who had lower limb pain at baseline and were found at both follow-ups. This finding requires confirmation in larger studies.
The appropriateness of the terms "persistence" and "recurrence" for describing occurrence of lower limb pain at 1- and 4-year follow-ups, respectively, might be argued. Occurrence of musculoskeletal pain during the 3 months preceding the 1-year follow-up assessment does not necessarily indicate that the child had musculoskeletal pain during the entire preceding year, which might be assumed by using the term "persistence." However, occurrence of musculoskeletal pain at 4-year follow-up might have been persistent musculoskeletal pain if the child had had pain during the whole 4-year follow-up period. We have used the short time scale (3 months) to avoid difficulties of pain recall in children. Recall difficulties have been reported in previous studies that have used a protracted recall time scale in collecting data about pain experience in preadult study populations.32–34
It must be noted that we categorized our baseline children (with lower limb pain) into 2 groups according to whether they have directly traumatized their lower limb area with pain. We did not collect complete data about the traumatic event (eg, injured during playing sports, stumbled) that initiated lower limb pain in the traumatic group. Furthermore, children who might have had overuse injuries that caused their lower limb pain were not included in the traumatic group but rather in the nontraumatic group, as they did not indicate a direct trauma to the lower limb in the pain questionnaire at baseline. The rationale of excluding pain caused by a direct trauma from our case definition of lower limb pain at follow-up assessments is to avoid spurious overestimated persistence/recurrence proportions, as pain initiated by a direct trauma at 1- and 4-year follow-ups most probably was unrelated to the history of lower limb pain at baseline.
Strengths of this prognostic study lay in its population-based design, fairly long follow-up period, and the use of a valid method for assessing the frequency of lower limb pain aided by a diagram. However, we did not evaluate pain intensity and did not gather information about sociodemographic factors. Another limitation of this study is that joint laxity was the only anatomic factor measured by physical examination. Although it was found that various anatomic and misalignment factors were unrelated to the long-term outcome of knee pain in young adults,26 some anatomic/structural factors associated with lower limb pain in our children may have played a role in pain persistence or recurrence.
We have been using the term "psychosomatic symptoms" to refer collectively to the following symptoms: headache, abdominal pain, depressive feelings, waking up during nights, difficulty in falling asleep, and day tiredness. Previous studies have demonstrated that the first 3 symptoms have a psychosomatic origin in most children.35,36 However, it might be argued that the last 3 symptoms were manifestations of lower limb pain rather than an expression of psychological stress.
In conclusion, our study shows that trauma-induced lower extremity pain in preadolescents has a favorable long-term natural course compared with nontraumatic lower limb pain. Furthermore, vigorous exercise predicts short-term outcome of lower limb pain, whereas hypermobility in preadolescence indicates a risk for pain recurrence at adolescence. These results might have implications both for understanding the natural course of this prevalent complaint in schoolchildren and for providing guidance for identifying children who are at high risk for pain persistence for better preventive and curative care.
ACKNOWLEDGMENTS
This study was funded by PATU and EVO Development Projects, the Signe and Ane Gyllenberg Foundation, the Medical Research Funds of the Rheumatism Foundation, and Tampere University hospitals.
We thank Tuija Sulonen, RN, for assistance in collecting the data at follow-up.
FOOTNOTES
Accepted Dec 23, 2004.
No conflict of interest declared.
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