Pediatric obesity has increased at an alarming rate in the last 30 years. As a result pediatric cardiovascular, endocrine and pulmonary obesity related morbidities have also risen. However, other pediatric complications of obesity important to public health and quality of life, such as bone, joint and muscle pains, are understudied and their prevalence, incidence and etiology remain unclear. In adults there is abundant evidence that obesity is a risk factor in the occurrence and progression of knee pain and knee osteoarthritis (KOA). In children, despite anecdotal and clinical impression there is sparse evidence on the link between obesity and musculoskeletal pain. Once this is understood the association between childhood obesity and its consequences for osteoarthritis can be investigated.

We will characterize the relationship of obesity to lower extremity (LE) pain in adolescents with the following aims:

A. Specific Aims

Specific Aim 1: To estimate the prevalence of LE pain cross-sectionally in all children aged 11-13 and specifically, compare the prevalence of obese adolescents to non -obese adolescents aged 11-13 years.

Hypothesis: Obese adolescents will have LE pain that is double that of their non-obese counterparts in an adjusted analysis.

Specific Aim 2: To estimate, using a cohort study design (in a subgroup with no pain at baseline), the incidence of LE pain among obese compared to non-obese adolescents over a period of 2 years (11 to 13 years).

Hypothesis: In looking at the subgroup with no pain at baseline, the incidence of LE pain will be 2 fold greater in the obese adolescents compared to the non-obese adolescents over these two years.

Secondary Aims:

Our secondary aims will examine other important relationships within the cohort.

To estimate the correlation and trend in the incidence of knee pain among adolescents at increasing levels of obesity.

To explore the effect of lean mass and fat mass in obese adolescents who develop knee pain at year 2.

To understand the effect of activity levels on the association between BMI and LE pain in all subjects at year 2.

To assess the impact of knee pain and obesity on functionality and quality of life.

B. Background and Significance

Childhood Obesity and the Musculoskeletal System

The prevalence of childhood obesity, defined as body mass index (BMI: weight/height2) at or above the 95th percentile of a reference population, has more than tripled in the United States since the 1970's to over 15%. Obesity leads to morbidities in children and is a risk factor for adult morbidity and mortality. Medical problems range from compromised cardiovascular, endocrine and pulmonary health. However, other pediatric complications of obesity important to public health or quality of life, such as bone, joint and muscle pains, are understudied and their prevalence, nature, and consequences unclear.

Certain musculoskeletal disorders such as Slipped Capital Femoral Epiphyses and Blount's disease are clearly linked to excessive weight but the association of obesity on non-specific lower extremity pain is unknown. Pediatric musculoskeletal (MSK) pain constitutes the third leading category for office visits among adolescents and prevalence estimates range from 6-33%, with the leading cause being trauma, followed by mechanical / overuse syndromes. In healthy Spanish children 10% of adolescents presented to doctors offices with MSK pain.In all children knee pain, soft tissue pain and other joint pains represented 65% of all complaints with adolescents localizing pain to the lower limb and lower back. [deInnocencio 2004]

The literature in obese children is sparse however two recent studies found the lower extremities to be the most common site of MSK pain in overweight adolescents compared to controls. A small Brazilian non-population based study demonstrated that obese adolescents had a two fold increase in pain compared to the normal weight counterparts. (sa Pinto 2006)

As the key structural elements for joint health rapidly evolve in healthy adolescents it may be adversely affected by obesity, through unsustainable levels of mechanical loading, which in the short term, may lead to pain and functional disability and in the long term, may irreversibly alter the lower extremity joint milieu.

C. RESEARCH DESIGN AND METHODS

C.1. Choice of Study Design

Until now, existing prevalence data on musculoskeletal pain has a wide range, has not been examined in a large population and has not looked at the impact of obesity. Thus our cross-sectional study design will estimate the prevalence of lower extremity pain in adolescents. Additionally, a longitudinal design using prospective data to estimate incidence has the advantage of assessing directionality and establish causality in the association of obesity on lower extremity pain at baseline (11 yrs) and at follow up (13 years).

C.2. Data source and study subjects

We propose to study subjects from the Avon Longitudinal Study of Parents and Children (ALSPAC) which is a large prospective birth cohort study investigating the health and development of children.

This cohort study is ongoing and starting at the age of 7 had annual assessments performed. Currently 6000 still attend clinic visits and data is being collected on the following variables of interest: age, gender, race, socioeconomic status, parental reports of pain, function and quality of life, height/weight, DXA, medical history and activity.

Inclusion criteria:

The entire ALSPAC cohort of ages 11-13 years will be included for study.

Exclusion criteria:

Subjects with underlying orthopedic conditions, surgery related to the lower extremities, juvenile idiopathic arthritis, other inflammatory lower extremity disorders and those with congenital abnormalities of the lower extremities will be excluded.

C.3. Data to be used:

We propose to use the existing data from the ALSPAC study in all children with visits at age 11 and 13 that include the following variables of interest:

Lower extremity pain is assessed by 2 questions on a validated questionnaire answered by the child and caregiver, as "yes" or "no" format with a followup one speculating on the cause.

Functionality and quality of life(QOL) will be assessed by questionnaire and QOL measures.

Anthropometric data from annual clinic visits include height and weight data. From that the BMI (body mass index) will be calculated using the formula weight/height2 as well as age- and gender-specific standard deviation scores (z scores) for weight, height, and body mass index , using the International Obesity Task Force (IOTF) definitions.

With DXA data we will assess lean and fat mass. Actigraph data will quantify activity levels. Socio-demographic data on socioeconomic status, age, gender and race will be analyzed. Finally, underlying medical history data from the clinic chart will be used to identify subjects for exclusion

D. HUMAN SUBJECTS RESEARCH

D.1. Protection of Human Subjects

a. Risks to the subjects: This protocol incurs minimal risk to the subjects as it uses an existing database with completed data. There will be no interaction with the subjects and no additional data is to be collected on behalf of this protocol.

b. Sources of materials: The data have already been obtained and are being requested to be shared with this investigator under the ALSPAC collaboration agreement. All the variables of interest will be shared as de-identified data.

c. Potential risks and benefits: There are no risks or benefits to the subjects under study. The results of the study will not be shared with the subjects and will not benefit them individually, although results will benefit public health policy initiatives.

D.2. Importance of the knowledge to be gained: The results of this study will provide prevalence and incidence of pain of lower extremties in obese children and reveal the short and long term impact of obesity on the musculoskeletal system with ramifications for further studies.