Femoroacetabular impingement (FAI) is a condition of the hip where there is a mis-fit between the femoral head (ball) and hip acetabulum (socket). The abnormalities on the hip bones collide or "impinge" during movements such as hip flexion and rotation. Typically, patients with this condition are young adults who present with hip pain, loss of hip function, and in many cases, osteoarthritis later in life. The rate of diagnoses of FAI has dramatically risen across all age groups, but it has been especially notable within adolescent populations. There has been a corresponding increase in the number of surgeries performed on younger and younger hips to treat pain and loss of function due to this condition. Preliminary small-scale research has hypothesized that increased activity, such as sport specialization (i.e. playing only one sport for most of the year) at an early age when the hip is still developing, may be the cause. In the past 20 years, sport injuries among children have dramatically increased, where close to 45 million young athletes participate in organized sports annually in Canada and the US alone. There is a current trend among coaches and parents to have children focus on one sport with the thought that this dedication will allow them to reach an elite level. We are proposing the first international, longitudinal cohort study to determine the effect of sport specialization on the development of FAI during the critical phase of hip development (i.e. between the ages of 12-14 years). Volunteer participants will be recruited across Canada and internationally and will be evaluated clinically and radiographically (i.e. using MRI) over 2 years. This study will not only prospectively evaluate the role of sport activity the development of FAI, but also inform preventative training protocols to potentially reduce its incidence among adolescents, and later as adults, as well as identify parameters to detect hips that are at risk for developing FAI.

This is a multi-centre, international longitudinal cohort study evaluating 200 participants between the ages of 12-14 that include sport specialists at the moderate to vigorous physical activity (MVPA) level and non-sport specialists at any activity level. Participant groups will be defined according to the AOSSM and AMSSM early sport specialization criteria (2016). We will monitor physical activity levels of all participants using an activity log and a wrist-mounted activity tracker, with synced data collected every 3 months during the study period. In addition, participants will be evaluated clinically and radiographically at time of enrollment and 6, 12, 18, and 24 months. The primary study outcome is the incidence of FAI between groups at 2 years, determined via MRI. Secondary outcomes include hip function and health-related quality of life between subjects diagnosed with FAI versus no FAI at 2 years, as determined by the HOS and PedsQL questionnaires.

Inclusion Criteria:

1. asymptomatic males and females between the ages of 12-14 years
2. ability to speak, understand, and read the language of the clinical site
3. provision of informed child assent (if applicable) and parental consent.

Exclusion Criteria:

1. hip is mature (i.e. closed physes) based on the baseline MRI scan
2. hip complaints or pain in the hip
3. previous trauma to the hip
4. previous surgery on the hip
5. significant medical co-morbidities (requiring daily assistance for ADLs)
6. history of or ongoing paediatric hip disease (Legg-Calve-Perthes; slipped capital femoral epiphysis, hip dysplasia)
7. participants that have contraindications and/or are unwilling to undergo an MRI (e.g. claustrophobia)
8. participants who will likely have problems, in the judgment of the investigator, with maintaining follow-up
9. any other reasons the investigator feels is relevant for excluding the subject.

The study population will be comprised of adolescents aged 12-14 with no prior or ongoing hip comorbidities, and consent to receiving MRI scans at baseline and 2 years.