Background We previously demonstrated an independent risk of sports specialization in young athletes. However, there is no longitudinal study on the risks of sports specialization and reinjury in young athletes.

Objective To determine the longitudinal risk factors for sports specialization in a clinical population of young athletes. To outline the patterns of reinjury in this clinical population.

Design Prospective cohort observational study.

Setting Multicenter clinical study from sports medicine clinics and pediatric/family medicine offices.

Patients (or Participants) Young athletes 7–18 years old presenting for sports-related injury to a sports medicine clinic or for for a sports physical.

Interventions (or Assessment of Risk Factors) Each subject is enrolled at baseline and then given follow up survey every 6 months for up to 3 years. We assessed the following risk factors: Sex, Age, Age of specialization, degree of sports specialization, training volume (organized, free play), year round training (>8 months).

Main Outcome Measurements Injury, injury type (acute, overuse, serious overuse), clinical diagnosis.

Results There were 1191 subjects analysed at baseline, with a total of 1083 follow up evaluations for up to 3 years of follow up. There were 39.4% (427/1083) injured follow up evaluations, 60.6%(656/1083) uninjured. Of the 427 injuries, 69.6% (297/427) were a reinjury (142 repeat injury (same location) and 155 recurrent injury. There were 134 new injuries. Injured follow up subjects were more likely to be female (p<0.02), report age of specialization <12 (p=0.03) and participate in year round training>8 mths/yr (p<0.03), and a higher proportion were more highly specialized.

Conclusions Young athletes are more likely to develop a reinjury than a new injury on follow ups up to 3 years. Athletes specializing <12 years old and female young athletes were more likely to develop injury. Similar to baseline, there was a higher proportion of injured highly specialized athletes.