Introduction Poor postural control measured as sway performance is an intrinsic risk of injury and re-injury among adults. This has not been investigated in children.

Objective To investigate the associations between balance, measured as sway performance, and the risk of both acute and overuse injuries in a population of children. Hypothesis: Excessive sway increases the risk of injury.

Design The current study is part of The Childhood Health, Activity and Motor Performance School Study-Denmark (CHAMPS Study-DK II), a natural experiment with a prospective, quasi-experimental study design. The follow-up period between baseline measures of sway and registration of injuries was 1 year and 3 months.

Setting 10 public schools participated in the study, in the municipality of Svendborg.

Participants 1096 participants, 48.7% male, aged 8–14, mean age 11.2.

Risk factor assessment The independent variable in the current study is balance measured as sway. Sway was measured on a force platform as centre of pressure path length excursion during four tests: Eyes open: Bilateral stance (test 1), unilateral stance on dominant (test 2) and non-dominant leg (test 3). Eyes closed: Bilateral stance (test 4).

Main outcome measurements Primary outcome was overuse and traumatic injuries, with special emphasis on ankle and knee sprains. Complaints were registered by SMS-track on a weekly basis, and after a telephone interview, clinicians examined and diagnosed the children with complaints. Injuries were diagnosed using ICD-10.

Results Injuries: 2276, traumatic injuries: 714, ankle sprains: 164, knee sprains: 42. Preliminary multivariate analysis taking into account competing risk showed significant odds ratios (OR) at test 1; A) 1.003 per cm increase of sway; B) overall traumatic injury OR=3.0, ankle sprain OR=5.5 for sway longer than 400 cm/minute.

Conclusion Children with an excessive sway has an increased risk of traumatic injuries, this warrants further research into treating reduced balance in children.