1. Biomechanics and Spine Research Group, Centre for Children's Health Research, Queensland University of Technology, Brisbane, Queensland 4101, Australia
2. Sealy of Australia, Wacol, Queensland 4076, Australia
3. Queensland Children's Hospital, Brisbane, Queensland 4101, Australia
4. Biomechanics and Spine Research Group, Centre for Children's Health Research, Queensland University of Technology, Brisbane, Queensland 4101, Australia; Queensland Children's Hospital, Brisbane, Queensland 4101, Australia