[1] Univ Toronto, Sunnybrook Hlth Sci Ctr, Dept Surg, Div Neurosurg, N York, ON M4N 3M5, Canada
[2] Univ Toronto, Sunnybrook Hlth Sci Ctr, Trauma Res Program, N York, ON M4N 3M5, Canada
[3] Univ Toronto, Sunnybrook Hlth Sci Ctr, Dept Res Design & Biostat, N York, ON M4N 3M5, Canada
[4] Washington Univ, Sch Med, Dept Surg, Div Plast Surg, St Louis, MO 63110 USA