[1] Boston Med Ctr, Dept Neurosurg, Boston, MA USA
[2] Boston Univ, Sch Med, Dept Neurosurg, Boston, MA 02118 USA
[3] Emerson Hosp, Dept Surg, Concord, MA 01742 USA
[4] Univ N Carolina, Natl Ctr Catastroph Sports Injury Res, Chapel Hill, NC 27515 USA