[1] Boston Med Ctr, Dept Orthopaed Surg, Boston, MA 02118 USA
[2] Thomas Jefferson Univ, Rothman Inst, Dept Orthopaed Surg, Philadelphia, PA 19107 USA
[3] Univ Toronto, Dept Neurosurg, Toronto, ON, Canada
[4] Combined Neurosurg & Orthopaed Spine Program, Vancouver, BC, Canada
[5] Univ Maryland, Dept Orthopaed Surg, College Pk, MD 20742 USA
[6] Thomas Jefferson Univ, Dept Neurosurg, Philadelphia, PA 19107 USA