Departments of *Orthopaedic Surgery and †Neurological Surgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, U.S.A.; ‡Department of Psychiatry, University of British Columbia, Vancouver, Canada; §Department of Family Medicine and Indiana University Center for Sports Medicine, Indiana University School of Medicine, Indianapolis, Indiana, U.S.A.; and ∥Pittsburgh Steelers Football Club, Pittsburgh, Pennsylvania, U.S.A.