1 Department of Neurological Surgery, Keck School of Medicine, University of Southern California, CA, Los Angeles, USA.
2 Department of Orthopedic Surgery, Musculoskeletal Biomechanics Laboratory, Edward Hines, Jr. VA Hospital, Hines, IL, USA.
3 Department of Orthopedic Surgery, Musculoskeletal Biomechanics Laboratory, Edward Hines, Jr. VA Hospital, Hines, IL, USA; Department of Orthopaedic Surgery and Rehabilitation, Loyola University Chicago, Maywood, IL, USA.
4 Department of Neurological Surgery, Northwestern Feinberg School of Medicine, 676 N Saint Clair St, Suite 2210, Chicago, IL, USA.