1 Department of Neurosurgery, MedStar Georgetown University Hospital, Washington, District of Columbia, USA; Department of Orthopaedic Surgery, Musculoskeletal Research Center, MedStar Union Memorial Hospital, Baltimore, Maryland, USA.
2 Georgetown University School of Medicine, Washington, District of Columbia, USA.
3 Department of Orthopaedic Surgery, Musculoskeletal Research Center, MedStar Union Memorial Hospital, Baltimore, Maryland, USA; Department of Orthopaedic Surgery, MedStar Union Memorial Hospital, Baltimore, Maryland, USA.
4 Department of Neurosurgery, MedStar Georgetown University Hospital, Washington, District of Columbia, USA.