1. Translational Musculoskeletal Research Center, Corporal Michael J. Crescenz Philadelphia VA Medical Center, Philadelphia, Pennsylvania, USA.
2. Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
3. Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
4. Comparative Orthopaedic Research Laboratory, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, Pennsylvania, USA.
5. Department of Biomedical Engineering, University of Delaware, Newark, Delaware, USA.
6. Department of Surgery, New York University School of Medicine, New York, New York, USA.