Introduction to chapter 17 in: Thomas J. Errico, Baron S. Lonner, Andrew W. Moulton (2009). Surgical Management of Spinal Deformities. Elsevier Health Sciences. ISBN9781416033721.{{cite book}}: CS1 maint: multiple names: authors list (link)
Page 250 in: Walter R. Frontera, Julie K. Silver, Thomas D. Rizzo (2014). Essentials of Physical Medicine and Rehabilitation (3 ed.). Elsevier Health Sciences. ISBN9780323222723.{{cite book}}: CS1 maint: multiple names: authors list (link)
