Approach to posterior aspect of spine. A, Muscle insertions are freed subperiosteally from lateral side of spinous processes and interspinous ligaments; dissection proceeds proximally, with periosteal elevator being held against bases of spinous processes. B, Spinous processes, laminae, and articular facets exposed. C, Courses of arteries supplying posterior spinal muscles, showing proximity of internal muscular branches to spinous processes.(Modified from Wagoner G: A technique for lessening hemorrhage in operations on the spine, J Bone Joint Surg 19:469, 1937.) SEE TECHNIQUE 37.27