The muscle retractor shown above is open. On turning the thumb screw, it goes through one arm, pushes the other arm open and holds it there (not shown). With it closed and after the muscle alongside the spine has been freed from bone, it can be slipped between the bony spinous processes and the paraspinous muscle, then opened to expose the interspace over the correct level without dividing any muscle. Then some of the lamina above and below is removed to widen access to the spinal canal. A special instrument for that will be shown next time. The laminae flare out from each spinous process (the bumps you feel down the middle of your back); only part of a hemi-lamina is removed on the side of leg pain. So technically it’s a partial hemi-laminectomy and not a laminectomy, The ligament running between each hemi-lamina is then removed to expose the inside of the spinal canal. Now we’re almost there.