Figure 1

Following the administration of anesthetic the mouse was positioned prone. A marker was used to mark the location of the spinous processes, vertical line, and pelvic crest, horizontal line (A). A line drawn across the pelvic crests corresponds to the position of the L5-L6 interspace. (B). An incision was made through the skin which was the held by a self-retaining retractor. (C) A single incision was made through the thoracolumbar fascia over the spinous processes and the paravertebral musculature was dissected by scraping a blade down along the spinous processes and pulling laterally. The dissection of the local musculature forms a pocket on either side of the spine, bounded medially by the spinous processes and inferiorly by the articular processes (D). The articular processes are consequently exposed and visualized using a small muscle retractor of our own design. Articular processes are subsequently decorticated with a 1 mm round diamond burr until punctate bleeding is observed. Following decortication of the visualized articular processes, a 7 mm × 2 mm collagen sponge impregnated with either saline or saline/rhBMP-2 solution is inserted into each of the pockets in contact with the posterior elements of the spine (E). The muscle and skin are then closed with continuous sutures using 5.0 Vicryl^®.