This is a prospective randomized study evaluating the use of a prophylactic incision wound vac dressing, applied in the OR, on patients undergoing posterior spine surgery with a BMI>35. Patients are randomized in the operating room to normal postoperative dressing vs. vac dressing. The vac dressing would be left on for 72 hours postoperatively. In the interim, the patients' postoperative care can proceed as usual. Our primary outcomes will be antibiotics or return trip needed to the operating room for wound related complications.