Denis classified sacral fractures by the location of injury (Fig. 12–33).19 In patients with fractures through the sacral ala (zone I) the incidence of neurologic injury was 6%, with the most likely injury being partial injury to the L5 nerve root. Fractures through the sacral foramina (zone II) had a 28% incidence of neurologic injury. Zone II fractures were most commonly associated with injury to the ventral roots of L5, S1, or S2. Fractures medial to the sacral foramina or horizontal fractures (zone III) had the highest incidence of neurologic injury at 57%. These fractures were not only the most common, but also the most devastating as nearly 80% affected bowel, bladder, or sexual function. Horizontal sacral fractures above the S2 level are uncommon, but are associated with a much higher incidence of neurologic injuries than fractures below S2.3