Midline sagittal sacral fractures in anterior-posterior compression pelvic ring injuries.

OBJECTIVE: To evaluate the outcome of an uncommon variant of the anterior-posterior compression pelvic injury, in which the posterior ring injury is a midline sagittal sacral fracture extending into the spinal canal.

DESIGN: Prospective, consecutive series. SETTING Two regional trauma centers.

PATIENTS: A consecutive series of 10 patients with rotationally displaced, vertically stable anterior-posterior compression pelvic ring fractures (OTA type 61-B1) in which the posterior ring injury is a midline sagittally oriented sacral fracture involving the spinal canal (Denis zone III). This injury pattern comprised 0.6% of pelvic fractures and 1.4% of sacral fractures treated at these two institutions during a 10-year period.

INTERVENTION: Patients were treated according to the same principles used in more commonly seen types of anterior-posterior compression pelvic ring injuries. Nine patients were treated with reduction and anterior pelvic stabilization at an average of 5 days after injury, 8 of whom were treated with open reduction and internal fixation and 1 with external fixation. No posterior pelvic fixation was used. One patient with nondisplaced bilateral pubic ramus fractures was treated nonoperatively. Immediate weight bearing was allowed as tolerated.

MAIN OUTCOME MEASUREMENTS: Prospectively collected clinical follow-up data emphasized a detailed neurologic examination, whereas radiographic evaluation involved anteroposterior, inlet, and outlet plain radiographic views of the pelvis.

RESULTS: An anatomical or near-anatomical reduction of the pelvis was achieved and maintained in all patients. Fractures healed at an average of 10 weeks. At an average follow-up of 31 months (range 20-46 months), there were no objective neurologic deficits that could be attributed to sacral root injury and no significant residual pain or gait disturbance related to the pelvic fracture. Loss of bowel or bladder function, loss of perianal sensation or sphincter tone, and lumbosacral radicular pain or sensorimotor deficit were specifically absent in all patients. Three patients, however, complained of sexual dysfunction at final follow-up. None of these patients had clinical evidence of sacral root/plexus injury secondary to the fracture. One additional patient, who sustained a urethral tear, required a chronic suprapubic catheter because of stricture. Six patients, one of whom had needed repair of a retroperitoneal bladder tear, had no urogenital sequelae.

DISCUSSION AND CONCLUSION: Patients who sustain sagittally oriented midline fractures of the sacrum that extend into the spinal canal (Denis zone III) as part of displaced, vertically stable anterior-posterior compression pelvic injuries, have a low incidence of neurologic deficit attributable to sacral root or plexus injury. This is in contrast to the high rate of neurologic deficit (>50%) otherwise reported in zone III sacral fractures, particularly in those associated with a displaced transverse component. In the midline sagittal fracture variant, simultaneous lateral displacement of both bony and neural elements through the midline may protect the sacral roots and plexi from significant traction or shear injury by maintaining the spatial orientation between the sacral foramina and sciatic notch. Long-term sequelae were related to urogenital complaints rather than to musculoskeletal problems, as 4 of the 10 patients in this series had either sexual or urologic dysfunction.