Sacral insufficiency fractures caudal to instrumented posterior lumbosacral arthrodesis.

STUDY DESIGN: Retrospective review of sacral insufficiency fractures.

OBJECTIVE: Determine incidence of sacral insufficiency fractures after posterior lumbosacral fusion. Review the pertinent literature. Describe the ability of lumbopelvic fixation to restore the alignment of these fractures.

SUMMARY OF BACKGROUND DATA: Fractures of the sacrum are rare injuries that have been described at the caudal end of lumbopelvic constructs. Without a high index of suspicion, this entity can be overlooked, causing a diagnostic delay.

METHODS: Review of patients treated at our institution from 2002 to 2005.

RESULTS: Nine patients meet our inclusion criteria. Sacral insufficiency fractures were recognized on an average of 5 weeks in the 6 patients with the index procedure performed at our institution (Incidence of fracture with short segment instrumentation is 1.3%, whereas long segment fixation has an incidence of 3.1%). The other 3 referred patients had an average delay in diagnosis of 8 months. Two patients underwent immediate fracture stabilization and fusion. The remaining 7 patients were initially treated nonoperatively. Four patients abandoned bracing an average of 3.3 months after initiation of treatment. For all of the surgical candidates, preoperative kyphosis measured 9.7 degrees and anterolisthesis averaged 10 mm. Postoperative measurement improved to a mean kyphosis of 2.3 degrees and mean displacement of 1.2 mm. All operatively treated fractures healed and the patients regained their ambulatory capacity.

CONCLUSION: Sacral insufficiency fractures are an uncommon complication of segmental posterior lumbosacral fixation in osteoporotic patients. They are potentially unstable fractures and kyphosis and displacement may contribute to persistent problems of pain and postural malalignment. The diagnosis may be difficult and should be considered in the differential diagnosis in patients who do not improve during the postoperative course. Lumbopelvic fixation is a useful salvage treatment modality for patients who fail nonoperative treatment.