Incidence, diagnosis, and management of sacral fractures following multilevel spinal arthrodesis.

Background: Fractures of the sacrum are a rare complication following instrumented spinal fusion, with only 34 cases previously reported in the literature. Previous series have generally been limited to less than five cases.

Purpose: The purpose of this study is to determine the incidence of sacral fractures caudal to instrumented spinal fusion constructs, identify risk factors for fracture and for failure of conservative management, and describe strategies for surgical treatment of these fractures.

Study Design: This is a retrospective review.

Patient Sample: Patients undergoing instrumented posterior spinal arthrodesis between 2002 and 2011 were included in the sample.

Outcome Measures: Clinical and radiographic data from hospital and surgeon records comprise outcome measures.

Methods: Methods include a review of clinical and radiographic data from a prospectively collected patient database recording all adjacent segment fractures during the study period.

Results: Twenty-four patients developed sacral fractures caudal to instrumented spinal fusion constructs during the study period. The overall incidence was 6.1% and was significantly greater in fusions greater than four levels (14.5%). The mean time from index surgery to fracture was 4.3 months. Only one fracture was evident on plain radiography at the onset of symptoms. Computed tomography, magnetic resonance imaging, and nuclear scintigraphy can all be used to establish the diagnosis. Eight patients were successfully treated conservatively. The mean time to fracture union was 21 weeks. Anterolisthesis of the fracture greater than 2 mm and kyphotic angulation were significantly associated with failure of conservative management. Surgical intervention included posterior extension of the fusion construct to S2 and the iliac wings with sacroiliac joint fusion. In 10 cases, a combined anterior and posterior approach was used that consisted of either revision anterior lumbar interbody fusion or transsacral posterior lumbar interbody fusion.

Conclusions: Sacral fractures following instrumented posterior spinal fusion are an uncommon complication; that is often unrecognized on plain radiographs. Risk factors include osteoporosis and long spinal fusions. Anterolisthesis and kyphosis of the fracture is associated with failure of conservative management.