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Sacral Insufficiency Fracture Following L4-S1 Circumferential Fusion in Corticosteroid-associated Bone Fragility: A
Ratko Yurac Barrientos1, Joaquín Zúñiga Soria2, Andrea Marré Chadwick2
1Spine Unit, Department of Orthopedic and Traumatology, Clinica Alemana de Santiago University del Desarrollo, Santiago, Chile.
Introduction:
Sacral insufficiency fracture (SIF) is an uncommon but increasingly recognized complication following lumbosacral fusion, particularly in patients with compromised bone quality. The biomechanical vulnerability of the L5-S1 junction, combined with altered load transfer after anterior and posterior reconstruction, may predispose to early sacral failure.
Case Report:
A 55-year-old male with lytic spondylolisthesis at L5-S1, repeated corticosteroid exposure, and neurogenic claudication underwent staged circumferential L4-S1 fusion (L5-S1 anterior lumbar interbody fusion, L4-L5 oblique lumbar interbody fusion, and percutaneous posterior fixation). Initial post-operative recovery was satisfactory. At 8 weeks, the patient developed recurrent lumbosciatica. Computed tomography (CT) demonstrated collapse of the S1 superior endplate with anterior cage subsidence and foraminal compromise. Revision surgery included bilateral L5-S1 foraminal decompression and posterior refixation. Persistent unilateral radiculopathy required re-exploration, revealing a mobile bone fragment causing dynamic nerve compression, which was resected. The patient subsequently experienced progressive pain relief and returned to functional activity. Radiographs at 8 months confirmed advanced fusion and fracture consolidation.
Discussion:
SIF after circumferential fusion may be precipitated by corticosteroid-associated bone fragility, preexisting pars defects, and increased shear forces across the lumbosacral junction. Early symptoms may mimic post-operative radiculopathy, contributing to delayed diagnosis. CT is the most sensitive modality for early detection. Revision strategies include posterior decompression and reinforcement of fixation; in higher-risk cases, pelvic fixation may be warranted.
Conclusion:
Sacral fracture after lumbosacral fusion requires a high index of suspicion in osteoporotic patients presenting with recurrent radicular pain. Comprehensive biomechanical planning and pre-operative bone density evaluation are essential to mitigate risk.
