Bone bridge formation across the neuroforamen 14 years after instrumented fusion for isthmic spondylolisthesis-a case report

Abstract

This case report describes the first case of a bone bridge formation across the left L5/S1 neuroforamen after instrumented posterolateral fusion for L5/S1 isthmic spondylolisthesis. Our patient was a 70-year-old lady who had grade 2, L5/S1 isthmic spondylolisthesis and bilateral S1 nerve root compression. She suffered from mechanical low back pain and neurogenic claudication, with radicular pain over both S1 dermatomes. She underwent in-situ, instrumented, posterolateral fusion and was asymptomatic for more than 13 years before developing progressive onset of left radicular pain over the L5 dermatome. Imaging revealed a bisected left L5/S1 neuroforamen secondary to a bone bridge formation resulting in stenosis. The pars defect in this case may have had sufficient osteogenic and osteoinductive factors to heal following spinal stabilization. Although in-situ posterolateral fusion is an accepted surgical treatment for isthmic spondylolisthesis, surgeons should consider reduction of the spondylolisthesis and excision of the pars defects to avoid this possible long-term complication.

Keywords: Spondylolysis; deformity; heterotopic ossification; spine; spondylolisthesis.

Figure 1

Radiographs of the patient’s lumbar spine at the recent presentation. (A) Anterior posterior radiograph; (B) lateral radiograph showing worsening degeneration from L1 to L5; (C) flexion radiograph; (D) extension radiographs showing retrolisthesis and dynamic instability at L2/3 level.

Figure 2

CT scans of the patient’s lumbar spine at the recent presentation. (A) Left parasagittal CT scan demonstrating the bone bridge bisecting the left L5/S1 neuroforamen. The arrow indicating reduced cross sectional area due to the bone bridge; (B) right parasagittal CT scan demonstrating normal cross sectional areas of the right L4/5 and L5/S1 neuroforamen. CT, computed tomography.

Figure 3

MRI scans of the patient’s lumbar spine at the recent presentation. (A) Left parasagittal MRI scan demonstrating the bone bridge bisecting the left L5/S1 neuroforamen. The arrow indicating reduced cross sectional area due to the bone bridge; (B) MRI scans showing an axial cut at the L5/S1 level showing compression of the exiting left L5 nerve root; (C) MRI scans showing an axial cut at the L4/5 level showing no significant compression of the traversing L5 nerve root. MRI, magnetic resonance imaging.