CT Evaluation of Lumbar Interbody Fusion: Current Concepts

Normal progression of interbody fusion in a 28-year-old woman. A, On a coronal reformatted CT image, obtained 6 months after surgery, new bone formation is evident within (black arrow) and adjacent to (white arrow) the LT-CAGE devices. B, Ten months after surgery, reformatted CT image shows additional new bone formation, especially lateral to the fusion devices (white arrows), with bony bridging across the disk space.

Subsidence of LT-CAGE devices at L5–S1. Sagittal (A) and coronal (B) reformatted CT images demonstrate subsidence of the LT fusion devices (small arrows) through the L5 inferior endplate into the vertebral body in a 60-year-old man. The sagittal image demonstrates new bone formation (large arrow) posterior to the fusion device with bony bridging taking place across the disk space.

Lucency at fusion device margins. Coronal (A) and sagittal (B) reformatted images at L5–S1 in a 45-year-old man demonstrate lucency (arrows) at the margins of both LT CAGEs, suggesting delayed or failed fusion.

Lucency surrounding pedicle screws. Coronal reformatted image at L5–S1 in a 58-year-old woman demonstrates lucency (large white arrows) surrounding the pedicle screws at S1 and subtle lucency around the L5 screws (small white arrows), signifying instrumentation loosening and fusion failure. Note the fusion devices (black arrows) within the disk space.

Cystic changes within the endplates adjacent to the implants. A, Five months after surgery in a 62-year-old woman, CT scan shows cystic changes (arrows) in the endplates at the L5–S1 level on an axial image. B, Twenty-one months after the application of posterior instrumentation, CT scan shows that the cystic changes are much less prominent as the fusion is progressing to solid bony union.

Broken pedicle screw. CT scan shows the fractured right S1 pedicle screw (white arrow). A Bone Dowel (black arrow) is present in the L5–S1 disk space.

Medial orientation of pedicle screw. In a 48-year-old man, an axial image demonstrates that the left L4 pedicle screw (arrow) has penetrated the medial cortex of the pedicle in the vicinity of the L4 nerve root.

Linear lucency parallel to the endplate in new bone formation in a 31-year-old woman. Coronal (A) and sagittal (B) reformatted images at L5–S1 demonstrate irregular linear lucency (arrows) through new bone formation within the disk space, indicating failed fusion.

Dislodged fusion device. In a 51-year-old woman, axial (A) and coronal (B) reformatted images at L5–S1 demonstrate the left-sided mesh titanium fusion device (straight white arrow) displaced laterally within and lateral to the intervertebral foramen in the vicinity of the left L5 dorsal root ganglion and nerve. A Bone Dowel (curved white arrow) is noted in the midline in the disk space. Bony bridging (arrowheads) across the disk space is evident.