Interbody Fusion Devices¶

Overview¶

Interbody fusion involves placing a structural device (cage or graft) into the disc space to achieve bony fusion between adjacent vertebral bodies. Various approaches are used depending on the spinal level and pathology.

Types by Approach¶

ALIF (Anterior Lumbar Interbody Fusion) — Anterior retroperitoneal approach. Large cage footprint.
PLIF (Posterior Lumbar Interbody Fusion) — Posterior approach, paired smaller cages placed bilaterally
TLIF (Transforaminal Lumbar Interbody Fusion) — Posterolateral approach through one foramen, single cage. Most popular current technique.
LLIF/XLIF (Lateral/Extreme Lateral Interbody Fusion) — Lateral transpsoas approach. Large cage, good for coronal deformity correction.
OLIF (Oblique Lateral Interbody Fusion) — Oblique approach anterior to the psoas

Imaging Evaluation¶

CT (Best for Fusion Assessment)¶

Cage position within the disc space (centered, no migration)
Bridging bone through and/or around the cage = solid fusion
Lucency around the cage = possible nonunion
Subsidence — cage sinking into the endplate
Cage migration — retropulsion into the canal is the most dangerous complication

Radiography¶

Cage position and any migration
Alignment
Associated posterior hardware

Clinical Pearl

On CT, look for continuous bridging bone through or around the interbody cage on sagittal and coronal reformats — this confirms solid fusion. A lucent halo around the cage without bridging bone suggests pseudarthrosis. Cage retropulsion into the spinal canal is a surgical emergency.

Key Points¶

Multiple approaches: ALIF, PLIF, TLIF, LLIF — each with different cage position and appearance
CT is the best modality for fusion and cage assessment
Bridging bone confirms fusion; lucency suggests pseudarthrosis
Cage retropulsion into the canal is the most dangerous complication
Subsidence into the endplate can lead to loss of disc height and foraminal stenosis

References¶

Mobbs RJ, Phan K, Malham G, Seex K, Rao PJ. Lumbar interbody fusion: techniques, indications and comparison of interbody fusion options including PLIF, TLIF, MI-TLIF, OLIF/ATP, LLIF and ALIF. J Spine Surg. 2015;1(1):2-18. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC5039869/
Wangaryattawanich P, Kale HA, Kanter AS, Agarwal V. Lateral Lumbar Interbody Fusion: Review of Surgical Technique and Postoperative Multimodality Imaging Findings. AJR Am J Roentgenol. 2021;217(2):480-494. Available from: https://ajronline.org/doi/10.2214/AJR.20.24074
Ghodasara N, Yi PH, Clark K, Fishman EK, Farshad M, Fritz J. Postoperative Spinal CT: What the Radiologist Needs to Know. RadioGraphics. 2019;39(6):1840-1861. Available from: https://pubs.rsna.org/doi/abs/10.1148/rg.2019190050
Williams AL, Gornet MF, Burkus JK. CT Evaluation of Lumbar Interbody Fusion: Current Concepts. AJNR Am J Neuroradiol. 2005;26(8):2057-2066. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC8148852/
Lumbar interbody fusion (overview). Radiopaedia. Available from: https://radiopaedia.org/articles/lumbar-interbody-fusion-overview