Pseudarthrosis¶

Definition¶

Pseudarthrosis (nonunion) is failure of bony fusion after spinal fusion surgery. It represents a persistent mobile segment that was intended to be rigidly fused. Pseudarthrosis is a common cause of persistent or recurrent pain after fusion surgery and is closely associated with hardware failure.

Imaging Findings¶

CT (Best Modality)¶

Absence of bridging bone — No continuous bone connecting the fused vertebral bodies through or around the interbody graft on sagittal and coronal reformats
Lucency at the graft-bone interface — A dark line between the graft/cage and the vertebral endplate, indicating fibrous nonunion
Hardware loosening — Lucent halos around screws
Rod or screw breakage — Strong indicator of pseudarthrosis
Gas in the fusion bed — Vacuum phenomenon at the intended fusion site indicates motion

Radiography¶

Dynamic flexion-extension views showing motion at the fusion level (>3–4° difference or >3 mm translation)
Hardware loosening or breakage

MRI¶

Less reliable for fusion assessment due to metal artifact
May show persistent disc signal or fluid at the intended fusion level
Can evaluate for associated soft tissue complications

Clinical Pearl

Thin-section CT with sagittal and coronal reformats is the best study for evaluating fusion. Look for continuous bridging bone — if you cannot trace a continuous bony bridge from one vertebral body to the next through the graft, pseudarthrosis is likely. The combination of absent bridging bone + hardware loosening or breakage is strong evidence for pseudarthrosis.

Key Points¶

Failure of bony fusion — persistent motion at the intended fusion site
CT is the best modality — look for absence of bridging bone
Hardware loosening and rod fracture are strong indicators
Dynamic radiographs can demonstrate motion
Common cause of failed back surgery syndrome
Revision surgery may be needed

References¶

Peters MJM, Bastiaenen CHG, Brans BT, Weijers RE, Willems PC. The diagnostic accuracy of imaging modalities to detect pseudarthrosis after spinal fusion—a systematic review and meta-analysis of the literature. Skeletal Radiol. 2019;48(10):1499–1510. doi:10.1007/s00256-019-03181-5. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC6702186/
Benson JC, Lehman VT, Sebastian AS, Larson NA, Nassr A, Diehn FE, Wald JT, Murthy NS. Successful fusion versus pseudarthrosis after spinal instrumentation: a comprehensive imaging review. Neuroradiology. 2022;64(9):1719–1728. doi:10.1007/s00234-022-02992-z. Available from: https://pubmed.ncbi.nlm.nih.gov/35701631/
Lin W, Ha A, Boddapati V, Yuan W, Riew KD. Diagnosing pseudoarthrosis after anterior cervical discectomy and fusion. Neurospine. 2018;15(3):194–205. doi:10.14245/ns.1836192.096. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC6226130/
Young PM, Berquist TH, Bancroft LW, Peterson JJ. Complications of spinal instrumentation. Radiographics. 2007;27(3):775–789. doi:10.1148/rg.273065055. Available from: https://pubmed.ncbi.nlm.nih.gov/17495292/
Radiopaedia. Complications of spinal surgery. Available from: https://radiopaedia.org/articles/complications-of-spinal-surgery