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“Bamboo spine” refers to a radiological appearance of the spine resembling a bamboo stick, caused by ankylosis of vertebrae due to syndesmophyte formation.

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• It is the hallmark radiographic feature of advanced Ankylosing Spondylitis (AS).

Pathogenesis

• Chronic enthesitis at annulus fibrosus and spinal ligaments.
• Ossification of outer annulus fibers → marginal syndesmophytes.
• Fusion of syndesmophytes across disc spaces → ankylosis of vertebral bodies.
• Associated calcification/ossification of spinal ligaments (interspinous, supraspinous, flavum).
• End result = a rigid, fused spine.

Radiology

X-ray (AP/Lateral)

• Thin vertical marginal syndesmophytes bridging adjacent vertebrae.
• Vertebrae appear square shaped due to “shiny corner sign”/Romanus lesion healing.
• Continuous syndesmophytes give the appearance of bamboo cane.
• Fusion of facet joints, sacroiliac joints, and costovertebral joints.
• Loss of lumbar lordosis; rigid, straight spine.

![Non-bridging syndesmophytes. Sagittal T1-weighted MR image shows anterior syndesmophytes (arrows) in a patient without SpA. No other disco-vertebral units besides Th3-Th4 and Th4-Th5 show bony changes. Note: b is an enlargement of the region outlined in a

Laloo, F., Herregods, N., Jaremko, J.L. et al. MRI of the axial skeleton in spondyloarthritis: the many faces of new bone formation. Insights Imaging 10, 67 (2019). https://doi.org/10.1186/s13244-019-0752-4](attachment:c407a551-1163-43ee-b960-85ccc9fb929a:image.png)

Non-bridging syndesmophytes. Sagittal T1-weighted MR image shows anterior syndesmophytes (arrows) in a patient without SpA. No other disco-vertebral units besides Th3-Th4 and Th4-Th5 show bony changes. Note: b is an enlargement of the region outlined in a

Laloo, F., Herregods, N., Jaremko, J.L. et al. MRI of the axial skeleton in spondyloarthritis: the many faces of new bone formation. Insights Imaging 10, 67 (2019). https://doi.org/10.1186/s13244-019-0752-4

![Vertebral corner bridging. a Sagittal T1-weighted MR imaging acquired in a 57-year-old man with SpA shows bridging syndesmophytes (arrows), and (b) radiography of the same vertebrae confirms these vertebral corner bridges (arrows) resulting in a “bamboo spine” configuration. Note that the smaller anterior syndesmophytes are more clearly visualized on radiograph than MRI, which is typical

Laloo, F., Herregods, N., Jaremko, J.L. et al. MRI of the axial skeleton in spondyloarthritis: the many faces of new bone formation. Insights Imaging 10, 67 (2019). https://doi.org/10.1186/s13244-019-0752-4](attachment:e8927fa4-ce65-4514-a572-c37e806502f5:image.png)

Vertebral corner bridging. a Sagittal T1-weighted MR imaging acquired in a 57-year-old man with SpA shows bridging syndesmophytes (arrows), and (b) radiography of the same vertebrae confirms these vertebral corner bridges (arrows) resulting in a “bamboo spine” configuration. Note that the smaller anterior syndesmophytes are more clearly visualized on radiograph than MRI, which is typical

Laloo, F., Herregods, N., Jaremko, J.L. et al. MRI of the axial skeleton in spondyloarthritis: the many faces of new bone formation. Insights Imaging 10, 67 (2019). https://doi.org/10.1186/s13244-019-0752-4

Differentials