Bamboo Spine¶

Definition¶

Bamboo spine is the end-stage radiographic appearance of ankylosing spondylitis, characterized by complete fusion of the vertebral column through bridging syndesmophytes, facet joint ankylosis, posterior ligament ossification, and interspinous ligament calcification. The term derives from the resemblance of the fused spine to a stalk of bamboo on frontal radiograph.

Imaging Findings¶

Radiography¶

AP view — The "trolley track" sign: three vertical radiodense lines representing the fused spinous processes (central line) and the fused facet joints/syndesmophytes (lateral lines)
Lateral view — Continuous vertical ossification along the anterior and posterior margins of the vertebral bodies (syndesmophytes), squared vertebral bodies, and fused disc spaces
"Dagger sign" — A single central radiodense line on AP view from ossification of the interspinous and supraspinous ligaments

CT¶

Continuous bridging bone connecting all vertebral bodies
Complete facet joint ankylosis
Posterior element fusion
Ossification of the interspinous ligaments

MRI¶

Low T1 and T2 signal in the fused syndesmophytes and posterior elements (mature bone)
Fatty marrow replacement in the fused vertebral corners (chronic "healed" Romanus lesions — bright on T1)
STIR may show areas of active inflammation even in an otherwise fused spine

Clinical Pearl

The "trolley track" sign on AP radiograph — three vertical radiodense lines — is pathognomonic of bamboo spine in AS. It must be distinguished from DISH, which produces flowing anterior ossification but preserves the sacroiliac joints and facet joints. In AS, the sacroiliac joints are fused; in DISH, they are normal.

Fracture Risk¶

The fused bamboo spine is extremely vulnerable to fracture:

Fractures behave like long bone fractures — they are inherently unstable because the fused spine has no mobile segments to absorb energy
Most common at the cervicothoracic junction (C5–T1)
All three columns fracture simultaneously, often with significant displacement
Epidural hematoma is common and can cause rapid neurological deterioration
Even minor trauma (ground-level falls) can cause devastating fracture-dislocations

Key Points¶

Bamboo spine is end-stage ankylosing spondylitis with complete spinal fusion
"Trolley track" sign on AP radiograph and "dagger sign" are characteristic
Distinguish from DISH by sacroiliac joint fusion (AS) vs preservation (DISH)
The fused spine is extremely brittle — fractures are unstable and often devastating
CT and MRI of the entire spine are essential after even minor trauma in AS patients

References¶

Bamboo spine (ankylosing spondylitis). Radiopaedia.org. https://radiopaedia.org/articles/bamboo-spine-ankylosing-spondylitis
Wenker KJ, Quint JM. Ankylosing Spondylitis. In: StatPearls. Treasure Island (FL): StatPearls Publishing; updated 2023 Jun 20. https://www.ncbi.nlm.nih.gov/books/NBK470173/
Shah NG, Keraliya A, Nunez DB, Schoenfeld A, Harris MB, Bono CM, Khurana B. Injuries to the rigid spine: what the spine surgeon wants to know. RadioGraphics. 2019;39(2):449-466. https://pubmed.ncbi.nlm.nih.gov/30707647/
Campagna R, Pessis E, Feydy A, Guerini H, Thévenin F, Chevrot A, Drapé JL. Fractures of the ankylosed spine: MDCT and MRI with emphasis on individual anatomic spinal structures. AJR Am J Roentgenol. 2009;192(4):987-995. https://pubmed.ncbi.nlm.nih.gov/19304705/
Westerveld LA, Verlaan JJ, Oner FC. Spinal fractures in patients with ankylosing spinal disorders: a systematic review of the literature on treatment, neurological status and complications. Eur Spine J. 2009;18(2):145-156. https://pubmed.ncbi.nlm.nih.gov/18791749/
Østergaard M, Lambert RGW. Imaging in ankylosing spondylitis. Ther Adv Musculoskelet Dis. 2012;4(4):301-311. https://pmc.ncbi.nlm.nih.gov/articles/PMC3403247/
Beckmann NM, West OC, Nunez D Jr, Kirsch CFE, Aulino JM, Broder JS, et al. ACR Appropriateness Criteria® Suspected Spine Trauma. J Am Coll Radiol. 2019;16(5S):S264-S285. https://pubmed.ncbi.nlm.nih.gov/31054754/