Bamboo spine | Radiology Signs

Answer:
Bamboo spine is a late radiological manifestation of ankylosing spondylitis (AS), a chronic inflammatory autoimmune arthropathy that primarily affects the axial skeleton. The sign develops through progressive ossification and ankylosis of the vertebral column. During AS flare-ups, the tissues connecting ligaments and tendons to bones become inflamed. With repeated cycles of inflammation and repair, aberrant bone formation occurs instead of normal tissue healing, leading to calcification. This pathological process results in the fusion of vertebral bodies through formation of marginal syndesmophytes—bone bridges that connect adjacent vertebrae. Over time, widespread ankylosis causes the individual vertebrae to lose their independent mobility and fuse into a single rigid osseous segment. The posterior vertebral elements also typically fuse. This complication does not occur in all patients with AS and usually develops only after many years of disease progression. The resulting spine is significantly less flexible, more fragile, and predisposed to serious complications including unstable vertebral fractures and Andersson lesions.

Why is it called so?:

The sign is named bamboo spine because the fused vertebral column on radiographs resembles the appearance of a stalk of bamboo. The continuous wavy edges created by the syndesmophytes and the grooved pattern of the ankylosed vertebrae visually parallel the segmented structure and grooved surface characteristic of a bamboo plant.

Pathophysiology:

Ossification begins with lysis of the anterior corners of vertebral bodies surrounded by peripheral reactive sclerosis (shiny corner sign). Syndesmophytes then form laterally and anteriorly, bridging adjacent vertebral bodies. These bone bridges progressively connect the vertebrae, eventually resulting in complete fusion. The intervertebral discs are replaced by bone, and the normal intervertebral spaces disappear. The spine progressively loses its natural curvature, typically straightening from its normal “S” shape. Vertebral mobility is eliminated as the ossified ligaments and fused elements prevent independent movement between segments. The reduced bone quality combined with loss of mobility increases vulnerability to fracture.

Alternative names:
Bamboo column, ankylosed spine

Other associated named signs:
Shiny corner sign (early manifestation of AS showing lucency at vertebral corners with surrounding sclerosis), Andersson lesion (vertebral fracture complication)