## Anatomical Distribution of Pott Disease **Key Point:** The thoracic spine is the most commonly affected region in spinal tuberculosis, accounting for approximately 40–50% of cases, followed by the lumbar spine (35–40%), cervical spine (10%), and sacral involvement (rare, <5%). ### Why Thoracic Involvement Predominates The thoracic vertebrae are affected most frequently because: 1. **Rich vascular supply** — the thoracic region has abundant blood flow, facilitating hematogenous seeding from a primary pulmonary focus. 2. **Larger vertebral bodies** — provide a larger target for tuberculous infection. 3. **Proximity to pulmonary TB** — the thorax is the primary site of TB in most patients; direct lymphatic and vascular spread favors thoracic vertebral involvement. ### Typical Pattern of Spread ```mermaid flowchart TD A[Primary TB focus<br/>usually lung]:::outcome --> B[Hematogenous seeding<br/>to vertebral bodies]:::action B --> C{Which vertebrae?}:::decision C -->|40-50%| D[Thoracic spine<br/>MOST COMMON]:::action C -->|35-40%| E[Lumbar spine<br/>2nd most common]:::action C -->|10%| F[Cervical spine<br/>3rd most common]:::action C -->|<5%| G[Sacral spine<br/>Rare]:::action ``` ### Clinical Pearl **High-Yield:** When multiple vertebrae are involved, the thoracic region is almost always included. Isolated lumbar or cervical TB is uncommon; if seen, always look for concurrent thoracic involvement. ### Vertebral Body Involvement Pattern - **Initial site:** Anterior vertebral body (metaphyseal region near the endplate). - **Progression:** Spreads to adjacent vertebrae via the anterior longitudinal ligament, causing the characteristic "skip lesions" or continuous destruction. - **Kyphotic deformity:** Results from anterior vertebral body collapse, most dramatic in the thoracic region due to the natural kyphosis. [cite:Campbell's Operative Orthopaedics 13e Ch 42]
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