In the Denis three-column theory of thoracolumbar spine stability, which combination of column disruptions always renders a fracture mechanically unstable?

• A Anterior column disruption alone
• B Middle column disruption with involvement of either the anterior or posterior column ✓
• C Posterior column disruption alone
• D Anterior plus posterior column disruption without middle column involvement

Explanation

Denis described three columns: anterior (anterior half of vertebral body, annulus, and anterior longitudinal ligament), middle (posterior half of vertebral body, posterior annulus, and posterior longitudinal ligament), and posterior (posterior osseoligamentous complex — pedicles, facets, ligamentum flavum, supraspinous/interspinous ligaments). The middle column is the key to stability. Disruption of two or more columns — especially when the middle column is involved — renders the spine unstable, as the middle column acts as the hinge preventing translation. Pure anterior column injuries (compression fractures with intact middle column) are stable; burst fractures disrupt both anterior and middle columns and are unstable.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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