A 38-year-old man falls from a height and sustains a displaced sacral fracture. He has saddle anesthesia, urinary retention, and decreased anal tone. According to the Denis classification, which zone of the sacrum does this fracture involve?

• A Zone I, lateral to the foramina
• B Zone II, through the foramina
• C Zone IV, spinous process avulsion
• D Zone III, medial to the foramina involving the central canal ✓

Explanation

Denis divided the sacrum into three longitudinal zones. Zone III fractures extend medially into the spinal canal and are the ones classically associated with cauda equina syndrome, producing saddle anesthesia and bladder and bowel dysfunction. Zone II (transforaminal) fractures typically cause L5 and S1 radicular deficits such as foot drop without sphincter involvement, and Zone I (alar) fractures are usually neurologically silent.

Reference: Rockwood and Green's Fractures in Adults, 9th ed.

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Written and medically reviewed by the StethoPrep medical team.