A
Posterior half of the vertebral body, posterior annulus fibrosus, and posterior longitudinal ligament (PLL)
B
Anterior half of the vertebral body and anterior longitudinal ligament (ALL)
C
Pedicles, facet joints, and ligamentum flavum
D
Spinous processes and interspinous ligaments
Explanation:The correct option is 'a'. The Denis classification divides the spine into three columns. The critical middle column consists of the posterior half of the vertebral body, the posterior half of the intervertebral disc/annulus, and the posterior longitudinal ligament (PLL). Disruption of the middle column is the hallmark of a burst fracture, distinguishing it from a simple anterior wedge compression fracture.
Reference: Denis F. The three column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine (Phila Pa 1976). 1983;8(8):817-831.