Middle-Column Gap Balancing and Middle-Column Mismatch in Spinal Reconstructive Surgery.

Background: Middle-column gap balancing (MCGB) is a reference measurement of the path of the posterior longitudinal ligament (PLL), which is reconstructed under tension and balanced by the combined height of the posterior one-third of the vertebral bodies and the posterior one-third of the disks, including any intervening load-sharing spacers. This measurement allows for a comparison of the ligamentous component of the middle column (PLL) with the load-sharing components (posterior one-third vertebral body + disk ). This difference gives rise to a "middle-column mismatch," which provides a linear measurement of the redundancy of the ligaments and neural elements, which relates to the correct cage, spacer, or load-bearing height, which is optimized.