Middle Column Gap Balancing to Predict Optimal Anterior Structural Support and Spinal Height in Spinal Reconstructive Surgery

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A total of 24 patients with normal flexion-extension cervical radiographs and a second group of 22 consecutive patients with multilevel deformities had middle column gap balancing (MCGB) height preoperatively and postoperatively as measured by three observers blinded to treatment. The aim was to determine a reliable method to obtain optimal spinal height in spinal deformity reconstruction without causing flat back syndrome and keeping the reconstruction angular correction within optimal sagittal and frontal plane alignment. Measurement and assessment of vertical instability as the “third” Eulerian axis in spinal deformity are validated. MCGB is a reference measurement of the path of the posterior longitudinal ligament that is reconstructed under tension and balanced by the combined height of the posterior one-third of vertebral bodies and the posterior one-third of disks and/or load-sharing spacers. Gap balancing in knee surgery is used to determine optimal anterior and posterior implant thickness, while simultaneously maintaining smooth ligament tension. If the thickness of the posterior spacer is too thin, a flexion gap is present and the knee joint is unstable in 90° of flexion (positive anterior and posterior joint laxity). This is analogous to our objective, which was to optimize anterior and posterior spacer thickness within intervertebral disk height by making use of spinal ligaments and annular tension. Therefore, MCMG is a method of “gap balancing” the ligaments of the spine, specifically, balancing posterior longitudinal ligament tension with the bony height of the middle column. This method can be effective in one or multiple vertebral segments (Figures 1 and 2).

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