Evaluating the ability of posterior elements to support new instrumentation for spinal fusion.

Posterior spinal plating devices have recently made a re-emergence as both stand-alone devices and for use in conjunction with anterior fusion. Yet, the structural integrity of the posterior elements to support loads throughout the spine and the impact of plating on posterior element strength has not been well characterized. This study aims to quantify the mechanical strength of the posterior elements (spinous processes/laminae) throughout the spine and to determine the effect of attaching posterior element plating systems on their ultimate load to failure. Vertebral levels from six cadaveric spines were grouped in pairs to account for varying geometries and sizes of the human posterior elements (a total of 59 levels in 5 groups). One sample from each pair was tested in its native state, and the complementary vertebra was tested via posterior plating. Posterior element plating caused moderate reductions in posterior element failure strength (15-24 percent) throughout the cervical, thoracic, and lumbar spine. Bone mineral density of the posterior elements had the most significant impact on ultimate load to failure (a decrease of 0.1 g/cm3, yields a 189N reduction in). The modest structural impact of posterior element plating motivates continued investigation into potential use of less invasive plating devices for posterior spinal fusion.