Clinically fused per classical radiographic assessment (≤ 2 degrees angular motion and evidence of bone bridging)

Definitive clinical evidence of pseudarthrosis (not fused, ˃ 2 degrees angular motion or absence of bone bridge) and scheduled for surgical exploration

Definitive clinical evidence of pseudarthrosis without scheduled surgical exploration.

The radiostereometric (RSA) patient exam (flexion and extension RSA images) presents additional radiation exposure to the patient above standard of care (additional radiographs). Assuming 120kV, using three protocols (two loaded and one unloaded) per RSA exam results in a typical effective dose of approximately 2.04mSv per exam(single lumbar spine RSA at 120kV yields 0.68mSv,). HBI recommends using 140kV for lumbar spine RSA and has conducted simulations to estimate the effective dose using higher kV settings. 140kV reduces the effective dose from 0.68mSv per spine RSA to 0.2mSV, resulting in a total effective dose per RSA exam of 0.6mSv. In comparison, the estimated effective dose for a single standard lumbar spine x-ray is 1.2mSv. This additional radiation exposure is considered to be minimal risk in consideration of the number of planar x-rays the patient will undergo as part of standard care, as well as average background radiation received by humans per year (3.1mSv).

The purpose of this radiostereometric analysis (RSA) evaluation is to measure relative intervertebral motion in lumbar spinal fusions. Two RSA loading provocation protocols will be employed in this study; sitting and supine extension. Both loading protocols will be compard to a standard supine position which is used as an unloaded baseline protocol. Induced intervetebral motion sets will be calculated between the two loaded states, sitting and supine extension, and the unloaded state. The RSA micromotion results will be calculated and reported as translations and rotations about the three anatomic axes, maximum total point motion (MTPM) will be calculated as well.