Neurosurgeons from 14 different spinal centers around the United States participated in this study. They compared spinal motion in three groups of spines. One group of patients had an ADR at one level (L45). The second group had a fusion at one level (L45).
And the third group was a series of eight human cadavers divided into four groups. Four different types of of spinal reconstructions were applied and compared: 1) the control group: nothing was done to the spine, 2) CHARITÉ disc prosthesis was inserted at L45, 3) BAK cage was inserted into the L45 disc space after the disc was removed, and 4) BAK cage with a fixation (fusion) rod at L45.
A special device called a six-degree-of-freedom spine stimulator was used to measure range of motion. Six movements were measured including flexion, extension, left and right sidebending, and left and right rotation.
Motion was measured at the operative level and the adjacent levels (above and below L45). Measurements and X-rays were taken before the operation and again two years later.
The results showed that a one-level ADR does the best job of relieving pain and restoring normal spinal motion. This was true for the operated level and the adjacent levels. In the case of spinal fusion, motion was decreased at that level as expected. It was also increased at both the adjacent levels (L34 and L5S1).
Using the cadavers, the researchers were able to show that the spine stimulator accurately measures spinal motion in all groups. This was true no matter what type of surgery was done. The authors also point out that voluntary motion increased with greater pain relief with the ADRs.