• Patient is able to read/be read, understand, and provide written informed consent and has signed the Institutional Review Board (IRB) approved informed consent.

• Male or female patient ≥ 18 years old.

• Patients with segmental mechanical spinal instability requiring arthrodesis surgery.

∙ Instability can be either caused by degenerative disc disease or by traumatic injury to the spinal column. Patient requiring a maximum of two-level instrumented posterolateral lumbar/thoraco-lumbar fusion (T11 - S1) will be enrolled. Mechanical instability is defined by the presence of one or more of the following:

⁃ instability (angulation ≥ 5 degrees or translation ≥ 3 mm on flexion/extension radiographs),

⁃ decreased disc height by \> 2 mm, but dependent upon the spinal level

⁃ Grade II or more listhesis

⁃ TLICS equal or greater than 5

⁃ Unstable burst fracture

‣ Failed conservative treatment (physical therapy, bed rest, medications, spinal injections, manipulations, or transcutaneous electrical nerve stimulation) for a minimum period of 3 months prior to study enrollment (if the patient undergoes elective surgery). Patients who have spinal instability (as defined above in inclusion criteria number three), caused by acute trauma requiring urgent surgical treatment are excluded from this criterion.