This is a phase IV post-marketing study for MagnetOs Flex Matrix. MagnetOs Flex Matrix is a synthetic bone graft extender product that is routinely used by surgeons as a treatment for patients with degenerative disc disease and undergoing spinal fusion surgery.

In this study, MagnetOs Flex Matrix will be used according to the latest U.S. Instructions For Use, specifically as a bone graft extender mixed with autograft in a 1:1 vol.% in the posterolateral spine.

Trinity Elite will also be used according to its latest IFU approved in the US. Specifically, this cellular based allograft is an allograft intended for the treatment of musculoskeletal defects.

In this study, following a screening period of a maximum of 30 days, 100 patients will undergo up to four-level instrumented posterolateral fusion (PLF) procedure. Prior to surgery, each patient will be randomized to receive MagnetOs Flex Matrix on the assigned side of the spine and Trinity Elite on the other at the diseased levels. They will be followed up at discharge, Week 2, Week 6, Month 3, Month 6, and Month 12. The primary endpoint will be analyzed at Month 12.

In this study, MagnetOs Flex Matrix will be applied according to the latest Instructions for Use approved in the United States. Specifically, MagnetOs Flex Matrix will be used as a bone graft extender mixed with autograft in a 1:1 vol% in patients with leg pain, and/or back pain requiring up to four-level instrumented posterolateral spine fusion procedure. The fusion procedure (PLF) will be left to the surgeon's discretion.

Radiographs will be obtained at Screening, Week 2, Week 6, Month 3, Month 6 and Month 12. CT-scans will only be obtained at Month 6 and Month 12.

Inclusion Criteria:

• Patient is able to read/be read, understand, and provide written informed consent and has signed the Investigational Review Board (IRB) approved informed consent.
• Male or female patient ≥ 18 years old.
• Patients with leg pain, and/or back pain requiring up to four-level instrumented posterolateral lumbar/thoraco-lumbar fusion (T11 - S1)
• 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.

Exclusion Criteria:

• Requires > four-level fusion or expected to need secondary intervention within one year following surgery.
• Had prior PLF fusion or attempted PLF fusion at the involved levels
• Had previous decompression at the involved levels.
• Women who are or intend to become pregnant within the next 12 months
• To treat conditions in which general bone grafting is not advisable.
• In conditions where the surgical site may be subjected to excessive impact or stresses, including those beyond the load strength of fixation hardware (e.g., defect site stabilization is not possible).
• In case of significant vascular impairment proximal to the graft site.
• In case of severe metabolic or systemic bone disorders (e.g., osteogenesis imperfecta or Paget's Disease) that affect bone or wound healing.
• In case of acute and chronic infections in the operated area (soft tissue infections; inflammation, bacterial bone diseases; osteomyelitis).
• When intraoperative soft tissue coverage is not planned or possible.
• Receiving treatment with medication interfering with calcium metabolism.
• Had leg pain, and/or back pain related to a benign or malignant tumor.
• Had history or presence of active malignancy.
• Has known substance abuse, psychiatric disorder, or condition which, in the opinion of the investigator, may influence the healing or ability to comply with protocol requirements.
• Is involved in active litigation relating to his/her spinal condition.
• Has participated in an investigational study within 30 days prior to surgery for study devices.