Clinical Outcomes of Lumbar Degenerative Disc Disease in Active-Duty U.S. Service Personnel

• Time to return to active duty [ Time Frame: 24 months ] [ Designated as safety issue: No ]
• No re-operations, revisions, removals or supplemental fixation [ Time Frame: 24 months ] [ Designated as safety issue: No ]
• No implant related complications [ Time Frame: 24 months ] [ Designated as safety issue: No ]

Degenerative disc disease (DDD) refers to a syndrome in which a degenerating disc causes chronic back pain, significantly impacting an individual's ability to function. The condition is most commonly diagnosed in the lumbosacral spinal segments L3-S1. The condition often starts with an injury to the disc space. The injury weakens the disc and creates excessive motion at the corresponding vertebral level. Over time, the segmental instability and associated neurological compromise combined with ongoing inflammatory processes that occur in and around the disc produce low back pain. The reparative processes in the disc are poor, thus the painful symptoms can become chronic.

Premature degeneration at adjacent levels of the spine remains one of the more vexing problems facing spinal surgeons when advising relatively young people to consider lumbar fusion surgery. Stopping the motion changes the mechanics of the back (which is designed for motion and flexibility) and results in the transfer of the loads and stresses to the adjacent vertebral segments. It is therefore intuitive to pursue total disc replacement, which allows for the treatment of pain due to DDD while re-establishing motion and stability, load distribution, and restoring the disc height, as an alternative to spinal fusion surgery.

The study hypothesis is that military personnel receiving Total Disc Replacement will return to the same level of active duty performance as at the time of their most recent successful physical readiness test.

Inclusion Criteria:

1. Degenerative Disc Disease (DDD) in one vertebral level between L3 and S1, where a diagnosis of DDD requires:

   1. Back and/or leg (radicular) pain; and
   2. Radiographic confirmation of any one of the following by CT, MRI, discography, plain film, myelography, and/or flexion/extension films:

   i. Decreased disc height > 2 mm; ii. Scarring/thickening of annulus fibrosis; iii. Herniated nucleus pulposus; or iv. Vacuum phenomenon.

2. Skeletally mature adult between the ages of 18 and 50 years at time of surgery.
3. Failed at least 6 months of conservative therapy.
4. Oswestry Low Back Pain Disability Questionnaire score ≥ 20/50 (40%) (Interpreted as moderate/severe disability).
5. Psychosocially, mentally and physically able to fully comply with this protocol including adhering to scheduled visits, treatment plan, completing forms, and other study procedures.
6. Plans to remain on active duty for a minimum of two (2) years.
7. Personally signed and dated the informed consent document prior to any study-related procures indicating that the subject has been informed of all pertinent aspects of the study.

Exclusion Criteria:

1. More than one vertebral level to be treated.
2. The involved vertebral endplates dimensionally smaller than 34.5 mm in the medial-lateral direction and/or 27 mm in the anterior-posterior direction.
3. Known allergy to polyethylene, cobalt chromium, or molybdenum
4. Prior fusion surgery at any lumbar vertebral level.
5. Clinically compromised vertebral body at the affected level due to current or past trauma.
6. Radiographic confirmation of facet joint disease or degeneration.
7. Lytic spondylolisthesis or spinal stenosis.
8. Degenerative spondylolisthesis > Grade 1.
9. Osteoporosis: A screening questionnaire for osteoporosis, SCORE (Simple Calculated Osteoporosis Risk Estimation), will be used to screen patients who require a DEXA bone mineral density measurement. If DEXA is required, exclusion will be defined as a DEXA bone density measured T score </= -2.5.
10. Known history of Paget's disease, osteomalacia, or any other metabolic bone disease.
11. Morbid obesity defined as a body mass index > 40 kg/m2 or weight more than 100 pounds over ideal body weight.