Exclusion criteria
| Any back or leg pain of unknown origin |
| Foot drop |
| Previous trauma to the study treatment level, resulting in compression or bursting |
| Sufficient previous surgeries that would preclude use of an anterior approach or previous retroperitoneal surgery |
| Other spinal surgery at affected level |
| Previous thoracic or lumbar fusion |
| Documented spondylolisthesis with >3 mm of slippage at study level |
| Isthmic (spondylolytic) spondylolisthesis at study level |
| Spondylitis (ie, inflammation of spine) at study level |
| Documented significant spinal, foraminal, or lateral stenosis at study level |
| Disc space height ≤3 mm at study level |
| Documented presence of free nuclear fragment at study level |
| Extensive facet arthritis or degeneration of facets at any level noted on MRI, CT, or radiography |
| Scoliosis of lumbar spine with >11° of coronal deformity |
| Metabolic bone disease |
| Active systemic infection |
| Active malignancy or history of metastatic malignancy |
| Any terminal or autoimmune disease |
| Any other disease, condition, or surgery that might impair healing |
| Recent history of chemical or alcohol dependence |
| Current or extended use of any drug known to interfere with bone or soft-tissue healing |
| Known metal allergy |
| Morbid obesity (body mass index >40 or >100 lb overweight) Transitional vertebra at level to be treated that has not clearly fused Pregnancy at time of enrollment (because this would contraindicate abdominal surgery) |
Abbreviations: CT, computed tomography; MRI, magnetic resonance imaging.