The purpose of this study is to evaluate the clinical, radiological, and surgical outcomes of the Annex™ Adjacent Level System for the treatment of adjacent level disease of the lumbar spine. The Annex™ Adjacent Level System is a spinal fixation system intended to be used with commercially available pedicle screw fixation systems in order to extend existing pedicle screw constructs. Subjects will be evaluated over a 2 year period and compared to historical control.

Inclusion Criteria:

• Men or women 18-85 years of age
• Single level adjacent level segment disease (ALD) in the lumbar spine (L1-S1).

Exclusion Criteria:

• trauma, tumor, pseudoarthrosis, revision, or same-level recurrent stenosis
• cervical fusion candidates
• extraspinal cause of back pain
• local or systemic infection
• pregnant / able to become pregnant and not following a reliable contraceptive method
• Severe osteoporosis or osteopenia
• Morbid obesity defined as BMI > 40
• Anatomy or other factors that prohibit safe surgical access to the surgical site
• Allergy or sensitivity to any component of the treatment procedure
• Inadequate tissue coverage over the operative site
• Inadequate bone stock or bone quality
• Fever or leukocytosis
• Uncorrectable coagulopathy or hemorrhagic diathesis
• Cardiopulmonary conditions that present prohibitive anesthesia risk
• Neuromuscular disease or disorder
• Mental illness
• Has an active workman's compensation claim

The subject population for both the treatment and control groups will include adult (skeletally mature) men and women who were previously implanted with rigid posterior fixation (pedicle screw/rod constructs) in the thoracolumbar spine and who later developed adjacent level disease (ALD) at a lumbar level.