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Table 1 Inclusion and exclusion criteria

From: The SNAP trial: a double blind multi-center randomized controlled trial of a silicon nitride versus a PEEK cage in transforaminal lumbar interbody fusion in patients with symptomatic degenerative lumbar disc disorders: study protocol

Inclusion criteria • Male and female patients age 18–75 years
• Chronic low back pain unresponsive to at least six months of conservative care
• MRI and standing x-ray evidence of Pfirrmann Grade III or greater disc
• Degeneration and/or degenerative or isthmic spondylolisthesis of Grade I or II
• Signed informed consent
Exclusion criteria • Osteoporosis
• Patients with prior failed fusion at the same level
• Degenerative scoliosis
• Degenerative spondylolisthesis greater than Grade II
• Pregnancy
• Psychiatric or mental disease
• Alcoholism (drinking more than 5 units per day)
• Active infection or prior infection at the surgical site
• Active cancer
• Insufficient language skills to complete questionnaires
• Participation in another study
• More than two symptomatic levels that need fusion
• Planned (e)migration abroad in the year after inclusion