TLIF is a popular lumbar fusion technique to perform interbody fusion. Pedicle screws providing initial stability have been developed to correct deformity, improve the rate of fusion and speed patient's postoperative recovery. Conventionally, bilateral pedicle screw fixation is a standard approach. Recently, studies have revealed that unilateral pedicle screw fixation provides equivalent clinical outcomes and fusion rates as compared with bilateral pedicle screw fixation in lumbar fusion. Meanwhile, the unilateral approach can reduce intraoperative blood loss and operating time. To our knowledge, few randomized controlled studies comparing unilateral versus bilateral instrumented TLIF in lumbar degenerative diseases have been reported. The purpose of this study is to compare clinical and radiographic outcomes in a series of patients with lumbar foraminal stenosis using instrumented TLIF with unilateral or bilateral pedicle screw fixation.

Inclusion criteria:

• Signed informed consent.
• Patient is willing to be available for each examination scheduled over the study duration.
• Lumbar foraminal stenosis diagnosed by patient history, physical examination and image confirmation.
• Patient has symptoms referable to the stenosis level (low back pain, leg pain, tingling, numbness or weakness), which are relieved after a selective nerve root block.
• Has not responded to conservative treatment for a period of 3 months (e.g. bed rest, physical therapy, medication, manipulations, other).

Exclusion Criteria:

• Has systemic infection, highly communicable diseases, inflammatory or autoimmune disease (e.g. osteomyelitis, crohn's, rheumatoid arthritis, systemic lupus, gout, HIV/AIDS, active tuberculosis, venereal disease, active hepatitis).
• Has presence of active malignancy
• Has a history of severe allergy
• Has a significant medical history that, in the investigator's opinion, would not make them a good study candidate.
• Pregnant, or may become pregnant within follow-up period of study
• Has other spinal conditions that will interfere with clinical outcomes (e.g. spinal structural deformities, spinal fractures, ankylosing spondylitis, spinal tuberculosis, spinal infection, spinal tumors, symptomatic cervical spinal disease)
• Spondylolisthesis at the target level
• Has undergone previous lumbar surgery
• Has severe osteoporosis (T-score ≤ -3.5)
• BMI > 35kg/m2
• Has a diagnosis, which requires postoperative medication that interferes with fusion, such as steroids.
• Has history of endocrine or metabolic disorder known to affect osteogenesis (e.g. Paget's disease, renal osteodystrophy, Ehlers-Danios syndrome or osteogenesis imperfecta)