This clinical study aims to find out if a modified mini-open spine surgery (modified mini-open transforaminal lumbar interbody fusion，mMO-TLIF) is as good as, or better than, the traditional open surgery (traditional transforaminal lumbar interbody fusion，traditional TLIF) for treating low back pain, leg pain, and walking difficulties caused by lumbar spinal stenosis with instability. The study will also look at the safety of both surgeries.

It is designed to answer these main questions:

Is the mMO-TLIF surgery as good as the traditional TLIF surgery at improving patients' lower back function and quality of life? Does the mMO-TLIF surgery reduce blood loss during the operation and shorten hospital stays and recovery time? What medical problems (like infections or nerve injuries) might patients experience after having the mMO-TLIF surgery? Researchers will compare the results of the mMO-TLIF surgery group with the traditional TLIF surgery group to see which one works better.

Participants will:

Be randomly assigned to receive either the mMO-TLIF minimally invasive surgery or the traditional TLIF open surgery.

Come back to the hospital for check-ups before surgery, and then at 1 month, 3 months, 12 months and 24 months after surgery.

During these check-ups, they will have physical exams, fill out questionnaires about their symptoms, dysfunction and quality of life, and get X-rays or CT scans to see how their bones are healing.

Inclusion Criteria:

• Patients aged between 18 and 80 years.
• Presence of unilateral neurogenic claudication or radicular pain in the lower limbs, with failure to respond to at least 3 months of conservative treatment.
• Presence of bilateral neurogenic claudication or radicular pain in the lower limbs, but with complete resolution of neurological symptoms in at least one lower limb during recumbency and an unremarkable physical examination, alongside failure to respond to at least 3 months of conservative treatment.
• Radiologically confirmed single- or two-level lumbar spinal stenosis on MRI, with evidence of instability specifically at the stenotic level(s) on standing lateral radiographs.
• The mMO-TLIF or TLIF surgical procedure is performed by the same lead surgeon at each participating investigational site.
• Subjects voluntarily participate and provide written informed consent.

Exclusion Criteria:

• Presence of bilateral radicular pain in the lower limbs that does not completely resolve at rest.
• History of previous lumbar spine trauma or surgery.
• Presence of spinal infection, tuberculosis, or tumor.
• Contraindications to surgery, such as severe systemic medical diseases, coagulation disorders, severe active infectious diseases, or osteoporosis.
• Significant intervertebral space collapse, presence of bony ankylosis, etc.
• Incomplete data.