Lumbar Spinal Stenosis (LSS) is a syndrome characterized by anatomical narrowing of the central canal, lateral recess, or intervertebral foramen of the lumbar spine, leading to compression of nerve roots, the cauda equina, and their associated blood supply. Its clinical manifestations primarily include neurogenic intermittent claudication and/or radiating pain and numbness in the lower extremities. LSS is a common cause of disabling low back and leg pain and neurogenic claudication in middle-aged and older adults. Epidemiological studies confirm that its prevalence increases significantly with age, affecting approximately 11% of the general population and rising to 19.4% among individuals over 60. Against the backdrop of accelerating population aging in China, LSS not only severely threatens the quality of life and physical and mental health of middle-aged and older adults but also imposes a substantial economic burden on society.

For patients who do not respond to systematic conservative treatment, surgery can provide rapid relief from low back and leg pain. In recent years, high-quality evidence from randomized controlled trials (RCTs) has shown that in specific LSS subgroups with Grade I lumbar spondylolisthesis, the two-year clinical outcomes of decompression alone are non-inferior to those of decompression with instrumented fusion. This finding suggests that fusion is not an absolute indication for such patients and challenges the potential trend of overuse of fusion in clinical practice, prompting surgeons to more carefully evaluate the risk-benefit ratio of fusion surgery. However, it is important to note that this evidence primarily originates from traditional open surgical approaches and highly selected study populations. Therefore, whether these conclusions can be directly extrapolated to full-endoscopic techniques and their applicability in complex middle-aged and older patient populations with multiple comorbidities remain unclear and warrant further investigation.

Against this backdrop, minimally invasive spine surgery technology, guided by the core principle of "achieving maximum efficacy with minimal trauma," has developed rapidly. Over the past decade, full-endoscopic spine techniques, representing the concept of "ultra-minimally invasive" surgery, have made significant progress. This technology, relying on high-definition endoscopic systems, enables precise decompression of neural structures under a magnified and clear surgical field through tiny skin incisions less than 1 cm in diameter and sequentially dilated working channels. Its clinical advantages in reducing perioperative pain and accelerating postoperative recovery have been widely confirmed. Innovations in full-endoscopic techniques have allowed the classic clinical debate of "decompression alone versus decompression with fusion" to be re-examined within a new technological platform. However, high-quality prospective studies directly comparing full-endoscopic decompression alone with Endoscopic Lumbar Interbody Fusion (Endo-LIF) remain scarce, especially evidence specific to the unique patient population of middle-aged and older adults. Consequently, in current real-world clinical practice, a surgeon's choice between these two endoscopic procedures often relies more on personal clinical experience than on support from high-level evidence-based medicine.

Based on the aforementioned background, this study aims to conduct a prospective randomized controlled trial comparing the efficacy and safety of full-endoscopic decompression versus endoscopic fusion in middle-aged and older adult patients with LSS, thereby providing a scientific basis for individualized and precise surgical decision-making for this patient population.

Inclusion Criteria:

1. Aged between 50 and 75 years, regardless of gender.
2. A definitive diagnosis of lumbar spinal stenosis, presenting with typical clinical symptoms (e.g., lower extremity radiating pain, neurogenic claudication) and signs, confirmed by imaging (MRI or CT).
3. The lesion involves only a single spinal segment (L2-S1).
4. Failed to respond to at least three months of systematic conservative treatment, with a significant impact on quality of life, and the patient has a clear willingness to undergo surgery.
5. (Clinical equipoise) After evaluation by at least two senior spine surgeons, both agree that the patient's condition meets the surgical indications for both full-endoscopic decompression and endoscopic lumbar interbody fusion.
6. The patient fully understands the randomized nature of this study (including random assignment and the relinquishment of choice by both the physician and the patient) and voluntarily signs the Informed Consent Form.

Exclusion Criteria:

1. Clear indications for fusion: Degenerative spondylolisthesis greater than Meyerding Grade I, presence of lumbar spondylolysis, or evidence of definite lumbar instability on flexion-extension radiographs (e.g., segmental translation > 3 mm or angular change > 10°).
2. Clear indications for decompression alone: Stenosis caused solely by soft disc herniation, without concomitant bony spinal canal or lateral recess stenosis.
3. Spinal stenosis due to non-degenerative causes: Presence of spinal stenosis caused by fracture, spinal tumor, active infection, or inflammatory disease (e.g., ankylosing spondylitis, rheumatoid arthritis).
4. Severe spinal structural abnormalities: Presence of severe spinal deformity (e.g., degenerative scoliosis with a Cobb angle > 20°).
5. History of relevant prior surgery: Previous lumbar surgery at the same or an adjacent segment.
6. Systemic diseases precluding tolerance to surgery: Presence of severe dysfunction of major organs (e.g., heart, lung, liver, kidney) or an American Society of Anesthesiologists (ASA) classification > III, indicating an inability to tolerate anesthesia or surgery upon evaluation.
7. Comorbidities that may confound outcome assessment: Presence of other conditions that could cause lower extremity claudication or dysfunction, such as severe hip or knee osteoarthritis (including a history of total hip or knee arthroplasty), peripheral vascular claudication, or polyneuropathy. Presence of other neurological or muscular system disorders that could seriously affect treatment evaluation (e.g., Parkinson's disease, amyotrophic lateral sclerosis).
8. Participation in other studies: Currently participating in other clinical trials that could potentially influence the results of this study.