Background Lumbar spinal stenosis with degenerative spondylolisthesis (DLS) is often treated with decompression and fusion because of concerns about postoperative instability. However, radiologic instability does not always correlate with symptoms. Some patients with grade I DLS mainly present with leg-dominant symptoms during walking and have minimal axial back pain. With modern facet-preserving endoscopic techniques, decompression without fusion may be sufficient in selected patients. Objective To evaluate 12-month outcomes of biportal endoscopic decompression without fusion in symptom-selected patients with grade I DLS and to descriptively compare the results with patients who had lumbar spinal stenosis associated with degenerative disc disease (DDD).

Methods: This retrospective, symptom-based case series included patients who underwent biportal endoscopic spine surgery (BESS) for lumbar decompression between 2022 and 2024. The DLS group consisted of 12 patients with grade I spondylolisthesis and leg-dominant symptoms with minimal axial back pain. The comparison group included 16 patients with lumbar spinal stenosis without spondylolisthesis, in whom degenerative disc changes were commonly present. Decompression was performed using unilateral laminotomy for bilateral decompression, with selective interlaminar and contralateral foraminal decompression when indicated. No fusion was performed during the initial procedure. Clinical outcomes were assessed using the Oswestry Disability Index (ODI) and visual analogue scale (VAS) for leg and axial back pain at 12 months.

Results: Both groups showed improvement in leg pain after endoscopic decompression. In the DLS group, disability improved and axial back pain remained minimal. Mild slip progression was observed in two patients without symptom recurrence or functional decline, and no patient required additional surgery. In the comparison group, leg pain also improved, although residual disability persisted at follow-up. One patient underwent fusion surgery during follow-up because of persistent symptoms.

Conclusion: In carefully selected patients with grade I degenerative spondylolisthesis and leg-dominant lumbar spinal stenosis, biportal endoscopic decompression without fusion can provide outcomes comparable to those seen in simple degenerative stenosis. Clinical symptoms, rather than imaging findings alone, should guide the decision for fusion.