A 65-year-old man with a 6-year history of lumbar spinal stenosis presents with progressive leg pain and paresthesias in a non-dermatomal distribution. Imaging shows severe central stenosis at L4–L5 with facet hypertrophy and ligamentum flavum thickening. He has failed 6 months of conservative management. Preoperative MRI reveals a dural sac cross-sectional area of 45 mm² at the level of maximal stenosis. Which of the following surgical approaches would provide the most direct decompression while minimizing destabilization in this patient?