A 62-year-old man with a 15-year history of degenerative disc disease and chronic low back pain presents to the orthopedic clinic. MRI shows multilevel spondylosis with central canal stenosis at L4-L5 and L5-S1, and bilateral foraminal stenosis at L4-L5. He has progressive neurogenic claudication with bilateral lower limb pain and numbness in the L5 and S1 dermatomes. Conservative management for 6 months has failed. During preoperative planning, the surgeon notes that the patient has significant facet joint hypertrophy and ligamentum flavum thickening contributing to stenosis. Which of the following surgical approaches would be most appropriate for this patient?