A 62-year-old man presents with 6 months of bilateral buttock and leg pain that is worse with prolonged standing and relieved with sitting. He denies symptoms with exercise on a stationary bike. Initial treatment including physical therapy, NSAIDS, and an epidural steroid injection provided only temporary relief of his symptoms, which have returned and are now severe. On physical exam he has normal motor strength in his lower extremities, negative straight-leg raise tests bilaterally, and palpable bilateral dorsalis pedis pulses. Lumbar flexion-extension radiographs show no spondylolisthesis or instability. An axial T2 MRI cut is shown in figure A. What is the most appropriate next step in management?