Bilateral versus unilateral interlaminar approach for bilateral decompression in patients with single-level degenerative lumbar spinal stenosis: a multicenter retrospective study of 175 patients on postoperative pain, functional disability, and patient satisfaction - den Boogert, H F; Keers, J C; Marinus Oterdoom, D L; Kuijlen, J M (J Neurosurg Spine, 2015)