Magnetic resonance imaging
All participants underwent MRI of the lumbar spine within 6 months before surgery (1.5 or 3 Tesla). The MRI protocol dictated sagittal T1- and axial and sagittal T2-weighted images with repetition time (TR)/echo time (TE) 1500–6548/82–126 ms for T2-weighted images and 400–826/8–14 ms for T1-weighted images, slice thickness: 3–5 mm, and FOV: 160–350 mm. The MRI examinations were anonymized and the PACS IDS7 (SECTRA) was used for the assessment of morphological changes.