Table 1 Abbreviations and definitions for measurement parameters

Length measurements

Anterior intervertebral height (AIVH)

Distance between anterior-superior and anterior-inferior corners at vertebrae located at relevant intervertebral disc

OsiriX ´length-tool` between most anterior point at superior corner and most anterior corner at inferior corner (Figure 1: a-b)

Posterior intervertebral height (PIVH)

Distance between posterior-superior and posterior-inferior corners at vertebrae located at relevant intervertebral disc

OsiriX ´length-tool` between most posterior point at superior corner and most posterior corner at inferior corner (Figure 1: c-d)

Intervertebral disc length (IVDL)

Distance between anterior and posterior boundaries of intervertebral disc

OsiriX ´length-tool` between midway of AIVH and midway of PIVH (Figure 1: f-g)

Anterior disc material length (ADML)

Distance between anterior and posterior boundaries of anterior herniated disc material

OsiriX ´length-tool` between most anterior located boundary of anterior disc material and midway of AIVH. Linear continuation of IVDL (Figure 1: e-f)

Posterior disc material length (PDML)

Distance between anterior and posterior boundaries of posterior herniated disc material

OsiriX ´length-tool` between midway of PIVH and most posterior located boundary of posterior disc material. Linear continuation of IVDL (Figure 1: g-h)

Antero-posterior dural sac length (ADSL)

Distance between anterior and posterior boundaries of dural sac

OsiriX ´length-tool` between most posterior located boundary of posterior disc material and most posterior located boundary of dural sac. Linear continuation of PDML (Figure 1: h-i)

Cross-sectional area (CSA) calculations

CSA of anterior intervertebral height (CAIH)

Sum of areas estimated by the product of length measurements of anterior intervertebral height, slice thickness, and inter-slice gap distance (Figure 2a)

Calculation of CSA using all slices for AIVH length measurements. (Additional file 2: Calculating software)

CSA of posterior intervertebral height (CPIH)

Sum of areas estimated by product of length measurements of posterior intervertebral height, slice thickness, and interslice gap distance (Figure 2c)

Calculation of CSA using all slices for PIVH length measurements. (Additional file 2: Calculating software)

CSA of intervertebral disc (CIVD)

Sum of areas estimated by product of length measurements of intervertebral disc, slice thickness, and interslice gap distance (Figure 2b)

Calculation of CSA using all slices for IVDL length measurements. (Additional file 2: Calculating software)

CSA of anterior disc material (CADM)

Sum of areas estimated by product of length measurements of anterior disc material, slice thickness, and interslice gap distance

Calculation of CSA using all slices for ADML length measurements. (Additional file 2: Calculating software)

CSA of posterior disc material (CPDM)s

Sum of areas estimated by product of length measurements of posterior disc material, slice thickness, and interslice gap distance (Figure 2d)

Calculation of CSA using all slices for PDML length measurements. (Additional file 2: Calculating software)

CSA of dural sac (CDS)

Sum of areas estimated by product of length measurements of dural sac, slice thickness, and interslice gap distance

Calculation of CSA using all slices for ADSL length measurements. (Additional file 2: Calculating software)

Volume measurements

Volume of anterior disc material (VADM)s

Calculated volume of anterior disc material, from tracing of sagittal areas in all slices

OsiriX ´pencil-tool` tracing area of anterior disc material anterior of AIVH at all chosen slices. Osirix ´Compute volume…` tool for volume read-out (Figure 3: a)

Volume of posterior disc material (VPDM)s

Calculated volume of posterior disc material, from tracing of sagittal areas in all slices

OsiriX´pencil-tool` tracing area of posterior disc material posterior of PIVH at all chosen slices. Osirix ´Compute volume…` tool for volume read-out (Figure 3: b)