Appendix 1. Common classifications of nerve root compression and lumbar disc herniation Jensen classification of lumbar disc herniation: The Jensen grading system classifies lumbar disc herniation using four grades. The four grades are as follows: Normal: the disc does not extend beyond the interspace; Bulge: symmetric circumferential extension of the disc beyond the interspace; Protrusion: asymmetric or focal extension of the disc beyond the interspace, in this case the base/origin of the disc material has a diameter greater than any other dimension of the protrusion; Extrusion: increased extension beyond the interspace in comparison to protrusion, in this case the base/origin of the disc material has a diameter less than any other dimension of the disc material found outside the original disc; this can occur with or without connection between the material and the original disc. Combined Task Force (CTF) classification of lumbar disc herniation: There are two types of disc herniation described based on the percentage of disc material that was outside its original anatomical bounds. The first is focal disc herniation, in which less than 25% of the total disc circumference is outside its original anatomical bounds. The second is broad-based herniation, in which the percentage of disc circumference is outside its original anatomical boundary between 25% and 50%. Greater than 50% of disc displacement was not referred to as herniation, but rather it was defined as disc bulging. Herniated discs are further classified as a protrusion or extrusion. Protrusion is present if in any plane, the greatest distance between edges of disc material beyond the disc space is less than the distance between edges of the defect cross-sectional, which allowed disc material to extend beyond its place of origin. Extrusion is present if in one or more planes, the greatest distance between edges of disc material beyond the disc space is greater than the distance between edges of the defect cross-sectional , which allowed disc to extend beyond its place of origin. Extrusion is also present when there is no continuity between disc material within the disc space and that beyond the disc space. When the displaced disc material has lost continuity with the original parent disc, the resulting type of extrusion is called sequestration. Disc herniation is additionally described as contained or uncontained. A contained disc herniation has the displaced portion covered by annulus, whereas an uncontained disc herniation does not have an annulus covering the displaced portion. Pfirrmann Nerve Root Compression Grading System: The Pfirrmann grading system assesses lumbar nerve root compromise. The grading system has four categories as follows: Grade 0 (normal): no nerve root compromise; Grade 1 (contact): visible contact between nerve root and disc material and the nerve root is positioned normally; Grade 2 (deviation): the nerve root has a dorsal displacement caused by disc material; Grade 3 (compression): the nerve root is compressed between disc material and the posterior spinal canal. van Rijn Nerve Root Compression Grading System: From paper “A five-point scale was used: definitely no root compression, possibly no root compression, indeterminate, possibly root compression, and definitely root compression.” This was then dichotomized into no root compression (first three categories) and root compression (last two categories).

Fig. 1 Fig. 2 Fig. 3 Fig. 4 Jensen Grading System: Fig. 1 Normal Disc: MRI showing that the lumbar disc does not extend beyond the interspace. Fig. 2 Bulge: symmetric circumferential extension of the disc beyond the interspace. Fig. 3 Protrusion: focal extension of the disc beyond the interspace, in this case the base/origin of the disc material has a diameter greater than any other dimension of the protrusion. This MRI depicts a right lateral protrusion of disc material. Fig. 4 Extrusion: the base/origin of the disc material has a diameter less than any other dimension of the disc material found outside the original disc. The MRI depicts extrusion of lumbar disc material into the right neural foramen. The CTF classification system would also classify this as a disc extrusion.

Fig. 1 Fig. 2 Fig. 3 Combined Task Force classification system: Fig. 1 Focal disc herniation: on the patient’s right there is less than 25% of the total disc circumference outside its original anatomical bounds. This is defined as a disc protrusion according to the CTF classification system. Fig. 2 Broad-based herniation: the herniation is inferior to the patient’s spinal canal; the percentage of disc circumference that is outside its original anatomical boundary is between 25% and 50%. This is defined as a disc protrusion according to the CTF classification system. Pfirrmann Nerve Root Compression Grading System: Fig. 1 Grade 3 (compression): on the patient’s right the nerve root is compressed between disc material and the posterior spinal canal; Grade 0 (normal): on the patient’s left no nerve root compromise. Fig. 3 Grade 1 (contact): on the patient’s right there is visible contact between nerve root and disc material; Grade 2 (deviation): on the patient’s left the nerve root has a dorsal displacement caused by disc material.

Fig. 1 Fig. 2 Fig. 3 Fig. 4 van Rijn Nerve Root Grading Criteria: Fig. 1 Bilaterally: definitely no root compression. Fig. 2 Patient’s right: possibly no root compression . Fig. 3 Patient’s right: possibly root compression; patient’s left: Indeterminate. Fig. 4 Patient’s right: definitely root compression.