ABCs of the degenerative spine

Abstract

Degenerative changes in the spine have high medical and socioeconomic significance. Imaging of the degenerative spine is a frequent challenge in radiology. The pathogenesis of this degenerative process represents a biomechanically related continuum of alterations, which can be identified with different imaging modalities. The aim of this article is to review radiological findings involving the intervertebral discs, end plates, bone marrow changes, facet joints and the spinal canal in relation to the pathogenesis of degenerative changes in the spine. Findings are described in association with the clinical symptoms they may cause, with a brief review of the possible treatment options. The article provides an illustrated review on the topic for radiology residents.

Teaching points: • The adjacent vertebrae, intervertebral disc, ligaments and facet joints constitute a spinal unit. • Degenerative change is a response to insults, such as mechanical or metabolic injury. • Spine degeneration is a biomechanically related continuum of alterations evolving over time.

Keywords: Degenerative spine; Intervertebral disc herniation; Modic changes; Spinal canal stenosis; Spondylosis.

Fig. 1

Functional spinal unit (FSU). The FSU represents the smallest motion segment of the spine and exhibits biomechanical characteristics similar to those of the entire spine. Approximately 70% of applied axial compression is transmitted by the vertebral body and the intervertebral discs, with the remaining 30% of the load being distributed through the facet joints

Fig. 2

Types of spinal degeneration. (a–b) Horizontal degeneration. Initial degeneration of the intervertebral disc (a) subsequently leads to the facet joint osteoartritis (b). (c–d) Adjacent segment disease. Severe degenerative changes on a segment result in abnormalities in the level above

Fig. 3

A-B-C degenerative changes. (a) A-changes. The degenerative process usually starts within the nucleous pulposus representing A-changes. (b) B-changes. The abnormalities extend to the disc, annulus fibrosus, end plates and bone marrow of the adjacent vertebral bodies. (c) C-changes. The advance degeneration may eventually involve distant structures and lead to facet joint osteoarthrosis, ligamentum flavum hypertrophy (not shown) and spinal canal stenosis (not shown)

Fig. 4

Intradiscal pressures. (a) The intradiscal pressures in the physiological postures in healthy individuals. (b) The intradiscal pressures in patients with mild, moderate and severe degeneration. (c) Maximum inflated pressures in tires and a soccer ball are presented for the purpose of comparison

Fig. 5

Stress distribution in a normal segment and in a segment with nucleous pulposus degeneration. (a) A schematic illustration of the normal balanced distribution of the loads in a disc. (b) In nucleus pulposus degeneration intradiscal pressure drops and the annulus fibrosus acts like a fibrous solid to resist compression directly

Fig. 6

A grading system of intervertebral disk degeneration

Fig. 7

Signs of intervertebral disc degeneration: (a). The vacuum phenomenon. This sagittal CT reformatting image shows the foci of air within the L2–L3 and L3–L4 discs (arrows). (b) Intradiscal fluid accumulation (arrow). (c) A sagittal reformatting CT image at the level of C3–C4 shows disc calcification (arrow)

Fig. 8

Annulus fibrous fissures: (a–b) Circumferential fissures. A drawing and an axial T2-WI scan at L4–L5 (arrow) showing a rupture of the transverse fibres without disruption of the longitudinal fibres representing circumferential fissures. (c–d) Radial fissures. A drawing and a sagittal CT discogram at L5–S1 showing (arrow) radial fissures extending from the periphery of the annulus to the nucleus, with disruption of the longitudinal fibres. (e-f) Peripheral rim fissures. A drawing and a sagittal T2-WI scan at L5–S1 demonstrating disruptions of Sharpey’s fibres at the annular periphery

Fig. 9

A classification of the disc displacements

Fig. 10

A classification of the focal disc displacements (herniations)

Fig. 11

Diffuse displacement of the disc material: bulging and annular folding. (a) Disc bulging. There is a circumferential displacement of the L4–L5 disc (yellow arrows). Nevertheless, the height of the disc is preserved. Note that the focal hyperintensity within the posterior L4–L5 disc is compatible with the annulus fibrous fissure (red arrow). (b) Annular bulging at the C5–C6 level. The nucleous pulposus material has migrated anteriorly (green arrow), emptying the disc and resulting in severe disc space narrowing and the folding of the annulus fibrosus radially outward (red arrow)

Fig. 12

Focal disc displacement: protrusion. Axial and sagittal T2-WI scans demonstrate focal left L2-L3 paracentral posterior protrusion. There is no disruption of the fibres of the overlying annulus fibrosus or the posterior longitudinal ligament

Fig. 13

Focal disc displacement: extrusion. (a–b) There is an 8-mm focal central L5–S1 extrusion on the sagittal and axial T2-WI. (c) The image shows disc material displacement with complete disruption of the annulus fibrosus; however, the posterior longitudinal ligament remains intact. The posterior aspect of herniation (blue line) is larger than its base (red line) in the sagittal plane, consistent with a full thickness tear of the annulus fibrosus. The herniation material tents the posterior longitudinal ligament without tear. Thus, by definition, this abnormality is a disc extrusion

Fig. 14

Focal disc displacement: extrusion with transligamentous sequestration. (a–b) Sagittal T2-WI scans demonstrate a large L4–L5 left-sided sequestered herniation with superior migration of the fragment. The disc material extends beyond the posterior longitudinal ligament margin suggesting its complete rupture. (c) The extruded disc material is round in the axial slides, which is a typical presentation

Fig. 15

The stages of the nucleus pulposus displacement. The migrated intradiscal nucleous pulposus fragment displaces posteriorly. The arrows indicate the separation of the intradiscal fragment from the remaining nucleous pulposus material. (a) Acute herniation. It occurs at the early stages of degeneration when the intradiscal pressure is still relatively high. It causes the annulus fibrosus fibres to rupture and lead to acute local inflammation. (b) Subacute herniation. This usually arises only when the disc material migrates peripherally with increasing intradiscal pressure increases and improves when the intradiscal pressure drops. The remaining intact fibres of the annulus fibrosus recoil to bring the extruded material back into the disc space. (a) Chronic herniation. Chronic protrusions persist because of high intradiscal pressure pushing the nucleous pulposus material out of the disc

Fig. 16

A classification of the end plate changes

Fig. 17

Degenerative bone marrow (Modic) changes. (a–c) Type 1 changes. (d–f) Type 2 changes. (g–i) Type 3 changes

Fig. 18

The claw sign in type 1 degenerative bone marrow (Modic) changes at L4–L5. T1-WI (a), T2-WI (b), T1-contrast-enhanced (c) and DWI sagittal images (B value 800) (d). The claw sign is identified in the DWI image as linear paired regions of high signal located within adjusted vertebral bodies at the boundaries between the normal and vascularised bone marrow (red arrows). Please note that type 2 degenerative bone marrow changes at L5–S1 and L3–L4 do not demonstrate the claw sign

Fig. 19

Vertical and horizontal instability of the spine. (a) Vertical instability in the settings of a vertebral body fracture. (b) Horizontal instability in spondylolystesis

Fig. 20

Features that are suggestive of the presence of instability in spondylolisthesis: (a) facet fluid, (b) synovial cyst, (c) interspinous fluid, (d) facet joint hypertrophy and (e) the vacuum phenomenon

Fig. 21

A classification of cervical degenerative spondylolisthesis: (a) type I, adjacent spondylolisthesis (arrow); (b) type II, spondylotic spondylolisthesis (arrow)

Fig. 22

A classification of lumbar degenerative spondylolisthesis

Fig. 23

Three types of osteophytes related to the degenerative spine: (a) traction osteophytes (arrow), (b) claw osteophytes (arrow) and (c) wraparound bumper osteophytes (arrow)

Fig. 24

Surgical treatment options for degenerative changes. (a) Herniations. Herniations are often associated with pain and neurological symptoms and most commonly occur on the lumbar spine. Treatment options include conservative treatment if the herniation does not compress the nerves and surgical removal of the herniation if neural compression exists. (b) Spondylosis. Chronic longstanding disc degeneration results in slowly progressive mild-to-moderate disc space narrowing and gradual osteophyte formation without apparent disc displacement. Spondylosis is considered an adaptive reaction to stabilise motion in the presence of instability or a compensatory mechanism to limit the range of motion and prevent further degeneration. Altered disc biomechanics and narrowed intervertebral disc space subsequently lead to facet joint degeneration. This is probably the most favourable type of degeneration as it is essentially asymptomatic, may be seen at all levels of the spine and typically does not require treatment. (c) Disc collapse. Disc collapse leads to annular folding, anterior bulging of the flaval ligaments and posterior bulging of the posterior longitudinal ligament, with consequential narrowing of the central spinal canal. The decreasing disc height of the involved spinal segment leads to increased stiffness and may cause vertical degeneration of the adjacent vertebral segments. (d) Progressive structural failure of the disc to maintain the integrity of the functional spinal unit leads to segmental instability. This may progress to degenerative spondylolysthesis and require spinal instrumentation

Fig. 25

Degenerative changes of the facet joints. (a–d) Radiological classification of facet joint osteoarthritis. (e–f) A synovial cyst at L4–L5. Bilateral degenerated facet joint effusions with a left-sided synovial cyst compressing the left dorsal aspect of the thecal sac

Fig. 26

Ligamentum flavum. (a) A drawing of the normal anatomy of the ligamentum flavum. (b) Normal ligamentum flavum (arrows) on axial T2-WI scans. (c) Severe hypertrophy of the ligamentum flavum on sagittal T2-WI (arrows). Note that there is fluid in the right facet joint, suggestive of segmental instability

Fig. 27

Spinal canal. (a) Normal spinal canal. The central portion of the spinal canal is bordered laterally by a lateral recess, dorsally by a vertebral arch and ventrally by a vertebral body and discs. The lateral recess is bordered laterally by a pedicle, dorsally by a superior articular facet and ventrally by a vertebral body and discs. The foraminal space is bordered by cephalad and caudal pedicles and facet joints dorsally and a vertebral body and discs ventrally. The extraforaminal space is lateral to the neuroforamen. (b) Spinal canal stenosis. There are four major causes of degenerative spinal canal stenosis: disc herniation, hypertrophic facet joint osteoarthrosis, ligamentum flavum hypertrophy and degenerative spondylolisthesis

Fig. 28

A grading system of cervical central and foraminal stenosis on the cervical spine

Fig. 29

A grading of severity of central, lateral and foraminal stenosis on the lumbar spine

Fig. 30

Grading of severity of degenerative changes in the atlanto-occipital, atlanto-dental and lateral atlanto-axial joints

Fig. 31

Uncovertebral joint. (a) Normal uncovertebral joint. The joint (arrow) is formed by uncinate processes above and below. (b) Uncovertebral arthrosis. Degenerative changes involving uncovertebral joints lead to uncovertebral arthrosis (arrow). (c) Hypertrophic uncovertebral arthrosis. Hypertrophic degenerative changes in the uncovertebral joint may result in foramen transversarium narrowing (arrow) and even vertebral artery compromise

Fig. 32

Secondary degenerative changes of the spine. Sagittal T2-WI of a 17-year old male with Hunter syndrome. Multilevel nulceous pulposus degeneration, advanced end plate changes and focal disc displacements are present. The L2 vertebral body shows anterior breaking, resulting in mild kyphosis