CLASSIFICATION OF HERNIATED DISC

STAGES OF PROLAPSED INTERVERTEBRAL DISC

• There are 3 main stages in which the disc undergoes various sequential changes resulting in PROLAPSED INTERVERTEBRAL DISC,  sometimes known as HERNIATED DISC OR SLIPPED DISC

• But before seeing the abnormal changes in the disc we need to learn about the normal disc function and structure to understand the condition properly.

NORMAL INTERVERTEBRAL DISC STRUCTURE

The structure of the intervertebral disc resembles that of “jelly-filled candy” having three components: The nucleus pulposus, The annulus fibrosus, and The vertebral endplates

The nucleus pulposus: 

• This broadly branched hollow mesh is filled initially with synovial fluid  and later by Gallert tissue (a jellylike substance produced by connective tissues)

• This Gallert tissue becomes less homogeneous and loses its elasticity with aging. 

• 75% of the weight is transmitted across the nucleus pulposus.

• The nucleus pulposus of the intervertebral disc is the only non-innervated structure.

• It consists of 88% water and works as a shock absorber during various movements of the spine. 

• Water content decreases in the nucleus pulposus with the aging process.

The annulus fibrosus: 

• The annulus has two layers, a thin outer collagenous layer, and a thick inner fibrocartilaginous layer.

• The concentric lamellae of collagenous fibers extend obliquely from one vertebra to another; helping in rotational movement. 

• The collagen bundles extend and form a cross-woven structure which ensures that the fibers are always tight in any direction of movement.

• At the ventral and lateral aspects, these fibers are strongest and dorsally weakest. 

• This provides flexibility and stability to the disc and the arrangement of collagen in “sharkskin” imparting the needed flexibility to it.

• The outer annulus transmits 25% of the weight.

The vertebral endplates (cartilaginous endplates): 

• These form the upper and lower margins of the intervertebral disc and form a primary junction between the disc and vertebral body, so they are connected to vertebral bodies side by side and the peripheral part is fused to the vertebral ring apophysis.

• The vertebral endplates are made of hyaline cartilage.

FUNCTIONS OF INTERVERTEBRAL DISC

• Separation of vertebral bodies physiologically

• Provides a strong and flexible structure for movements between vertebrae

• 25% of spinal column height is because of the intervertebral disc

• Acts as a shock absorber for axial loads  

• Water bed effect for flexion and twisting movements

• Also helps in countering the compressive loads from the weight of body and muscle contraction

• Anchoring the vertebral bodies to each other.

CLASSIFICATION OF PROLAPSED INTERVERTEBRAL DISC

Following are the different types or stages of Disc Herniation 

Stage 1- Nucleus Degeneration:

SEQUENCE: NORMAL-BULGING

• In this stage, only degenerative changes of the disc occur with no displacement.

• This degenerative changes include softening of the nucleus and it fragmentation, weakening and disintegration of the posterior part of the annulus fibrosus, reduced disc height

• There is disc bulging with no evidence of neural impingement

Stage 2- Neural Displacement 

This stage consists of 4 different level of displacement of the nucleus

• Protrusion

• Subligamentous Extrusion

• Transligamentous Extrusion

• Sequestration

1. Protrusion:

SEQUENCE:  NORMAL - PROTRUSION

• At this level, there is a focal or asymmetric extension of the disc beyond the vertebral border because of constant positive pressure on the disc.

• As the annulus fibrosus becomes weak, may it be because of the disintegration of a small area of its entire thickness spontaneously or because of injury or trauma, the nucleus gets prone to bulge through the defect.

• This is known as a disc protrusion. 

• This likelihood of protrusion is greatly increased if there are degeneration and fragmentation of the nucleus.

2. Subligamentous Extrusion

SEQUENCE: NORMAL-SUBLIGAMENTOUS EXTRUSION

• Further displacement of the disc beyond the annulus fibrosus but beneath the posterior longitudinal ligament (PLL).

3. Transligamentous Extrusion:

SEQUENCE: NORMAL-TRANSLIGAMENTOUS EXTRUSION

• Once the disc is extruded, it does not go back and the posterior longitudinal ligament is not strong enough to prevent the nucleus from further protrusion.

• Finally, in this stage, the nucleus comes out of the annulus fibrosus and a transligamentous extension of the disc occurs through the ruptured posterior longitudinal ligament (PLL), though it has not lost contact with the parent disc. 

• This is called disc transligamentous extrusion.

4 Sequestration

SEQUENCE: NORMAL-SEQUESTRATION

• In sequestration, the extruded disc loose its contact with the parent disc

• It may lie behind the posterior longitudinal ligament or can be a free fragment in the canal.

Stage 3: Stage of fibrosis

• This is the stage of repair and starts alongside degeneration. 

• The residual nucleus pulposus becomes fibrosed and the extruded nucleus pulposus becomes flattened, fibrosed, and finally undergoes calcification.

• Simultaneously, the new bone formation occurs at the points where the posterior longitudinal ligament (PLL) has been detached or stripped from the vertebral body and spur formation occurs.

Disc prolapse commonly occurs between L4-L5 in the lumbar spine and C5-C6 in the cervical spine. 

In the lumbar spine, disc prolapse rarely occurs above L3–L4 level.

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EXERCISES FOR LUMBAR PROLAPSED INTERVERTEBRAL DISC (HERNIATED DISC OR SLIPPED DISC)