Hip Joint Pathologies; causes, treatment and managment

PATHOLOGY OF THE INTERVERTEBRAL DISK

Injury and Degeneration of the Disk

Definitions

Various authors have defined the terms herniation, protrusion, prolapse, and extrusion differently.The following definitions are used in this text.

Herniation: a general term used when there is any change in the shape of the annulus that causes it to bulge beyond its normal perimeter.

Protrusion: nuclear material is contained by the outer layers of the annulus and supporting ligamentous structures

Prolapse: frank rupture of the nuclear material into the vertebral canal.

Extrusion: extension of nuclear material beyond the confines of the posterior longitudinal ligament or above and below the disk space, as detected on magnetic resonance imagine (MRI),87 but still in contact with the disk

Free sequestration: the extruded nucleus has separated from the disk and moved away from the prolapsed area

Hip Joint Pathologies


Fatigue Breakdown and Traumatic Rupture

A decrease in the continuity and integrity of structure of the annulus fibrosus may occur with

 (1) repeated stress over time causing fatigue breakdown 

(2) traumatic rupture.

Fatigue breakdown. Over time, the annulus breaks down as a result of repeated overloading of the spine in flexion with asymmetrical forward bending and torsional stresses. With torsional stresses, the annulus becomes distorted, most obviously at the posterolateral corner opposite the direction of rotation. The layers of the outer annulus fibrosus lose their cohesion and begin to separate from

each other. Each layer then acts as a separate barrier to the nuclear material. Eventually, radial tears occur, and there is communication of the nuclear material between the layers. With repeated forward bending and lifting stresses, the layers of the annulus are strained; they become tightly packed together in the posterolateral corners, radial fissures develop, and the nuclear material migrates down the fissures. Outer layers of annular fibers can contain the nuclear material so long as they remain a continuous layer. After injury, there is a tendency for the nucleus to swell and distort the annulus. Distortion is more severe

in the region where the annular fibers are stretched.  If the outer layers rupture, nuclear material may herniate through the fissures. Healing is attempted, but there is poor circulation in the disk. There may be self-sealing of a defect with nuclear gel or proliferation of cells of the annulus. Any fibrous is weaker than normal and takes a long time because of the relative avascular status of the disk.

Traumatic rupture. Rupture of the annulus can occur as a one-time event, or it can be superimposed on a disk where there has been gradual breakdown of the annular rings. This is seen most commonly in traumatic hyperflexion injuries.

Axial Overload

Axial overload (compression) of the spine usually results in end-plate damage or vertebral body fracture before there is any damage to the annulus fibrosus.

Age

Individuals are most susceptible to symptomatic disk injuries between the ages of 30 and 45 years. During this time the nucleus is still capable of imbibing water, but the annulus weakens owing to fatigue loading over time and therefore is less able to withstand increased pressures when there are disproportionately high stresses. The nuclear material may protrude into the tears of fissures, which most commonly are posterolateral and, with increased pressures, may bulge against the outer annular fibers, causing annular distortion; or the nuclear material may extrude from the disk through complete fissures in the annulus.

Degenerative Changes

Any loss of integrity of the disk from infection, disease, herniation, or an end-plate defect becomes a stimulus for degenerative changes in the disk. Degeneration is characterized by progressive fibrous changes in the nucleus, loss of the organization of the rings of the annulus fibrosus, and loss of cartilaginous end-plates.

As the nucleus becomes more fibrotic, it loses its capacity to imbibe fluid. Water content decreases, and there is an associated decrease in the size of the nucleus. Acute disk protrusions caused by a bulging nucleus pulposus against the annulus or extrusions of the nucleus through a torn annulus are rare in older people. It is possible to have protrusions of the annulus fibrosus without bulging from nuclear pressure. Myxomatous degeneration with annular protrusion has been demonstrated in disk lesions in older people.

 

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