Spondylosis (plural: spondyloses) is used as a broad descriptive term referring to degeneration of the spinal column from any cause 1; it is usually further qualified by the part of the spine affected, e.g. cervical spondylosis and lumbar spondylosis 1.
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Pathophysiology
Spondylosis can be divided into static causes (degeneration) or dynamic causes (due to movements) 1.
The earliest spondylotic change is disc desiccation. Repetitive movements wear down the vertebral body endplates, compromising vascular supply to the central part of the intervertebral disc (made up of the nucleus pulposus and annulus fibrosus). This results in loss of proteoglycan matrix, due to loss of water content and chondroitin sulfate, being replaced by keratin sulfate. Thus, the intervertebral disc becomes easily compressible and the height is reduced. Part of the disc bulges posterior to the posterior annulus, as this part of the disc is thinner. As the disease progresses, the spine is unable to maintain its normal alignment (as in normal lordosis in the cervical and lumbar spine), causing an abnormal kyphotic spine 1.
Further disc desiccation results in disc herniation through the posterior annular tear. The bulging disc causes the posterior longitudinal ligament to peel off from the surface of the vertebral body 1. Disc herniation irritates the posterior adjoining ends of the vertebrae, causing the new bone formation, known as an osteophyte. As osteophyte formation increases, it causes the narrowing of spinal canal, compressing the spinal cord, resulting in a condition known as "hyperostotic myelopathy". Osteophytes of the adjacent vertebrae may fuse, slowing the pathologic process and provides stability for the spine. However, the "awkward" kyphotic position of the spine gives rise to more stress of the other vertebral levels, resulting in progression of spondylosis to other vertebrae. Uncovertebral joint (that relates laterally to the disc) will also be affected, especially at C5/C6 and C6/C7 levels (most spine movements occur here). Other changes includes facet joint (located between lamina and pedicle) and ligamentum flavum hypertrophy (located on the lamina itself) that also contributes to canal narrowing 1.
When spinal stenosis is present, either forward (impacting the osteophytes) or backward movement (impacting the hypertrophied ligamentum flavum) of the spine will cause further canal narrowing and compresses the spine, increasing the risk of spinal cord damage, thus causing compressive myelopathy or chronic spinal cord ischemia. Spinal cord ischemia is usually due to small perfusion defects as a result of long period of small collisions with the narrowed canal instead of absence of larger blood supply to the spinal cord 1.
History and etymology
Spondylosis derives from the Ancient Greek word σπόνδυλος (spóndylos) meaning "a vertebra".
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