Neck Solutions Blog

Relationship of facet tropism with degeneration and stability of functional spinal unit

From: Yonsei Med J. 2009 Oct 31;50(5):624-9

Facet tropism is defined as asymmetry in both the facet joint angles of the lumbar and lumbosacral regions. For many years, the effect of facet tropism on the development of intervertebral disc degeneration has been debated. However, the specific details regarding the effects of facet tropism on the development of degenerative disc disease remains as the subject of debate. Most of the previous facet tropism studies have focused on the relationship between facet tropism and lumbar disc herniation.

The role of facet tropism in the pathogenesis of lumbar degenerative disc disease is not fully understood Currently, controversy exists surrounding the question of whether or not any significant relationship exists between facet tropism and the development of disc or facet joint degeneration. Additionally, the relationship between facet tropism and degenerative spondylolisthesis and translational segmental motion is highly controversial.

In the current study, the authors attempted to evaluate the effect of facet tropism on disc and facet joint degeneration. Additionally, the relationship between facet tropism and changes in translational segmental motion was investigated.

Facet tropism is defined as asymmetry between the left and right facet joint angles of the lumbar spine. Asymmetry in the orientation of the zygapophyseal joint surfaces is not uncommon, with estimates of its occurrence at 10-70.5% of the population. Our study revealed an incidence of facet tropism in 35% of the spinal units which were taken into consideration. Facet tropism is most common at L5-S1, followed by L4-L5.

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Increased expression of matrix metalloproteinase-10, nerve growth factor and substance P in the painful degenerate intervertebral disc

From: Arthritis Res Ther. 2009 Aug 20;11(4):R126. [Epub ahead of print]

The human intervertebral disc is an avascular and aneural tissue comprising a central gelatinous region (the nucleus pulposus), surrounded by a fibrous ring of highly organised collagen fibres (the annulus fibrosus). The extracellular matrix of the nucleus pulposus is rich in type II collagen and proteoglycans, predominantly aggrecan, which produces a highly hydrated matrix capable of withstanding the loads experienced within the spine. This extracellular matrix is constantly being remodelled in a process driven by the constituent nucleus pulposus cells.

During intervertebral disc degeneration there is an imbalance in the normal homeostatic mechanisms, which favours matrix catabolism and leads to a loss of disc height,
coupled with ingrowth of both nerves and blood vessels into both the annulus fibrosus and nucleus pulposus. The authors have previously demonstrated that this ingrowth of nerves into the degenerate intervertebral disc is associated with low back pain. While low back pain is multifactorial, studies have shown that this debilitating condition affecting around 80% of adults at some stage of life is associated with intervertebral disc degeneration in approximately 40% of cases. Indeed in a recent study by Cheung et al (2009) it has been shown that there is a significant association of lumber disc degeneration imaged by MRI with low back pain.

The nucleus pulposus of the normal human intervertebral disc is an avascular and aneural environment, comprising of chondrocyte like cells embedded within an extracellular matrix rich in proteoglycans and collagens. This matrix is continuously remodelled in a process controlled by the nucleus pulposus cells and closely regulated by anabolic growth factors and catabolic cytokines. In intervertebral disc degeneration there is disregulation in this finely balanced homeostatic matrix turnover mechanism, leading to an increase in catabolic processes over anabolic matrix formation. Over time this results in breakdown of matrix, until the disc loses both height and function and in a large proportion of cases there is innervation and initiation of the pain response which leads to low back pain.

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Direction of the formation of anterior lumbar vertebral osteophytes

From: BMC Musculoskelet Disord. 2009 Jan 13;10:4

X-ray images of lumbar degenerative diseases often show not only claw osteophytes, but also pairs of osteophytes that form in a direction away from the adjacent disc. We have investigated the direction of the formation of anterior lumbar vertebral osteophytes across the lumbar vertebrae using a sufficient number of lumbar radiographs, because osteophytes images can provide essential information that will contribute to the understanding of the pathology and progress of lumbar spine degeneration.

Kirkardy-Willis et al. reported that lumbar degenerative diseases began with disc degeneration, and, during a period characterized by the development of different pathologies including disc herniation, spinal instability and spinal canal stenosis, ended with the formation of anterior lumbar vertebral osteophytes that would stabilize the spinal column. According to the radiographic Nathan’s classification of anterior lumbar vertebral osteophytes, in a claw osteophyte, a bone bridge forms across the intervertebral disc space as a result of the curve and extension of a cranial osteophyte and a caudal osteophyte across the adjacent disc.

Actually, X-ray images of lumbar degenerative diseases often show not only claw osteophytes, but also pairs of osteophytes that form in a direction away from the adjacent disc. The latter type is called traction osteophytes or traction spurs, and have been described as indicators of intervertebral instability on a plain radiographic image by Macnub et al. Besides, Pate et al. reported from their studies in 200 cadavers that both claw and traction osteophytes had the same histology, and that traction osteophytes could turn into claw osteophytes during the lumbar degenerative process. In 1998, Heggeness demonstrated that both claw and traction osteophytes formed as a result of the same degenerative process. For a decade after these reports, researchers have no longer paid attention to the types of osteophytes and the direction of their formation. We have investigated the direction of the formation of anterior lumbar vertebral osteophytes across the lumbar vertebrae using a sufficient number of lumbar radiographs, because osteophytes images can provide essential information that will contribute to the understanding of the pathology and progress of lumbar spine degeneration.

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