Mechanoreceptors in the Lumbar Spine’s

A study 1 published in the ‘Journal of Clinical Neuroscience’ decided to analyze mechanoreceptors present in the lumbar spine’s intervertebral discs. With such receptors linked to Low Back Pain, the study presented certain conclusive results.

What Was the Context?

Low back pain or LBP has been observed to impact people around the globe. Such ailment effects a person’s social, financial, physical, and psychological wellbeing. Research continues to create therapies to address LBP. When talking about such a condition, the nerve structures present in the intervertebral discs can’t be ignored. 

Intense muscle spasm of the vertebral musculature is an important component of LBP, elicited through reflex arches mediated by specialized nerve endings. Joint receptors have been classified into four categories. 

Type 1 is encapsulated mechanoreceptors with similarity to Ruffini endings. Type II are encapsulated mechanoreceptors that are similar to Pacinian corpuscles. Type III are encapsulated mechanoreceptors that share similarity to Golgi endings. And Type IV are unmyelinated free nerve endings as well as non-encapsulated plexuses that have nociceptive function.

While mechanoreceptors present in the human intervertebral disc have been studied, there is limited data available.

The objective of the current study was to help determine the different types of mechanoreceptors present in the two lower intervertebral discs. A review of available literature was also part of this study.

What Was the Methodology?

The current study involved a total of 25 intervertebral discs being removed during routine autopsy from a total of 15 human cadavers. The team only harvested the L4-L5 (13 discs) along with L5-S1 (12 discs). From the cadavers, 8 were male, while 7 were female. The mean age of the selected cadavers was 45.4 years from a range of 15-66 years.

Take note; none of the cadavers had a history of chronic LBP or underwent an operation on their vertebral column. Upon visual inspection, all of the specimens were deemed normal. Also, autopsy specimens were removed within 6 hours after death.

The discs’ anterior and posterior halves were dissected at the midsubstance between the endplates. Everything was studied separately. 

The team evaluated the degree of disc degeneration by using a semi-quantitative method. The morphologic criteria of Freeman and Wyke was used to distinguish the different receptors. A quantitative analysis was also performed for determining the mechanoreceptor’s density in each disc section.

A comparison was made through Fisher’s exact test. The Kruskal-Wallis test was administered to record the age comparison among the mechanoreceptor groups. Statistical analysis was conducted by using SPSS version 12.

What Were the Results?

According to the results, the team couldn’t find nerve structures in 2 of the 25 disc samples. The mean density of receptors per disc was 1.4 in the discs having Ruffini receptors. The density of Golgi receptors was 1.2, while it was 1.3 for free nerve fibers in each specimen. Take note; Pacinian receptors weren’t identified in the samples.

A significant association was seen between the type and level of mechanoreceptor present when observing the disc tissue’s anterior part. Discs with Golgi and Ruffini-type receptors were analyzed to be more frequent (around 78%) at the L5-S1 level. Also, a statistically significant difference wasn’t observed between the (type and frequency) of receptors and the sex, age, and degree of disc degeneration.  

Furthermore, the receptors that showed up a lot showed morphology similar to the Ruffini receptor. The second most frequency of corpuscular receptors showed similarities to the Golgi tendon organ. Free nerve fibers were another frequent finding.

What Was Concluded?

The current study confirmed the existence of an abundant network of non-encapsulated and encapsulated receptors in the human lower lumbar spine’s intervertebral discs.

According to data, it has been assumed that the primary role of encapsulated structures is the continuous monitoring of position, acceleration, and velocity. As for free nerve fibers, they are likely involved in nociception or regulation of vessel tone.

Through the results of this study, one can see that further research is required to better understand mechanoreceptors to aid with effectively addressing LBP and related ailments.

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