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Study of Primate and Human Skeletons Demonstrates Low Rate of Spinal Disease in Apes

vertebral osteoarthritis

An investigation of degenerative joint disease (DJD) studied data from chimpanzees, lowland gorillas, bonobos, and human samples to ascertain the relative rate of osteoarthritis and peripheral joint osteoarthritis in each species and found that all types of apes were significantly less prone to DJD than humans.

The Study

Museum skeletal samples of adult chimpanzees, lowland gorillas, and bonobos were examined and analyzed for vertebral osteoarthritis (VOP) and osteoarthritis (OE). The resulting data was compared to data sets from a series of adult human skeleton sets wherein comparable analytic methods had been used to determine the rate of VOP and OE. All samples were evaluated for DJD and the presence of VOP. The relative severity of the conditions was scored using ordinal scaling criteria, categorizing the groups into: none, slight, moderate, or severe DJD. The researchers discarded the “slight” sample data and focused instead on the “moderate” to “severe” data sets for the study.

Results

There was a low prevalence of VOP in the ape samples (0-3.8 %) across all vertebral segments, while the human prevalence was between 11 and 85 times that of the apes, with more uniform involvement throughout the vertebral column.

OA of the spinal joints was also rare in African apes, with chimpanzees being least affected, followed by gorillas, and bonobos. Though OA is less prevalent than VOP in humans, it is still three to four times more common in humans than in apes. Broken down into spinal segments, gorillas were more susceptible to cervical and thoracic segments than chimpanzees. Where chimps showed no lumar involvement, gorillas were variably affected at the level. Humans were uniformly more prone to OA at all levels than any of the apes sampled.

Conclusion

Ape samples were much less likely to show signs of spinal degeneration at all levels than comparable human samples. Although it makes sense to assume that the divergence is due to the greater compressive stress on the bipedal human form, the patterning of VOP data in apes and humans suggests that other forces—such as torsional loads related to axial spinal rotation— are likely contributing to the higher incidence of DJD in humans.

 

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Radiographic Study Indicates Optimal Standing Lordosis Angles Could Help Reduce DJD

lordosis. degenrative joint disease

A radiographic study of the effect of hypo- and hyper-lordosis in the lumbar spine concluded that a lordosis angle of between 65-68 degrees can be considered ‘optimal’ in the reduction of degenerative joint disease (DJD) of the lumbar spine. The results of the study should be helpful in the treatment of spinal pain and rehabilitation.

The Study

Archival standing radiograph images from a single clinic of 301 adult female and male chiropractic patients aged 4 to 79 were analyzed in a blind study using RadiAnt DICOM viewer software. All the images were scored for the severity of DJD by one experienced clinical investigator to ensure consistency using the Kellgren-Lawrence (K-L) criteria—categorizing the results into three groups: 1 and below (no DJD); 2 (mild DJD); 3 (moderate DJD); and 4 (severe DJD). The Cobb angle (CA) was used to measure lumbar lordosis.

Results

In examination of the data, researchers found significant quadratic correlations between the Azari-LeGrande Degenerative Index (ALDI) and the CA values in nearly all study subjects. (No correlation was found in younger men). The correlations were more pronounced in all five spinal motion segments in women under and over the age of 40 than in their male age-counterparts. The findings indicate that too little or too great lordosis can contribute to lumbar spinal degeneration, particularly in women.

Conclusion

Though the effects of lumbar lordosis angles on lower DJD was modest—between 17 and 18 percent in women, and roughly 13 percent in older men—the information is significant because, unlike other contributing factors to DJD, such as genetics, lumbar lordosis can be modified to the optimal degree of between 65 and 68 degrees to reduce the risk of DJD (73 degrees in older men). An increased incidence of DJD was found whenever subjects deviated outside of these optimal weight-bearing parameters, either through hypo— or hyper-lordosis. This information may help prevent, treat, or rehabilitate patients with lower back pain.

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Research Finds Difference between Office Chair Angles on Postural Stress

postural stress, chair, design, seat pan

A study on the impact of different office chair features on spinal posture while sitting found that seat pan tilt and some types of lumbar supports may offer negligible improvement in sitting postures, but overall, sitting for extended periods of time puts stress on the spine and may generate spinal injury. Perhaps something new needs to be invented to minimize end range postural stress and spinal compression over time.

What’s at Stake

Sitting involves flexing the hips and back and moves joints out of their neutral zones, which contributes to stress in the lower back. Even 20 minutes of spinal flexion can cause laxity in the ligaments and change the reflex action of spinal muscles. Over the years, office chair manufacturers have attempted improvements in their products that would lessen stress on the back and improve overall sitting postures, but standing postures that incorporate a neutral posture—where the lower back maintains its convex curvature and the pelvis keeps a slight forward tilt— remains the optimal stance for preventing back damage and pain.

Studies have found that chairs that help the sitter to extend their lumbar spine and anteriorly rotate their pelvis while sitting are the most helpful in reducing the likelihood of damage to the ligaments, muscles, and vertebrae. These types of chair features fall into three categories: thoracic supports, lumbar supports, and seat-pan tilting mechanisms. Of these three modifications, only one type of seat pan mechanism and lumbar supports have been radiographically studied. It is also unclear if men and women have similar lumbar lordosis and pelvic inclination.

This study examined lumbar spine and pelvic postures radiographically using three available seating features to determine which, if any of the three features caused an improvement in spinal or pelvic positioning during sitting. It also looked at posture responses in men and women to see if there were differences between them.

The Study

The study involved 28 participants (14 males and 14 females) with no recent history of lower back problems. The volunteers, whose mean age was 25 years, were not told about the conditions being tested or the relevant features of the products being tested. They were each radiographed in the standing and sitting postures using standardized postural and breathing instructions during their x-rays. Their radiographic measures were then compiled into the software program, and a statistical analysis was performed.

Results

Researchers found that the lumbar postures of all participants were significantly flexed and extended in the seating position compared to the standing position. There was trivial improvement between those using postural interventions and the control groups whose chairs did not employ those features.  There were slightly reduced levels of flexion with seat pan tilt features and lumbar support mechanisms, indicating potential value in these accommodations, but lumbar lordosis or intervertebral joint angles were not affected in any significant way across the improvement features.  At the pelvic level, researchers found statistically significant results: The seat pan tilt configuration produced more anterior rotation of the pelvis and less flexion. The male subjects showed greater flexion during sitting than females.

Conclusion

Sitting places strain on the lower back, particularly at the L4/L5 and S5/S1 disc levels. Lumbar supports and some seat pan tilt features may be slightly helpful in reducing the stress put upon the lower back while in the seated position, but overall, there was minimal difference between the various office chair features on reducing lumbar lordosis or IVJ joint strain. What improvement was evident was local to the spinal segment, rather than posture as a whole. Male and female subjects displayed angle differences in the effects of sitting at the L1/L2 and L2/L3 IVJ joints and pelvis.

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Study Finds Evidence Asymmetrical Postures During Loading Contribute to Disc Failure

disc failure

A microstructural analysis of how healthy discs respond to compression and complex loading postures—specifically those incorporating flexion and facet-constrained shear—found evidence that the required load contributing to disc failure was reduced when complex postures, rather than simple flexion, were utilized in load-bearing situations. In addition, when asymmetric postures were used during lifting, rather than simple compression or flexion, there occurred more infiltration of the nucleus material as it made its way to the annular periphery. The results of the study indicate that asymmetric postures during lifting are more likely to contribute to disc degeneration and lower back pain and should therefore be avoided.

The Study

The study 1 involved 30 motion segments from 10 sheep spines that had no previous signs of disc degeneration. The discs were frozen, thawed, and then rehydrated fully prior to the compression experiments to be in agreement with previous similar experiments and maximize the annular load. Researchers created a bending, twisting, lifting scenario that involved axial rotation, lateral, anterior, and posterior shear, and flexion, adapting the mechanical rig to compress and rotate the disc segments to failure using compressive force.

The typical failure was lower under complex loading conditions than in conditions of simple flexion. Microstructural damage included fractures of the vertebrae and three variations of annular damage, including mid-span direct tearing, non-continuous mid-span tearing, and annular-endplate tearing. Combinations of all three types of damage occurred, as well as circumferential failure, in all 30 discs.

The complex postures utilized in the study lessened the discs abilities to withstand compressive loading and contributed to failures. The complex loading conditions contributed to instances of dual modes of failure, including the circumferential (circuitous tracking of nuclear materials towards the annular periphery) evident in all study samples. This suggests that the lateral parts of the disc may be especially vulnerable during flexion because of shear loading in the area. Circumferential damage was evident in all 30 discs involved in this study, which suggests that it is likely an important type of damage involved in disc failure under complex loading conditions.

Conclusion

Complex postures during load-lifting may contribute to herniation and disc failure. Asymmetrical postures (in addition to flexion) should be avoided during lifting to reduce the likelihood of sustaining a lower back injury.

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Increasing Gradients of Compressive Stress Can Lead to Annular Delamination, Collapse, and IVD Degeneration

delamination, annulus

A ISSLS Prize-winning study 1 examined how increasing gradients of compressive stress within the intervertebral disc (IVD) contributed to the progress of dis degeneration. The research findings suggest that an increased grade of disc degeneration created decreased nucleus pressure and compressive annulus stress, but anterior annular stress gradients increased by approximately 75 percent, and by 108 percent in the posterior annulus—findings that are clinically significant.

The neural arch may provide a stress-shield for the degenerating disc during mechanical loading, but delamination and collapse of the annulus are most likely caused not by loading, but by increasing gradients of compressive stress, leading to advanced disc degeneration, despite the stress-shield.

The Study

Using 191 motion segments from 42 cadavers of varied ages, researchers measured the intradiscal stresses under 1 kN of compression. A pressure transducer was pulled along the midsagittal diameter of the disc to measure the intradiscal stresses. Stress gradients in the annulus were quantified using a formula that averaged the rate of increase in compressive stress between the area of maximum stress in the anterior or posterior annuls, and the nucleus. Measurements were compared before and after applied creep-loading, as well as in flexed or erect postures. A scale of 1to 4 was used to describe the amount of macroscopic disc degeneration observed.

Results

An increase of disc degeneration from 2 to 4 decreased by 68 percent the amount of pressure in the nucleus, and compressive stress in the annulus was decreased by 48-64 percent, depending on the simulated posture of the segment and the location of the disc. However, anterior annular stress gradients showed an average 75 percent increase in the flexion position, and posterior annular stress gradients increased 108 percent in upright posture.

Conclusion

The neural-arch provides stress-shielding, but compressive stress gradients are significantly increased with an increasing grade of disc degeneration. Adjacent lamellae are sheared by the stress gradients, which may contribute to the delamination and collapse of the annulus.

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Lumbar Disc Herniation and Resorption – What does the literature say?

A professional lumbar spine model with a flexible and totally dynamic herniating (or prolapse) nucleus pulposus.

Lumbar disc herniation is a very common condition which often generates pain and disability. It is a physiological process that starts from the inside out as the nucleus pushes radially into the annulus fibrosus. But not all disc herniations cause pain, and many of them don’t cause long-term disability.

The literature has been quite varied in answering questions surrounding resorption rate. Yes, many disc herniations resorb, and it is believed to be due to the anaerobic and avascular nature of the nucleus pulposus. Once the material extends beyond the annular outskirts, the immune system identifies it as foreign and macrophages begin to chew it up.

But not all lumbar disc herniations are equal while some respond to manual therapy and some do not. Some cases require surgery to remove the offending material.

In a recent meta-analysis titled: ‘Incidence of spontaneous resorption of lumbar disc herniation’ 1 a group of authors looked at 11 cohort studies but found only a very limited number of high-quality papers on the subject. What they found was the phenomenon of lumbar disc herniation resorption to be 66.66% and suggested that conservative treatment may be a first line approach to reduce costs associated with unnecessary surgical bills.


Disc herniations are quite varied in nature, and this is likely why there is such variability in the outcomes reported regarding resorption and pain. As a spine modeling company which continuously invests in the property characteristics of materials, we have found that subtle changes to the nucleus pulposus make-up and annulus fibrosus tensile properties have a significant impact on the biomechanical behaviour of our lumbar disc herniation model.

Many mechanically anatomical variations exist which can cause a wide spread of varying symptoms. These symptoms are likely related to the type of herniations with some more central within the spinal canal and others are more lateral. Further to that, Depending on the severity, an astute clinician can be relatively accurate in the anatomical location to help in the mechanical management of lumbar disc herniation.

flexion, lumbar, model, pain, relief

Flexion lumbar loading

To see how a spine surgeon uses the model to explain a lumbar disc herniation while referencing an MRI, we present Iona Collins of fixmyspine below.

 

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Degenerative disc and impact on flexibility

Degenerative disc, flexibility, model

Aging and Degenerative Disc Changes of the IVD’s Impact on Spinal Flexibility

A publication reviewed several studies involving the biomechanics of the intervertebral discs (IVD) with macroscopic changes associated with degenerative disc disease with the aim of finding out how spinal flexibility was affected by dehydration, tears, fissures, osteophytes, and the inevitable collapse of the intervertebral space. The studies under review used cadavers and did not contribute to information about how degenerative disc disease may cause symptomatic back pain. However, the review can contribute to the understanding of disc degeneration disease and its progression, as well as offer insight into what surgical treatments could be beneficial in improving flexibility and spinal functionality in patients.

About Disc Degeneration

Degeneration of the IVD causes mechanical and biochemical changes in the disc and its surrounding structures. The space between the discs can collapse, and proteoglycan and water content can be greatly reduced, contributing to the damage of endplates and osteophytosis. The entire motion segment of the IVD is affected macroscopically and biomechanically by the degenerative process, and this can cause a loss of functionality and mobility that contributes to further progression of disc disease in the spine.

How the IVD Works

A properly functioning IVD evenly distributes weight-bearing loads across the spinal segments and allows the spine to suffer intense compressive loads without collapsing or losing its range of motion. Inside each IVD is a nucleus pulposus (NP)—a gelatinous substance with proteoglycans, elastin fibers, and Type II collagen. The NP is enclosed by the annulus fibrosis (AP)—a lamellar structure made up of Type I collagen fibers. The angle of the collagen fibers in the AP (30 degrees), alternates with that of the adjacent lamellae, which contain gel rich in proteoglycan and may be surrounded by connective bundles of collagen. Endplates connect the IVD to the surrounding vertebrae. The NP transitions to the AF in a transitional zone that is indicated by diverse types of tissue, rather than a distinct border. Negatively charged proteoglycans are balanced by positive cations within interstitial fluids, contributing to osmotic pressurization in response to its environment. Because of this, the IVD absorbs copious amounts of water, which helps the nucleus to adjust in reaction to high compressive forces.

The NP is bookended by the endplates and the AF, which allows the resulting hydrostatic pressure to balance any swelling pressure during active loading and at rest so that the disc will not bulge or collapse under compression. The structure of the lamellae in the AF is tension-loaded and assists with bending and shear. Vicious fluids flow through the permeable endplates, which help evenly distribute pressure within the nucleus or annular tension. The AF’s collagen bundles create an elasticity that absorbs compressive loads. The exchange of fluids within the IVD creates a balance between tension and flexibility that is integral to the function of the spinal unit.

Degenerative disc, flexibility, model

Degenerative disc model

Effects of Degenerative Disease and Aging on the IVD

  • Cellular/matrix alterations—

    Aging and degenerating IVD exhibit early changes in the endplates which in turn cause changes to the nucleus and annulus. A progressive reduction of cells begins in childhood and continues throughout a lifetime, decreasing and fragmenting the proteoglycan content in the nucleus and surrounding areas. In time, this leads to a reduction of the disc’s ability to repair itself. As the cells lose their ability to synthesize, there is further loss of proteoglycan content. Changes at the cellular level create biochemical alterations throughout the entire matrix. In time, the NP loses the ability to attract and retain adequate water and an increase in fibrous tissue takes place. A similar –though lesser—loss of water and collagen in the AF leads to reduced swelling pressure and contributes to the degenerative state.

  • Structural changes

    —Structural failures including tears and clefts follow (or are perhaps caused by) alterations in the NP and AF. Considered a symptom of degenerative disc disease, these changes are related to, but distinct from, the simple aging process. Endplate separations, radial tears, and rim lesions increase in the aging population, and approximately 50 percent of the cadaver specimens in one study showed evidence of IVD degeneration in subjects over 30. Calcification of the cartilaginous endplates cause biomechanical changes that reduce the flexibility of the endplates and make the IVD vulnerable to fracture, reduced water intake, and a lower solute exchange rate between the disc and vertebrae. Collapse of the intervertebral space occurs often in a degenerated IVD, though disc height reduction is not a common result of simple aging. In addition to a reduction in disc height, osteophytes may form around the affected vertebrae. Studies have suggested that these osteophytes may be the body’s attempt at providing supplemental stabilization in the degenerated spine segment.

  • Pain

    —A common cause of back pain, degenerative disc disease undermines the spine’s structural integrity and creates tension and spasms in the surrounding muscular structure. In severe cases of disc degeneration, disc prolapse, and collapse, radial tears that cause a leakage of collagen and fluids can increase the frequency and amount of back pain. Another common source of back pain is lesions or uneven loading in the endplates. When there is a reduction in disc height, nerve roots located in between the vertebrae may be squeezed or pinched into the space near the capsule joint, causing radicular pain. This type of pain can intensify with activity or prolonged sitting or standing. Facet join arthritis can cause a decrease in cartilage between the apophyseal or zygapophysial joints and may contribute to back pain.

  • Changes in Flexibility

    —When the IVD are in a degenerative state, the entire motion segment(s) can become more rigid and less flexible. Researchers have theorized that the spine loses its flexibility over time, triggered by an initial dysfunction and followed by instability, which leads to an attempt at stabilization. Thus, disc degeneration is a progressive event which is the result of the spine’s attempt to handle physiological loads. However, there is no evidence that shows a definitive connection between reduced range-of-motion therapies (such as surgical implants that inhibit the range-of-motion) and an improvement of disc degeneration.

Conclusions

Research into the biomechanics of the IVD systems clarifies some aspects of degenerative disc disease but offers little insight into the specific causes of lower back pain. Degenerative changes of the IVD systems cause changes to the functionality of the spine, with some inconclusive evidence of a loss of flexibility and increasing stiffening over time.  Further studies of the effects of disc degeneration and a possible link to spinal instability are recommended.