Spinal manipulation, DDD

A follow-up MRI study 1 of how non-specific lower back pain (LBP) patients responded to spinal manipulative therapy (SMT) showed that, while there were no significant differences in spinal degenerative features across responding and non-responding groups studied, the non-responding patient group appeared to have more severe degenerative features and lower baseline ADC values in their MRI scans than those who responded well to SMT. The study indicates that patients who respond well to SMT have fewer degenerative changes in posterior joints and disc diffusion than those who do not respond positively to SMT. The study suggests that treatment for patients with extreme degenerative changes should be tailored to address their LBP, as SMT may not provide a desired outcome for their condition.

What’s at Stake?

LBP –in particular, non-specific LBP—is one of the leading causes of disability and lost income potential across the world. Though SMT has been proven an effective form of treatment for many patients with non-specific forms of LBP, not all patients respond favorably to spinal adjustments or report satisfaction with their levels of pain relief and physical comfort, post-SMT. While many patients demonstrate measurable clinical improvements after 1 -3 SMT treatments, a subset of non-specific LBP patients do not respond to SMT. A previous study demonstrated a reduction in spinal stiffness, improvements in modality and an increase in lumbar multifidus contraction, and water diffusion at the L4-L5 disc level in a group of SMT responders after one week of treatment, while these benefits did not manifest in a group of non-responders or a control group. The current study was conducted to use MRI to look for significant differences between responders and non-responders that might account for the discrepancy in SMT outcomes.

The Review

A secondary analysis of the original non-randomized clinical trial involving subjects between 18 and 60 years of age who experienced non-specific LBP with an intensity of at least 2 on an 11-point scale and at least 20 percent on the modified Oswestry Disability Index (mODI) was conducted. Exclusion criteria included prior lumbar surgery, scoliosis, pregnancy, SMT within the past four weeks, and spinal tumors, fractures, or any issues that might exclude the subject from MRI scanning.

The 32 subjects attended three sessions—the first, with an MRI scan and standardized SMT, the second, with SMT only, and the third, where an evaluation of their mODI score, spinal stiffness, and multifidus function was analyzed. No SMT was performed at the last session. Subjects with greater than 30 percent improvement at the third session within one week were deemed “responders.” Those with less than 30 percent improvement were considered “non-responders.”

MRI findings were graded on a 4-point scale of joint degeneration and clinical value. Considerations included space between joints, osteophyte presence, hypertrophy of the articular process, subchondral cysts, and subarticular erosion. Other spinal irregularities were also analyzed and graded on subsequent rating scales.

Results

Baseline spinal structure demographics were similar across the board for all subject groups. A total of 15 subjects were labeled as “responders” based on the mODI scores, and 17 were considered to be “non-responders” to the SMT. The non-responders had more disc degeneration in their facet joints, as seen in the MRI scans. IVD and MC grading was similar in both groups. There was a higher prevalence of degeneration in the L4-L5 and L5-S1 levels in those with disc degeneration. Modic endplate changes were more prevalent in the non-responder group, at 58 percent (46.7 percent in the responder group).

Baseline ADC mean measurements and post-SMT disc diffusion responses varied between the two groups, with the lower scores of non-responders suggestive of higher rates of L4-L5 disc degeneration—a potential source of pre-and-post-treatment pain. The limited mobility of the degenerated discs could also be a factor in the non-responder group’s outcomes. The authors of the review suggest further studies with a larger sample size be conducted in the future to investigate the relationship between spinal degeneration, SMT response, and lower back pain.

The review did find beneficial post-SMT ADC level increases in the group of responders with LBP that suggests the therapeutic value of spinal manipulation in improving disc diffusion in and around painful spinal segments. However, 26 percent of the responders with LBP had no significant change in the ADC levels, so the beneficial effects of SMT may have more to do with mechanical or neurophysiological alterations, rather than diffusion.

Pathologies that are not biomechanical in nature, including bone inflammation, are unlikely to respond to SMT, according to the study. The findings highlight that non-specific LBP is treatment-specific, since its origin may be caused by a number of different conditions. Therefore, the review’s authors caution against using a single SMT approach in treating all non-specific LBP.

 

 

inflammation, re-absorption

A review  1 of the clinical literature regarding lumbar disc herniation (LDH), particularly as it relates to the phenomenon known as “spontaneous LDH regression,” in which the herniation reduces or resolves without surgical treatment, concludes that the inflammatory response that contributes to nerve pain and damage may also be responsible for the spontaneous re-absorption of the herniation. Therefore, except in extreme cases where a neurological deficit or intolerable pain is experienced by the LBP patient, treatment for LDH should be conservative and custom-tailored to address the specific biochemical mechanisms at play in the patient.

What’s at Stake?

The pain and economic disability caused by LDH affects roughly 9 percent of the world’s population and is strongly associated with the aging process. Recent studies have indicated that the malady is more often caused by a failure in the endplate junction, rather than an annulus fibrosis (AF) failure, with its associated nerve ingrowth. This explains why up to 40 percent of patients diagnosed with LHD after imaging tests are asymptomatic.

Typically, LDH and degenerative disc treatments may be surgical, or conservative (non-surgical), with the decision about which approach is appropriate determined cooperatively by the clinician and patient. Because disc herniations often regress spontaneously, without surgical intervention, the authors of this review emphasize the need for clinicians to better understand the biomechanisms at work in LDH in order to make better-informed decisions about which treatment approach might be best for their patients.

Subtypes of LDH that More Frequently Regress

Magnetic Resonance Imaging (MRI) and CT Scan evidence of LDH regression indicate that particular subsets of herniations are more likely to spontaneously regress than others. Specifically, large-sized and sequestered herniations at the L4-L5 spinal segment level are more apt to partially or completely regress than other types of herniations. It is thought the regression is facilitated by the herniation’s exposure to the epidural vascular supply when the posterior longitudinal ligament ruptures. In fact, MRI studies have shown that the spontaneous regression of herniated disc materials is associated less with the size of the rupture and more with the vessels extending beyond the ligaments and supplying blood and nutrients to the inflamed herniation.

Of 36 analyzed herniations imaged in one study, 25 of them resolved spontaneously—17 percent subligamentous, 48 percent transligamentous, and a whopping 82 percent of sequestered herniations, respectively. This suggests the size of the hernia is less of a factor than the PLL rupture. In another study, all sequestered discs self-resolved within 9 months, while extruded discs took a full 12 months to resolve. Disc protrusions did not resolve, even after a full year.

Conclusion

Clinicians should pay particular attention to the subset type of LDH in their patients when deciding whether to treat their condition surgically or conservatively. Further study into the biochemical mechanisms involved in LDH and its potential for self-resolution would be beneficial in long-term LDH patient outcomes and should be a focus of research for clinicians treating patients with LDH.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

degenerative, MRI, low back pain

A retrospective magnetic resonance imaging (MRI) analysis 1 of lumbar degenerative changes in 283 patients with chronic low back pain (CLBP) found more severe disc degeneration (DD), lower disc height, and more extreme disc displacement at the L4–L5 and L5-S1 of patients with work-related CLBP. The results of the study help to elucidate MRI-visible changes and clinical attributes of work-related CLBP.

What’s at Stake

Lower back pain (LBP) affects up to 84 percent of the world population at some point in life and can contribute to acute or chronic disability in up to 12 percent of those affected. As of 2016, LBP was the leading cause of years lived with a disability, and the U.S. economic burden of LBP is estimated to be somewhere between 84.1 billion to 624.8 billion dollars. Understanding the various stages and degenerative characteristics of LBP can help with appropriate and timely treatment, which may help to reduce cases of CLBP. MRI allows physicians to recognize pathologies, so they can appropriately plan treatment for their LBP patients.

Study Design

The study involved the retrospective review of medical records of adults who had sought treatment for CLBP that had lasted for a period of greater than three months. Inclusion requirements included MRI scans of the entire lumbar spine and clinical lumbar evaluations. Excluded were patients under 18, or those whose LBP was intermittent or had not occurred every day for at least three months. Those experiencing pain that outranked their LBP elsewhere in their body were also excluded from the study, as were patients who could not have an MRI, who had a lumbar infection, spinal trauma, tumor, deformities, or spontaneous septic spondylodiscitis or epidural abscess, previous back surgery, osteoarthritis of the hip, and significant psychological disturbances.

Subject demographics were collected and analyzed, including their occupations, how many hours per week they worked, heavy lifting or lengthy desk sitting involved in their jobs, and the age, sex, body mass index, education level, smoking history, and duration of their LBP. Their LBP scores were recorded using a Visual Analog Scale (VAS) from 0 to 10 (no pain to worst pain). The Oswestry Disability Index (ODI) was used to rank each subject’s functional capacity, where those with a lower percentage were rated healthier.

Imaging Analysis Results

Pre-treatment MRIs of three positions—neutral, flexion, and extension—were performed on each subject by two experienced radiologists and then independently evaluated by an orthopedic surgeon. The subjects were grouped according to their MRI results. The four groups included: normal disc (ND), degenerative disc (DD), bulging disc (BD), and herniated disc (HD). Statistical analysis was performed using special software, and clinically-significant value was assigned. Of the 283 patients with CLBP taking part in the study, 110 were women, and 173 were men, and they ranged in age from 18 to 80, with a mean age of 41.8. The post-MRI groups included 37 subjects in the ND group, 85 in the DD group, 123 in the BD group, and 38 in the HD group. The mean age of the patients in the ND group was significantly lower (31.9) than that of the DD group patients (42.8), HD group (39.3), and the BD group (44.9). The ratio of male to female across all groups was 6:4, but the ratio in the HD group was 84.2 % male to 15.8 % female. The duration of CLBP across all groups was roughly 25 months, but when analyzed group-to-group, it progressively ranged from 15 to 25 months, with the ND group at the lowest range, followed by the DD, BD, and HD groups. The duration of pain was significantly increased from the ND group to the BD group. There were few differences in age, smoking history, or education levels across the groups.

The subjects were further categorized into 10 groups based on their occupations. The three groups that were most prominently represented in the ND, DD, BD, and HD groups were manual workers, desk workers, and technicians. They were similarly represented within their groups. Working hours were also similar across these groups, between 59.7 and 63.2 hours per week. The percentage of subjects who were required to manually handle weighty objects at work was significantly lower than those with no manual handling. The number of working hours spent sitting at a desk was much higher in the DD group, as compared to the other three groups.

When comparing clinical CLBP, the VAS pain scores in the DD, BD, and HD groups were much higher than those of the ND group members. The ODI scores of these three groups were also higher than those of the ND group, and those in the HD group were significantly higher than subjects in the DD and BD groups, indicating less functionality.

The MRI looked for the degree of DD in the neutral, flexion, and extension positions, as well as the vertebral height (anterior and posterior), slipping distance of spondylolisthesis in all three positions, height of the L1-S1 discs, disc bulge or herniation distance, AP diameter of the spinal canal, and translational motion. The data was analyzed and classified indicating the severity of disfunction or damage. The worst degeneration was at the L-4/L-5 and L-5/S-1 level, followed in severity by L-3/L-4.

The disc bulge distances of L-3/L-4 and L-4/L-5 were higher in the BD and HD subject groups. Also, the distance of L-4/L-5 was much higher in the HD group than in the BD group in the neutral position. The distances of L-4/L-5 were much higher in the BD and HD groups than in the ND and DD groups during flexion position, and that of L-3/L-4 was much higher in the HD group than in the ND and DD groups. The distances of L-4/L-5 and L-5/S-1 were much higher in the BD and HD groups during extension MRIs.

Conclusion

This study used MRI to analyze and compare four types of lumbar disc degeneration in patients with CLBP and found that the ND group represented a significantly younger demographic than that of the other three group members. This suggests that age is a likely contributor to DD in CLBP. The subjects in the BD group had a much longer mean pain duration than those in the ND group, suggesting a less successful clinical future outcome for those patients. There appeared to be little-to-no association between BMI and smoking history and CLBP in any of the subjects involved in this study.

There was a positive correlation between hours worked sitting at a desk—with those in the BD and HD groups working on average more than 60 hours per week and those in the ND and DD groups working fewer hours. Interestingly, the data collected indicated that most CLBP patients did not perform heavy manual labor at work and were highly educated—suggesting a strong connection between office work and CLBP. The MRI scans showed that lower lumbar disc segments (L-4/L-5 and L-5/S-1) were the most significantly degenerated in the CLBP patients, with lower disc height and displacement.

 

 

 

properties of the annulus, shear force

An in vivo study 1 of the effects of shear force loading applied to the L5-L6 spinal segment of lab rats revealed histological evidence of IVD degeneration in the unit and surrounding discs of sacrificed study rats that had been exposed to shear force via a custom-designed loading device, while no such evidence was evident in the post-mortem rat control group. The results of the study showed that shear force, applied at .33 MPa (a lower level of compressive stress than previously shown to cause IVD degeneration in rat tail discs), creates degeneration of rat IVDs. This information may be instrumental in providing preventative and treatment-oriented care for people who may be at risk of developing IVD degeneration.

The Study of Shear Force

Researchers tested the hypothesis that sustained shear force on a spinal segment would create IVD degeneration in rat lumbar spines. They used 15 young male rats divided into three groups—one sham control group, and two experimental loading groups that would be exposed to loading for one, and two weeks. The shear loading device used was created especially for the experiment and was made of stainless steel. It was applied to the L5 and L6 vertebral rat bones and delivered a static shear load of up to 4 N.

When the shear loading experiment was completed (1 week, and 2 weeks), the rats were sacrificed. The lumbar segments were removed, viewed microscopically, and tested histologically. A degenerative score from 0 to 3 was assigned each sample, with “0” representing no changes, “1” showing minimal changes, “2” representative of samples with moderate changes, and “3” assigned to those samples showing severe changes, including some with NP disappearance. The slides were blinded and randomized to prevent observer bias.

Results

All the rats involved in the study survived the surgery and post-op period, with no signs of distress. Each of the rats that underwent shear loading had IVD degeneration in most of their lumbar discs, across all levels. The sham control rats, however, demonstrated no degeneration after the experiment.

There were differing levels of degeneration in the IVDs of the shear stress-exposed rats. After the shear loading, the posterior annulus of the exposed rats curved into the dorsal area of the NP, creating a reduction in demarcation in these samples and a disappearance of notochordal cells. The anterior NP remnants were disaggregated, collapsing into smaller sections composed of multiple cells, which, along with the NP, later disappeared. There was also a blending of NP, AF, and CE, and it was difficult to see where one began and another ended. The lamellar wall of the inner and middle annulus dissolved, creating disorganization in the AF.

Discussion

Isolating the effects of different loading modes on IVD degeneration and response is helpful in developing a more complete understanding of IVD biomechanics. Understanding the consequences of shear force applied during compressive spinal loads through in vitro studies can elucidate how shear applied during bending and torsion loading can cause damage to the IVD at the microstructural level and contribute to AF degeneration and failure.

The results of this in vivo study on the disc segments of rats undergoing shear force stress on the L5-L6 IVD segment demonstrated evidence of degenerative changes in all the rats exposed to shear force, while no degeneration occurred in the rat sham control group. The disc damage noted in the experiment groups occurred not only at the L5-L6 levels, but was also evident at adjacent levels (L3-L4, L4-L5, L6-S1). This is further confirmation that the effects of shear force can create damage, proteoglycan depletion, NP content loss and/or collapse, and severe degeneration to disc segments within one week of exposure.

 

intensive patient education, pathoanatomy

This study 1 published in JAMA (Neurology), randomly selected 202 acute low back pain patients to compare pain education to non-pain education. The results demonstrated not much difference between the groups.

The Methods

Participants engaged with their common physician and in addition to this familiar interaction, each participant was then randomly partitioned into two groups. Each of these groups experienced, in addition to the advice and interaction of their physician, an additional two x hour sessions of either:

Group 1: Normal engagement with doctor PLUS intensive one on one patient education (delivered by clinical psychologist in pain management (M.K.N.) trained) for an additional 2 (1hr) sessions. This patient education was delivered based on Butler’s and Moseley’s work. 2

Group 2: Normal engagement with doctor PLUS placebo patient education (delivered by the same clinical psychologist) for an additional 2 (1hr) sessions. Participants in the placebo patient education group received no information, advice, or education about low back pain from the trial clinician. Participants were encouraged to talk about any topic that they desired.

The Results

Retention rates remained high for both groups at ninety percent. Intensive patient education was not more effective than placebo patient education at reducing pain intensity at the three months. There was a small effect of utilizing intensive at one week and at three months but not at six or twelve months.

 

Discussion

In this study, patient education was used through a psychological framework model rather than a biomechanical model. It is important to understand that this study does not mean that patient education is ineffective or as effective as a placebo. This patient education angle does not attempt to help patients understand the cause of their pain. This approach is more of a top-down psychological strategy of patient education. Methods to subclassify these acute low back pain patients into specific biomechanical categories and then, offer those patients specific education and movement strategies would be helpful to study as groups within the acute low back pain group. These sub-groups could then be compared to placebo.

 


At Dynamic Disc Designs, we believe that empowering patients with a greater sense of self-awareness on the probable mechanical cause of the acute low back pain can be helpful in the management. Initially, pain-reducing strategies through movement awareness of painful structures should be prompt and focus on reducing nociceptive inflammation for the patient. Following the acute phase of low back pain, professionals using our dynamic disc models can further promote the physical awareness of specific postures to help prevent the recurrence and avoid a progression of the condition. Our models allow the practitioner to explain patho-anatomy in a patient-friendly way that does not induce fear avoidance behaviours for the long term.  They also enable the practitioner to provide a realistic forecast of the temporal biological adaptation process within the degenerative cascade framework of natural ageing with a dynamic 3d model. In other words, our dynamic disc models assist the patient engagement process with the opportunity to bring up anatomy in a non-scary and empowering way. We look forward to more research on this topic.

 

 

3d modeling, endplate lesion

An October 2018 study compared MRI’s of 966 lower back pain (LBP) patients to introduce a simplified, reliable method of classification for common endplate lesions. The study also noted associations between endplate lesions and variables, including age, rate of disc degeneration, sex, and Modic changes. The researchers then demonstrated the new system’s reliability by repeated observational rating over a period of days, using outside raters evaluating a percentage of the total sample results. The demographic and physiological findings of the study were largely in agreement with previous IVD endplate lesion studies but also added novel findings that had not previously been published.

basivertebral nerve, bone marrow edema, modic changes

Modic vertebra model- midsagittal cut exposing the basivertebral nerve.

The Study

The subjects in the study were all LBP sufferers under the age of 70, excluding patients with a history of back surgery, spondylodiscitis, or vertebral fractures. Data including age and sex were collected on all patients, and images were scanned and evaluated by an experienced radiologist.

A scoring and classification system for the Lumbar IVD spaces was noted on the images, with the descriptions:

  • Normal—Physiological curvature of both endplates, without the detection of any visual lesions in any of the sagittal MRI IVD space slices.
  • Wavy/Irregular—Curvature in at least one of the endplates, without detectable IVD lesions.
  • Notched—The presence of at least one circular small or V-shaped lesion on an MRI saggital slice.
  • Schmort’s Node—Clearly evident vertebral endplate deep focal defect, where the endplate is rounded, with a smooth margin
  • Fracture—Thickened bone fragment at the edge of an endplate, or any evident fracture of the endplate with similarly-sized fragments

A sampling of the image data was also evaluated multiple times over a period of two days by independent raters to ensure observer reliability. To determine how often each type of endplate lesion appeared associated with disc degeneration and alterations of the MRI signals, subgroups of the study subjects were created, and comparisons were made based on age and sex. A scatter-plot chart was created to track Modic changes, and the relative percentages were calculated and identified against an established threshold.

 

Results

The findings indicated minimal association between patient age at the time of the scan and disc degeneration, as well as minimal Modic changes in older patients, as opposed to entire population studied. The most common types of endplate lesion observed were the “notched” and “Schmorl’s Node” type lesions, and both were more common in male patients than in females. Few of the patients studied had “Wavy/irregular” or “fracture” lesions, which occurred in nearly equal numbers of male and female subjects.

There was a strongly evident correlation between disc degeneration and endplate defects across all LBP subjects in the study. All lesion types increased in all IVD levels where disc degeneration was evident. There was a significant increase in “wavy/irregular” endplate types whenever severe disc degeneration was present. This can be considered a reliable marker for the process of extreme disc degeneration.

Signal alterations were found to be associated with endplate lesions, specifically in “notched,” “wavy/irregular,” and “Schmorl’s Node” endplates. There were nearly twice as many notches in Modic changes of types 1 or 2 corner signal alterations. Schmorl’s nodes showed even more evidence of association.

 

Discussion

Though this study was conducted with the intention of developing a reliable method of endplate defect classification in LBP patients and to find correlations in the distribution of LBP by analyzing a large population of subjects via MRI, previous studies have indicated a correlation between back pain and lesions—something this study did not specifically address.

The results of this study agreed with previous studies that indicated male LBP patients are more likely to have IVD lesions than female patients, though similar lesion-levels were observed in male and female patients who showed evidence of severe disc degeneration, as is found in Schmorl’s nodes and in those with disc fractures.

Most of the patients showed no evidence of endplate lesions on the lumbar MRIs. Of those who who did have lesions, most (18.7 %) experienced them only in a single IVD level, and males were more likely than females (20.7 % to 16.7 %) to show evidence of lesions. Progressively fewer subjects had lesions involving more IVD levels.

There was a very slight correlation between age and lesions in this and some previous studies. That correlation appears to be stronger in the female LBP population than in males—a new observation that has not been discussed in previous studies.

The association between endplate defects and disc degeneration was evident, especially where “wavy/irregular” endplates occurred, indicating severe degeneration of the discs. Signal alterations and endplate lesions also showed a positive correlation, specifically in “wavy/irregular,” “notched,” endplates. This association was significantly evident in Schmorl’s nodes.

 

Disc pressure, spine, patient education, models

A study 1examining cadaveric intervertebral discs (IVD) indicates disc degeneration is more closely related to reduced pressure associated with mechanical loading than levels of endplate porosity or thickness. Though endplate porosity increases as the IVD degenerates, the results of the study demonstrated that IVD degeneration is caused by reduced pressure in the nucleus—not the reduction of nutrient transport caused by endplate thickening and a reduction of porosity—and that mechanical loading from nearby discs contributes to endplate porosity in age-related disc degeneration.

disc pressure, degeneration

Disc pressure reduction with degeneration.

What’s at Stake?

Understanding the role of IVD endplate thickness and porosity and the role of mechanical loading, age, and sex on determining the efficacy of endplate function is important in the future diagnosis and treatment of disc degeneration. The enervated endplates, when damaged or degenerated, can cause back pain. When properly functioning, they are responsible for the transport of nutrients to the IVD, regulate fluid pressure and metabolite transport between the body of the vertebrae and its nucleus. Disruption in this process can contribute to disc degeneration, inflammation in the vertebrae, and possible infection to the disc.

The level of porosity inside the bony endplates affects the amount of nutrients delivered to the nucleus and the mechanical stability of the vertebrae. A porous endplate allows more nutrients and pressure-regulating fluid to flow into the nucleus of the IVD. A thickened, less porous endplate reduces the nutrient and fluid flow, but creates more structural stability in the IVD, reducing the potential for injury. The proper balance and porosity of the IVD unit is integral to the overall health of the disc, but understanding the mechanism by which the degenerative process occurs is essential in anticipating how a body’s mechanical functions might contribute to a disruption of disc health.

The Study

Researchers compared the relative thickness and porosity of IVD endplates in 40 cadaveric motion segments from 23 cadavers between the ages 48 to 98 years old. The segments were subjected to compression, and the intradiscal stresses were measured and analyzed. Stress profiles were created to determine the average nucleus pressure, as well as the maximum anterior and posterior annulus pressure. The segments were dissected, and discs with endplates on each side were scanned and analyzed for their thickness and porosity in the midsagittal regions. An average value was calculated for the anterior, central, and posterior regions of each of the endplates. A macroscopic and microscopic examination determined the scope and level of disc degeneration in each segment.

The Results

The results of the data sets indicated that nucleus pressure and posterior and anterior annular stresses decreased as the disc degeneration levels increased. There was a slight increase of intradiscal pressure (IDP) with age, but there was no maximum stress increase of the annulus with age. Lower spinal levels were associated with a decrease in IDP.

The endplates were thinner nearer the nucleus, with a 14 % reduction in thickness in the inferior endplates. An analysis of the averaged data set from the three regions of both endplates showed no association between age or level of degeneration and endplate thickness, but there was an inverse relationship between the disc degeneration and endplate thickness. There was a strong relationship between endplate thickness and IDP in an analysis of adjacent discs.

Endplate porosity was more pronounced in the center of the endplate and became less so opposite the annulus. This porosity was not age-dependent but—with the exception of the anterior endplate region— was positively correlated with disc degeneration levels. The levels of endplate porosity was inversely associated with adjacent disc pressure and stress.

Discussion

Endplate thickness was the major determinant of endplate porosity levels. Disc degeneration and mechanical loading measures were also indicated as predictors. The most apparent predictors of endplate thickness (after porosity) included disc pressure and spinal level. IDP was the dominant predictor of disc degeneration.

The study found that disc degeneration was associated most often by disc stress, rather than porosity of the endplate or its thickness. As the levels of disc degeneration increased, porosity of the endplate increased. The porosity of the adjacent disc was inversely affected in terms of pressure and mechanical stress.

Wolff’s law posits that the body’s bone mass and design will compensate for the pressures of mechanical stresses and subsequent anatomical deformation, strengthening the endplates and vertebrae that are subjected to the most physical activity. Reduced loading can thin endplates that are not subjected to pressure. This eventually leads to them becoming more porous. The results of this study affirm this theory, as the lower central endplate regions were harder, thicker, and stronger than those of the anterior-posterior endplate regions. There is an apparent compromise between the strength of the outer bone and the porosity of the central endplate, which allows for stability and nutrient flow where they are needed the most.

There is an evident drop in nucleus pressure during progressive disc degeneration. The reduction of fluid pressure lessons the endplate’s thickness and makes it more porous, leading to bone degeneration and loss. The bone is more likely to buckle and further degrade as it becomes more porous and less stable, reducing nucleus pressure further. This cycle of abnormal pressure reduction is responsible for the continuation of the degenerative process—not the reduced metabolite transport. There is an increased risk of bone fracture with increased porosity and endplate thinning. A fracture would increase stress on the IVD and contribute to the cycle of degeneration, in spite of the increased availability of nutrients that can reach the nucleus through the endplate’s porosity.