vacuum sign

Vacuum sign is a common radiological finding. It is also referred to as a vacuum phenomenon and often associated with degenerative spinal discs, knee joints, hip joints, and shoulder joints.  Degenerative spondylolisthesis is a spinal condition whereby one vertebra slips on another. However, it is sometimes difficult to ascertain whether this slippage is stable or not. A more than 4mm movement defines instability, but some have indicated only 2mm as clinically significant.

degenerative spondylolisthesis model

Degenerative Spondylolisthesis Dynamic Disc Model

In a research paper published in World Surgery, 1 a group of authors looked at the vacuum sign in the facet joint as an indication of degenerative instability of the spine. They wanted to investigate the relationship between the vacuum facet phenomenon and lumbar instability. Why, you may ask? More and more research is directing spine researchers to the cause of pain and disability to the imbalance of motion of the individual vertebral segments of the spine. Some have coined this motion sharing.

Each vertebral motion segment consists of two vertebrae, and a disc should have a certain stiffness level. That is, it should move similar to its adjacent segment above and below in the spinal column. For this study, they looked at L4 on L5 (which is a prevalent spinal level to degenerate with age) and used flexion/ extension X-rays in both the fully bent forward (flexion) and the fully bending backwards (extension) with degenerative spondylolisthesis. Additionally, when available, they also looked at CAT scans of these same patients. To determine the slippage degree, they used a dynamic motion index to measure the degree of slippage.

In a total of 67 patients examined, 35 patients had vacuum signs on their CAT scan, and 32 patients did not. The degree of slippage appeared to correlate with the vacuum sign as well. That is, the more the vertebrae had slipped forward, the more likelihood of the presence of the vacuum sign. With this, the authors concluded a linear correlation between the degree of slippage and the presence of vacuum sign.

Commentary by Jerome Fryer

Vacuum sign or vacuum phenomenon is often considered an incidental finding. However, based on the modelling research I’ve done, I believe that the vacuum sign can be a clue into joint mechanics’ stiffness. In 2017 I published an article related to the cracking event we are familiar with, and in there, I believe in having revealed the vacuum phenomenon. In the presence of cavitation, a joint will have less stiffness, and in time I hope we can collectively use these radiographic findings to help us determine which joint requires more stability in the treatment of them. JF

facet osteoarthritis

Facet osteoarthritis pain is common and thought to be a significant contributor to back pain in the US. Within the United States, it costs 100 Billion dollars annually to combat this endemic problem. However, back pain can originate from many anatomical structures, and the facet joint is only one of them but thought by many as significant. Other common pain structures are the intervertebral discs in the case of disc bulges, disc extrusions, disc protrusions and frank nuclear sequestration. There are also more severe causes of back pain like aneurysm and other organ pathology, so it is crucial to have a professional look carefully at the diagnostics of each case.

In the case of mechanical lower back pain (others use the term non-specific lower back pain), the facet joint garners good attention. The word ‘facet’ comes from the French facette (12c., Old French facete), diminutive of face “face, appearance” and are two anatomical structures that reside behind the intervertebral disc.

Facet osteoarthritis

Modeling facet osteoarthritis is tricky because of the complexity of motion at the spinal level. The intervertebral disc height plays a role with respective facet compression because it resides on the front of the spinal motion segment. It is this compression thought to be contributing to back pain.

Clincally, facet osteoarthritis pain is often unilateral in nature

In a study conducted recently 1, researchers worked to induce facet joint arthritis by creating compression with a spring. Over time the researchers found the increased expression of interleukin‑1β and tumour necrosis factor‑α expression. In other words, with more compression elapsing over time, the more the expression of the molecules related to many low back pain patients.

This is an important study linking the mechanics of compression and the associated physiology of molecules, which are thought to be markers of back pain patients.

At Dynamic Disc Designs, we have developed models to help explain the associated compression of facet joints as it relates to disc height loss and gains. We are committed to bringing the best in modelling. Explore our website for more.


A very recent study 1 published in the ‘Journal of Biomechanics’ analyzed the dynamic interactions present between the human lumbar intervertebral motion segments during flexion and return. It wanted to help further understand the components linked to disability and pain.

What Was the Context?

Low back pain or LBP causes millions of people (around the globe) to experience physical, psychological, and economic stress. That’s why research continues to develop a more efficient means of LBP management.

Understanding of the biomechanics involved in back pain has increased due to continuous dynamic multi-segmental studies of the human lumbar motion. Such knowledge is required before attempting in vivo studies of loading during bending tasks.

However, the readings collected during bending tasks tend to be variable, and establishing normative values is challenging. That’s why, during bending tasks, there’s a need to further explore the interactions present between motion segments.

If one wants to model contemporaneous kinematics and loading for estimating relative intersegmental stresses occurring during bending motion, certain factors need to be studied. These factors include continuously measuring the proportions of the flexion as well as return motion that’s accepted by individual levels. The dynamic interactions between them, during bending, needs to be measured, too.

The current study set out to analyze the adjacent lumbar level’s motion contributions during flexion (active weight-bearing) and the return protocol while using quantitative fluoroscopy or QF.


Demonstrate flexion using LxH Dynamic Disc Model

What Was the Methodology?

The study involved a total of 8 patients (5 males and 3 females). Each of them had chronic non-specific LBP. An obvious mechanical disruption wasn’t present in the patients. All of them went through QF during the flexion as well as return motion. The patients were matched with 8 healthy controls. The same tasks had been performed by the controls, too.

The dynamic motion sharing of segments were calculated throughout the person’s bend and return. The segments were from L2 to S1.

Furthermore, the statistical analysis included the SPSS’s Shapiro Wilk test, independent t-tests, and the Mann-Whitney U.

What Was Concluded?

The results revealed that there were no significant differences between the groups with regards to age, weight, height, or BMI. However, the asymptomatic controls did show higher ranges of intervertebral motion with the only significant reading being at the L5-S1 level. The patient population showcased a significantly less range of motion at the L2-S1 level.

In simple terms, the results revealed that the patient and control groups displayed consistent yet non-significant differences in motion sharing patterns.

According to this study, the results could offer an advantage to help identify components that have a link to disability and pain. For example, this study shared that patients and controls have significant differences in their Average Motion Share or AvMS at the L3-L4 level. Take note; the IV-RoM data was unable to reveal these differences.

The said differences could be due to involuntary muscle activity, bending strategy, or passive tissue restraint.

Hopefully, the current data could help others conduct further research while also covering the muscle’s electrical activity, oxygenation, kinematics, and loading.

cartilage damage and osteoarthritis

A very recent study 1 in the journal ‘Osteoarthritis and Cartilage’ has offered some helpful results. It focused on OA-induced pain in relation to mechanical joint loading and cartilage damage.

Why Conduct Such a Study?

Osteoarthritis or OA is defined as a degenerate joint disease that involves cartilage damage and the loss of cartilage. It tends to physically, emotionally, and economically impact numerous people around the world. And even though a lot still remains to be understood, progress has been made to look at osteoarthritis with a multifactorial lens.

Due to multiple joint tissues having identified pathologies as well as their relationship with OA, many have questioned the role pathologies play with regards to the clinical presentation of pain associated with OA.

When it comes to patients, the clinical presentation of their pain happens to be the most problematic oesteoarthritis symptom. And much remains unknown about knee pathology’s link with OA-related pain.

The current study’s primary objective was to better understand the complexities of the pain-structure relationship. The team used MJL or the mechanical joint loading model of OA for investigating knee pathology as well as nociceptive behavior.

What Was the Methodology?

The study used the MLJ model for inducing OA in the right knees of male mice. These mice were 12-weeks-old. A two-week loading regime was administered through an electronic testing machine.

A total of 36 mice had OA induced. Another batch of 36 mice (with no induced OA) acted as non-loaded controls. The team sacrificed separate groups of non-loaded and loaded mice during the one, three, and six-weeks points of post-loading for post-mortem analysis.

The study conducted behavior analysis before loading. At weeks one, three as well as six post-loading, nociception was verified (a day before the mentioned sacrifice points).

Coming to the post-mortem samples, half were used for µCT analysis, OA as well as synovitis grading. The other half ended up being used for nerve analysis.

The collected data was analyzed using the GraphPad Prism. Statistical analysis also included repeated two-way ANOVA, parametric two-way ANOVA, and Levene’s test.

Early cartilage damage

The Professional LxH Dynamic Disc Model can be used to show early cartilage damage.

What Were the Results?

According to the results, increased mechanical hypersensitivity paired with altered weight-bearing was shown by loaded mice. The initial ipsilateral cartilage lesions (that were at the one-week post-loading point) grew worse at the three and six-week points. The observed increase in lesion severity correlated with the development of mechanical hypersensitivity.

Furthermore, loaded mice also showed increased synovitis when compared to the control mice at the one-week post-loading points. However, the said increase returned to normal during the third and sixth week. Also, cortisol levels increased only during the one-week post-loading timeline.

Take note; there was no change in the subchondral bone integrity and nerve volume.

What was Concluded?

The study indicated that even though initial stress reaction, as well as local inflammation, was induced by loading, the said processes aren’t directly deemed responsible for the observed nociceptive phenotype.

However, allodynia induced by MJL is mainly associated with the cartilage lesions’ OA-like progression.

The team also noted that more still needs to be done to improve the understanding of how nociceptive behavior is induced by cartilage damage as well as which types of tissue pathologies could potentially play a role in pain associated with OA.

The current study’s team hopes that their current research might help others analyzing the MJL model’s pain-structure relationship.

facet, lumbar spinal stenosis model

A retrospective CT scan and medical record review [ 1. The Prevalence of Asymptomatic Cervical and Lumbar Facet Arthropathy: A Computed Tomography Study] of 50 patients with no history of spinal pathology used a four-point scale to grade the severity of evident arthritis and found that arthritic spinal changes were frequently evident—even in asymptomatic patients. The incidence of these changes corresponded positively with aging and was more prevalent in scans of the lower lumbar spine.

What’s at Stake?

Chronic neck and lower back pain affect between 66 and 84 percent of the U.S. population and is responsible for approximately 87 billion dollars of lost income and medical expenses annually—a figure that is only surpassed by the yearly wage loss and expenditures on diabetes and heart disease.

Diagnosing CNP and LBP is problematic due to the number of possible factors—including dysfunction of the intervertebral discs (IVD’s), facet joints, spinal nerve roots, ligaments, and muscles surrounding the spine— that can contribute to these disorders.

Some studies have indicated that facet arthropathy, rather than nerve root irritation, cause axial neck and back pain. The increase of CNP and chronic LBP in aging populations may be associated with a progressive degeneration of the IVDs that subsequently increases facet joint loading and creates favorable conditions for the development of facet arthritis. Facet joint blocks by injection have been shown to be ineffective in providing symptomatic relief in up to 90 percent of patients diagnosed via CT scan in previous studies. This suggests that scan observations alone may provide prevalent false positive results and therefore cannot be a reliable diagnostic tool.

Disc replacement may alleviate pain and restore spinal fluidity of motion, but the presence of facet joint arthritis is considered a contraindication to this surgical procedure. Understanding more about facet joint arthritis can assist practitioners in developing effective treatment plans for LBP and CBP patients—including the determination of which patients may be ill-suited for IVD replacement. This study of asymptomatic patients was conducted with the aim of understanding the prevalence of facet joint arthritis to help quantify the percentage of patients for whom facet injections are ineffective.

The Study

An approved review of archived CT scans of 100 total non-spinal patients was conducted using scans of 500 cervical facet joints from 50 subjects and 500 lumbar facet joints from an additional 50 subjects. All of the patient subjects’ medical records and scans were previously analyzed and evaluated as spinally asymptomatic for the purpose of this study.

The images were each graded and evaluated by an orthopedic spinal surgeon, neuroradiologist, and trained medical student on an independent basis. An additional three observers with separate clinical backgrounds also conducted a review of the facet joints to ensure no bias existed due to training backgrounds of the first group. The severity of facet joint arthritis symptoms were graded and statistical analysis was applied across different subject age groups. An average of all groups was then calculated using a coefficient.

The Results

Cervical Data

Of the 500 cervical facet joints from 50 patient subjects studied, asymptomatic cervical facet joint arthritis was evident in more than 33 percent of the scans. Nearly 60 percent of these patients showed only mild narrowing of the joint space and irregularities. About half of the subjects over the age of 40 demonstrated signs of arthritic changes. There were fewer “normal” or non-degenerated facet joints in patients in the aging (over 45) subject population. The prevalence of degenerative changes increased at all cervical levels in the aging subjects.

In all age groups, greater changes occurred more prevalently in the caudal spine area. At the C6-C7 spinal level, 78 percent of patients over-40 demonstrated facet joint arthritis. At the C2-C3 level, however, only 29 percent of the patients of the over-40 age group showed arthritic changes.

Lumbar Data

Thirty-seven percent of the patient subjects in the lumbar data group demonstrated asymptomatic lumbar facet joint arthritis, and up to 2/3 of these subjects showed grade 1 changes. As with the cervical data set, the lumbar set demonstrated a positive correlation with aging (over 45) and arthritic changes and degeneration of the facet joints. Caudal levels (L5-S1, for example) were more likely to show increased arthritic degeneration compared to cephalad levels. Only 12 percent of the patients over 50 years old showed changes at the L1-L2 levels, while 54 percent demonstrated these changes at the L5-S1 level.

Lumbar Spinal Stenosis Model


This study found a statistically significant positive correlation between aging and asymptomatic arthritic changes and degeneration of the facet joints of patients over the age of 45. These changes were evident at all spinal levels but were most prevalent in the lumbar facet joints and the C2-C3 and C6-C7 levels of the caudal spine. Approximately one third of the patient population in this study were found to have evident facet joint arthritic changes that were asymptomatic and associated with aging. When considering motion-preserving spinal implants, the age of the patient should be considered, as the treatment may not be as effective in patients over the age of 45, who are more likely to have or develop asymptomatic facet joint arthritis—a contraindication of the implant procedure.





arthritic changes, lumbar models, cervical models

Arthritic changes are very common. They are often related to a person’s pain with neck pain as one of the highest ranked common causes of disability. In this specific research article 1, the authors looked at the micro-details of neck synovial joints. With osteoarthritis known to be related to neck pain, they were looking to reveal higher anatomical detail and they were also curious about whether men or women have more of these problems.

With both neck and back pain being multifactorial (which may include both psychological and social aspects) degenerative changes within the synovial joints play a significant structural role with the development of spondylosis. This is a general term to describe a disorder of the musculoskeletal system with an emphasis on joint space narrowing, intervertebral disc height loss and frequent formation of bony spurs.

The architecture of the cervical facet joints is quite well known with most of the current knowledge around the smooth (or lack of smoothness) hyaline cartilage to allow the joint to receive and distribute loads in an efficient manner. However, there has not been much quantitative data revealing the anatomy under the hyaline cartilage designated as the subchondral bone. This bone under the cartilage (sub, meaning below and chondral, meaning cartilage) has been of recent interest as there exist nerves in this area that can cause pain. This is thought to be similar to the basivertebral nerve of the vertebral body. The innervation of the facet, however, has ascending fibres travelling through the posterior primary division which can be seen in this Medial Branch Dynamic Disc Model.


modeling hyaline cartilage, models

Hyaline Cartilage Modeling in our Professional and Academic LxH Dynamic Disc Models

basivertebral nerve lumbar model

Basivertebral nerve of a lumbar vertebra.

Previous research has shown that the thickness of the hyaline cartilage is .4mm in women and .5mm in men with the subchondral bone making up approximately 5% of the total cartilage thickness. It is also known that with increasing age the cartilage starts to flake off (called fibrillation) and researchers also coin the stripping of cartilage from the bone, denudation. This means being nude. A joint surface within a covering. Other terms used to describe the break down of the hyaline cartilage is erosion, fissuring and deformation. All in all, the terminology all mean that the hyaline is thinning.

arthritic changes, subchondral, joint, model

Subchondral thickening – arthritic changes

How did they do it?

These researchers looked at 72 recently deceased people and examined their joints. They used microscopes to look closely at the facet joints to help understand the pathogenesis of the arthritic changes.

When they observed the osteocartilaginous junction, the morphological changes included: flaking, splitting, eburnation, fissuring, blood vessel invasion and osteophytes. They looked at the length of the cartilage, the hyaline cartilage thickness, the calcified cartilage thickness and the subchondral bone thickness.

They found that males tended to have more severe degenerative changes described by flaking and severe fissures in the facet cartilage. Click To Tweet

Points of Key Interest

  • this was a study that looked at 1132 unique cervical spine facets from 72 humans
  • males were found to have more degenerative changes of the osteocartilaginous junction
  • the thickness of the calcified cartilage and subchondral bone increased with age whereas the hyaline cartilage decreased
  • the osteocartilaginous junction is particularly important in the pathogenesis of osteoarthritis in the cervical spine facet joints


At Dynamic Disc Designs, we work to bring research to the practitioner so when there is a teaching moment, Professionals are ready to explain pain triggers as they relate to a patients symptoms and movements. Empowering people about their own anatomy helps in the crafting of customized treatment plans for each unique pain patient. Explore our dynamic models and help a patient understand their arthritic changes and what that means to them.

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.


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.


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.