At Dynamic Disc Designs, we believe research to be the foundation of our spine models so practitioners in musculoskeletal health feel confident in the use of an accurate model while they educate patients about their findings.  Historically, models have been inaccurate and most critically, static, making it very difficult for the doctor to be convincing to the patient in the accuracy of diagnosis.

Research is at the roots of any practice. It fuels practice guidelines and directs both the patient and practitioner down the best path of care. Our models help support that voyage. We have worked hard to bring the best to practitioners of musculoskeletal science by scouring databases of spine science, to arrive at the most accurate model for teaching possible.

With over 1000 papers read in full text, Dr. Jerome Fryer leads the way by making sure our models are keeping up to the standards of best evidence. Weekly literature searches on keywords that surround musculoskeletal health are at the core roots of Dynamic Disc Designs.

Dynamic Sitting Exercise

Goal of the Study?

The objective of this study [1. An Evaluation of an Innovative Exercise to Relieve Chronic Low Back Pain in Sedentary Workers] was to examine the effectiveness of a unique supported dynamic lumbar extension with the abdominal drawing-in maneuver (ADIM) technique on stature change, deep abdominal muscle activity, trunk muscle fatigue and pain intensity during prolonged sitting in chronic low back pain (CLBP) participants.


Why are they doing this study?

Low back pain (LBP) is a global issue among the working population. In Thailand, where this study is based, the prevalence of LBP across various occupations is approximately 83%, and 60% of workers in call centers have reported that their LBP is aggravated by sitting during the workday. 

Previous research has demonstrated that continuous sitting results in trunk muscles’ contraction, causing muscle fatigue and reducing muscular support to the spine. This increases stress on ligaments and intervertebral discs, ultimately leading to LBP. Existing research, such as that by lead author Jerome Fryer (the CEO of Dynamic Disc Designs Corp.) et al. (2010), has demonstrated the value of the dynamic sitting exercise on restoring disc height. Moreover, the ADIM technique has been shown to be effective in reducing the spinal lumbar load in patients with chronic LBP. 


What was done?

This is the first study investigating the combined use of a supported lumbar extension with the ADIM technique on stature recovery in CLBP patients.

They recruited 30 patients (15 males and 15 females) between the ages of 20-39 years old. All participants included had CLBP lasting more than 3 months, had low to moderate pain levels and reported sitting for at least 2 hours at work.

The participants were randomly assigned to one of two groups: 1) control – sitting without exercise; 2) sitting with supported dynamic lumbar extension with the ADIM technique. The control group sat for a 41-minute testing period. The intervention group sat in a neutral posture for 27 seconds; at the 28th second, they straightened their lower back and drew in their lower abdomen and extend their lumbar spine with their upper limbs supported to transfer the spinal load to the upper limbs, with their chest up slightly and chin in for 5 seconds. Participants were then repositioned to a neutral position and relaxed their lower abdomen for 3 seconds. This was completed 3 times over the 41-minute sitting period.


What did they find?

This study found that a dynamic lumbar extension with the ADIM technique protected from the detrimental effects on stature change and deep trunk muscle fatigue that can result from prolonged sitting. They found the intervention significantly reduced stature loss compared to the control group. Additionally, they found that this combined approach prevented an increase in pain intensity during prolonged sitting in people with CLBP. 



This study has several limitations, including the use of young participants, setting the study in a laboratory rather than the workplace, self-reported data, lack of consensus on body positioning, and limiting the findings to immediate effects rather than long-term outcomes.


Why do these findings matter?

Clinicians can implement this intervention for patients who sit for long periods of time as a way to prevent LBP problems. 

degenerative spondylolisthesis model

Goal of the Study?

In this paper 1, the authors review the general principles of degenerative spondylolisthesis, including the diagnosis, characteristics, management and treatment.


What is degenerative spondylolisthesis?

Degenerative spondylolisthesis results from the progression of degenerative changes in the intervertebral disc (IVD) and facet joints that lead to destabilizing one or more vertebral segments. The term degenerative spondylolisthesis was first used in 1964 by Newman and was initially related to slipping of the anterior vertebral body in the lumbar region of the elderly female population. Spondylolisthesis was further classified in 1963 by Wiltse, Newman and Macnab into six categories, with degenerative spondylolisthesis defined as Class III.



Who does it impact and what are the symptoms?

Degenerative spondylolisthesis predominantly impacts elderly female patients with a ratio of 5:1 compared to men and is generally found in those over 50 years of age. Black women are three times more likely than Caucasian women to develop the condition. While there has been no correlation between body mass index (BMI) and degenerative spondylolisthesis in men, there is a significant relationship between BMI and the development of L4 listhesis in women. 

In degenerative spondylolisthesis, vertebral slipping usually occurs in the L4-L5 and rarely exceeds 30% of the vertebral body’s anteroposterior diameter. This condition may be asymptomatic, and there is no clear relationship between symptoms and the degree of slipping. However, the degree of degeneration does increase the risk of progression to lumbar spinal stenosis and the possible presentation of clinical symptoms. When there are symptoms, the most common is low back pain, with or without radicular pain. Neurogenic claudication occurs in 75% of patients. As slipping progresses, facet hypertrophy, thickening of the yellow ligament, and disc bulging can increase compression and sometimes trigger cauda equina syndrome symptoms. This can then disrupt motor and sensory function to the lower extremities and bladder.  


Diagnosis and Treatment?

Most often, radiography is the first approach to diagnosis, with a standing lateral radiograph to evaluate instability in the flexion and extension. If neurological symptoms are present, an MRI is used as this tool can assist in evaluating the spinal cord and nerve roots and the assessment of disc degeneration. 

First-line treatment generally includes pain management with anti-inflammatories and analgesics and, or physiotherapy. Surgical intervention is only required on approximately 10-15% of patients. 


Lumbar Disc Model

Goal of the Study?

In this review 1 the authors evaluated the efficacy of physical therapy interventions such as electrotherapy, exercise therapy, lumbar traction and manual therapy in the management of lumbar prolapsed intervertebral disc (PIVD).

Why are they doing this study?

Lumbar PIVD (or herniation) is one of the most common musculoskeletal disorders affecting approximately 10% of the population. It has a significant impact both individually and societally as it is associated with disability, pain and a loss of productivity. Currently, both surgical and non-surgical approaches are used for treatment. However, recently there has been a push to reduce the need for spinal surgery as this approach has several complications, including pain, infection and, in some cases, post-operative paralysis. Unlike surgical interventions, conservative approaches such as physical therapy do not have such complications and are cost-effective. However, there is a need to understand the efficacy of physical therapy for lumbar PIVD.


What was done?

The authors did a systematic review and meta-analysis using randomized controlled trials (RCTs) focused on the efficacy of physical therapy management in lumbar PIVD. They included all trials published in English from the beginning to January 2019. They then used specific software to review the included studies. In total, 2594 studies were collected from the database queries, with 11 fitting the selection criteria; however, six were excluded as they did not contain sufficient data.


What did they find?

This meta-analysis showed statistically significant improvement in pain and disability after physiotherapy treatment in patients with lumbar PIVD, compared to control. While physiotherapy interventions did increase single leg raise (SLR) range, the finding was not statistically significant compared to the control group. 

Overall, the researchers found that physiological and biomechanical interventions such as correction of the displaced disc, decompression, opening of the foramina and increase in intervertebral space may lead to improved spinal mobility, contributing to a reduction in pain and disability.


Why do these findings matter?

Providing evidence-based care for LBP is important for patient quality of life and reducing the economic and societal burden of illness. 


facet osteoarthritis, facet joint pain

Goal of the Study?

The objective of this study 1 evaluates the feasibility of sensory mapping of lumbar facet joint pain in patients scheduled to undergo radiofrequency (RF) denervation. 


Why are they doing this study?

Lower back pain (LBP) is a widespread condition that can result in chronic pain.  While there are many treatment approaches, one of the most established interventions uses diagnostic blocks to identify the source of nociception. Though many parts of the back can be involved in LBP, facet joints are among the most common sources contributing to back pain. Most often, for treatment in clinical practice, the medial branches are anesthetized to establish the diagnosis of facet joint pain. RF denervation of these nerves, which is a process to stop nerves from transmitting pain, is used as pain management. 

The authors argue that while this approach has been well established, the use in a clinical setting has been questioned due to the high rates of false-positive (30%), cost-effectiveness and lack of standardization and anatomical variation. For this reason, the authors hope to develop a strategy for a more precise identification of the nerves involved in LBP.

facet capsule nerves, facet joint pain


What was done?

In total, they had 15 participants for this study. After written consent, participants completed a pre-procedure pain diagram and rated their pain on a scale of 1-10. The researchers used a standard procedure for RF denervation, including a single diagnostic block and imaging in determining cannula placement. To reproduce the pain in patients with chronic back pain, medial branches were stimulated using 50Hz electrical stimulation to determine the threshold. This was then increased threefold to achieve the suprathreshold stimulation, after which participants were asked to map their pain and compare this against the initial pre-procedure pain diagram.


What did they find?

A total of 71 nerves were scheduled for RF denervation. Sensory stimulation was successful in 68 out of 71 nerves using 50Hz electrical stimuli. All 15 participants reported either pain or paraesthesia (tingling or prickling) during suprathreshold stimulation, and 14 (93%) reported complete coverage of their usual painful area. In one participant, the upper lumbar pain was not covered by suprathreshold stimulation. For 60% of the participants, they reported pain/paraesthesia outside of their normal pain area during suprathreshold. Overall, in their population, 7.5% of the denervated nerves did not contribute to pain transmission. The average sensory detection threshold was 0.3V, with the suprathreshold was 0.6V.


Why do these findings matter?

Using suprathreshold stimulation, lumbar facet joint pain can be mapped and offers objectivity by reproducing patients’ back pain. This approach can also improve patient safety and experience by limiting RF denervation to nerves involved in pain transmission. This can improve patient safety and experience. 

Degenerative disc disease

In this paper 1, the authors provide an overview of the causes, symptoms and treatments of cervical degenerative disc disease (DDD).

Overview of the intervertebral disc (IVD)

An intervertebral disc (IVD) acts as a shock absorber between each vertebra in the spinal column and is critical for spinal mobility and stabilization. It comprises two parts: the annulus fibrosus (AF) and the nucleus pulpous (NP). The AF is made up of type 1 collagen in layers and forms a strong shell for the NP. The NP has a gel-like consistency composed mainly of water but also contains type II collagen and proteoglycans.

Dynamic cervical model, cervical disc disease

Cervical disc degeneration model

Cervical Degenerative Disc Disease: who, what, why?

Cervical disc degeneration is a normal part of ageing, starting in the late teens and continuing through life. The prevalence of cervical DDD increases with age regardless of whether a patient has symptoms. Some environmental and genetic factors can predispose individuals to the development of this disease, including handheld electronics, contact sports and prior surgeries.

Typically, changes occur within the NP first, followed by progressive degeneration of the annulus. With ageing, the disc loses water, becoming less compliant. This leads to a decrease in disc height and collapse. These changes can increase the force exerted on the degenerated NP, which is then transmitted to the AF, causing it to tear and fracture. This may lead to a herniation where the NP is pushed out of the AF. 

The spine segments become hypermobile leading to instability, stiffness and a decrease in motion of the spine. While not all patients with cervical DDD experience pain, it is one of the most common findings.



Making a patient history is important to ensure that the symptoms (if they are present) result from degeneration and not other conditions that have similar symptoms, such as carpal tunnel syndrome or rheumatologic disorders. Additionally, a comprehensive neurological assessment must be done, testing upper and lower extremities, gait, balance, reflexes and range of motion.

Most commonly, patients will present with axial neck pain and difficulty moving. Some may have headaches, shoulder pain or pain on one side of the back, arms or legs that can worsen with movement. Other signs and symptoms may include changes to deep tendon reflexes, muscle atrophy or weakness. 

Most often, the earliest and most significant degeneration occurs at C5-C6. However, different parts of the cervical spine have symptoms in different areas. For example, with a herniation at C7, patients will often complain of pain from the neck radiating to the forearm, palm, and middle finger. With the C6 nerve affected, patients may present with pain radiating to the neck, shoulder and down to the thumb and index finger.

As cervical DDD may be asymptomatic, degenerative changes might only be seen with CT, X-ray, or MRI imaging. Laboratory testing can help in diagnosis by ruling out infections, autoimmune arthritis or a metabolic disorder.



The focus of treatment for cervical DDD is to decrease pain, improve function and minimize symptoms. Generally, treatment begins with a nonoperative approach but can lead to surgery.

Nonoperative treatments range from rest, activity changes, physical therapy such as ROM and isometric activities, and medications including anti-inflammatories, muscle relaxants and steroids. 

For patients that do not respond to non-operative approaches, surgery may be required. This is particularly the case for patients in pain, experiencing neurological symptoms or patients with cervical myelopathy. Several surgical options are depending on the case. One option is decompression surgery, which can take many forms. For example, these procedures may involve removing a disc (or discs), may include the fusion of different segments or may involve the insertion of a plate to increase stability and mobilization. 

The pain and disability often associated with cervical DDD can significantly impact the quality of life for patients both personally and professionally. Therefore, a timely diagnosis and support from other health care professionals and patient education are key to minimizing negative outcomes. 

Centre of Rotation

Goal of the Study?

In this study 1, the authors investigated the flexion-extension range of motion (ROM) and centre of rotation (COR) of lumbar motion segments in a large population, as well as the relationship between lumbar movement and sex, age and intervertebral disc degeneration (IVD).

Why are they doing this study?

Research on the in vivo motion of the spine has a long history. However, many of these studies have used non-invasive technologies with inherent limitations impacting their accuracy and precision. Moreover, many studies have included a lower number of subjects, preventing the data’s ability to represent the general population.

The authors argue that the use of radiographic techniques in this study helps to overcome these limitations as the images allow for better visualization of each vertebra and movements of the lumbar segments. Additionally, the use of a large sample size for this study addresses the issue of representation and is the largest study to date looking at in vivo lumbar motion. 

What was done?

The researchers did a retrospective study looking at the lumbar spine radiographs in full flexion and extension for 602 patients, with the age and sex documented for each one.  Additionally, they used MRI scans of 354 patients. 

All spinal levels between T12-L1 and L5 – S1 were analyzed, resulting in 3612 lumbar motion segments from the radiographic images. They also examined 2124 images from the MRI scans looking at disc degeneration. ROM and COR were calculated for all lumbosacral segments using the software. They then examined the associations between motion and age, sex, spinal level and disc degeneration.

What did they find?

The median ROM in this study was 6.6 °. The researchers found an association between age and ROM, with older individuals, have lower ROMS. They argue these findings clearly demonstrate a relationship between age and lumbar spine flexibility independent of any signs of spinal degeneration. They also found that lower ROMS were associated with disc degeneration. However, they did not find any association between sex and ROM.   

In this study, they did not find an association between the COR and the spinal segment’s position. The most common COR was at the centre of the lower endplate of the IVD or slightly lower. With degeneration, particularly severe degeneration, they found the COR location spread randomly around the centre of the intervertebral space.


One of the main limitations of this study was the sole focus on the lumbar spine’s flexion-extension motion rather than including information on movements of different areas of the back. 

Why do these findings matter?

This study comprises the largest examination of the in vivo lumbar spine in flexion-extension, paying attention to age and spinal degeneration issues. Understanding the relationship between age and spinal mobility provides patients and doctors with information to better treat back pain and instability.

Facet pain

Goal of the Study?

The objective of this study 1, is to determine the prevalence of “pure” lumbar Z joint pain.


Why are they doing this study?

The prevalence of lumbar Zygapophysial joint (Z joint) is disputed, with rates ranging from 5% to 45%. The reason for this disparity lies in the use of different criteria for diagnosis. The criteria are focused on relief of pain after a diagnostic block, an injection of numbing medication into 1 or more small joints on each side of the vertebrae. However, these criteria can range from 50% to 80% to complete pain relief after a diagnostic block. Additionally, some diagnostic criteria focus on relief from pain after a single diagnostic block, with no controlled blocks. However, the researchers argue that for diagnostic blocks to be valid, pain must be abolished whenever an active agent is administered, and the use of repeat blocks provides validity.

The authors contend that no research has been able to determine the prevalence of “pure” lumbar Z joint pain, defined as complete relief of pain following a placebo-controlled diagnostic block. 

Facet pain


What was done?

All 206 patients for this study came from a private practice where they were referred for back pain. To be eligible, they had to have back pain longer than 3 months, with symptoms compatible with a potential diagnosis of lumbar Z joint pain. Patients with imaging that pointed to tumours or infections were excluded from this study, as were patients who were pregnant or had pain in the lower limbs.

The researchers used two protocols for this study. The first protocol was a placebo-controlled local anesthetic comparative blocks. For this, each patient received a local anesthetic on two occasions and normal saline on one occasion.  For the second protocol, patients could receive the same or a different local anesthetic on two or three occasions and normal saline on one or no occasion. Using saline as a placebo showed whether patients could tell the difference between an active control from a placebo.

Patients were considered to have Z joint pain if they had complete relief of pain three times when a local anesthetic was used, if they had complete relief of pain two times when the anesthetic was used, and if they had no relief, saline (the placebo) was used. 


What did they find?

The majority of patients did not report any pain relief from the initial block and therefore did not satisfy the criteria for lumbar Z joint pain. Only patients who had complete relief of pain from their initial block were eligible to continue. 

Of eligible patients, the researchers found that 45% of patients in group 1 and 30% in group 2 did not get relief from the second block. Moreover, 20% of patients in group 1 and 3% in group 3 had no relief from the second block but were completely relieved by the placebo. Results for the two groups combined showed a prevalence rate of “pure” lumbar Z joint pain of 15%. This is much lower compared to when a diagnostic criterion is less stringent. Moreover, they did not find any statistically significant differences between the two groups for gender and age. 


Why do these findings matter?

Determining the appropriate diagnostic criteria for lumbar facet pain has important implications for patients who need to have the right diagnosis and treatment for their pain.