Wolff's law and injuries

The last 2 podcasts have discussed ways to help time date injuries with MRIs.  We talked about modic changes, degenerative changes, and subjective radicular pain.  Today I want to focus more on changes to the bone surrounding injuries.  I want to go over Wolff’s Law and 2 separate research articles. 

Wolff’s Law came out in the 1800’s and says Bones will adapt to the loads under which it is placed.  One of my favorite examples of Wolff’s Law is loss of bone density in astronauts after being in outer space for an extended period of time.  On earth we have gravity that is constantly placing forces on our bodies and this helps the bones grow, but once the force is taken away the bone density will decrease. 

We talked in prior podcasts about the mechanical changes that occur with disc herniations.  Once a disc herniates it will over time loose height.  This places the vertebra above and below closer.  The endplates and facets all function differently after a herniation.  This places new loads on the bones.  These new loads will lead to bone growth called osteophytes. 

The first study I want to go over today is  “The numerical simulation of osteophyte formation on the edge of the vertebral body using quantitative bone remodeling theory” by Gone He and Zhu (Zjoo) xinghau (zingwha) in the spine Journal 2006.    This study showed that osteophyte formation is an adaptive process in response to a change in mechanical environment.  This study showed that osteophyte formation is accelerated by changes to the bones in trauma.  They reported quote “The main pathology of osteophyte formation was associated with the structural deterioration of intervertebral discs” end quote.

This shows that changes in vertebral discs is the main cause of pathology and will cause osteoarthritis.  They went on to show that these osteoarthritic changes will not be seen clinically for at least a half year.  This means that on MRI or x-rays we will not see osteoarthritic changes following trauma for at least 6 months.  This gives the body time to adapt to the new forces placed upon it.

Now lets say we just got an MRI for a patient in a MVC and we see a disc herniation.  Is the herniation focal (remember degenerative old disc damage is circumferential).  Are there modic changes surrounding the disc (Type 1 would indicate a new injury).  Is there a loss of disc space height (loss of disc space height will take time after trauma).  Are there osteophytes surrounding the disc herniation?  We would not expect any osteophytes to surround a new disc herniation for a minimum of 6 months after the MVC. 

The lack of osteophytes can really help time date an injury.  It is possible to have an old injury with osteophytes and a new injury superimposed upon it.  This makes time dating injuries with MRI much more difficult.  Remember it is important to know all the different characteristics of a new disc herniation to help time date difficult cases. 

Todays first study showed that this bone remodeling process is caused by altered forces and will continue until the bone reaches an equilibrium.   This study showed that osteophyte formation will halt the process of disc slipping. 

I’ve always said that osteophytes from when a joint has too much movement, not enough movement or abnormal movement.  Today’s study brought up another important cause of osteophytes and that is inflammatory conditions.  We can have autoimmune diseases such as rheumatoid arthritis and psoriatic arthritis that can cause osteophytes, but for the most part this will be known and more wide spread. 

How fast to osteophyte grow after altered mechanics following an injury?  This study showed that formation rate varies per person and injury type.  They make note that mechanical changes caused by disc damage is associated with higher formation of osteophytes. 

The second study I want to go over today is   Effects Induced by Osteophytes on the Strain Distribution in the Vertebral Body Under Different Loading Configurations published 2021 in the frontiers in bioengineering and biotechnology by Daniele Marras et al.  I often see and hear reports of elderly people having normal osteophytes for their age.  This brings up the question of is osteophyte formation caused by age.  This study showed that osteophytes are seen in 20-30% of the elderly population.  That means that the vast majority of people should not have osteophytes and that there is no normal osteophytes for elderly people. 

With age we do increase our risk of having injuries that alter the mechanics of a joint and lead to osteophytes.  This study reported that osteophytes will typically grow by 4% per year.  This study agreed that the overall consensus seen in the literature is that osteophytes are formed by altered mechanics typically the intervertebral discs due to Wolff’s law and what they called quote “bony adaptive remodeling” end quote. 

To summarize: this podcast covers part of time dating injuries with MRI.  Keep in mind that injuries typically alter the mechanics of a joint.  In particular injuries to intervertebral discs will alter the mechanics of the vertebra above and below.  As we covered today once a disc herniates, we will have some osteophyte formation.  This osteophyte formation will start instantly after the mechanics of the joint have been altered, but not be seen on imaging for a minimum of 6 months.  Even at 6 months we will likely see very mild osteophyte formation. 

Real world example

I have had a lot of patients like today’s example.  I have a patient in their 60’s with no history of prior back pain.  They get in a MVC and have back pain with radicular complaints.  I order an MRI and we see a disc herniation.  The disc herniation is classic for a new injury.  There is a focal herniation, no loss of disc space height, no osteophytes, and often have type 1 modic changes surrounding the disc.  These are all indicators of a new injury. 

The adjuster for the insurance company will often try to deny the claim or will not offer a reasonable settlement.  The response is that a certain level of degeneration or disc damage will be seen in the elderly population and that this is not a new injury.  They will often have a radiologist that will state normal level of degeneration for the patient’s age.

As seen on todays study only 20-30% of the population will have osteophytes.  As seen on today’s study these osteophytes will grow slowly over the years following damage to a disc.  These osteophytes will come after disc damage, but as seen today will take a minimum of 6 months to be seen on MRI or x-rays. 

So, the adjuster and radiologist clearly have no logic in their argument.  If there is disc damage and it is old and due to age, then we would see osteophytes surrounding the disc.  The lack of osteophytes surrounding disc damage is almost a sure give away that the disc damage is new.    

I see this argument all the time from insurance companies. This is an easy argument to win with objective x-rays and MRIs and an understanding of Wolff’s law.  On the other side of the equation, I have seen physicians report that a patient has new disc damage when we have the opposite.  We have  a circumferential disc bulge, loss of disc space height, moderate osteophyte formations surrounding the disc and a past history of back pain. 

Hopefully today’s study helps you understand the role Wolff’s law and boney remodeling plays in time dating an injury.  Keep in mind that this is just one part of the picture and when time dating an injury, we need to look at all options.  I will continue to share ways to time date injuries with MRI over the next few podcasts.

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