Lumbar AOMSI

We talked on the second podcast about the origins of cervical alteration of motion segment integrity or AOMSI.  If you have not listened to that podcast, I strongly recommend giving it a listen.  Today I want to spend some time talking about origins of the lumbar AOMSI.  I will be using a research article and one text book.

The article is A biomechanical analysis of the clinical stability of the lumbar and lumbosacral spine by IRA Posner et al.  This was published in the spine journal in 1982.  This came out 7 years after the white study on cervical AOMSI.  Once again, his study was published by a lot of surgeons.  This study appears to have been done to determine if the surgeons could justify doing lumbar fusions.  The article starts with quote “The surgeon is often faced with the dilemma of determining whether or not the lumbar or lumbosacral spine is clinically stable” end quote.   The study was done to determine what makes an unstable spine and they reported quote “Instability is a critical one and should be made with as much accuracy as possible” end quote. 

The defined clinical instability as quote “the loss of the ability of the spine under physiologic loads to maintain relationships between vertebrae in such a way that there is neither initial damage nor subsequent irritation to the spinal cord or nerve roots and, in addition, there is no development of incapacitating deformity or pain due to structural changes” end quote. 

This study was done in order to give guidelines and checklists for immediate clinical applications for lumbar spine instability.  Very similar to the White study in 1975 they took several cadavers and preserved motion segments or 2 vertebrae.  They took these motion segments and double wrapped them in plastic bags and frozen at -20 degrees Celsius.  The reported that this method has been shown to not affect the mechanical properties on the motion segment. 

Similar to the 1975 white study they built an apparatus to attach the motion segment and pull the motion segment apart to assess what ligament damage looks like.  Prior to testing each spine was thawed slowly at room temperature in a humidification chamber that maintained 100% humidity at 27 degrees C. 

These motion segments went through a series of flexion and then extension forces until failure occurred.  Failure was defined by sudden and total giving away of the ligaments.  This is similar to the 1975 White study where they showed that there is micro tearing of ligaments and then sudden and complete failure of ligaments.

They tested the different cadavers at different levels.  They tested L1-2, L3-4 and L5-S1.  They brought in a portable x-ray machine to show that the ligaments were damaged and not bone fractures.  This is an interesting concept.  I have had lawyers in depositions ask wouldn’t the bones brake prior to a catastrophic ligament failure.  This is once piece of evidence that supports ligaments can have catastrophic failure without bone fractures. 

They were able to assess the changes in translation of the motion segments once failure or quote “sudden and total giving away of ligaments” end quote.  They were also able to assess for changes in angular motion.  They showed the way to measure translation as draw a line on the superior endplate of the inferior bone.  Then draw a perpendicular line from the posterior superior corner of the lower vertebra.  Then we measure the distance from this perpendicular line to the inferior posterior corner of the superior vertebra.  This is the same method seen in the impairment rating guides.  They used the disc angle for angular displacement.   They were able to take their data and make it possible to read from x-rays. 

They reported that all modes of failure were similar among all specimens.  They showed that there was no significant difference between L1-2 and L3-4.  This is why the impairment rating guides have difference in changes in angular motion once we get to L5.  They showed that the displacements seen on this study can occur in a physiologically loaded intact spine.  They reported that quote “it may be illogical to assume that displacements of this magnitude indicate clinical instability” end quote.  They showed that this displacement can be altered by orientation and thickness of the disc.  The thicker the disc often correlates to additional motion.   Keep in mind that this study showed Quote “Failure in all cases was sudden and complete” end quote.   

I want to cover some of the findings about displacement by using a text book.  The book is Clinical biomechanics of the spine 2^nd edition by Augustus A. White III and Manohar Panjabi.  Chapter 5 covers the instability of the lumbar spine.  They used the study we just went over as well as other studies.  This text book is the origin of the instability or AOMSI in the lumbar spine seen in the impairment rating guides.  Page 354 shows that the lumbar spine is unstable at 4.5mm translation or 15% translation.  This was used in the AMA’s 5^th edition. 

Figure 5-63 on page 355 covers instability seen with changes in angular motion.  The method involves drawing a line on the superior endplates of the vertebra.  The angles are measured in both flexion and extension.  Any lordotic angle is negative and any kyphotic angle is positive.  We take the flexion angle and subtract it from the extension angle.  If the angle is above 15 degrees at L1-L4 then there is potential instability.  If the angle is above 20 degrees at L4-5 then there is potential instability.  If the angle is above 25 degrees at L5-S1 then there is potential instability.  This is the exact method used for the AMA’s 5^th edition in assessing lumbar AOMSI seen with change in angular motion.   

This is also the same method seen in the original AMA guides 6^th edition change in angular motion showing AOMSI in the lumbar spine.  The 6^th edition update requires the exact same measurements for change in angular motion, but added at the end quote “compared with adjacent level angular motion” end quote.  This addition makes no sense in the lumbar spine. 

The AMA guides 6^th edition assess AOMSI in the lumbar spine with translation different than the textbook and the original study.  The text and study reported 4.5mm translation or 15% translation.  The AMA 5^th edition went with 4.5mm translation.  The AMA 6^th edition went with L1-5 8% translation anterior and 9% translation posterior.  For L5-S1 they went with 6% anterior and 9% posterior translation. 

I would assume at this point there may be some confusions about all the measurements, angles, mm, and percentages.  I am hoping this study does a couple things.  I hope it helps you understand some of the origins of lumbar instability or AOMSI.  I hope that there is also an understanding that this type of instability or AOMSI was shown to be sudden and complete failure.  This has been shown with ligament damage that we have micro tearing and then sudden and complete failure.  I hope this podcast helps you understand where some of the numbers used in the assessment and guides comes from.  I also hope this podcast helps you understand that the methods used for assessment have changes over the years.  This change has led to a wide variety of companies doing different types of AOMSI assessments.  This has led to confusion with insurance companies and attorneys.  This confusion has led to no value being added or considered with settlements for a lot of AOMSI cases.       

Real World

I have been doing around 3-4 IME a week right now.  That has given me an opportunity to see a wide variety of patients from all types of injuries.  I just did an IME where the patient had multiple 3^rd degree burns.  After 3 skin grafts, he was placed at MMI and needed an impairment rating.  This type of IME and impairment rating is simple in a lot of ways.  There is no disputing causation in this case.  This was a work injury and he was a mechanic and 300 degree antifreeze drained out of a semi-truck onto him.  No one is disputing the burns were not caused by this injury.  Causation was not an issue.  I was able to include pictures of the burns which showed great detail.  There was no argument as to the extent of the injury.   The impairment rating follows the guides and there was no dispute about the rating.  Future management and ongoing symptoms were not an argument.  This is a straight forward case that probably did not need an IME, but for the worker’s compensation program did need the impairment rating.    

The typical IME is not this straight forward.  Most of my IMEs although not all are from motor vehicle collisions.  I would do a lot less IMEs if the MVCs cases had the same simple results as this injury.  If every MVC the injury was as objectable as the 3^rd degree burns.  These burns were simple to see and very obvious how extensive this injury was.  All injuries if possible, need some sort of picture or visible evidence of an injury.  Often this is not possible with spinal injuries.   Spinal injuries that involve disc damage can be shown on MRI.  With the proper understanding of disc damage and MRIs damage can be shown on pictures.  As I covered in the last 2 podcasts we can show evidence of facet injuries with diagnostic injections.  As covered in today’s podcast we can show pictures of an unstable spine.

  This is the first step to making a MVC case as simple as the burn victim’s case.  We need Objective evidence of injury.  Although the history of lumbar instability or AOMSI is complicated and the measurements have changed over the years if we do it the proper way we can show damage.  The problem we then have is the general population understands instantly how severe the injuries are of my patient with the 3^rd degree burns is , but would not understand the significant injury of lumbar AOMSI.  Not only will the general public not understand the objective evidence of AOMSI in the lumbar spine with x-rays, but insurance companies, attorneys, doctors and patients will struggle to understand the injury. 

This is where I find a deposition or court fun.  Education of what these injuries mean and how they can be seen on imaging can be fun.  We have talked a lot about what this type of sudden and complete ligament damage can mean to patients.  This was covered in my first 3 podcasts.  This was also covered in the 13^th, 15^th, and 16^th podcasts.  This will never be as simple to get others to understand like the burn patient, but can be done. 

The next struggle a lumbar AOMSI case would have that the burn case would not is causation.  If we educated enough and show that in fact the patient does have a visible injury we need to show the cause.  No doubt the hot antifreeze caused burns that needed surgery, but how can we know what caused the lumbar sudden and complete ligament damage. 

Prior medical records and prior injuries are a good starting point to address causation.  Another important aspect to causation is degenerative bony changes.  This was covered in my first 3 podcasts as well as podcast number 6.   All the studies show that ligament damage to this extent will alter the biomechanics of the spine.  This alteration of biomechanics or movement will 100% of the time lead to degenerative osseous changes.  This occurs with Wolff’s law which was covered in podcast 6.   Wolff’s Law came out in the 1800’s and says Bones will adapt to the loads under which it is placed.

These boney degenerative changes take time.  The study we covered in episode 6 shows that the degenerative changes will take a minimum of 6 months to form after an injury.  If we see no degenerative bony changes surrounding a damaged lumbar spine with AOMSI then it is more likely than not that this injury is new.  If there was trauma then we have a mechanism of injury.  If we have no prior complaints and no prior traumas then we are starting to paint a clear picture of causation.  Again, this takes a lot of education that the burn case would never have to do.  It can be done and can be fun to educate others. 

It is not hard for anyone looking at the burn patient or pictures of him to have an instant understanding of how bad that must have felt.  Everyone can relate to the pain and suffering.  Once again this is not that straight forward with the lumbar AOMSI.  Again, education is key.  Explaining the lack of healing and ongoing symptoms.  The loss of the ligament reflexive control of muscles.  Muscle spasms when the muscles should be relaxing.  Progressive degenerative changes over time.  Altered mechanics lead to inflammation and intense facet pain.  The burn patient reported that 3 years after his injury he has no ongoing pain, but does have some tightness in the skin.  The lumbar AOMSI patient will have significantly higher chances of ongoing chronic pain and need for future management of the injuries. 

In a lot of ways the AOMSI case should be easier to settle and for higher limits if we only consider ongoing future pain.  The burn case would have more visible disfigurement and the pain at time of injury may have been much more intense.  I would hope that after listening to this podcast that you will consider a lumbar AOMSI case as a significant objective injury with potential of showing causation with significant future symptoms and management. 

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