Ligament Pathology as Sequella to Trauma Coupled with Alteration of Motion Segment Integrity (AOMSI) or Ligamentous Laxity
By: Ray Wiegand, D.C.
Mark Studin DC, FASBE(C), DAAPM, DAAMLP
A good read to understanding alteration of motion segment integrity (AOMSI) is the article “Biomechanical Analysis of clinical instability in the cervical spine” White, et al., Clin Ortho Relat Res, 1975;(109):85-96.
AOMSI is a biomechanical analysis. It’s all about numbers that have clinical meaning and significance. Threshold values have been determined that quantify without a doubt the patient has serious injury. It is a test of structural integrity of the ligaments interconnecting the motion segments. In this case, structural integrity has to do with the material properties of ligament tissue. Those properties include strength and flexibility. When a material is both strong and flexible, it’s called a semi-rigid material. Strength is related to the composition of the material. Strength might be thought of as load carrying capacity before failure.
Ligament tissue has previously been bench tested to describe its physical characteristics of stress/strain. That is, given so much load (stress) how much elongation will occur (strain). During normal physiologic loads the ligament remains intact and recoils to its original length when the load is removed. If the load becomes too large the materials (ligaments) begin to yield. They go past their elastic limit. When this happens the (strained) ligament fibers will not return to their original shape. The ligament loses its restraining capacity to hold the joint in normal stabilization and hypermobility occurs.
The ligaments, if sufficiently strained or avulsed results in AOMSI. The following paragraphs illustrates that if AOMSI is found there must be gross destruction or yielding of multiple ligaments. We need to build a BIG motion segment with Velcro ligaments. When you tear them off, they make a really nice ripping noise. That drives home the point.
In the White et al work, they found that the motion segment stayed intact i.e., less than 11 degrees’ rotation (angualr mtion) and less than 3.5 mm translation, until they transected over 50% of the ligaments from an anterior or posterior approach. And when they transected from either approach the loss of stability was not linear but suddenly catastrophic. And they meant that suddenly the two vertebra totally separated in rotation or translation.
Suddenly Separated: pulled apart, head off of body, all neural components compromised, paralysis. Keeping that in mind, what are the injuries of someone just under the threshold? Severe to very severe. They stand the possibility of a serious event with much less force.
If AOMSI is detected, think about more than 50% of ligaments transected. That will start to explain the seriousness of the finding. In a patient/child that demonstrates hypermobility everywhere, then you take a statistical average of all segments, and look at the aberrant statistical finding if it exists. There are clues to injury everywhere when you understand what the numbers mean in reference to stability and function.
To diagnose ligament laxity, it is imperative that imaging be performed and a basic flexion-extension x-ray is all that is required. In today’s medical economy, advanced imaging of MRI or CT Scan, although accurate becomes an unnecessary expenditure and an x-ray renders very accurate demonstrative images to conclude a definitive diagnosis. In determining if there is an impairment, it is necessary to follow the AMA Guides to the Evaluation of Permanent Impairment as the 4th, 5th and 6th editions all render an impairment for AOMSI as sequella to ligament laxity, which is damage to the ligament from trauma.
This document is intended to serve as a simple explanation as to the severity of ligament damage and how to demonstrably diagnose the injury. It is also critical to remember that ligament do “wound repair.” In normal physiology, ligaments grow during puberty from cells within the ligaments called fibroblasts. They produce both collagen (white) and elastin (yellow) tissue, which gives the ligaments both tensile and elastic strength. Upon puberty the cells stop producing tissue and remains dormant. Upon injury, the fibroblast reactivates, but can only produce collage leaving the joint wound repaired in an aberrant juxtaposition (place) with poor movement abilities due to the lack of the requisite elastin. In turn, according to Hauser et. Al (2013) this leads to permanent loss of function of the ligament and arthritis of the joint. This is not a speculative statement; it is based upon Wolff’s that dates back to the late 1800’s and has been a guiding principle in healthcare for more than a century.