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Thread: Injury model questions

  1. #1
    Senior Member mk99's Avatar
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    Injury model questions

    What is the difference between a compression clip injury model and the Impactor model?

    Is the Impactor basically a "better" & standardized compression clip injury model? Which model most closely approximates a human contusion injury?

  2. #2
    Mk99, the contusion model produces a rapid stretch of axons in the spinal cord. At rates of greater than 0.5 m/sec, axons reach their breaking point and the contusion tends to damage larger axons selectively. In addition, the contusion also damages blood vessels, causing petechial hemorrhage. The contusion model was first described by Reginald Allen in 1911 when he described a weight drop contusion of the dog spinal cord and pointed out that the spinal cord looked almost undamaged immediately after the contusion but developed central hemorrhagic necrosis over a period of several hours. Because of this progressive tissue damage, he proposed that it should be possible to treat the spinal cord shortly after the contusion and prevent "secondary" injury.

    The crush compression model is a combination of mechanical damage and ischemia. I believe that the original clip compression model was described by Charles Tator in the late 1970's. The clip squeezes the spinal cord and is left on for a minute or two, and then removed. It produced an injury that looked similar to the contusion. However, because the clip is applied at a rate slower than 0.5 m/sec, most of the damage must be a result of tissue crushing rather than tissue stretching. There is likely to be a component of hemorrhage-induced injury and possibly ischemia as well.

    I chose to do the contusion model because I felt that it was more reproducible and can be used to create graded injuries. We have shown that dropping the weight 12.5, 25.0, and 50.0 mm onto the spinal cord can produce a variety of outcomes, ranging from incomplete, to severe incomplete, and almost complete loss of axons across the injury site. The Tator model is a dorsoventral compression (i.e. the clip is applied to the back and front of the spinal cord). About a decade ago, Andrew Blight described a lateral clip compression model that may is easier to apply and may produce more consistent in rats. Most of the studies today use a pair of flat tipped forceps (sort of like the forceps used to pick up stamps or slides) and apply the compression from side to side.

    Which one is better models of the human condition? I think that both are reasonable models in that they produce similar pathology. It is likely that human spinal cord injury is a combination of contusion, transient compression, and prolonged compression (ischemia). Some people of course have had their injuries as a result of ischemia, resulting from primarily vascular reasons.

    Vascular induced injuries differ from contusion in several respects. First, vascular injuries tend to affect gray matter, particularly in the lumbosacral region, and can cause neuronal loss some distance from the apparent level of injury. Second, ischemia selectively damages smaller axons first and large myelinated axons are more resistant. Therefore, people with vascular-induced ischemia may have preserved proprioception but may lose temperature and pin-prick sensations.

    I don't know if this is what you wanted to know.

    Wise.

  3. #3
    Senior Member mk99's Avatar
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    That was exactly what I wanted to know, thank you very much.

    I had no idea that Dr. Tator was so influential with his "compression clip" injury model. I think many researchers up here are still using it.

    Last question: would it make sense to encourage researchers to use the Impactor model as opposed to the "compression clip" model? (Assuming that the goal is to bring a cure to humans ASAP). Is it likely that using the "compresssion clip" model yield different results to the Impactor model and if so what does this mean when trying to reproduce results?

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