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medial knee o/a and knee aDduction moments

Discussion in 'Biomechanics, Sports and Foot orthoses' started by markjohconley, May 24, 2016.

  1. markjohconley

    markjohconley Well-Known Member


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    Goodaye, in a laid-back, relaxed, rested; carefree, devil-may-care, happy-go-lucky, lighthearted way i'm, again, a little confused; this time by this article; and I thought the aim was to reduce the knee aBduction moments to reduce the compression on the medial knee compartment

    Disabil Rehabil Assist Technol. 2016 Mar 15:1-9. Baghaei Roodsari R et al[/]

    'The effect of orthotic devices on knee adduction moment, pain and function in medial compartment knee osteoarthritis: a literature review.'

    which was referred to by the ....
    http://semrc.blogs.latrobe.edu.au/top-3-foot-orthoses-biomechanics/

    mark
     
  2. efuller

    efuller MVP



    Without looking closely at the site, the most common confusion here is the difference between external moments and internal moments. Looking at a tibia in the frontal plane: In our example there is tibial varum. The force of gravity pulls the body down ward and applies this force from the bottom of the femur to the top of tibia. Ground reaction force applies an upward force on the bottom of the tibia. With tibial varum those two forces will create an external adduction moment on the tibia. The tibia will rotate unless there is an internal abduction moment from compression in the medial compartment of the knee and tension in the lateral collateral ligaments. The specific force couple for the internal abduction moment acting on the tibia is a downward force from the femur acting on the top of the tibia and an upward force from the lateral collateral ligaments acting at their attachment on the tibia.

    The interesting thing to think about as you look at those individual forces is that when you compare the vertical tibia, to the tibial varum tibia, there is greater compressive force at the knee with the tibial varum tibia, even with the same body weight.

    Often, writers will get lazy and forget to say whether they are talking about external or internal moments. Yes, the idea is to decrease medial knee compartment compressive forces.

    Eric
     
  3. markjohconley

    markjohconley Well-Known Member

    Eric, thanks; is this total knee or just medial compartment, "... ..is that when you compare the vertical tibia, to the tibial varum tibia, there is greater compressive force at the knee with the tibial varum tibia, even with the same body weight.", mark
     
  4. efuller

    efuller MVP

    The way to think about it is center of pressure of the knee. The center of pressure is the average point of force over the entire surface. There are many different ways to get the total center of pressure to shift in one direction. The simplest is to just increase the force in one compartment. another way is to shift the center of pressure of both the medial and lateral compartments. By whatever method the total center of pressure would have to be shifted. However we can't tell how without direct measurement of the pressure distribution of the joint surface.

    Eric
     
  5. markjohconley

    markjohconley Well-Known Member

    Thanks Eric, it was my simple misunderstanding that 'knee abduction' was abduction of the knee rather than abduction of the KNEE JOINT. ......... a basic error biom101, can't blame the medications
    for that one, mark
     
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