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Re: Joint stability, any standard definition?

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  • Re: Joint stability, any standard definition?

    Dear Paolo

    It might first be worth precisely defining what you mean by unstable. It may
    be like trying to define the height of a 'low table' or its usefulness in
    terms of its height.

    Is the/a joint unstable when it exhibits an unusualy large range of motion?
    Is it unstable when the joint has a large range in a plane that is not the
    usual primary plane of motion? Or is it unstable when the joint cannot
    maintain a fixed position under a certain load? or is it when the joint
    cannot maintain the expected supporting role during a dynamic or static
    action. Is it unstable just when the patient / subject says it is or is it
    when they experiences symptoms or show clinical signs that could be
    attributed to one or some of the above.

    If you have a fixed definition of an unstable joint, e.g. a certain joint is
    unstable when it exhibits 'x' range of motion under 'y' load during an
    activity of interest, is it then determined to be stable if it does not
    fulfil those criteria even tho the patient describes the joint as unstable
    because it gives way during the activity of interest. This is the problem
    with defining such a parameter, how do you apply it to your patient if they
    dont fit in the box?

    Without those pre set criteria the clinician has the freedom to determine
    what the problem is with the joint (or any other part) based on his own
    skill, judgement and education.

    It might be useful to classify joint stability in an attempt to achieve some
    standardised comparative assessment data. However if the patient says it is
    better, then it is better.

    If the patient or the clinician thinks that the joint is problematic because
    of its instability, then make it more stable. Why would you want to
    precisely define how stable it is or unstable it was before, or after, the
    patient said it was better?

    Not critisizing, just some thoughts

    Regards Dave Smith
    Podiatrist, MSc App Biomech
    FootHouse Podiatry
    ----- Original Message -----
    From: "Caravaggi, Paolo"
    Sent: Wednesday, August 04, 2010 4:27 PM
    Subject: [BIOMCH-L] Joint stability, any standard definition?

    Dear Biomech-l subscribers, I was wondering if any of you is aware of an
    objective test to assess joint stability. According to my literature
    research neither a standard definition of joint stability nor standard
    evaluation tests to determine the degree of instability at joints have been
    established. In most cases the level of instability is subjectively assessed
    by clinicians by applying dislocating forces to the joint. When more
    scientifically-objective approaches were taken, joint rotations to triplanar
    joint displacements (or rotations) are normally shown. However, although
    differences to the normal/stable joint are graphically presented, when/if
    the joint can objectively be considered unstable is not reported.

    As far as our specific case, we are trying to quantify the level of
    instability at the proximal interphalangeal joint of the finger in-vitro
    through active flexion/extension of the joint following the release of
    supporting ligaments and the disruption of the joint by systematic resection
    of bone at its proximal aspect. We are indeed finding significant
    differences in the flex/ext rotation to joint displacement curves across
    different configurations (intact, disrupted..) but we are now facing the
    issue of establishing some kind of objective index for joint-stability. In
    other words, which variable is more relevant here and how far from the
    normal/non-pathological configuration a joint can still be considered to be

    Any suggestions and/or further comments on this matter are welcome.


    Paolo Caravaggi, PhD
    Joint Biomechanics Lab, Orthopedics dep.
    University of Medicine and Dentistry of New Jersey
    185 South Orange Avenue, Newark, NJ 07103
    Tel. +1 973 972 1426

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