View Full Version : Re: Joint stability, any standard definition?

08-04-2010, 03:21 AM
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

No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.851 / Virus Database: 271.1.1/3050 - Release Date: 08/04/10