No announcement yet.

Re: BioNet Controversial Topic #4: knee joint DoUF

This topic is closed.
  • Filter
  • Time
  • Show
Clear All
new posts

  • Re: BioNet Controversial Topic #4: knee joint DoUF

    Dear colleagues
    I am very much interested in this topic both from a scientific and
    medical point of view, for the reasons summarized by Alberto Leardini in
    his introduction to the topic.

    Basically I think, like Ton van den Bogert, that the answer to the
    problem depends on the resolution you need to describe the knee motion,
    therefore on the application or problem you are addressing. And in my
    opinion the "resolution" of the investigation is mainly determined by
    the method used to observe the knee motion.

    In most clinical diagnosis and examiniations the knee laxities and the
    knee passive range of motion is tested manually by the physicians, and
    all my colleagues at the hospital agree to say that the passive range of
    motion (PROM) is repeatable for all individuals, even if the amount of
    internal-external rotation or the anterior-posterior displacement during
    PROM is probably "different" in each patient. Therefore I would say
    that in manual kinematic tests for diagnosis purposes the normal knees
    show 1 DoUF, because a unique internal-external or varus-valgus rotation
    and displacement is associated to each flexion angle.
    However in pathological knees the DoUF seem to increase: in ACL -
    deficient knees there is an evident anterior - posterior laxity with
    makes PROM less contrained in this direction during PROM, especially in
    flexion, while after collateral ligament injuries the variability of the
    varus - valgus rotation associated to flexion is much more than in
    normal knees (as reported also by wolf Schweitzer yesterday). It is
    difficult to say if in this case the DoUF are 2 or more, as the debate
    on the effects of secondary restraint for ligaments is still open, and
    in ACL or MCL-LCL injuries the internal - external laxity is sometimes
    considered significant. However let's say that pathological knees have
    more than 1 DoUF, and a successful treatment (either rehabilitation,
    trining or surgery) is able to recover the normal 1 DoUF in PROM.
    This conclusion is true within the accuracy reached by manual test,
    which I think is certainly not less than 3° and 3mm , measured in our
    cadaveric studies of knee kinematics by means of spatial linkages and
    optical trackers. Standard clinical scores, such Muller score, or forms
    for clinical trials report ranges of 5° and 5mm.

    As a scientist I feel that recent instrumentation can and therefore
    should certainly improve the accuracy of the description, reasonably to
    1-2 deg for rotations and mm for displacements. Unfortunately a few
    reliable data are available in literature reporting instrumented tests
    with equipment able to contrain or control more than 1 dof like KT
    machines, and not only to monitor the motion executed manually like
    spatial linkages and navigation systems. I am aware only of the work
    done in Pittsburgh with a 6dof robot, who's method is reported by van
    den Bogert in the previous message.
    Our team has done some experiments on pig and human knees (mainly
    cadaver, up to now occasional intraoperative tests on patients under
    anesthesia) and we are collecting data about the passive kinematics in
    normal knees (cadaveric specimens), arthrotic knees undergoing total
    knee replacement and ACL-deficient knees undergoing ACL reconstruction.
    Although results are not yet available for a definitive conclusion we
    are trying to verify whether 2 DoUF are enough to define the knee
    behaviour, that is try to verify whether flexion angle and
    internal-external rotation only can determine the PROM, possibly both in
    normal and pathological knees. This would be simpler (i.e. less) than in
    robotic tests and would reflect the feeling that these two degrees of
    freedom in the knee are more important than the others. Whether the
    translations are independent or not from these rotation is still not
    clear to me, but the work by Hollister, Churchill, Pinskerova and M.
    Freeman suggest than they may be dependent provided appropriate axes of
    rotation or reference frame for the knee joint is choosen.
    Probably the interpretation of sexperimental data and therefore the
    problem of how many DoUF has the knee joint is closely related to the
    problem of the deomposition of the motion in a suitable joint reference
    frame, which affects the accuracy of the conclusions more than the
    resolution of the spatial linkages used for acquisitions. It would be
    interesting to discuss also this issue, within this or in another topic.

    At present I think that attempts to achieve a submillimetric accuracy in
    the description of the knee motion is certainly beyond the technical
    capability of current equipment, either 3D imaging like MRI or RSA or
    optical-mechanical like patial linkages. In fact if the equipment
    capability can attain 0.2-0.3 mm accuracy its application on human
    joints imply tioo deal with soft tissues, difficult fixation to the
    bone, the manual adjustment of the frame to image the knee, or similar
    problems drastically enhancing the uncertainty of acquired data, that is
    reaching the accuracy mentioned above.

    Sandra Martelli

    Sandra Martelli e-mail:
    Laboratorio di Biomeccanica URL:
    Istituti Ortopedici Rizzoli
    via di Barbiano 1/10 tel:
    I-40136 Bologna, Italy fax:

    To unsubscribe send SIGNOFF BIOMCH-L to
    For information and archives: