ISB, JCS and marker placement

[jean jeuvrey]

Hello,
I have a question about the recommendation of the ISB. the ISB propose marker placement for the definition of different LCS. These LCS are defined from skin-mounted markers placed on anatomical landmark. However Angeloni et Al. (1993) reported that significantly greater displacement occured with skin-mounted markers than with markers mounted on rigid plates and suggested that the latter markers were preferable to skin-mounted markers for both practicality and accuracy. I want to calculate different joint angle and i wonder if i have to follow the isb recommendation or if i should better use rigid plate?

Thanks!

[Ross Miller]

Re: ISB, JCS and marker placement

Hi Jean,

Typically the skin-mounted markers are used to define a segment (i.e. embed a coordinate system on it) during a static trial based on the subject's anatomy, and the cluster markers are use to track that segment's position in space during a movement trial (after reconstructing the LCS).

You can also define an LCS using the cluster markers too (no skin-mounted markers even in the static trial), which I think works fine if you are planning to "normalize" the kinematics to the static trial, but then you are assuming all the LCS are coincident with the GCS (not always a good assumption) and also don't have any joint center information.

Personally I prefer skin-mounted markers for tracking in gait because I worry about the clusters moving around (e.g. sliding down the thigh if they are attached by a wrap), but I think the clusters are better for accurate tracking in a lot of cases.

Hope this helps!
Ross

[Alberto Leardini]

Re: ISB, JCS and marker placement

Dear Jean and all, yes, we've been investigating whether the skin-motion artefact was larger for the single markers typically placed over anatomical landmarks (condyles, malleoli, great trochanter, etc.) or in rigid plates fastened at mid segments. We have used both in our practice, see Benedetti et al. 1998 and Leardini et al 2007. The work on 1993 was based on measurements on patients wearing external fixators, which provided a gold standard rigid with the underlying bone. I understand that single markers stuck close to joints suffer of the skin sliding associated infact to the joint motion (see Cappozzo et al. 1996); those at mid thigh and shank suffer more of skin-motion artefacts associated to muscle activation and inertial effects of the soft tissue, and less of joint motion. A careful map for all these locations was reported also in Stagni et al. 2005. So I think the option depends on the subject, and the motor task to be analysed. Perhaps a most complete and recent comparison between a number of marker fixation options in this respect is in K. Manal, I. McClay et al. Gait Post 2000.
Hope this may help.
Alberto Leardini

[jean jeuvrey]

Re: ISB, JCS and marker placement

Thanks for your response,
I read some article you write out.
A lot of researcher seems to be agree that the use of rigid structure is the most accurate, particularly with rigid structure included a marker placed on a rod that project laterally out from the segment. Except for some particular application (transient impact for example) the skin-mounted marker seems to be the less accurate. However the skin-mounted method is good enough for some specific rotation (flesion extension for the knee for example). However it wonder if the rigid plate is not a little bit invasive esppecialy with the arm(and maybe it is difficult to interlock correctly the rigid plate with the anatomical segment). Maybe the most important is to know if for my task the deviation is acceptable.
Thanks for your help!