Dear all,

Please find the below summary of responses from my questions on marker
placement of prosthetic feet. There were some good suggestions and
references, many thanks to all contributors. Most of the responses agreed
that placing the marker on the centre of rotation would yield accurate
information, whilst this might be difficult in practice, in particular
trying to find the ankle joint centre for the three foot designs.




Dear Tam, thank you for your interesting topic. I have no established

answers, but perhaps the same interest, so I will look forward to your

summary. Rather, I may suggest that this is a perfect topic ... at the

Congress we are organising here in Bologna. You might have come across to

the i-FAB initiative and the relevant Congress (see in case

In addition to the topics addressed at the scientific sessions, meeting will

be dedicated to consensus activities, and tutorials are being designed to

meet perhaps these interests. Your topic is particularly appropriate also

because of the presence and co-chair of people from INAL in Budrio

(basically our National Insurance Institute for Occupational Diseases,

taking care of thousands of amputees every year). Do not hesitate for any

recommandation / suggestion from your side.

Kind regards,

************************************************** ***********************

Alberto Leardini, DPhil

Movement Analysis Laboratory

Director Prof. Sandro Giannini

Centro di Ricerca Codivilla-Putti

Istituti Ortopedici Rizzoli

Via di Barbiano 1/10, 40136 Bologna ITALY

tel: +39 051 6366522

fax: +39 051 6366561


2. Dear Tam,

If you have not come across the following paper yet, I think you may
find it helpful:

Prince, F., Winter, D. A., Sjonnensen, G., & Wheeldon, R. K. (1994). A
new technique for the calculation of the energy stored, dissipated,
and recovered in different ankle-foot prostheses. IEEE Transactions
on Rehabilitation Engineering, 2(4), 247-254.

This paper discusses some problems associated with modeling the ankle
complex on the prosthetic limb and presents an alternative approach to
modeling the ankle and foot of the prosthetic limb other than simply
matching the marker placement on the intact limb.


Jeremy D. Smith
School of Sport & Exercise Science
University of Northern Colorado
Greeley, CO 80639
Phone: 970.351.1761 Fax: 970.351.1762

3. Dear Tam

I do not consider 3DGA ankle marker to be a crucial factor.

I view complete prosthetic foot as an inverted offset "T" into

Hence an adjustable pyramid (ankle) location may ease the alignment

The below mentioned points should be considered in selecting a prosthetic

1) Location of pyramid (ankle) with respect to length of foot.

2) Length of foot with reference to sound foot in case of unilateral BK

3) Stiffness of fore foot as well heel damper.

Answers to your question mentioned below.





Mr.Rabinder Sahni

Prosthetics R&D, Designer lower limbs, Self user


4. Tam,
There does not appear to be a standard marker placement for foot-ankle
motion in prosthetics. Most mimic the contralateral limb in unilateral
amputees, although I have never understood the logic there. The goal is to
accurately capture the motion of the prosthesis, and presupposing anatomical
symmetry where it clearly does not exist could confound that goal.

Your suggestion to place the marker at the ankle joint center is a good
idea, but difficult in practice. The SACH foot you plan to test and many
dynamic feet have a solid ankle and a deformable leaf spring. Finding the
center of rotation of a joint is fairly straightforward, and even if we
allow that the instantaneous center of rotation changes, our errors will be
small. However, finding the ICR of a beam deforming in bending is far more
complex. Add to that the fact that the cosmetic cover of a prosthetic foot
deforms as well, and the traditional placement of a marker at the ankle
joint axis becomes less attractive.

A better approach, though it can still have problems, is to place a marker
triad on the dorsum of the prosthetic foot. This permits 3-D tracking of the
foot segment independent of any shared ankle marker.

The marker triad method is described here (and elsewhere, undoubtedly):
Siegel KL, Kepple TM, Caldwell GE. Improved agreement of foot segmental
power and rate of energy change during gait: inclusion of distal power terms
and use of three-dimensional models. Journal of Biomechanics

More information on errors associated with the shared ankle approach in
prosthetics is here:
Geil MD, Parnianpour M, Quesada PM, Berme N, Simon SR. Comparison of methods
for the calculation of energy storage and return in a dynamic elastic
response prosthesis. Journal of Biomechanics 2000;33(12):1745-1750.

Mark Geil

> > > >

Mark D. Geil, Ph.D.
Associate Professor and Director, Biomechanics Laboratory
Department of Kinesiology and Health, Georgia State University
P.O. Box 3975
Atlanta, GA 30302-3975
NEW Phone: (404) 413-8379

5. Tam,
I would answer your questions in the reverse order:
3-yes, placing the marker at the axis of the prosthetic foot would be more
accurate for measuring the dorsiflexion/plantarflexion angle of the given
2-As a prosthetist, we TRY to align the prosthesis such that it mimics
the unaffected side as best as possible. This is not always possible as
feet are made in only select sizes (length and width) and the heights are
not adjustable. Placing the marker at the level of the unaffected malleolus
would appear to give better knee angle measurements of symmetry, but any
initial flexion built into the prosthesis would negate the accuracy.
And 1- I have not seen any 'standard protocal' for marker placement on the
prosthetic side versus the unaffected side.
I would advise you to specify your placement on EACH foot type, including
rationel for the placement. And to chart the level of the marker off of the
floor for each individual foot, as mentioned above, not all feet have the
same height: so their axis will be in different places.

Good luck, I look forward to reading your results.

Kyle Sherk, CPO/LO
Oklahoma City, Ok, USA

On Mon, Feb 11, 2008 at 2:11 PM, Tam Nguyen wrote:

> Dear all,
> We are about to begin a study looking at the functional performance
> between three prosthetic feet (SACH, dynamic and multi-axial)using 3D gait
> analysis in our VICON equipped laboratory. We found the following articles
> with description of the ankle marker placement as on the spot corresponding
> to the lateral malleolus on the unaffected side.
> * Sjodahl et al. Kinematic and kinetic gait analysis in the sagittal plane
> of trans-femoral amputees before and after special gait re-education.
> Prosthet Orthot Int 2002; 26: 101-112
> * Bateni and Olney. Effect of weight of prosthetic components on the gait
> of tran-tibial amputees. JPO 2004; 16(4):113-120
> We also found a few similar articles but the authors did not specify the
> location of the ankle maker placement. We want to make sure that maker
> placements are appropriately placed to represent the function of the feet
> design and to avoid potential errors in the kinematics and kinetics
> measurements. So our questions are:
> 1. Is there a standard maker placement for prosthetic feet study?
> 2. What would be the reasons for choosing the same spot to the lateral
> malleolus on the unaffected side?
> 3. Would it be more accurate to place the maker where the approximate
> ankle joint centre/ axis of rotation is located? (As these locations are
> definitely different within the three feet designs and certainly are
> different from the unaffected side)
> Look forward to your responses and will post a summary.
> Regards,
> Tam Nguyen
> Manager, South Australian Movement Analysis Centre
> Department of Rehabilitation & Aged Care
> Repatriation General Hospital
> Daws Rd, DAW PARK, SA 5041
> Australia
> e:
> t: +61 8 8275 2848
> f: +61 8 8275 1130