Recently I was at an orthopedist’s appointment with my son, having his shoes fitted with some inserts to relieve discomfort in the boots he wears while traversing around Colorado flyfishing. I couldn’t help but ask the orthopedist what he thought about 3D printing in his industry. His response was enthusiastic, indicating that he had seen great progress with the technology recently, and that the affordability factor was impressive.

We have followed so many companies lately using 3D printing to deal with the different needs we humans have for our feet that I lost count a while ago. A new study recently popped up on the radar though in regards to using a magnet based 3D printed marker wand for analyzing and measuring feet, usually in the case of impairments.

‘A novel magnet based 3D printed marker wand as basis for repeated in-shoe multi segment foot analysis: a proof of concept,’ by Maarten Eerdekens, Filip Staes, Thomas Pilkington, and Kevin Deschamps, goes into great detail about their efforts to expand tools in foot kinematics. There have been several difficulties in this area so far, such as challenges in applying markers to the skin, a lack of shoes suitable for a variety of foot ‘morphologies,’ as well as sufficient repeatability during a ‘repeated measure condition.’ Their goal was to create 3D printed markers for innovative measuring while employing adapted shoes for a foot model with multiple segments.

The researchers worked with ten participants during the study, which was approved by the Ethical Committee of University Hospitals of Leuven. They recorded and measured movements of the participants’ hindfeet, midfeet, and forefeet.

“Dynamic trials were conducted to check for intra and inter-session repeatability when combining novel markers and modified shoes in a repeated measures design. Intraclass correlation coefficients were calculated to determine reliability,” stated the researchers.

“Both repeatability and reliability were proven to be good to excellent with maximum joint angle deviations of 1.11° for intra-session variability and 1.29° for same-day inter-session variability respectively and ICC values of >0.91.”

Novel magnet based in-shoe marker. Top: novel designed magnet based 3D printed marker, consisting of the baseplate (left) and the retro-reflective sphere unit (right). Bottom left: markers placed barefoot according to Rizzoli foot model. Bottom right: markers placed on foot within modified shoes for in-shoe multi segment foot analysis using the Rizzoli foot model.

This study and its results were important as kinematic analyses for the foot have become much more popular. This is because multi-segment models are so much more helpful, although previously they only analyzed bare feet. The use of non-invasive, in-shoe foot kinematics has been ‘delicate’ due to a number of problems. The research team made new shoes, hoping their modifications would allow for skin-mounted markers independent of orthotics.

“The objective of the current study was to develop and assess reliability and repeatability of a thin and solid in-shoe marker wand, consisting of a baseplate and marker-unit, with user-friendly features that allow for repeated in-shoe multi-segment foot analyses using modified shoes.”

The shoes were modified with eight ‘windows’ cut out in each upper. These openings, on a diagonal, ranged from 3.5 cm to 8 cm. The researchers adapted them depending on the shape and size of each foot. They sewed the edges for reinforcement, offering the shoes in unisex sizes 36-48 (European).

“The novel 3D printed markers, consisting of a baseplate and a wand marker, are a reliable basis for future settings using in-shoe multi segment foot analysis when shoes aught to be taken on and off repeatedly. Results showed a solid robustness of the magnet fitting principle that allows for reliable kinematic outcomes in a repeated measurement design conducting in-shoe walking trials,” stated the researchers in conclusion.

Discuss in the Foot Kinematics forum at 3DPB.com.

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