MASS foot position theory for orthotic therapy was first proposed by Ed Glaser, DPM from Sole Supports Inc. This grew out of Ed’s analysis of his perception of the problems with the traditional based Root biomechanics theory that underpins the traditional use of foot orthotics. MASS stands for Maximum Arch Subtalar Supination. It is a position that is much more inverted than the traditional subtalar joint neutral position, but also maintains the forefoot on the same place as the rearfoot. Ed advocates the use of semi-weightbearing foam box as opposed to plaster (though it is not difficult to reproduce the position non-weightbearing with plaster bandage).
At the Boot Camps, we do a practical on the use of foam for this position as well as a foam impression of the traditional neutral position. This always generates a lot of discussion and always receives good feedback. There is no doubt that the two positions are radically different, especially in the posterior medial longitudinal arch profile. It is also interesting to see participant’s reactions to observing the two radically different shapes. Most are somewhat initially negative to the MASS position, but the problem with that is, they are observing the MASS position from the mindset of years of use of the neutral position. That does not mean that one position is right and one is wrong.
I do currently wear a pair of orthotics made by Ed’s lab in my gym shoes and have used the MASS position method in patients who’s traditionally made foot orthotics have failed. Adjustments to them were not successful and I still felt that foot orthotics were indicated. The use a MASS type device gives a very different shaped foot orthotic in situations like these.
I also like using devices of the MASS position in those who have a large amount of forefoot supinatus (as the position allows for maximum correction). I am not very comfortable using them in patients with a more medially located subtalar joint axis, as the higher arch profile in a MASS foot orthotic tend to push on the axis (and can be uncomfortable) or push lateral to the axis (and doesn’t work too well).
What MASS position theory and the use of orthotics based on that position has taught me (and the reason we cover it in the Boot Camps) is that there are many positions in which we can create a negative model of the foot. Sometimes subtalar joint neutral is indicated; sometimes slightly pronated is indicated; sometime slightly supinated is indicated; and sometime maximally supinated (MASS) is indicated. The challenge now is to come up with better clinical assessments to derive the prescription variable of which position to model the foot in.
Podiatry Arena has had a number of threads on MASS Foot Orthotc theory (some get a little heated!).