Functional hallux limitus is a theoretical construct. There is no doubt that the phenomenon that is functional hallux limitus exists, but that can often be as far any any agreement or consensus gets with this. There is no doubt that there are some feet when the foot is up in the air that there is a full range of motion available at the the first metatarsophalangeal joint yet when that foot is weightbearing during gait, that joint just does not want to move. That is the definition of what functional hallux limitus is.
I have written about this a lot, speculating that functional hallux limitus has many possible causes and that it may be better to conceptualize it as a nothing more that each person having a variable stiffness range of motion at the first metatarsophalangeal joint and that this may be related to the windlass mechanism. If this is the case then what we typically considered to be a functional hallux limitus is really the extreme of this variable stiffness and that functional hallux limitus probably exists as a continuum and not as an either/or entity.
The abductory twist is an observation that is frequently made during a gait analysis. Just recently I have started to notice a common terminology issue and I am somewhat confused if they are the same thing or separate things. Most people seem to use the term ‘abductory twist‘ as the same thing as a ‘medial heel whip‘. I believe they are probably different things and they get confused as to what the entity actually is.
I consider an abductory twist to be that sudden medial or abductory movement of the heel just as the heel come off the ground. I wrote here about the possible reasons for this, one being an ‘overpronation’ and the other being a functional hallux limitus. I do not consider that this comes from a more proximal problem like others do. Some people also call this a medial heel whip. They only way to help this is to deal with the ‘overpronation’ or functional hallux limitus. Exercises can not help this.
However, when you listen to or read about what some people consider to be a medial heel whip they are talking about the heel being whipped medially, especially in runners, after the foot has come off the ground. That is something different to the abductory twist that has been previously described. I do consider that this medial heel whip could be due to a proximal problem around the hip and pelvis. The only way to deal with this is deal with the proximal causes and exercises may be very helpful.
If you hear or read someone talking about an abductory twist and/or medial heel whip try to ascertain which one of the two entities they are talking or writing about and just when in the gait cycle that they are observed.