What is it?
The abductory twist is considered as the rapid medial movement of the heel just has it starts to come off the ground.
What does it look like during a gait analysis?
See this video:
What causes it?
there are two reasons or explanations as to what might be causing an abductory twist during gait:
1. As the foot ‘overprontes’ it usually rotates the tibia internally an excessive amount at the same time that motion at the hip and pelvis above is trying to externally rotate the same limb. As the heel comes off the ground, that lack of friction between the ground and the foot suddenly allows that external rotation to happen as the friction is not longer restricting the motion.
2. A functional limitation of dorsiflexion at the first metatarso-phalangeal joint (functional hallux limitus) will limit dorsiflexion at the joint as the heel comes off the ground, so the foot has to suddenly abduct to roll around that restricted joint to move forward.
There are many claims that this abductory twist can also be due to functional problems around the hip, but those make that claim are generally confusing the abductory twist with the medial heel whip which occurs later in the gait cycle and could be due to issues around the hip.