An abductory twist (also called a medial heel whip) is an observation noted during a gait analysis. When present it is observed at the time weight starts to come off the heel when there is a rapid abduction or medial whip of the heel.
Video description of the abductory twist by Kevin Kirby:
Abductory twist vs medial heel ship
1. If the foot is overpronated beyond about midstance or around 50% of the stance phase (with a lot of variation from person to person), the foot is trying to internally rotate the tibia at the same time the opposite leg and is in the swing phase and moving forward. The swing phase leg is rotating the pelvis and leg externally. This means that the foot is trying to rotate the tibia internally and the other leg and pelvis is trying to rotate it externally, creating a conflict! In an abductory twist, it is assumed that initially the pronated foot causing the internal rotation moment wins the battle and foot does not supinate to accommodate that proximal external rotation moment that is coming from above due to the action of the other leg. As soon as some weight comes off the heel, the friction between the ground and foot can no longer resist that external rotation moment that is coming from above and all the pent up energy is released in the form of the abductory twist. There are many different causes of overpronation, but any one of them that overpronates the foot beyond that stage where the foot should be supinating is potentially going to create an abductory twist.
2. The second alternative explanation is that there is something blocking motion at the first metatarsophalangeal joint (big toe joint). As the heel starts to come off the ground that joint has to start bending so the body can progress forward over the ground and if it can't move (for whatever reason), the body has to compensate for that block in motion. One of the ways it moves to get around that blocked joint is for the foot to roll off the medial side of the first metatarsophalangeal joint so it does not have to dorsiflex, resulting in the abductory twist at the heel. A number of different things can block motion at that joint, such as hallux rigidus (+/- osteoarthrtis), a functional hallux limitus, a high force to get the windlass mechanism established, or a shoe that is very stiff in the forefoot. Sometimes these do not actually demonstrate an abductory twist: as that metatarsophalangeal joint does not want to move, they can just lift the foot off the ground and circumduct the leg around to the side to get around the block at the joint.
observation not a diagnosis or clinical condition
Theoretically this is easy. You just make sure that the foot is not overpronated past the point when it should be supinating (to stop that you treat whatever is causing it; bearing in mind that there are multiple possible causes of this and there is no one size fits all treatments for it). You also have to make sure the first metatarsophanageal joint can easy dorsiflex under load (to encourage that you treat whatever is causing it; bearing in mind that there are multiple possible causes of this and there is no one size fits all treatments for it). In some cases (eg hallux rigidus), this is not possible and the only solution is to admit defeat and use something like a rocker sole to facilitate that sagittal place movement. The treatment is based on the caveat that its actually causing a problem and needs treating.
Story form CCPM
if abductory twist is "ballistic" in its motion may get greater loads in tissues if not ballistic - esp plantar fasciitis