Abductory twist is not a dysfunction or a condition, it is however, an observation that can be assessed during gait, which represent a array of different possible factors along the lower limb chain that contributes to the presentation. The presentation involves 2 distinct phenomenon that I personally look for during a gait assessment. I will be discussing the phenomenon along with the physiology and biomechanics that is behind each of these observations.
In a normal gait pattern, our foot goes through a change from pronation to supination. The initiation of stance phase (single limb control) is when our heel contacts the surface in preparation for loading response. The body has to combat 2 different reaction forces at this stage, one from gravity and weight, the other from the ground up.
To best make this bipedal motion efficient, the femur is in relative neutral position in the transverse plane in order for the calcaneous to strike the floor in neutral position (transverse plane), because at this stage the knee is fully extended, hence, the position of where the heel strikes at this stage is highly dependant on the lumbo/sacral and hip joint mechanics. Ideally, the talocrural and subtalar joint should be in neutral position for weight acceptance. Once heel strikes, initiation of pronation needs to occur for shock absorption. Pronation of the ankle is facilitated by the actions above the joint, simultaneously while the ankle is initiating pronation, the pelvis is initiating posterior rotation (from around a 30 degree hip flexed position), the sacrum is initiating nutation from a coutnernutated state, the femur internally rotates and tibia internally rotates (in the slightest manner), the popliteus unlocks the knee to better absorb shock. Once these actions occur, the talus is able to adduct while the calcaneous produces a countermovement into eversion to fully unlock the calcaneocuboid joint and the talonavicular joint, this allows the forefoot to better adapt to different terrains like a well equipped tire suspender.
Once toes strike down (loading response), this marks the end of pronation in the foot. The body now propels forward, and as the gait proceeds into single limb support, around midstance, the ankle moves into a supination strategy. The stance limb will continue to posteriorly rotate at the pelvis, nutate at the sacrum, externally rotate (by means of glut med, and deep lateral rotators) at the hip joint, externally rotate (by means of long head and short head bicep femoris) at the knee joint, and supinate the foot to lock the bones in to provide efficient lever system for the extrinsic muscles at the foot (for example, the peroneus longus requires the calcanocuboid joint to be rigid, so it can be efficient as a pulley system). The psoas also starts to actively be involved with gait during this stage in order to combat the frontal and transverse forces acting upon it. It is important to remember that these actions in the body happens gradually, in a gradient manner.
The body at this stage will proceed from force absorption to propulsion. Most of the propulsion comes from stored elastic energy in the hip extensors such as the gluteus maximus, and the tricep surae, once the elastic energy depletes, the muscles will actively contract to concentrically propel the body forward. The hip will begin to externally rotate more from the actions of gluteus maximus. To create further propulsion, the foot has to assist, this is done by creating the windlass effect in the plantar aponeurosis. When the heel lifts, the plantar aponeurosis is capable to withstand more stress to help with eventual toe off. Abductory twist is generally a result of a maladapted gait pattern. The medial whip of the calcaneous is a preclude to the abdcutory twist that will happen right after. When the foot mechanics cannot catch up with the rest of the lower limb, this medial whip can be observed. What that means is, as we start to ipsilaterally rotate the lumbosacral joint, and externally rotate the hip in late mid stance, if the foot is over pronated, or has lost proprioception and become less efficient in controlling proper mechanics, it will delay in its supination strategy. When this happens, because gait is a closed-chain activity, the foot will store these external rotation drives from the tibia and upwards as elastic energy, and at the moment of heel off and toe off, the medial whip and abductory twist (sometimes used as synonym) will be apparent. Other possibilities include: a lack of dorsiflexion in the ankle cause the heel to lift up during a pronated phase (during single limb support) cause the increased discrepancy between the ankle and the rest of the lower limb; or when the stance limb externally rotates more than it should.
When I see the presence of an abductory twist, usually it is more clinically relevant if there is a unilateral presentation. Just like anything else, a symmetrical presentation may not be functionally significant even if it is "not the norm". Once you deem the observation as clinically significant, then keep in mind of all the things that entails gait and assess from the sacrum downwards to best facilitate your client's movement capacity.