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Biomechanics of abductory twist

Discussion in 'Biomechanics, Sports and Foot orthoses' started by frederic G, Nov 5, 2008.

  1. frederic G

    frederic G Active Member

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    Could someone explain to me the biomechanics of abductory twist?
    Last edited: Nov 6, 2008
  2. Craig Payne

    Craig Payne Moderator

    Two possible reasons:

    1. Foot pronates beyond midstance--> internal rotation moment to leg; the opposite leg is swinging forward and rotating the pelvis --> externally rotation moment to leg on ground --> conflict between proximal external rotation and distal internal rotation moments -- initially the pronated foot causing the internal rotation moment wins the battle and foot does not resupinate to accommodate that proximal external rotation moment ..... eventually as heel comes off ground, friction between the ground and foot can no longer no longer resist the external rotation moment coming from above --> abductory twist

    2. As heel starts to come off the ground a functional hallux limitus kicks in (for whatever reason); as the body has to move forward over the first MPJ, it can do so by a number of mechanisms; one of these is to abduct the foot to roll off the medial side of the blocked first MPJ --> abductory twist
  3. Frederic:

    Here is the lecture I gave on "Biomechanics of Abductory Twist" at the 2004 PFOLA International Foot Biomechanics and Orthotic Therapy Seminar in Boston. Hope this helps.

  4. David Smith

    David Smith Well-Known Member


    Don't know if these diagrams will help. (terms torque and moments are interchangeable) Probably best to print off the diagrams first.


    1) Resting stance = no torque in femur and tibia, which I will call the shank.

    2) To progress fron position diagram 2 to position diagram 3 it is neccessary to rotate the pelvis about the right hip joint.

    3) During this transition and in normal function there must be a position, which is during left swing thru, that the foot, ankle joint, shank and hip are aligned perpendicular to the pelvis (for the sake of evaluation). At this point muscle M (diag 2a) has a certain tensile force that produces a torque about the hip joint. This is equalised by the torque of the body mass rotating about the hip in the opposite direction and which produces torque P. (diag 2). These torques cannot exist in space on their own and so this torque is transmitted down the shank and is equalised by horizontal frictional forces on the ground (FE+ & Fi- Diag 6). This is shank torque x.

    4) Imagine now that at the same point in the left swing thru the right foot is internally rotated. This internal rotation distance K will increase the muscle tension M and so increase the torque acting on the shank ie P1 = x+KM (in terms of moments about the hip). You will notice that the angle between hip and pelvis in diag 2a is 90dgs and the same angle in diag 4 is less than 90dgs.

    4a) You will now see that the diplacement K is achieved by STJ pronation and internal tibial rotation but the foot is straight ahead. In this way the muscle M increases its tension and again we see P2 = x+KM in terms of moments about the hip.

    Now as the pelvis rotates about the right hip it is restricted by the increased muscle tension and this torque is transmitted down the shank. If the tibia / shank was free to externally rotate this is what would happen. How ever the Vertical ground reaction force VGRF (diag 5) causes pronation and so by the mechanism of the ankle/stj complex also internal rotation.

    5) To get from the pronated position 5a)to the vertical position 5c) there must be a supinatory force. This can be produced by a combination of -Fz and Tp (shank torque)

    6) These forces and torques are balanced by equal and opposite force * lever arm acting about point c below the ankle. IE (Fe + Fi-) = TP.

    If we now remove force FE+ as happens at heel lift, we are only left with Fi-, which cannot resist the torque TP since we require two forces for a force couple to produce an opposing torque.

    The rotation point c now moves to the forefoot (P2), since this is the only point of contact and still in fact forces there exists forces Fi- and FE+ but their lever arms are too short and or the frictional force is too low to produce enough enough torque to resist the external rotational torque of the shank TP.

    Therefore the shank, and with it the foot, externally rotate and we see an abductory twist at heel off.

    Is that clear :dizzy: Tried to keep it as simple as possible, dunno if I did tho.

    All the best Dave
  5. efuller

    efuller MVP

    I think that Craig and Kevin have it, but I'll try a short explanation as well.

    In gait with abductory twist, the trunk is applying an external rotation moment to the leg. The bottom of the leg can externally rotate at two locations: the STJ and the foot versus ground interface. The external rotation moment applied to the leg will attempt to externally rotate the talus on top of the foot and rotate the foot relative to the ground. A pronation moment (e.g. from ground) at the STJ will resist the supination moment (external rotation moment of talus) so the leg wont externally rotate relative to the foot. When the heel is on the ground there is more friction preventing external roation of the foot relative to the ground. As the heel lifts off of the ground there is less friction preventing external rotation of the foot relative to the ground and the whole leg will rotate and that is what you see with an abductory twist. Anecdotally, you will see more adductory twist with leather shoes on linoleum as compared to rubber soled shoes on carpet.


    Eric Fuller
  6. frederic G

    frederic G Active Member

    Thank you Craig, Kevin, David and Eric for all of these explanations!
  7. Here's a video of abductory twist, now with narration.

    Last edited by a moderator: Sep 22, 2016
  8. David Wedemeyer

    David Wedemeyer Well-Known Member

    I have been trying to capture this phenomenon to show patients and thus far failed. I need to invest in better equipment...

    Thanks Kevin for the vid and Eric for the explanation.

  9. Steve The Footman

    Steve The Footman Active Member

    Very thorough explanations by all. (That is one lecture I would love to hear Kevin.)

    I would like to add that any sagittal plane block can sometimes lead to an abductory or adductory twist in compensation. I am not convinced that there is always a straight-forward reason why one occurs over the other. It may be a reflection of individual structure, the position of the limbs or even neuromechanics and movement patterns. Abductory twist is certainly more commonly found.

    Other possible theories for a mechanism of action:
    • Greater stiffness in the forefoot of the shoe relative to the midfoot.
    • Elevatus or short first ray causing late phase pronation and asymmetrical ground reaction force after heel off.
    • Correction of external or internal rotation of the stance phase limb to guarantee clearance of the foot when it passes the opposing limb during float/swing phase.
    • Excessive or Inadequate Base of Stance correction.
    • Forefoot Valgus or Varus deformity.

    I think that the direction of propulsive force may be a factor in some patients. One intriguing question is why everyone with a Functional Hallux Limitus or a Hallux rigidus do not all have a transverse plane twist after heel off. Some may have other transverse plane compensations but others seem to have sufficient muscular control to dampen the forces internally. It is fun to see patients who you predict will have a certain biomechanics which just does not occur during function.

    Perhaps others may be able to comment on why running vs walking seems to exacerbate the twist in different patients.
  10. maxants33

    maxants33 Active Member

    Hello, just a quick question - can adbductory twist be responsible for plantar metatarsal soft tissue irritation? And if the cause of the twist was lack of supination late in gait - would you Tx with medial wedging?
    Many thanks!
  11. efuller

    efuller MVP

    No proof, but it would certainly make sense. You've got the entire body weight on that forefoot and then you are spinning it at the same time. That would be more stress than just the body weight alone.

    In some feet the pronation moment that prevents external rotation of the leg at the STJ will be caused by ground reaction force and in other feet that pronation moment will be caused by the peroneal muscles. A varus heel wedge would be good for those with the pronation moment caused by ground reaction force and it would be bad for those feet with the pronation moment caused by muscles. Make your decision of whether or not to add a medial wedge based on whether the STJ axis is medial or lateral.

  12. NewsBot

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    Medial and Lateral Heel Whips: Prevalence and Characteristics in Recreational Runners
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