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The Potentailly Injurious Effects of Forefoot Varus Posting

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Craig Payne, Nov 28, 2010.

  1. Steve, Yes an increase in dorsiflexion stiffness at the 1st MTPJ is a Functional hallux limitus.


    Not quite,

    say we have the 1st MTPJ on the left side which takes x newtons of force to dorsiflex at the 1st MTPJ 50 degrees.

    then we have right side which takes y newtons of force to dorsiflex the 1st MTPJ at the 1st.

    y is twice the newtons of force than x . So we would say that the right side has an increased dorsiflexion stiffness at the 1st MTPJ than the left.

    ie the harder the hallux is to dorsiflex the higher the dorsiflexion stiffness.

    so the muscle that need to overcome the dorsiflexion stiffness are those that dorsiflex the hallux and the major thing Ground Reaction force distal to the 1st MTPJ. In this case it makes the gastroc/sol complex very important.

    so anything that increases dorsiflexion stiffness will plantarflex the hallux (or increase the plantarflexion moment )at the 1st MTPJ such as tension in the plantarfascia.
     
  2. efuller

    efuller MVP

    Hi Steve,

    What do you mean by overcome increased dorsiflexion stiffness.

    I would bet that the functional hallux limitus is caused by tension in the plantar fascia which creates a plantar flexion moment at the first MPJ. See my paper
    Fuller, E.A. The Windlass Mechanism Of The Foot: A Mechanical Model To Explain Pathology J Am Podiatr Med Assoc 2000 Jan; 90(1) p 35-46

    The force that tries to dorsiflex the hallux in gait is ground reaction force on the hallux at heel lift.

    The problem from functional hallux limitus is that the limitus is caused by the force couple of tension in the fascia and joint compressive force at the MPJ. When these forces are high there will be damage to the articular cartilage of the MPJ and possibly osteophyte formation. So, increased tension of any muscle (FHL, EHL and intrisics that cross the 1st MPJ) that would increase compressive forces at the MPJ could potentially increase the problems of damage of the joint.

    Yes, peroneus longus will tend to decrease tension in the plantar fascia (see Hicks), but it will also tend to increase pronation moment of the STJ. Pronation of the STJ can lead to increased tension of the plantar fascia, so the peroneus longus may not improve the problems created by functional hallux limitus.

    Eric
     
  3. Peroneus longus. Its own antagonist. The paradox muscle. Generates internal plantarflexion moments and external dorsiflexion moments at the same time on the same first metatarsal.

    Got to love it.
     

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