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Can a metatarsal stress fracture be caused by a metatarsal pad?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by ArnoLutin, Apr 17, 2018.

  1. ArnoLutin

    ArnoLutin Welcome New Poster


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    Hello everyone

    I'm trying to better understand the biomechanics of a metatarsal pad.

    What I understand:

    Using a metatarsal pad for a MPJ capsulitis or plantar plate injurie: you will place the metatarsal pad proximal to the are of maximum tenderness? This way you will increase the GRF at the metatarsal neck and decrease it at the MPJ level. Correct?

    A stress fracture is caused by the bending moments acting on it. So to reduce the bending moments on the metatarsal, the pad should go directly plantar to the are of maximum tenderness?
    This will increase the GRF but decrease the bending moment acting on it?

    - Is it correct that a metatarsal stress fracture is always caused by a bending moment and never by an increase in GRF?

    - If you treat a plantar plate injury and you'll place a pad proximal to the metatarsal head. Will you increase the bending moments at the base of the metatarsal? So can a metatarsal pad cause a stressfracture at the base of the neck while treating a plantar plate injury??

    - Reason of question: had a case of someone who receveid orthotics for a plantar injury. The pain of the plantar plate injury was gone after 3 weeks. Yet a new dorsal midfoot pain arised (3/4 weeks after the orthotics) and ptt came for second opinion. Xray showed a stress fracture at the basis of metatarsal neck. No displacement, no angulation. Only cortical widening at the base. I was wondering if this could be an unwanted side effect? And how would you place the pad if you want to treat an stress fracture at the base of the metatarsal AND a plantar plate injury?
     
  2. efuller

    efuller MVP

    This depends on the height of the pad. You can have the same amount of ground reactive force in a different location.


    Ground reaction force is what causes the bending moment.

    Moment = Force x distance. The moment on metatarsal will be determined by the placement of the force. The metatarsal pad will decrease the distance, but if high enough it could increase the force more than the distance is decreased. This is very unlikely but theoretically possible.

    One theory of plantar plate injury is that there is more load on a particular metatarsal and that increases the load on the corresponding plantar plate. Using a met pad would keep the load on that metatarsal (maybe shortening the lever arm which should reduce bending moment, but maybe not enough.). If you wanted to treat a plantar plate injury of the 2nd metatarsal you should increase the load on metatarsals 1, 3,4, and 5. This would decrease the load on the 2nd.
     
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