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lock and load

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Simon Spooner, May 17, 2011.

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    In another thread:
    Which got me thinking about neutral suspension casting as defined by Root et al. and direct pressure beneath the 5th metatarsal head as defined by....? The concept was to maximally pronate the midtarsal joint (to lock it) if memory serves. So, in modern times is this concept still employed? If so, why? Maybe David is right and we should be maximally supinating the midtarsal joint?

    "Lock and load, marine" Never been good at taking orders, so why should I start now...?
  2. David Wedemeyer

    David Wedemeyer Well-Known Member

    Simon I feel that you misunderstood the point in that post and that point was that in MASSSS casting the MTJ is maximally supinated in the foam cast. That IS the main feature of their method and this particular provider does send his casts to a lab in Lyle, TN. I illustrated this to the patient and he stated that this was not how he was casted.

    I never stated that I advocate this method of casting.
  3. David, you miss the point of the thread. I just want to know the rationale for casting the midtarsal joint in a specific position be that maximally pronated viz. "locked and loaded" or maximal supinated. Nothing personal, just a topic worthy of discussion in my opinion. Don't know the answer, hence I asked the question.
  4. well I guess 1st you need to decide whats more important the casted position or the finished modified positive.

    If casting it is then changing the position of the midtarsal joint will effect the geometry of the arch of the device and it´s stiffness.
  5. So, if I "lock and load" by pushing up on the 5th metatarsal head, what specifically will this do to the geometry of the device, and the load/ deformation characteristics of the orthosis? moreover, how will this variation likely influence the reaction forces?
  6. It should invert the forefoot, which will increase the arch height. Similar but not as effective as plantarflexing the 1st ray when casting. Be also a type of instrinsic FF valgus posting.

    increased arch height should increase the MLA stiffness of the device.

    CoP should be more medial and the foot come into contact with the device at the arch earlier.

    I think

    If Im thinking right seems root casting technique is very sound, but not for the locked MTJ part.
  7. Now there's a study that needs to be done. Along with a study which shows that initial contact with the foot and the orthosis is more medial as the rearfoot varus posting increases... At the moment, both of these concepts are speculation at best.
  8. Griff

    Griff Moderator

    Will pushing up (from plantar to dorsal) on the 5th metatarsal head invert the forefoot?
  9. Evert of course sorry about that. Nice catch sir
  10. footdrcb

    footdrcb Active Member

    I've had more success over the years by actually "grabbing" the fifth metatarsal , pulling distally and slightly inverting the forefoot.

    The casts I have done that way seem to have a much better result when the finished othotics are returned, and, a better cure rate ,particularly for Heel spurs and Plantarfasciitis.

  11. RobinP

    RobinP Well-Known Member

    I would have thought the vector of the push on the 5th met head will influence the forefoot alignment, shape of the cast as a whole and hence the load deformation characteristics.

    It's part of the reason that I have never really understood the method. I've always felt that it is trying to capture an alignment that doesn't mean much(or perhaps more accurately something that I cannot explain)
  12. David Smith

    David Smith Well-Known Member


    What are you trying to get at here? I've read through a number of times but don't get what your trying establish. Isn't it best to cast in the position that best suits your purposes for the prescription required?

  13. Dave, that's the real trick isn't it. I'm trying to work out what the suspension part of a suspension cast or the direct pressure part of a direct pressure neutral cast bring to the party.
  14. efuller

    efuller MVP

    My rationale is that you want to load the lateral forefoot at the point where stiffness of the MTJ increases. Another way of saying this is have the plantar lateral ligaments tight. (As you go from a maximally plantar flexed midtarsal joint to "maximally" dorsiflexed midtarsal joint, there is a point where the stiffness will increase when the ligaments become tight. ) My rationale was that when the lateral forefoot is relatively less loaded the lateral plantar ligaments will bear less stress than the medial plantar ligaments. To treat medial slip plantar fasciitis, one of the things you need to do is shift the load to the lateral plantar ligaments.

    To achieve this dorsiflexion of the lateral forefoot, you will often have to add an intrinsic forefoot valgus post as just capturing the shape of the "loaded" foot may not lift the lateral forefoot high enough to get the shift in load. I will admit this untested arm chair theory. However, I do know you can get lateral forefoot or lateral column pain if you make the valgus wedge too big.

    What think you,

  15. David Wedemeyer

    David Wedemeyer Well-Known Member

    I was taught that not properly loading the 4th and 5th met heads results in a supinated STJ, erroneous forefoot varus and a increased calcaneal inclination angle. It was also mask a forefoot valgus deformity.

    On a side note when I began POP casting I was self-taught and did not perform loading of the 4th & 5th mets, it's difficult to admit that now. Many of these devices were not tolerable, especially those with PF. Eric's post makes a great deal of sense to me, had to stop and think about it a bit.

    Every one of these patients looked to have a forefoot varus deformity. At the time I bought into some very poor information that suggested that the greater number of forefeet had this feature. I see very few true varus forefoot deformities now, save for very planus feet or congenital varus.
  16. gaittec

    gaittec Active Member

    Help me out if I'm wrong here guys. I'm just an old C.Ped.

    I was taught to lock the calcanus in neutral and dorsiflex the fourth and fifth
    while allowing the first to plantarflex freely.

    I never questioned this. It seemed to work out.

    Holding back the fourth and fifth seems to maintain the neutral heel position, prevent excessive curvature of the lateral arch, determine forefoot varus/valgus in relation to the neutral heel, and account for proper ROM in the first ray. Not to mention, it frees up the off hand to scratch my nose and click the capture button on my scanner. That last part was so wrong.

    Here is where I'd like to know if I'm screwy. It seems like not dorsiflexing the fourth and fifth was the culprit in cases I have seen where patients developed halux limitus and stress fractures at the fourth met after receiving non-root orthotics.

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