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How to Reduce Jack's Test Force

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Donna, Aug 18, 2008.

  1. Donna

    Donna Active Member


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    Hi everyone,

    We have a patient, (61 year old very active female bushwalker), that is responding really well to orthotic treatment (history of 2nd MPJ capsulitis, 3rd & 4th MPJ degeneration, ankle instability, navicular stress reaction, ankle instability, calf cramps - all now going great with orthotics)... except for one residual problem... she is complaining of increased pressure under hallux (right worse than left), which is causing pain and blisters.

    For those interested:
    Her biomech assessment revealed: hypermobile cavus foot type, severe level of increased ankle joint dorsiflexion stiffness (equinus), extreme grading of supination resistance, short 1st metatarsal (4mm bilaterally) with long 2nd metatarsal (right foot only, 2-3mm), everted forefoot (5 degrees bilaterally), 6-7 degree inverted NCSP.

    So basically, she has the influence of 3 major factors responsible for increasing MPJ1 stiffness, ie. high pronation moment at subtalar joint, increased dorsiflexion moment at forefoot and increased plantar flexion moment at rearfoot.

    On review this morning, the orthoses looked great, good conformity, apart from mild gapping at the anterior MLA. Jack's test was again performed, and the result was early onset, high force.

    What else can be done to reduce the force at the 1st metatarsophalangeal joint?
    These things have helped her:
    - metatarsal dome
    - MLA support
    - medial heel skive
    - plantar fascial accommodation
    And other things that we know can help (but this patient cannot tolerate) are:
    - forefoot valgus wedging
    - rearfoot varus posting

    Does anyone know of anything else that can be done to decrease the force at MPJ1? Is it worth increasing the depth of the plantar fascial accommodation to see how this helps? :confused:

    Thanks for your help!

    Regards

    Donna ;)
     
  2. Adrian Misseri

    Adrian Misseri Active Member

    G'Day Donna,

    Sounds like (and I'm only guessing without seeing the patient), that there might be a shift of center of pressure at heel off as the MTPJs load, resultant form the short first metatarsal taking extra pressure as the foot moves around the long second metatarsal. This may be seen as a very late abductory twist and/or a medial roll off as the heel lifts. Might be worth trying a bit of padding on the shell, just proximal to the first metatarsal head so that the metatarsal (shaft specifically) loads up earlier at propulsion. Alternatively try a first ray extension on the device and stop the motion at the first MTPJ.
    Good Luck!
     
  3. Craig Payne

    Craig Payne Moderator

    Try the modified version of the FnHL test discussed here; otherwise it sounds like you done pretty much everything that should be done to lower the force.
     
  4. Donna

    Donna Active Member

    Thanks Craig... we'll try that test too... does this test have a name? Or can we call it Payne's FnHL Test? :D

    And thanks Adrian, you must be psychic... I should have mentioned that we have added a wedge today under the anterior MLA to see how this helps to unload the plantar fascia... will see how this goes...

    Regards

    Donna
     
  5. Craig Payne

    Craig Payne Moderator

    I call it either the 'Modified FnHL test' or the 'Brucie Test'
     
  6. DSP

    DSP Active Member

    Donna:

    Have you considered trialing a reverse mortons extension in conjuction with a medial heel skive? This may help reduce the GRF plantarly to the 1st MPJ/hallux.
    She may find this modification more comfortable than a forefoot valgus wedge extension.

    What did your current orthosis prescription consist of?

    Regards,

    Dan
     
    Last edited: Aug 18, 2008
  7. Bruce Williams

    Bruce Williams Well-Known Member

    Craig;

    AAARRRRGGGGHHHH!!! "Modified FnHL test or Williams test" is fine! :dizzy:

    Bruce
     
  8. Bruce Williams

    Bruce Williams Well-Known Member

    Donna;
    all the suggestions so far are very valid. I would consider increasing the size of the 1st ray c/o and backfilling w/ PPT or Poron to make it a kinitec Wedge.

    Consider as well overfilling teh 1st ray c/o w/ PPT or Poron if you feel the 1st Met is elevated. Over time decrease the PPT or Poron as the ray "adapts" or plantarflexes.

    Check for LLD on the opposite limb and accomodate for that appropriately as this will often help to decrease unilateral pronation which will often affect teh hallux in such a way.

    Finally, consider a Cluffy Wedge or a digital extension under the toes 1-5. I use 3mm EVA for starters and taper it proximally to the toe sulcus. Often you have to get the hallux DF'd to overcome the DFion stiffness / FnHL at the 1st mpj. You might be surprised to see how well this can work. I will sometimes substitute PPT or Poron for the EVA, or use both in varying thicknesses under the hallux.

    Good luck!
    Bruce
     
  9. Donna

    Donna Active Member

    Hi Dan

    The orthoses are full length CADCAM EVA devices, with medial heel skive and medial MLA wedging, lateral heel through to midfoot wedging, 1st met extension and mild 5th met extension...

    The patient was unable to tolerate much support under the lateral forefoot, but we'll look in to that again and see if it works... my concern is that with the short 1st met that by adding extra lateral forefoot wedging the long 2nd met will then be under increased shearing force during toe off...

    And thanks Bruce for your help, the digital extension sounds like it might be worth a shot, the patient has a 1mm LLD in the tibia (R > L) which we haven't chosen to accommodate as yet, although of note is that the supination resistance is 5 on the right and 3-4 on the left (we grade on a scale of 0 - 5), which is probably accounting for the increased stiffness of the right MPJ1.

    I'll keep you all posted with what happens with this patient! Thanks again for your help!

    Regards

    Donna ;)
     

  10. Donna:

    In patients such as these, where I want to decrease the loading force on the 1st metatarsal head and plantar hallux in a patient that already has orthoses, I do two things to the orthosis:

    1. Add a 2-5 forefoot extension of 3 mm korex (i.e. reverse Morton's extension).

    2. Increase the varus support under the heel and medial longitudinal arch from the orthosis.

    In a typical patient, for example, with a 4-5 mm thick polypropylene plate with a polypropylene rearfoot post, I may initially add a piece of 3 mm thick adhesive felt plantar to the 2nd - 5th metatarsal heads (to the sulcus) on the forefoot extension of the orthosis to simulate #1. Then to accomplish #2, I will add plantar arch filler of adhesive felt to the plantar medial arch of the orthosis and add a varus rearfoot and forefoot wedge of 3 mm adhesive felt to the orthosis to invert it more to the ground. Adhesive felt pads may be permanently replaced with a suitable material such as korex or EVA once the felt pads are found to be helpful for the patient.

    The goal of the combination of these two orthosis modifications is to:

    1. Increase the external subtalar joint supination moment.

    2. Decrease the external medial forefoot/1st ray dorsiflexion moment.

    3. Reduce the tensile force within the medial slip of the central component of the plantar aponeurosis.

    4. Reduce the internal hallux plantarflexion moment due to reduction of the tensile force within the plantar aponeurosis.

    5. Reduce the ground reaction force plantar to the hallux during weightbearing activities due to factors #1-4.

    This orthosis adjustment works in 95% of patients with similar problems that I have seen over the past 23 years of clinical practice.

    Hope this helps.
     
  11. Donna

    Donna Active Member

    Hi Kevin,

    Thanks a lot for all of those points, very impressive... Your help is always muchly appreciated!

    Is a 2-5 forefoot extension something that the patient will likely be able to tolerate more readily over time? So far she hasn't been comfortable with any extra support under the 2-5 MPJ's, I'm thinking this is due to the combination of short 1st and long 2nd metatarsals... but we'll try it again to see how she responds... ;) Would a 3-5 bar be worth trying, taking into consideration the long 2nd metatarsal? Or am I just being silly with that idea?:eek:

    Regards

    Donna :D
     

  12. Considering the sub-2nd pain, you may try either a pad sub 3rd-5th or a pad only sub 4th-5th. Anything that shifts ground reaction force laterally on the forefoot should decrease the tension within the slip of the plantar aponeurosis that attaches to the sesamoids and contributes to the hallux plantarflexion moment that creates the patient's sub-hallux symptoms.
     
  13. Donna

    Donna Active Member

    Thanks Kevin, we'll have to give that a shot! I actually just spoke to the patient earlier (she called to confirm her appointment time), her next scheduled check up is due in October... She tells me that she hasn't got any "important" or big walks (her idea of a big walk is a 1 week long trek!) between now and then, and since it was mainly during one of her mega walks that she experienced the hallux pain, she's going to persevere with the current wedging and look at further adjustments when she returns for her next visit...

    Thanks heaps for your help! It's got me thinking alot more about forefoot modifications and their effects...

    Donna ;)
     
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