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Mechanical therapy confusion

Discussion in 'Biomechanics, Sports and Foot orthoses' started by David Singleton, Dec 14, 2011.

  1. David Singleton

    David Singleton Active Member

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    A patient presented to my clinic today, referred from higher management. Diagnosis bilateral Posterior Tibial Tendinopathy the left side more symptomatic. An MRI is being performed on Monday.

    Diagnosed also with Sjogrens syndrome.

    Pain was located to the Navicular tuberosity, with some pain radiating proximally.

    My task was to provide replacement custom orthoses, as it was deemed the old devices were obviously not controlling the foot sufficiently to reduce the pull of the tendon.

    I took casts, and also modified the old devices with 5 deg wedged EVA in clinic, thinking the extra support would help improve the patients symptoms.

    She walked and had more pain instantly in the region of the navicular tuberosity?

    I removed the wedging and she felt more comfortable again over a once up and down the corridor. I then tried a 3 deg wedged EVA rear foot addition, guess what? more pain than the old orthosis alone, but less than the 5 deg rear foot post. So pain seemed proportional to the level of extra rear foot posting applied.

    Patient asked me if I had ever noted this previously?

    Does anyone have any ideas what has occurred here?

    Kind regards David
  2. efuller

    efuller MVP

    I've seen it before. My explanation: An increased arch height doesn't raise the arch. The increased arch height makes the orthotic somewhat uncomfortable and then the posterior tibial muscle contracts more to raise the arch and match the height of the orthotic. Except in the case of active tendinitis. It will hurt to contract the muscle and it will hurt the arch.

    Very often feet with pt dysfunction will have medially deviated STJ axes. So far medial that the medial arch may be on the pronation side of the STJ axis. This is why increased arch height does not directly supinate the STJ.

  3. David Singleton

    David Singleton Active Member

    Thanks Eric, that does make sense.
  4. Mark B Reyneker

    Mark B Reyneker Welcome New Poster

    Hi David and Eric

    Increasing the arch height of a rigid device often times applies pressure to the navicular directly causing more pain. Which leaves you with a dilemma.

    I find it helps tremendously to raise the arch to a tolerable level with a rigid device but then use a 3-5mm poron valgus pad as a cushion on the orthotic. Works like a charm.


  5. David Singleton

    David Singleton Active Member

    Thanks Mark, used that technique many times with the same success you describe, however, not with the same rationale as you. Cheers! I have heard of a navicular 'sweet spot' made from soft poron to reduce pressure on the navicular tuberosity.

    Regards David
  6. I do something similar when required. Horse shoe type of pad where the cut out is under the naviclar where the pain is felt. Increased ORF in the area where the pad comes in contact with the foot reduced under the navicular.

    I do wonder if this type of pad due to the medial STJ axis position will lead to increased pronation moments but comfort is king.
  7. David Smith

    David Smith Well-Known Member


    2 or 3 things occur to me:

    1) Is the mid tarsal joint compliant to GRF? If you increase the medial rear foot post and the midtarsal joint cannot pronate to the ground in response then the medial foot will ride on the medial arch of the orthosis and you will get high/increased pressure on a prominent joint like the navicular. If the midtarsal joint is compliant and especially if the 1st ray is stiff to plantarflexion then adding a medial rearfoot post will effectively make the medial arch of the orthosis higher and as the forefoot pronates to the ground the navicular will lower and the forefoot will abduct and push the navicular onto the orthotic medial arch. In this case a medial skive will invert the STJ but not raise the orthosis medial arch.

    2) If you invert the STJ then you will exaggerate an ankle equinus because you will reduce the flexibility of the foot. This may cause the peroneals to fire in an attempt to increase pronation and reduce saggital plane progression perturbation (SPPP) (otherwise known as saggital plane block) and push the medial arch on the the arch of the orthosis or the patient uses a more toe out strategy to compensate for the SPPP, which again will cause increased Nav-orthosis interface pressure. There may be elements of both these scenarios going on. In this case heel lifts and ankle mobs may be required.

    3) The original reason for increased stress in the PTT was due to pronation moments caused by increased peroneal activity compensating for lateral instability of the STJ (due to valgus forefoot or lateral STJ axis or both for instance). This activity could be passive or active i.e. the CNS initiates increased peroneal activity via muscle activation or a relatively low 1st ray is dorsiflexed by GRF relatively early and / or to a greater magnitude and so increases PL stress passively.
    Which ever it is the answer may be to increase forefoot valgus / lateral posting and not increase medial rearfoot posting that will increase lateral instability and so increase pronation moments due to increased peroneal activity..

    David, One final point ( forgive me for sounding harsh but I can't seem to make the point without sounding over critical) You might have started off on the wrong foot (excuse the pun) I would say that 'your task' was not to do what seemed obvious but 'your task' was to assess the patient and treat according to your own assessment and not make assumptions based on someone else's observations and recommendations. Maybe you did do that but your post does not indicate this.
    You seem to have made the assumption that PTTD needs more support and your definition of support is medial rearfoot posting 'obviously'. However as you have found out, things are not always so obvious.
    I've always resisted the temptation to 'do as your told/directed' by " higher management' (orthopaedic referral for instance) but I take the view that I'm in control and responsible for my patient.

    best regards Dave Smith
  8. efuller

    efuller MVP

    I don't really like this explanation. When compare the barefoot weight bearing arch height to the arch height of the orthosis, if the orthosis arch height is heigher you will get a lot of pressure in the medial arch unless the posterior tibial tendon is used to supinate the foot. (This can be a good thing in feet without PT dysfunction) The orthoic is not going to raise the resting arch height of the foot by itself, especially in feet with medially positioned STJ axes. Of course, if the orthotic is too narrow you can get arch irrriation as the foot hangs over the edge of the orthosis.

    What is the largest change in heel bisection people have seen with a foot on top of an orthosis? Does the STJ move far enough to change the rigidity of the MTJ? Especially in a foot with PTTD and / or a medially positioned STJ axis.

    There are some feet where the pronation you see is caused by the peroneals, but I really doubt that the PTTD foot is one of those. People are basicially lazy and will tend to walk with minimum energy expenditure. The scenario that you describe is a tendonitis from muscles fighting each other. If the peroneals are contracting so hard that a problem is created the body has a choice of increasing posterior tibial tension or decreasing peroneal tension. I just can't imagine the body choosing an increase in posterior tibial tension.

    If a foot had a medially deviated STJ axis and PTTD I would never put in a rearfoot valgus wedge. If there was very high loads on the medial forefoot and low loads on the medial forefoot I might put in a forefoot valgus wedge, but this would be to treat the high medial forefoot loads and not to treat the PTTD,

  9. David Smith

    David Smith Well-Known Member


    In principle I agree with much of your queries to what I have written but, you might agree that the problem of the OP is an unusual one and so I proposed some unusual things that might be happening.

    As an example a couple of weeks ago I had a lady who had posterior tibial tendon pain in the right foot. She was 160cm tall and 120kg in weight. The STJ did not pronate much in gait and in fact at early stance it supinated and at late stance it pronated but not a lot. The foot was fairly cavus and not very compliant in the joints. The STJ axis was lateral. My AM3 pressure mat showed that she was weight bearing mainly on the lateral foot and only lightly and for a short period of propulsion was she weight bearing on the 1st MPJ.

    Open chain examination revealed that the STJ was restricted in eversion and by hand strength the calc bisection did not go beyond vertical or parallel to the tibial bisection. Not a typical scenario of PTT pain, you might agree again? I was a bit doubtful at first that my diagnosis was correct but the pain on palpation was definentely along the trac of the PTT.

    I decided that what was happening in this case was that the PTT was naturally short and restricting STJ eversion RoM. The reason that she was weight bearing on the lateral aspect of the foot was to avoid inversion sprains, however this meant that there was a significantly large pronation moment arm about the STJ from mid to late stance phases and with the PTT being short and the forefoot not able to reach the ground then the opposing moments for equilibrium where borne almost solely by the PTT. On top of this the woman was 157cm (5' 2") tall and 120kg so although the pronation moment arm at any time was relatively small, the body weight or force acting on the lever arm, was twice that of what might be usual. She had ankle equinus and so came early of the heel and so spent more time on the forefoot, which is also increasing time of applied pronation moments i.e. pronation moment integral is greater.The result being excessive stress in the PTT.

    My prescription was ( as far as I can remember because I can't think of this woman's name at present so I can't look up her records) to post laterally from cuboid to heel and medially from cuboid to MPJs. This would reduce lateral instability in early stance and transfer supination moments from the PTT to the forefoot posting in mid to late stance. Also heel lifts and ankle mobs to reduce time and force on the forefoot.

    The result was immediate reduction of the PTT pain.

    Regards Dave
  10. David Singleton

    David Singleton Active Member

    Hi Dave,

    Thanks for taking the time post extensively on this case. All points gladly noted!

    I didn't think you sounded harsh at all!

    Regards David
  11. RobinP

    RobinP Well-Known Member

    Just a suggestion, as there was no indication of age or other examination information but if there is an accessory navicular, increasing the arch height by medially posting the rearfoot can pu tcompressive force on a potentially unstable ossicle.

    I had the unfortunate experience once of causing an insertional tib post tendinopathy by being too aggressive in treating a youth with accessory naviculars that I assumed to be stable but that turned out not to be

    Unlikely, that this is your case but always something to keep in mind
  12. David Singleton

    David Singleton Active Member

    Thanks Robin,

    We are actually awaiting an MRI scan. Will let you know if an accessory ossicle is noted!



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