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Primacy of PTTD

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Scorpio622, Oct 16, 2005.

  1. Scorpio622

    Scorpio622 Active Member


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    After reading several articles of posterior tibial tendon dysfunction, I began to get the impression that adult progressive flatfoot is due to weakness of tibialis posterior. I have always viewed this as a secondary issue, with some other factor causing excessive pronation and the PT muscle succumbing to overuse and degenerative changes (which certainly adds to the progressive deformity). I've seen clinicians treat this primarily with strengthening exercises without addressing the biomechanical issues. It seems to me that the gamut of proper treatment for this does not involve the muscle itself (orthotics, bracing, arch stabilizing sugeries, etc). Does the moniker of PTTD misguide treatment in some way? Is the PT muscle the chicken or the egg?

    Nick
     
  2. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    IMHO, PTTD is NOT due to a weak post tib muscle (I actually think the muscle is very strong).

    Our work that is 'in press' has shown that the force needed to supinate the foot in those with PTTD is around 320 newtons (can't recall exact value) whereas the population normal is around 140-180 newtons.

    Our published research shows that the force to supinate the foot is approx ~30% explained by variation in the transervse plane psoition of the STJ axis --> more medial axis in PTTD --> post tib muscle has very poor/short lever arm to joint axis --> appears weaker, when its not really. Strengthening the muscle is not going to do a lot of good as its probably very strong already, its just a very inefficient invertor as it has the short lever arm to the joint axis.

    As we have shown the force needed to supinate the foot in those with PTTD is so high, it gives a pointer to the probable cause --- ie the muscle has spent a lifetime of working so hard, it just can't keep on doing it ---> degenerative changes in tendon.
     
  3. pgcarter

    pgcarter Well-Known Member

    When ever you see one of these pay particular attention to the actual track of the tendon as it descends...so many are well anterior and pass superficial to the malleollus...rather than posterior to it...very short lever.
    Regards Phill
     
  4. GarethNZ

    GarethNZ Active Member

    From a clinical perspective I have found this "diagnosis" an interesting area of biomechanics. To be able to reduce a patients symptoms, obviously controlling the necessary biomechanics is the first aim, and the offering a strengthening programme of the is any tendinosis present the next (ina nut shell).

    But how to control this patient? One one hand I have wanted to control that excessively pronated, rearfoot collapse with a solid semi rigid device. Maybe around 14/18 deg mod root and a firm medial block in the shoe, that available in the Brook Beast or the Brooks Synergy (two examples, but there are others that are of use). But have noticed that you get them back 2-3 months later and they have compressed the shoe laterally which would happen if they are controlled too much medially/or the shoe to soft laterally which sometimes os the case.

    SO, Craig suggests that the STJ is more medially deviated....so you should need more control medial to STJ axis-increase moments on this side for increase supination...BUT...this foot ends up walking out the lateral side of the shoe... I tend to agree with Craig, but still find myself a little lost. I feel that this does come back to the kinetic vs kinematics arguement, where Kirby has mentioned previously, that the kinetics may have changed slightly but the kinematics may have changed alot (correct me if I am wrong :) ). Hence visually biomechanics may have not changed, but the patients symptoms may have changed.

    Your thoughts??
     
  5. pgcarter

    pgcarter Well-Known Member

    I'll vote for that....non-visual stuff changes and you get improvement...very common I think.
    Regards Phill
     
  6. I do believe that there are a few things happening simultaneously in posterior tibial dysfunction (PTD):

    1. There is a relatively medial STJ axis location.
    2. The more medial STJ axis location causes increased magnitudes of STJ pronation moment.
    3. The more medial STJ axis location causes a decrease in supination moment arm for PT muscle.

    As a result of these above factors, increased tensile stress occurs within the PT tendon that causes some form of tendon damage, either a partial or complete tear or a lengthening of the tendon. All of these factors will also cause some reduction in ability for contraction of the PT muscle to generate PT tendon tension which will then continue the cascade of events:

    4. Decreased internal STJ supination moment (from loss of PT tendon tensile force) which, in turn, causes a net increase in STJ pronation moment.
    5. Increased tensile stress on spring ligament complex.
    6. Tear or lengthening of spring ligament complex.
    7. Increased abduction of forefoot on rearfoot due to #6.
    8. Increased medial deviation of STJ relative to forefoot due to #7.
    9. Start again at #1 again. Flattening of medial longitudinal arch and abduction of forefoot relative to rearfoot will only stop when no other ligaments stretch or tear so that the foot can finally stabilize in a new, more deformed, structure.

    I have reviewed these above factors in a series of newsletters I wrote in 2000 and also in an invited article I did for Podiatry Management magazine.

    (Kirby KA: Conservative Treatment of Posterior Tibial Dysfunction, Podiatry Management, Vol 19, No 7, pp. 73-82, 2000, pp. 99-106.

    Kirby, Kevin A.: Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002.)
     
  7. carolethecatlover

    carolethecatlover Active Member

    I love you Kevin Kirby! You make it so clear. I have been given an assignment on PTTD. I have so many valuable leads thanks to you.
     
  8. Carole:

    Because of your comments above, I am providing you with the text from my latest lecture on posterior tibial tendon dysfunction which I will give this Friday at the 2009 Squaw Valley Foot and Ankle Seminar. Hope this helps.

     
  9. Admin2

    Admin2 Administrator Staff Member

    and don't forget all the other thread we have on posterior tibial tendon dysfunction
     
  10. bartczak b

    bartczak b Welcome New Poster

    To Dr.Kevin Kerby,

    I know I am late to forum but here goes. I am a Certified Pedorthist dealing with PTTD pretty regularly. I was trained when making a UCBL to cast semiweight bearing with a casting board and to wedge the board medially essentially adding the heel skive in to the cast itself. Then posting it to neutral externally after plastic is pulled and trimmed. I was wondering your thoughts on this process. Also my boss recently asked me to show him research on a wedge of this sort to help patients as he doesnt want to wedge like this and just crank the arch up non weight bearing, which i have found causes skin break down during usage. Your advice would be greatly appriciated.

    B Bartczak
    Bartczak42@gmail.com
     
  11. I've never used a UCBL to treat posterior tibial tendon dysfunction, so I don't know if I can help you any if you are set on only using UCBL designs which are not used very frequently here in Northern California for that condition. I prefer, instead, to use a medial heel skived foot orthosis with deep heel cup, good medial longitudinal arch contour, increased width and adequate medial arch stiffness to resist deformation in a more traditional orthosis with a 16-20 mm heel cup and rearfoot post. This specially costructed foot orthosis, when combined with either a motion-control low quarter shoe or a high top hiking boot (depending on the subtalar joint axis location and severity of the PT muscle weakness) has worked quite well for my patients with PTTD for the past quarter century. I have probably treated well over a 1,000 patients with this condition over the past three decades. I have attached an article I wrote over a decade ago on using orthoses for this condition, along with the theory behind the biomechanics of PTTD and the orthosis design features necessary to treat it effectively.

    Hope this helps.:drinks
     
  12. bartczak b

    bartczak b Welcome New Poster

    Thank you. The doctors down here in so cal ask for ucbl's quite often for pttd, thanks for the quick response.
     
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