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Biomechanical treatment post-op Hyprocure

Discussion in 'Biomechanics, Sports and Foot orthoses' started by mike weber, Jul 6, 2010.

  1. Members do not see these Ads. Sign Up.
    Following on from Roberts Biomechancis of Hyprocure thread, Ive had a patient in 4 weeks post op.

    The patient had his left side done 1st and will return to the surgeon to have the right side in 3 weeks.


    Left side symptoms include patellafemoral syndrome and PPTD (Posterial tibialis tendon dysfunction), bascially had adult aquired flat foot.

    Right side symptoms include Tibialis anterior tendon discomfort, and a history of plantar fascia related issues.

    Did a basic assessment today, STJ axis on the left was more lateral than the right post op , but would still class it as medially deviated. Right side very much medially deviated.

    BUT the reason for this thread is 2 fold. He now has the biggest FF supinutas Ive ever come across as now developing lateral column pain on the left side . Is this common post Hyprocure ops ?

    My plan is to deal with this after the right foot has been operated on, with mobilisation and slowly increasing the amount of lateral FF posting ( Forefoot Valgus posting)

    Point 1 is a FF supinatus common after this type of surg, I would think so. At what stage would Treatment be able to begin without negative affects on the implant ?

    Point 2 Simon made a point in the thread above about the implant making a new STJ equilibrium point
    , if the STJ axis is still medially deviated as it is in this case, I would like to use a medial Skive device, but will the ORF (Orthotic reaction force ) of the medial skive have any negative effects on the function of the implant. I would think not but though I would ask. I am a little concerned due to the change in vector angle from ground reaction force to orthotic.
  2. You Said:-

    This suggests one of two things to me. Either that the Mid tarsal joint was inverted (fixed or correctable) OR that the mid tarsal joint was so flaccid that it inverted / dorsiflexed when the patient put the weight on it.

    Thats the problem with terminology like "flat foot", It not the clearest as to whether its a foot-which-is-flat or a foot-which-flattens. Shame on you. ;)

    Now comes the surgeon and pops a bolt in the STJ to stop it pronating so much on WB. Where does that leave the forefoot? Waving in the breeze. The medial bit of it at least! Or, if its a flaccid one, on the ground with very little GRF able to be transmitted through it to the STJ.

    So now, lets match up our moments.

    Weight bearing under the forefoot is now primarily under the lateral column cos the medial bit does not touch the ground on account of the supinatus. All the weight shifted to the furthest point lateral to the axis so MASSIVE pronation moment.

    In the blue corner, we have a little bit of GRF medial to the axis under the heel, no deltoid ligament function (because it will have been stretched in the pre op STJ position), whatever the tibialis group can muster and I suspect damn little windlass.

    Oh and the bone on bolt compressive force. Lots and lots and LOTS of bone on bolt compressive force.

    My advice, be afraid. Be very afraid. I'd love to see an Fscan of this but i'd suspect that there is massive overload on the lateral column. I don't know if lateral forefoot wedging will evert the forefoot or just push it further in the air! I guess much depends on whether there is a functional windlass to pull the 1st met down. But then if you medially post the forefoot you reduce the pronatory moment at the expense of potentially worsening the supinatus and killing whatever windlass there is.

    I'd be going hard and heavy with the medial heel skive and the proximal part of the arch for sure though. Try to take a bit of load of the stent.

    Be interesting to see how long the stent lasts. But I bet it looks lovely and straight with a nice arch and everything. So thats OK and doubtless a roaring success in the surgery ledger.

    Having an angry day.
  3. Fair call shame of me for using crap terms. :D
    At the moment no bone changes so definetly soft tissue contracture for FF supinatus, so think mobs will have a good result, time will tell.

    That was what I was thinking medial skive , but had some concerns about the inverted ORF against the stent, will I be messing with it so it lasts less ?

    As for a nice looking foot, Rear foot ok midfoot, forefoot inverted like you have never seen, I´ll try and get some photos its a ripper.

    some music for you http://www.youtube.com/watch?v=fkuOAY-S6OY
  4. Last edited: Jul 6, 2010
  5. So [​IMG]

    Anyway. Back to the feet.

    Not sure what you mean here. The stent is lateral isn't it? Are you concerned you'll shove the foot into the shoe so the shoe aggravates it directly or are you thinking something clever with vectors?
  6. Ok back to feet.

    Vectors but notsure if clever or not.

  7. Lawrence Bevan

    Lawrence Bevan Active Member


    Your case history makes me wonder if the surgeon should have considered a medial column procedure. Maybe Steve can contribute?

    The only thing I can add is make sure they are an orthotic case, not a surgical failure.

    What are the criteria for these STJ plugs?
  8. Greg Quinn

    Greg Quinn Active Member

    This might help... or not. For the UK, NICE have some guidelines that demonstrate how uncertain the use of this procedure is.
  9. bob

    bob Active Member

    Hi Michael,
    It sounds like your local surgeon has a poor appreciation for the indications for isolated arthroeresis. Your patient probably needed a medial column procedure as well (or totally different flatfoot surgery not being party to the original workup to surgery and only having the knowledge that the procedure is not entirely satisfactory). Is the first ray touching the ground in static/ dynamic stance? Apologies for my poor terminology around biomechanics, but it sounds like you either bring the medial column down towards the ground (surgery) or bring the floor up to meet it (orthotic with some sort of medial arch fill/ forefoot extension under medial aspect of forefoot). If a hyprocure has caused the patient lateral forefoot pain/ overload, adding a medial heel skive would surely have a similar effect? After midstance and through propulsion how effective is a heel skive? I'm lead to believe not very by some of my colleagues, so I would have though any rearfoot modification on your orthotic would be less successful than forefoot modifications? - just re-read your post and noticed that it's only 4 weeks post op. It may be that the patient is consciously laterally weightbearing as a pain avoidance technique following surgery? Is tibialis anterior constantly firing?

    Robert - sounds like you're having a bit of a bad time with your surgery patients? I would have thought the hyprocure will outlast some of the surrounding anatomy, unless the surgeon realises his new kit isn't the answer to all his flatfoot patient's problems and takes it out. ;)
  10. bob

    bob Active Member

    As per NICE guidelines, but very generally flexible flatfoot that's passively reducible that has failed conservative care. Adjunctive procedures are used to address any other associated problems (eg, tendoachilles lengthening for ankle equinus, medial column procedures for varus forefoot/ supinatus). :)
  11. Hi Bob thanks,

    1st I only saw this guy for 30 min so full mechanical exam still to be completed.

    and not wanting to get into if the correct procedure was completed so my phone does not ring and get told " I´m a simple podiatrist who should know his place, again". it would appear that the STJ has a new equilbrium point but is still maximally pronated ( ie Simon post quoted in my 1st post).

    My main concern is the FF supinatus, the 1st ray does not touch the ground due to the plantarflexion of the Hallux, but with a little pressure is does.

    My orginal plan was no rearfoot post, large FF Valgus post and mobs to reduce the FFsupinatus , but as the STJ axis is still medially deviated and he still is having PTTD symptoms he still requires a change in STJ moments, so wondering about the change in Vector angle if it would negative effects on the stent?

    As the supinatus is able to be reduced without too much force manually the use of the FF Valgus post will/should help with windlass and in many ways lead to reduced loads on the Tibialis anterior, tibialis Posterior etc. If the supinatus was a fixed FF Varus I might consider the varus post, but not at the moment, unless the supinatus can not be reduced.

    I also agree that the patient is not so used to the increased force on the lateral column while walking in his new position, as have discussed this with him.
  12. I agree

    Thanks Greg I look through this.
    Ps when are we getting the mechancial break down of the prefabs we were discussing last week ?
  13. My local surgeon team is not (yet) trained on hyprocure, a fact for which I am profoundly grateful.

    I can see the application for hyprocure, I really can. But I also have huge concerns about it's widespread use.

    The sad truth is that pronation is still considered the root of all the evil in the world by a lot of pods and pod surgeons. A device which promises to limit or prevent pronation will be immensley attractive to these folk, and I can see it being horribly abused and overused.

    In general, and this is by no means a blanket critism, I see a lot of surgeons of both orthopaedic and podiatric variety, far too concerned with position and militantly indifferent to function. I see so many patients who go on to develop unstable 1st rays and ff supinatus because their windlass does not function any more post HAV surgery, and these are to a one considered in the "successful outcome" column because the toe is straight and the foot looks nice. And I don't just mean the 70 year olds who had no function to start with, I'm talking about people in their 20s and 30s.

    The idea of a world where the "overpronation" which 90 % of patients get diagnosed with is treated with a stent terrifies me to the very core of my being. Especially when the operation is superficially straightforward and reversable. As you say bob, I fear the surrounding anatomy would break down before the stent.

    Pronation is the fall guy for every twinge of pain from jaw to toe. We already have orthotics being optimistically used to treat almost every, no strike that, every msk problem there is. Will the stent be used the same way?

    As mikes patient illustrates, function and morphology can go hang so long as overpronation is blocked.
  14. Some fascinating Data on the Nice information (thanks Greg)

    Two things strike me about this Data. One is that some of it is very postive and encouraging. The other is the huge degree of variation between the outcomes.

    The last one, for eg, describes extrusion on 9% of patients within the first year. That's a lot inside one year. If that was the figure for a screw coming loose in an HAV surgery, that would be a concern.

    The case series described in 2.4.1. Describes a MASSIVE variation in the "requirement for implant removal", from 1% to 39% One person only had to remove 2 out of 234 proceedures, another 11 out of 28!

    Given that these are "case series" and therefore the patients are selected specifically, it would seem that either some people are much better at using the stent, or that some people are much better at selecting the patients. I suspect the latter. This returns to my earlier point. I can well see the application for some patients, but I fear it will be overused for patients who are not so suitable.
  15. bob

    bob Active Member

    I totally agree with you Robert. I would like to credit most of my colleagues with some intelligence and the ability to realise an arthroeresis by any name is still an arthroeresis and carries the same indications as they ever did. The company marketing this product are particularly good at their job and seek to re-demonise pronation in order to sell units. I guess the difference between blindly dispensing anti-pronation insoles and doing hyprocure procedures for 'curing hyperpronation' is that hyprocures are a bit more difficult to take out. Having said that, it could be worse and surgeons could be performing more invasive surgery for the same reasons.

    Your paragraph on hallux valgus is interesting and probably needs a new thread. It's very difficult to quantify what a good post-op result is (from everyone's point of view), but I can certainly spot bad one (sadly). As ever, we are only ever going to see each other's failures/ complications and all the good results are walking around forgetting they've ever been to see us.
  16. bob

    bob Active Member

    Hello Michael,
    Shame your local surgeon sounds like an idiot. How about using an orthotic with a varus forefoot wedge and gradually reducing the amount of wedging to a neutral position over a period of time while the patient recovers from the op? Again - I'm no biomechanics specialist so feel free to tell me if I'm talking rubbish.

    Does the patient have any scans of tibialis posterior? Did the surgeon actually do anything to the tendon?
  17. I know that the right side ( not the side that´s had the stent, yet) he had a Deltoid ligament repair which did not help.

    As for scans I´m not sure to be honest, we discsused the mechancial stress on the Posterior tibialis, it has not had any surg repair. Which is why the medial Skive will be so important in his device.

    As for talking rubbish Ive never had a patient with a STJ stent before so there can be no rubbish talk and all talk is good in this case, I think. You understand the STJ stent function at a much higher level than me, so thanks for taking the time.

    I´m not a big fan of the varus FF post but do use them from time to time, I´m not sure if it the right way to go with the flexiable FF supinatus ( I would never use it if he did not have a STJ stent)

    does anyone have an option on this ?


  18. Can't really see how. Obviously a big part of the Vector angle will be informed by the friction coefficient of your top cover so if you are concerned you could always steer clear of the slippy topcovers. Otherwise I can't see where there would be a problem. As far as the stent is concerned, the only significant factor (I suspect) would be the change in residual moment, how that change is affected should'nt matter.

    Unless I'm missing something, in which case please someone jump in.

    That's what I'm afraid of. If its a straight up fight between truth and profit I know who my money would go on.

    And there still are a few who cheerfully go ahead and do a triple arthrodesis for a flat foot. I have a letter somewhere from a surgeon to a GP stating that he was surprised they had complications as this op is 95% effective.

    Here's a nostradamus type prediction and I will take bets on it. At the moment a relatively small number of people are offering Hyprocure, all established and respected surgeons with clinical integrity (to my knowledge). Sooner or later a specialist private clinic will open with less integrity, probably in london, which will offer little or nothing else. They'll be a big national advertising campaign for the new wonder op which "cures pronation" and people will form queues for it (think Parish and Bell but with surgery instead of orthotics). Later, people will form queues at the local podiatists to have their feet fixed because the biomechanics were not considered when their feet got bolted.

    Any takers?

    I think we should rekindle the ff valgus / ff varus debate on another thread. Been a while since we did that one.
  19. No, I thought. A company selling a surgical device would know better. Bob must be overstating.

    Before I rant, In deference to those I respect using the stent to good effect I will re-iterate that IMO its a good idea for some cases, has a place, and that many a sound product has overzealous marketing.


    Go here http://hyprocure.com/welcome.php

    and look at the video "self - check"

    That is the biggest steaming pile of cynical, profit driven, outdated, unsupported factually bankrupt rubbish I've seen in a long, long time!

    Apparently in a normal foot the heel and lower leg will be perfectly straight and perpendicular to the floor. If its not you have "hyperpronation".

    "Hyperpronation" being such a funkier term than "overpronation". I may patent the term "ultrapronation" and get ahead of the field! Megapronation perhaps. Uberpronation.

    The website even has shades of Rothbart
    Note the absence of the word "may" in that sentance.

    So there you go. Anyone who has a flexible foot is a candidate. Any foot which is not straight down the back of the leg is hyperpronated and hyperpronation causes red lines everywhere.

    Stents for everyone then.


    To quote Simon's hero

    "The story so far: As usual, Ginger and I are engaged on our quest to find out what the hell is going on and save humanity from my nemesis, some bastard who is presumably responsible."
  20. Griff

    Griff Moderator

    Just had a peek at the website


  21. bob

    bob Active Member

    Say what you mean Robert, why dilly-dally? :D

    The 'inventor' of the device is clearly commercially driven. The reality as we've said before is that a hyprocure is an arthroeresis. I presume the people who buy into the marketing hype and stick hyprocures in everyone will be quite busy watching x-factor, big brother, drinking slimfast and out shopping for JML's latest products anyway so some of their patients might get lucky. Like I said before, I'd like to think that most of my colleagues are intelligent people and can see through it. Regardless, like any operation, there will never be a 100% success rate.

    Michael - I love the bit in your post where you said I have a higher understanding of the stent's function - how I laughed. Seriously though, I doubt it. McGlamry's text on foot surgery has a chapter on arthroeresis that is a worthwhile read, but I don't believe it improves knowledge of the function of an arthroeresis anymore than Kevin Kirby's old lecture notes that were posted on here a while ago, so it's a pretty level field. I've performed quite few arthroereses in my time and had experience, but I'm not sure you biomechanics guys would rate a surgeon's real grasp of the function of anything!
  22. Actually, beleive it or don't, that was the positive and nice version. I deleted what I first wrote because I thought it was "a bit harsh".


    Yeah. Be afraid.
  23. efuller

    efuller MVP

    When I was at the college we had the EMED and I did a post op on an arthroresis and it did have high lateral loads.

    The plug reduces the range of motion of the STJ in the direction of pronation. So, if the heel bisection could evert 10 degrees before surgery, it will only be able to evert to perpendicular after surgery. (Numbers out of thin air, for illustration purposes only.) That is what causes the "supinatus". I have a hard time calling it a supinatus as that was originally described as a forefoot deformity. The plug creates a rearfoot varus and inverts the maximally pronated position of the whole foot.

    A forefoot valgus wedge would be the exact wrong thing to do. The problem now is lateral column overload with an STJ that cannot evert any further.

    I had a patient once who was in a motorcycle accident and had an STJ fused in varus with pain under the cuboid. He had a bag full of orthotics that didn't help. I made him a device with a forefoot varus extension and he was happy as could be.

    The problem is not enough medial forefoot load and you have to bring the ground up to the foot. The other option is to wait until the lateral column breaks down, or the plug breaks down under the huge pronation moments that are being resisted by the plug. In this situation the center of pressure is very far lateral and the STJ axis is still medial (less medial than it was). But the center of pressure being under the lateral column will still create a huge pronation moment that is resisted by the end or range of motion in the direction of pronation of the STJ. The end of range of motion is the plug and it is being crushed. So, a medial heel skive would be nice to add in addition to the forefoot varus extension out under the metatarsal heads. The medial skive would reduce the pronation moment that is crushing the plug.

    Maybe your patient will go back to the surgeon and talk about how his lateral forefoot hurt after the surgery and your massive device is the only thing he can walk around in without pain. And by the way, I don't want the other side done because the device on the other foot is making walking bearable. Wishful thinking that the surgeon would realize his mistake from that scenario. I wonder if high lateral loads were mentioned in the informed consent part of the pre-op discussion

    Last edited: Jul 8, 2010
  24. Thanks Eric, Bob you were on the money.

    Thanks also to Robert for working through it all with me
    Last edited: Jul 8, 2010
  25. bob

    bob Active Member

    Woo hoo! Thanks for teaching an old dog new tricks guys!
  26. Mike:

    Sorry for not answering sooner....

    I did a lecture on just this topic on the Biomechanics of the Subtalar Arthroereisis (STA) Procedure twice in the last year. Eric Fuller's posting was right on.

    The STA procedure (the hyprocure implant is only one of many STA implants) works by adding a spacer into the sinus tarsi therefore limiting the range of subtalar joint (STJ) pronation available and basically "resetting" the maximally pronated rotational position of the STJ. The STA procedure will make the STJ axis spatial location more lateral (i.e. less medial) in the weightbeaing foot since the talar head can no longer adduct and plantarflex as much as it could preoperatively. While this procedure can limit the medial STJ axis deviation, it is not without its potential painful sequellae.

    By resetting the STJ maximally pronated position to a point where the medial forefoot cannot load fully, the lateral column will become overloaded creating increased magnitude of dorsiflexion moment on the lateral column, especially during late midstance. The increase in external STJ pronation moment by transfer of ground reaction force from the medial to lateral column also causes increased compression force between the implant and the talar lateral process and floor of the sinus tarsi of the calcaneus which may also lead to increased risk of sinus tarsitis post-surgically. Thankfully, the STJ implant may be removed fairly easily to reverse the all-too-common problems that occur when foot surgeons are over-utilizing this implant without understanding the biomechanics of what they are doing.

    I also had a patient that developed a painful dorsal-lateral midfoot (at the 4th and 5th metatarsal-cuboid joint) from another podiatric surgeon's use of the STA implant that was too large in diameter (and the implant was used for treating plantar fasciitis, no less!). Another podiatric surgeon removed the implant which resolved the lateral dorsal midfoot interosseous compression syndrome (i.e. lateral DMICS), but then her plantar fasciitis returned. The patient was referred to me, I made a better pair of custom orthoses for her than what was made by the original STA implant surgeon and she became pain-free within three weeks of my dispensing orthoses to her. She wondered why the first surgeon didn't make better orthoses in the first place to save her 9 months of pain and suffering from the ill-advised and poorly-performed first surgery and revision surgery.

    This brings up a philosophical question that I have noted over the past quarter century of clinical practice but not yet have had answered to my satisfaction: Why is it that the podiatrists who have the least understanding of the complex biomechanics of the foot are also often the ones doing more surgery when compared to the podiatrists who understand biomechanics the most and are doing more foot orthoses than foot surgery? Shouldn't the ones (i.e. surgeons) that risk permanent harm to their patients by doing foot surgery be also the ones who have a much better understanding of the complex biomechanics of the mechanical appendage that they are making permanent structural changes to? Something doesn't seem quite right to me when the podiatrists or orthopedic surgeons who are most ignorant in biomechanics are often also the ones doing the most foot surgery.:confused:

    Anyone want to propose an answer to this perplexing observation?
  27. bob

    bob Active Member

    Good question, but perhaps you ought to start a new thread on it Kevin? And be prepared to remain unsatisfied.......... :D
  28. IMO, and with exception of everyone reading this thread because by definition these are the surgeons who have a desire to constantly improve themselves...

    Because Biomechanics is the "road less traveled." It requires ceasless study and re-examination of ones self and yet the more one learns, the less one realises one knows. In many senses it demands that one constant re-invent ones knowledge base. Surgery, by contrast, requires bigger initially investment in technical and manual skill but once that is learned one can coast happily, enjoying the prestige and earnings with no more study than one desires.

    A surgeon may feel they have "arrived" when they get their consultant status (in the UK at least). A biomechanist, perhaps, never truly "arrives".

    The two are different and appeal to different Id's within us.

    And dare I say because it is easier to cut a foot open than to try to understand how it works?

    Or, if you want a bumper sticker, surgery is for sadists, biomechanics is for masochists and the surgeons who like biomechanics (ie you if you're reading this) are by inference Sado-masochists. ;)

    I love biomechanics. Love it. I've never had the slightest urge to upgrade to be a podiatric surgeon. I know surgeons who've no understanding of biomechanics and, more, desire none.

    Perhaps that is not how it SHOULD be but I think that is how it IS.
  29. bob

    bob Active Member

    Robert - whilst I don't disagree entirely, there's hopefully a bit more to all facets than we could possibly type out on here. Anyway, I'm starting a new thread using your post as a starter with Kevin's quote in there. :D
  30. Deborah Ferguson

    Deborah Ferguson Active Member

    Hi All
    I've been following this thread with both interest and alarm. Having watched the sales video I wonder what the long term implications are for children if this procedure is carried out on kids over the age of 3 ! as stated in the pitch.


  31. bob

    bob Active Member

    Hello Deborah,
    Short answer is - I don't know. I don't do paediatric cases. As I said in an earlier post, the company marketing their product are doing their job and marketing their product. The surgeon using the device should have a reasonable understanding of the indications and potential post-op sequellae prior to offering the surgery. This particular design of arthroeresis has not been around long enough to give you an accurate answer to your question, but I know colleagues that have used other arthroeresis designs in children over the years. Again, I do not know their long term results, so they would be better placed to give you a more accurate answer (although I doubt they will do 10 or 20 year follow-ups on their patients). The only returns they will see will usually be people that have a problem with the original site or other foot problem, which may skew their follow-up results (unless a significant number of the original patients returned with a similar complaint).
    My personal opinion of the hyprocure is that it is an arthroeresis. Currently, it is my favourite arthroeresis as it has less chance of moving than some of the other designs I have used or seen. I hope that myself and my colleagues see through the hype and use the product where necessary.
  32. Here is a lecture that I have given a few times over the past year, along with some illustrations I made specially for this lecture, on the Biomechanics of the Subtalar Joint Arthroereisis Procedure that may help answer some questions on this procedure.


    Attached Files:

  33. Here are some posts on the subtalar arthroereisis procedure from the thread on Biomechanics V Surgery.

  34. Thanks Kevin for trying to get the right discussion into the right thread. I'm afraid this post might not be in the right place either :eek:. I was just thinking about Bob's point re: forefoot to rearfoot relationship and I was trying to think of how many patients I had seen in which all five metatarsal heads where not weightbearing in static stance . On reflection the vast majority of these had undergone 1st ray surgery. I've not seen any patients that have had a stent fitted to the sinus tarsi, so am unaware of how many post op who are not weightbearing on all five met heads?

    In regard to a foot that has forefoot supinatus pre-operatively: supinatus is an acquired soft tissue thing, as oppose to a fixed osseous deformity, i.e. forefoot varus. So post operatively does the supinatus correct itself over-time in such cases? Just some musings.
  35. The supinatus may reduce ( my thoughts about speeding up the procss was to add a FF valgus post) but though the discussions with Robert, Bob, Eric and Kevin I would think the lateral column would become a huge issue, before the supinatus corrects itself.
  36. Hi Deborah
    As someone who sees mainly children I share your concern!

    If you want a scare, go to the testimonals page and look at the before and after pics.

    How old is that foot do you reckon. 3, 4? And the deformity looks like about 3000 I've seen self resolve with a only little help. And they stuck a bolt in.


  37. The lateral column overload, generally evidenced from pain in the plantar aspect of the lateral metatarsal heads or pain in the dorsal-lateral midfoot with overcorrection from a subtalar joint (STJ) arthroereisis is not a common complication that I have seen. The surgeon must be able to preoperatively assess whether they will be able to laterally deviate the STJ axis enough with the implant to improve STJ mechanics while not also overloading the lateral column. I have only done the procedure on cadaver feet and it it is not a technically difficult procedure to perform. Most surgeons that use this procedure in their practices will use it in isolated fashion (without adjunctive procedures) in more severely pronated juvenile flexible flatfoot. In the surgeons that use it in adults, it is more commonly performed along with other surgical procedures to minimize the compression load on the implant while attempting to also optimize foot shape and foot and lower extremity function.

    The biomechanics of the subtalar joint arthroereisis procedure is a fascinating subject for me. Understanding how spatial location of the STJ axis affects the forces on the implant requires a good understanding of subtalar joint axis location/rotational equilibrium theory....which, unfortunately, not many podiatric surgeons, that I know of, seem to truly comprehend. Again, if the podiatric surgeons understood foot biomechanics more fully, I think there would have fewer post-op sequellae from their foot surgeries due to better conservative and surgical procedure selection for their patients.

    Another paper that needs to be written......:morning:
  38. Deborah Ferguson

    Deborah Ferguson Active Member

    Hi Robert
    I'm not even sure the before and after pictures of the children's feet are the same feet !. Surely it must be a last resort to operate on potentially such young children not a first option and is it entirely ethical given there seems to be very little research evidence for this procedure.
    Wouldn't let them loose on my kids.


  39. bob

    bob Active Member

    Am I wrong in thinking that the axis of pretty much every joint moves constantly as the foot and ankle move? I thought (through fairly recent reading) that the axis was defined by the relative motion of the two bones. So, as these bones rotate around the axis at a certain measurement point, it is possible to provide a description of where this axis lies in space. However, at the next measurement point, the two bones move and the axis defined by their relative motion for the new measurement point has moved as well. Am I way off here and have I become confused (I'm feeling it a bit!) ?
    If my reading and basic understanding of the above are right, I suspect that (partly based on the idea that an arthroeresis blocks motion into pronation) the axis of the subtalar joint is not laterally deviated by the device, but there is less medial excursion of the axis. If you were to take an average of the transverse plane positions of the subtalar joint axis during stance, I suspect that the AVERAGE of a foot with an arthroeresis would be more laterally deviated than a foot without. I do not think that the arthroeresis would laterally deviate the most laterally based axis (where the foot is most supinated) measureable as its function is to block pronation, not wedge open the sinus tarsi throughout the function of the joint. If it did, surely the patient would experience minimal subtalar joint motion and quite a lot of pain - possibly accounting for the problems Michael's original patient was complaining of?
    Again, I might be way off here, but I'm struggling to grasp why arthroereses work so well clinically in the right patients if there is a single axis that does not move as above, but is simply laterally deviated?

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