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Biomechanical Quandary

Discussion in 'Biomechanics, Sports and Foot orthoses' started by ianb, May 2, 2018.

  1. ianb

    ianb Member


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    Hello fellow pods. I have a client who has had a previous HX of Left 5th Met fracture, and who is now presenting with pain in the 4th met region, indicative of a plantar plate tear. (Dorsal drawer test elicited pain)

    O/E The client has a Medially deviated STJ axis, with a High Oblique MTJ Axis. Ankle Joint dorsiflexion is slightly limited indicative of tight soleus / gastrcoc complex (No difference between straight leg and bent knee.) B1st MTPs are +60degrees, and has a High medial arch profile, this is possibly due to a forefoot equinas. NWB the forefoot is distinctly lower than the level of the rearfoot.

    Dynamically - At heel strike there is STJ pronation but not excessive, however during midstance there is a failure to re-supinate resulting in forefoot abduction unlocking the MTJ. The Talo/Nav and Nav/Cuneiforms joints appear to elongate / sag collapsing the medial arch. Now I'm assuming there is a lack of the windless effect, even though on the video it would appear that the hallux is going through its 60+ degrees of dorsiflexion. It would seem that there is a decreased first ray dorsiflexion stiffness (I did read K.Kirbys paper on plantar plate tears)

    With regard to treatment, am I to assume that controlling the STJ pronation should In theory stabilise the MTJ and therefore the windless effect should be more efficient. However, I am either overthinking this (or I'm plane daft) but my concern is the loading of the 4th and 5th met area. With a Hx of fracture and now pain in the 4th met do I try to unload the pressure / force going through that area. If so, how? I have read pro's and cons of using forefoot additions, (varus wedges, mortons and reverse mortons extensions). This is my quandary do I try and add a forefoot extension, (and which? as this has fried my brain!) or do I leave alone.

    Any information, ideas would be gratefully accepted. Please excuse my terminology, and if I have missed anything, as I've composed this in haste!

    Oh, the client is very active, walks (for her job), walks her dog (a long way 3/4 miles daily) and is a keen runner. (I said that quietly)
     
  2. Trevor Prior

    Trevor Prior Active Member

    Whilst one cannot be certain from your email, I wonder if the forefoot equinus is actually a plantarflexed lateral column (4/5 mets plantarflexed) which will increase load through the 4/5 met heads. Furthermore, this often compensates by forefoot abduction and the degree of midfoot motion observed dynamically is determined by the mobility of the foot. In this instance, it is quite possible that the fractured 5th has now resulted in more load to the 4th. Load through the lateral column will be exacerbated by the calf inflexibility.

    From your descirption, I would be considering a device which stabilises the medial column / midfoot, I would add a heel raise which will help with both the calf inflexibility and forefoot equinus component and then consider a metatarsal dome. If the lateral column is plantareflexed, I would not consider a redistributive pad at this stage as it may load the 5th.

    I would be inclined not to add any medial rearfoot wedge / skive at this time as you state the rearfoot motion is not much - increasining rearfoot supination moments may increase load through the lateral column and the foot you describe is fairly classic for what I see with the plantar lateral column - this is the defroming force assuming no proximal factors (external hip position, reduced tibial rotation etc.). The rearfoot and redistributive pad can always be added if not responding. BTW, they also have to reduce activity for a while.

    Hope that helps.

    Trevor
     
  3. ianb

    ianb Member

    Thank you Trevor for that. That could well explain what is happening, (never thought of plantarflexed lateral column) thank you! I shall re-check that one. I did mention reducing activity levels..........mmmmmmm.
     
  4. efuller

    efuller MVP

    Was the fifth met fracture a stress fracture, or caused by blunt trauma?

    In tissue stress you should approach this with the idea of what is causing the high loads on the 4th metatarsal head. Is there deformity post fracture fifth? What is the maximum eversion height. Lack of eversion range of motion could cause high lateral forefoot loads (A plantar flexed lateral column fits here). Are there high lateral forefoot loads? (sock liner, calluses). Late stance phase pronation can happen in a laterally deviated STJ axis foot. In stance a laterally deviated STj axis foot can have high lateral forefoot loads.
     
  5. ianb

    ianb Member

    Thank you Eric for your thoughts.
    The met fracture was a stress fracture, there doesn't appear to be any obvious deformity, I'll double check that.
    I will assess the max eversion height next time is see her (next week) hopefully that'll shed some light.
    I totally understand Trevor's treatment aims, of adding a heel raise to improve the calf flexibility. I've just had in my head to try and alleviate the lateral column, both of your thoughts have helped with my understanding of the situation.
     
  6. David Smith

    David Smith Well-Known Member

    Ian - here's my thoughts, presenting problem for the patient is 4th mpj pain that you Dx as plantar plate tear so your objective is to resolve that but without causing pathology elsewhere by your intervention and so you keep in mind the previous 5th met stress fracture.

    My first thought is that this foot type you describe would usually have a lateral stj axis, often medially rotated, so the projection of the STJ axis is from lateral heel to, say, the 2nd MPJ. Is it possible that this is so in your subject?

    2nd the first line of treatment for plantarplate tear is to off load the MPJ and reduce dorsiflexion moments about the joint, this can be done with met pad with cut out and taping the toe to add dorsiflexion resistance, this can be enough in itself and won't add any increased stress to the 5th ray.

    However if you thought it necessary to go further then you might address internal stress within the PFascia. The forefoot or lateral column is plantarflexed giving an equinus appearance, you also note ankle equinus. It would appear from your description that the midfoot RoM is also flexible and so as the longitudinat arches extend on weight bearing there will be a concommitant increase in PF stress and/or plantarflexion of the toes, the windlass action acting in the lesser toes will increase stress in the 4th plantarplate as it is a slip extension of the PF band for that toe. So by reducing the extension of the longitudinal arches will tend to reduce internal stress in the PF and so the plantarplate. This might be achieved by heel lifts, a bit less arch fill in your orthotic precription to keep some arch height captured in your cast or scan, maybe keep the arch profile a bit higher but the shell a bit more flexible. increase pitch a little say from 4dgs to 6dgs.

    Now, as is your concern, what about reducing (dorsiflexion) stress in the 5th ray?

    Does the rearfoot evert enough to allow the forefoot medial column to be fully weight bearing? you say video shows full RoM of hallux thru stance. So either there is not hallux limitus or the subject inverts the foot to avoid it or the rearfoot does not evert far enough and the medial column is not fully weight bearing.

    How to post will depend on many factors you've not mentioned like is the 1st ray low, stiff or flexible relative to the lesser rays, how flexible is the lateral column compared to medial column and how does he compensate in gait for ankle and f/foot equinus? is there early heel lift, toe out, calcaneal gait, extensor sustitution, knee hyperextension or trunk leaning thru hip flexion. As a general rule I might think about medial 2-5th f/foot post with 1st MPJ c/o (maybe cluffy wedge). rearfoot posting may not be necessary but a lot would depend on the STJ axis projection, is it medial, central or lateral and to what degree.

    hope thi shelps someway

    regards Dave smith
     
  7. ianb

    ianb Member

    David,
    Definitely thought provoking!! Again, thanks for the information. I had to read it a few times for my addled brain to comprehend it.

    Anyway, firstly I will certainly check the deviation of the STJ axis... This has had me thinking, as my instinct led me towards a medially deviated axis. However, as yourself, Eric and Trevor have alluded to a laterally deviated axis, I will need to double check this. Initially I did strap the 4th digit, and it did respond well to that.
    I would say the medial column does not fully weight bear, and there is definite extensor substitution and toe out, but no early heel lift. Knee's hips look OK with no obvious issues. The f/ft post you speak of, is that a reverse Mortons or a graduated post?

    It has certainly got me thinking out of the box
     
  8. efuller

    efuller MVP

    Always check the STJ axis location. There are the rare flat very flexible feet with lateral STJ axes and there are high arched feet with medially deviated STJ axes. The location of the axis is not something you can get from across the room.
     
  9. ianb

    ianb Member

    Eric, I'm starting to appreciate this now.
    :)

    Thanks
     
  10. David Smith

    David Smith Well-Known Member

    Ok Ian, all the classic compensations for equinus. The first thing I do in this case is to mobilise the ankle to increase Rom and compliance in dorsiflexion. If your not familiar with this then review this paper https://www.ncbi.nlm.nih.gov/m/pubmed/15266000/?i=3&from=dananberg HJ AND
    dananbergs saggital plane theory and ankle joint mobilisation technique is a good starting point. This is such a powerful treatment tool that every Podiatrist should become familiar with (imo of course)

    Cheers Dave
     
  11. Trevor Prior

    Trevor Prior Active Member

    I think it is unlikely that there is a plantar plate tear of the 4th MTPJ - the dorsal stress test caused pain but there was no reference to instability. Overload to the joint will cause symtpoms but there does not have to be a tear.

    Just to clairfy, I did not make any reference to the STJ axis position in my response as I am not convinced it is relevant in this case.
     
  12. ianb

    ianb Member

    Thanks for the link Dave, I'll have a read of that later on.

    Trevor, I wasn't sure if the 4th met pain was coincidental or not, but I need to check the lateral column and see if its plantarflexed first, as you stated to begin with.

    Thanks again.
     
  13. stevewells

    stevewells Active Member

    Hi Dave - can you explain this comment please - I was under the belief that a STJ axis position lateral heel to 2nd met would be described as an average/normal axis position. Are you saying that it may be lateral but has rotated medically in testing? Of course, I appreciate that the axis position moves but just trying to assimilate your post in my head and I tripped over this bit! I think I have lost something in translation
     
  14. David Smith

    David Smith Well-Known Member

    kirby STJ axis FB.jpg Kirby Lateral STJ FB.jpg
    Yes Steve, The STJ axis can be translated or rotated or both. So the projection of a normal STJ axis will be a bit lateral to the bisection of the heel and point toward the 2nd MPJ (although in later publication Kevin Kirby seems to define the normal STJ axis location as more medially rotated than his original drawings indicate, this is not my experience.) Sometimes you find the stj is very medially translated and sometimes it is very laterally translated. So the axis can be more laterally translated but still medially rotated to the 2nd. Therefore the projection at the heel is very much more lateral than normal.
     
  15. stevewells

    stevewells Active Member

    Thanks for that Dave - I never realised that the axis might project outside of the calcaneus - you have it starting around the cuboid which I assume means that wherever you press on the heel you supinate the STJ (in the second picture)?
     
  16. David Smith

    David Smith Well-Known Member

    Yes precisely Steve, and those Pics are not mine they are copied from Kevin Kirby's facebook page, note the signatures on the bottom right. This type of lateral translation with medial rotation results in high pronation moments in late stance and high supination moments in early stance, so in resting stance there can be heavy supination resistance test but light Jacks test.
     
  17. Petcu Daniel

    Petcu Daniel Active Member

    How these can be explained ?
    Thanks,
    Daniel
     
  18. efuller

    efuller MVP

    The height of the arch is independent from the STJ axis location. Why would one expect all high arched feet to have a lateral STJ axis? Why would one expect all low arched feet have a medially deviated STJ axis?
     
  19. Petcu Daniel

    Petcu Daniel Active Member

    Because of the assumption that 'the anterior exit point of the subtalar joint axis is stationary relative to the
    dorsal aspect of the talar neck' [ https://www.ncbi.nlm.nih.gov/pubmed/16707632 ]. Of course, if I have a right understanding of this assumption! If not, why I'm wrong? When can we have a low height of the arch [probably measured through navicular height] and a 'laterally' deviated talar neck?
    Thanks,
    Daniel
     
  20. Trevor Prior

    Trevor Prior Active Member

    Hmm, I am not sure the diagrams quite stack up. If the axis of a joint is defined by the relative position of the two bones forming the joint (accepting it is only theortetical and only occurse on movement), how can the axis sit 'outside of those two joints?

    What we are seeing there is a balance point between pronation and supination whihc seems to be governed by more that the STJ alone.
     
  21. stevewells

    stevewells Active Member

    On some patients I find locating the axis easier in supine than in prone and often wondered if that was to do with the influence of the Triceps surae on the foot in those positions (ie gravity tending to plantaflex the ankle in supine and dorsiflex the ankle in prone). I often also wonder if it influences my result!
     
  22. Petcu Daniel

    Petcu Daniel Active Member

    I think the joint's axis is defined by the relative positions of the contact surfaces and not the bones volume. A bone surface could have a different orientation compared with that of the bone's volume. Probably this could be an explanation, at least in theory

    Daniel
     
  23. efuller

    efuller MVP

    Those two anatomical landmarks are very good predictors of where the axis is in the rearfoot. However, forces applied to the forefoot also contribute to the moment about the STJ. With the same rearfoot, the axis will project distally to different locations on the forefoot, in a foot with a metatarsus adductus as opposed to a rectus foot.
     
  24. efuller

    efuller MVP

    The axis represents relative motion of the talus and calcaneus. When we palpate the axis location we orient ourselves relative to the transverse plane of the body. There are some feet that can invert quite a bit relative to the leg. As the STJ inverts the plantar surface of the foot can move medially. (or with external rotation of the leg, the axis can move laterally) I guess these feet would have to have the exit point of the Axis some distance up the posterior surface for that amount of inversion. h

    The axis of the joint is determined by the shape of the joint surfaces especially when body weight is compressing those surfaces together. There was a paper by Cahil in the 60's that described how the joint surfaces of the STJ can be part of a double cone. There are two cones pointing toward each other. You can circumscribe an area of the cone to represent the joint surface. The closer you are to the point of the cone, the tighter the radius of curvature of the surface will be. This explains how when you look at the joint surfaces of the calcaneus the anterior/middle facet is concave and the posterior facet is convex.

    Eric
     
  25. Trevor Prior

    Trevor Prior Active Member

    I still do not see how assessing the STJ axis alone would have the axis outside of the two bones.

    When Simon and Kevin described the STJ axis locater, the used the relative motion of the soft tissue at the posterior and anterior aspects to determine the location. Whilst this needs validating, there is no way the locator would be placed where the axis in the diagram is drawn.

    I accept that other joint may be assessed and thus this could be the position but then it is not the STJ axis
     
  26. stevewells

    stevewells Active Member

    Maybe Kevin will see this and put in his twopennuth!
     
  27. Sorry, Steve, I have not been following this thread closely and just got back from a lecture-vacation and am still trying to catch up. Let me see if I can answer most of the questions about subtalar joint (STJ) axis location and help clear up a few misunderstandings.

    The photos included are, indeed, ones that I took. The normal STJ axis is of my son's feet when he was about 16 (he is now 35). The other photo is of a patient that had one of the most laterally deviated STJ axes that I have ever seen from about 15 years ago. The posterior exit point of the laterally deviated STJ axis was not from the cuboid as someone suggested but rather from the lateral aspect of the calcaneal body. Most commonly, the posterior exit point of the STJ axis is within the superior-lateral quadrant of the posterior calcaneus.

    If the STJ axis is lateral enough, it can exit through the lateral calcaneal body, and not on the posterior calcaneus, as illustrated in my patient's photo. I have never seen the STJ axis exit at the cuboid. That does not make sense biomechanically.

    When Simon Spooner and I did the STJ axis locator research, we used the method for finding the STJ axis that was previously described by Jack Morris and Lester Jones, two of my biomechanics professors at CCPM (Morris JL, Jones LJ: New techniques to establish the subtalar joint's functional axis. Clinics Pod Med Surg., 11(2):301-309, 1994). I would not describe this technique as using the "relative motion of the soft tissue at the posterior and anterior aspects to determine the location", as previously suggested. Rather, it involves marking a grid (with an ink-pen) on the anterior-dorsal talar neck and posterior-lateral calcaneus to find the point on the skin where there is the least translational motion, and more pure rotation.

    Morris and Jones' technique is similar in concept to time-lapse photos of the northern sky at night where the north star, Polaris, is seen as a point location while all the other surrounding stars circumscribe circular paths around Polaris. Polaris is in line with the axis of rotation of the Earth and therefore does not translate, but only rotates. In other words, when using the technique by Drs. Morris and Jones to find the posterior and anterior exit points of the STJ axis, we are trying to find the "Polaris" of the STJ axis.

    The STJ axis location can be palpated either prone or supine. I prefer the supine technique. The location of the Achilles tendon will not directly affect STJ axis location palpation results, but the tension within the Achilles tendon when performing the technique is necessary to reduce talus to tibial rotational motions in order to get more reproducible results (Lewis GS, Kirby KA, Piazza SJ: Determination of subtalar joint axis location by restriction of talocrural joint motion. Gait and Posture. 25:63-69, 2007).

    I can't agree with Eric that "The height of the arch is independent from the STJ axis location." In general, the STJ axis becomes more medially deviated and less inclinated as the medial longitudinal arch (MLA) is lower and the STJ axis becomes more laterally deviated and more inclinated to the transverse plane as the MLA becomes higher. Of course, in the middle of the bell-shaped curve of STJ axis medial-lateral deviation, the MLA height may vary some. But I have never seen an extremely flat MLA foot have a lateral axis and an extremely high MLA have a medial STJ axis. I don't think that this can occur biomechanically.

    However, if during weightbearing exam, the high-arched foot excessively pronates on the ground, then the STJ will become, of course, more medially deviated. One must be careful when discussing STJ axis location since what we see in the non-weightbearing exam is not always what we see with weightbearing assessment of the STJ axis location.

    Jack's Test (Hubscher maneuver) will generally correlate well to STJ axis location and MLA height. The higher the MLA and more lateral the STJ axis, a lighter force will be needed during the Hubscher maneuver. The lower the MLA and more medial the STJ axis, the harder the force that will be needed with the Hubscher maneuver. This is quite predictable in 90-95% of patients as I often show during the demonstrations during my lectures and can easily be explained using biomechanical modelling techniques.

    Finally, in the most normally-functioning feet, the anterior projection of the STJ axis seems to be in the area of the fibular sesamoid on the plantar foot when using the STJ palpation technique. However, in the weightbearing foot, the STJ axis projects directly over the first metatarsal head, in the most normally-functioning foot. In other words, from non-weightbearing to weightbearing, the STJ axis rotates a small amount medially in the most normally functioning feet probably due to the increased compliance within the MLA compared to the lateral longitudinal arch in nearly all feet and due to the fact we are not loading the medial column during the STJ axis palpation technique, but only the lateral column.

    Hope this clears up some confusion. However, everyone following along, you must remember that our understanding of the biomechanics of STJ axis location is still a "work-in-progress" and will require much more research, probably most of it occurring well after I'm no longer around. We still don't how how clinically significant the STJ axis is in determining the biomechanics of the foot and lower extremity and in determining injury risk in the human population. That being said, I believe that focusing on STJ axis spatial location is a step in the right direction for us in order to make "podiatric biomechanics" more scientific than what I was taught as a podiatry student in the late 1970s and early 1980s. As stated earlier, more scientific research is needed!
     

    Attached Files:

    Last edited: May 10, 2018
  28. efuller

    efuller MVP

    The axis is still within the two bones. However, when you invert the foot, the projection of the axis down to the transverse plane can be "outside" of the bones. It's a 2-d vs. 3-d problem.
     
  29. stevewells

    stevewells Active Member

    Hi Kevin

    thank you for your explanation. Have you ever noticed or looked at whether there is a correlation between the STJ axis and the Foot to thigh angle (measured in STJ neutral in prone)? I have noticed in my last 4 patients that when I look at the foot thigh angle the subtalar joint axis (marked earlier in the exam) lines up with the posterior thigh. I never noticed it before. I am going to carry on looking at this but just wondered if it had ever actually been studied before?
     
  30. efuller

    efuller MVP

    I stand corrected. There is a correlation between arch height and STJ transverse plane projection. Flatter feet will tend to have more talar adduction. I agree that at a given arch height there will still be a range of STJ axis locations. (Most likely dependent on the amount of forefoot adduction.)

    I have seen 3 pairs of feet with very low medial arches with laterally positioned STJ axes. It is rare, but does happen. I did not think at the time to look at the amount of metadductus.



    I agree with this. The plantar parallel position described in Kevin's paper tends to be slightly inverted from the stance position.
     
  31. I don't know what the "foot to thigh angle" is? Do you have a reference for this measurement? The thigh is rather cylindrical on cross section. How do you determine the angle of the thigh within the transverse plane?
     
  32. RobinP

    RobinP Well-Known Member

    Measurement of tibial torsion. Mainly used in paediatrics
    Taken prone with the knee flexed to 90 degrees. Bisection of the plantar aspect of the foot versus the bisection of the thigh. Intra tester reliability is OK but I personally think the test is inherently flawed. The amount of dorsiflexion applied at the ankle and how the dorsiflexion force is applied greatly changes the foot thigh angle and makes the test largely irrelevant.
    If the foot is dorsiflexed by loading the lateral aspect of the forefootfoot, the STJ pronates and the foot thigh angle externally rotates. If the dorsiflexion force is applied to the medial aspect of the forefoot, the foot supinates and the foot thigh angle reduces (assuming average STJ axis spacial location)
     

    Attached Files:

  33. stevewells

    stevewells Active Member

    This was just something I noticed and thought I would investigate - I'm doing both measurements during my assessment anyway - I realise the foot thigh angle is flawed and I tend to eyeball it - it may give an indication of the possibility or otherwise of tibial torsion being involved and may lead me to look further if torsion is suggested as part of the picture. I am curious by nature and it made me wonder if there was a link.
     
  34. ianb

    ianb Member

    Kevin,

    Thanks for clearing a few things up. Initially, I think I was clouding my own judgement. Just confused myself. Everyone's point of view is appreciated, and I have a much clearer picture of the STJ "Galaxy"
     
  35. David Smith

    David Smith Well-Known Member

    Here's some variations on a STJ axis position theme - just for interest
     

    Attached Files:

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