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Bojsen-Mollers high gear/low gear

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Craig Payne, Apr 29, 2006.

  1. Craig Payne

    Craig Payne Moderator

    Articles:
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    In the thread on Rothbarts Insoles, I alluded to BM's high gear/low gear axis concept (transverse/oblique axis). Simon mentioned some problems with it.

    I have been meaning for a while to post this case:

    This is a 14 yr old boy with non-specific pain in the midfoot/midtarsal region of one foot (look at pics below and see which foot you think it is). He also has pain in the low back and sacroiliac joint.

    This is the left foot at midstance on digital video (from SiliconCoach):

    [​IMG]

    This is the right at midstance on digital video (from SiliconCoach):

    [​IMG]

    Which one do you think is the symptomatic one?
    If you thought left, then you wrong - he has no pain in that foot (he is only 14, so that does not mean he won't in the future).

    So why is the right symptomatic? .... look at the left during propulsion:

    [​IMG]

    Propulsion is via met heads one & two (ie BM's high gear or transverse axis) ... a good thing.

    Look at these two sequential frames of propulsion of the right foot:

    [​IMG]
    [​IMG]

    Propulsion is via met heads 2 to 5 (ie BM's low gear or oblique axis) ... a bad thing.

    Here is the picture above marked with SiliconCoach drawing tool to illustrate this:

    [​IMG]

    This is why the right foot is probably symptomatic. Also note the "direction" the foot seems to be heading during propulsion .... its heading laterally, when body weight should be going medially towards the other foot. There must be a "battle" going on proximally as the body deals with this conflict --- ie bodyweight is heading off laterally when it needs to be going medially ---- this may account for the proximal symptoms he was having.

    Using Rothbarts approach, padding/posting would have gone under met head one --> worsen the problem.

    This patient was treated with Blake inverted orthoses (supination resistance has very high) to control the rearfoot pronation. Additionally on the right, the foot was casted with the first ray plantarflexed (to get it to the ground). The plaster cast was modified to increase lateral column support (to move body weight medially) and the orthoses shell was modified with a 2-5 bar (valgus post) to further move weight medially. The foot and postural symptoms disappeared in 2 days.

    What say you?
     
    Last edited by a moderator: Apr 29, 2006
  2. DaVinci

    DaVinci Well-Known Member

    Interesting!

    I keep hearing about these high and low gear axes, but never really understood them. Craig, can you (or anyone else) please give an explanation of them.

    Thanks.
     
  3. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    ...happy to oblige...
    BM originally proposed that there were two axes across the metatarsal heads. The transverse axis consisting of met head one and two. The oblique axis consisting of met head 2 thru five.

    If you draw these lines/axes across an outline skeleton of the foot, then draw a perpendicular line from the axis to the insertion of the achilles tendon.

    Look at the length of the line from the achilles insertion to the axis...the distance to the oblique axis is shorter than the distance to the transverse axis.

    When weight starts to come off the heel during gait (ie to pivot about the MPJ's), "weight flow" (or whatever you want to call it) will follow the path of least resistance ---- as the distance from the achilles insertion to the oblique axis across met heads 2 to 5 is shorter, this lever arm is much shorter than the distance to the transverse axis (across met head 1 and 2), so "weight flow" will be lateral as this shorter lever arm is easier for the body to use .... this is exactly what you see on the centre of pressure maps under the foot (ie the path of the CoP is initially laterally) - BM's concept of the oblique axis and shorter lever arms is a theoretically coherent and biologically plausible explanation of what you see with CoP.

    The problem with the body using this path of least resistance (ie the oblique axis) during propulsion is:
    1) that body weight is going laterally when it needs to be moved medially towards the other foot (see my comment above about proximal "conflict")
    2) as the lever arm to the oblique axis is relatively shorter, its not very efficient at generating power/thrust for forward progression.

    According to BM, the body needs to switch to the transverse axis (ie met heads 1 & 2) because:
    1) Body weight needs to be moved medially to the other foot
    2) The lever arm from the achilles insertion to the transervse axis is longer than to the oblique axis, so this is more efficient for the generation of power/thrust for forward progression.

    This is exactly what is seen in progression of the CoP - ie it moves medially towards met heads 1 and 2 after initally heading laterally. BM's concepts provide a theoretically coherent and biologically plausible explanation for what is seen.

    This is where the high gear/low gear comes in -- the obique axis is the low gear and the transverse axis is the high gear (just like the gears in the car).

    Many things can interfer with this, for eg:
    1) First MPJ range of motion (ie hallux rigidus; structural hallux limitus; functional hallux limitus)
    2) Dysfunction of windlass
    3) Metatarsal length/parabola problems
    4) Proximal influences
    5) I have even seen it suggested (and have no reason to doubt it) that the foot types proposed by Root et al, (ie forefoot varus; forefoot valgus etc) actually exert there pathological effects via interference with this transfer from the oblique to the transverse axis.
    6) etc

    Does that make sense? ... it is a bit difficult sometimes without the diagrams to explain it (just ask the students :eek: ). For those in Australia, it will be gone over with pictures at the seminars I am doing.

    I know Simon Spooner has a problem with some of BM's concepts, so hopefully he will chip in and add to this thread.
     
    Last edited by a moderator: Apr 30, 2006
  4. Bruce Williams

    Bruce Williams Well-Known Member

    Craig;
    Wow, that is problably the single best synopsis I've ever read on BM's paper on High and Low gear propulsion. You actually helped me to get some discrepancies much more clear in my mind. Now I think that I understand your test to decide on whether a pt may need a FF valgus post on their device. Please correct me if I'm still wrong, but if, when the pt stand on one foot, they have lateral movement and they don't put pressure sub 1st mpj, then they would probably need a lateral FF wedge, correct? But, if they both move medial and put pressure sub 1st mpj, then they probably would not need a lateral FF wedge. Now, what about those who do put pressure sub 1st or equally, but move more lateral? Also vice a versa? I'd probably be inclined to Valgus post the FF in all pts' but the ones whoe both move medially and put pressure sub 1st mpj.
    Excellent post in both instances Craig! Also, I do not envy your Australian and UK touring schedule, but do wish that we could get you to do that one day presentation in the U.S. Maybe we could start to put someting together in Chicago before or after PFOLA in December??? I could try to drum up some support if you are up to it?
    Take care!
    Bruce :)
     


  5. I wrote this literature review some years ago, but never got around to finishing it :mad: Maybe this will inspire me to get the job done...

    THE STRUCTURE OF THE METATARSAL ARC
    The metatarsal arc is a graphic representation of the relative position of the metatarsal heads in the transverse plane. The metatarsal arc represents "the area of weightbearing transmission of the forefoot" (Sansone 1956). Variation in the metatarsal arc occurs as a function of variation in the relative metatarsal lengths and there spatial orientation.
    It has been suggested that differences in relative metatarsal length patterns (and thus, the metatarsal arc) are characteristic of different races (Hawes et al. 1994). This observation is largely intuitive, being made from the differences in the portrayal of digital and metatarsal protrusion in ancient art (Klaue et al. 1994). Craigmile (1953) and, later, McCarthy and Gessner (1993) maintained that relative metatarsal length patterning is genetically determined at the time of fertilisation and remains constant throughout life; they provided no empirical evidence to support this conjecture.
    The metatarsal arc is often but wrongly, called the metatarsal parabola (Robbins 1981). A parabola is a U-shaped open curve, the extremities of which tend towards parallel lines as they approach infinity. A parabola is symmetrical about its focus. The inflection point of the assumed metatarsal parabola occurs at the second metatarsal head. Robbins argued that the metatarsal arc was asymmetrical about the second metatarsal head and could therefore, not be parabolic. Demp (1964, 1971, 1975, 1976, 1978, 1983,1990a, 1990b, 1994) demonstrated that the metatarsal arc is rarely a parabola, but more commonly a hyperbola or an ellipse. Pointing to a lack of symmetry as a flaw in Demp's contentions, Robbins (1981) disputed the use of hyperbola's and ellipses too. He maintained that a semi-logarithmic model best described the relationship between the metatarsal heads, following his study of 25 dorsoplantar radiographs.

    Both Demp and Robbins modelled the metatarsal arc as a static structure, fitting equations to describe the relative positions of the metatarsal heads observed during static bipedal stance. It seems unlikely that the static relationship between the metatarsal heads remains unchanged and constant during dynamic function.

    Huson (1999) believed that the metatarsal rays are part of a non-constrained tarso-metatarsal mechanism in which each metatarsal ray has independent stiffness (resistance to dorsiflexion) and range of motion. He suggested that the second metatarsal ray is the stiffest and described it as a "fixed spoke". The biomechanical modelling performed by Salthe et al. (1986), and the dynamic forefoot pressure analyses performed by Hughes et al. (1991) supports this conjecture. Alteration of a metatarsal's position in the sagittal plane will alter the relative protrusion of that metatarsal in the transverse plane (Barnett 1956, Heden and Sorto). Stokes et al. (1979) and later, Hughes et al. (1991) showed that during gait the metatarsals do not load and unload simultaneously with one another; they load and unload on independent time-scales. As each metatarsal is loaded it is deformed and displaced dorsally (Salathe et al. 1986, Winson et al 1995) and its relative protrusion in the transverse plane increases (Heden and Sorto 1981). Conversely, as load decreases beneath each metatarsal, dorsal deformation and displacement is reduced and relative protrusion decreases. The resultant change in relative protrusion is dependent upon the length of the metatarsal and the amount of dorsal displacement of the metatarsal head (Janis and Donick). This is dependent upon the metatarsal "stiffness" and the load applied beneath it (Salathe et al), i.e. the position of the metatarsal at any given time is dependent upon the moments acting on it about the tarso-metatarsal joint axes. Thus, at any given moment in time during the forefoot loading / unloading cycle the metatarsal arc may describe a different mathematical function. This function may be of the same general form as the static arc e.g. hyperbolic, ellipse etc. or it may transform e.g. from hyperbolic to ellipse, to parabolic, to ellipse and back to hyperbolic. Further research is required to determine the accuracy of this "dynamic metatarsal arc" hypothesis.

    PROPULSIVE FUNCTION AND THE METATARSAL ARC
    The metatarsal arc has three major functions:
    1. Balance
    2. Weight transmission
    3. Fulcrum
    Morton (1930) claimed that in the later stages of gait, weight is transferred to the medial forefoot and the foot is levered forward about an axis that passes transversely through the heads of the first and second metatarsals. Morton provided no data to support his conjecture.
    Henenfeld (1953a) theorised that structural arrangement of the metatarsal arc determined the propulsive characteristics of the foot. He suggested that the characteristic relative protrusion of the second metatarsal resulted in a forefoot propulsive mechanism involving two axes with the second metatarsal head acting as a fulcrum. Propulsion was possible either through a lateral pivotal axis formed by the heads of metatarsals 2-5 or a medial pivotal axis formed by the heads of the first and second metatarsals. Henenfeld contended that this gave the foot the ability to thrust-off in two different directions.

    Bojsen-Moller and Lamoreux (1979) did not acknowledge the work of Henenfeld, but drew similar conclusions. They also maintained that propulsion occurs around two co-operative axes with the second metatarsal acting as a pivot. Noting that the obliquely orientated lateral pivotal axis has a relatively short radial arm with the ankle joint axis, they termed this the "low-gear axis". The transversely orientated, medial pivotal axis has a relatively longer radial arm with the ankle joint and was therefore termed the "high gear axis".

    Both Henenfeld, and Bojsen-Moller and Lamoreux believed that the axis employed during each step was dependent upon the set of conditions that confront the foot at that particular time. Henenfeld stated that uneven, slanting, or sloping surfaces determine which axis is used. Bojsen-Moller and Lamoreux went further and stated that the variation in the length of the lever arms between the two metatarsal propulsive axes and the ankle joint complex results in variation in the resistance arms of the foot. They believed that this allowed the two propulsive axes to be employed for different mechanical demands. These workers suggested that the high gear axis is used for fast level walking and the low gear axis is used in uphill walking. Both sets of workers report that the two axes enable adjustment in the direction of propulsion without disturbing balance. Neither provided data to support these hypotheses. Moreover, in a more recent report, Vogler and Bojsen-Moller state that both propulsive axes are sequentially loaded during the course of a step. They note that the oblique low-gear axis engages early in the propulsive phase of gait, while the transverse high-gear axis is engaged in very late stance and produces rapid acceleration. Thus, it is unclear whether propulsion occurs around one or both of the axes during a single step.

    Little direct experimental evidence exists to support the twin propulsive axis model of the forefoot. Henenfeld reports that he made observations on symptomatic and asymptomatic subjects. However, he does not state the size of the sample and provides no demographic details or data analyses. Bojsen-Moller and Lamoreux's observations were based on a series of only 30 subjects and employed skin surface markers. The theory of variable use of the propulsive axes for different mechanical demands has not received empirical support. Thus, the results of these workers should only be interpreted with caution. However, studies of dynamic forefoot pressure-distributions may shed some light on the role of the metatarsal arc during propulsion and thus, provide evidence to support or dispute these theories.

    Bojsen-Moller and Lamoreux suggested that the high-gear propulsive axis is used during fast level walking. If it can be extrapolated from this that the low-gear axis is used for slower walking, then Stott et al.'s observation that: "the forefoot distributes the load more to the lateral side of the foot at the slowest rate of walking" appears to support the twin axes model.

    Pollard et al. (1983) studied shear forces beneath the metatarsal heads in ten male subjects. They concluded that the longitudinal shear component is a forward or deceleration force under the lateral metatarsal heads, and a backward or acceleration force under the central and medial metatarsal heads. This lack of backward acceleration shear beneath the lateral metatarsals appears to question their role in propulsive function. However, it is possible that these subjects were using only high-gear propulsion or alternatively, as Tappin and Robertson suggested, that at push off the final motion is an elevation rather than a motion in the forward direction. Pollard et al. did not report the walking speed or the metatarsal arc configuration of subjects. Furthermore, it is unclear which metatarsals were considered as the "lateral" ones, although the use of the pleural "metatarsals" does suggest that Pollard et al. were referring to both the fourth and fifth metatarsals.

    Gross and Bunch (1987) measured vertical in-shoe stress under the hallux and the heads of the first, second, third and fifth metatarsals in one subject during rearfoot-strike running. From an evaluation of the impulses (force x time) at these sites it was concluded that the hallux and second metatarsal head were the primary propulsive mechanism; the first and third metatarsal heads were lesser contributors to propulsion and the fifth metatarsal head was mainly a supporting mechanism used during the transition from braking to propulsion. The loading sequence was from lateral to medial. They state that: "time to maximum stress was produced in a distal pattern (first and third, second and hallux). This seems to suggest that the subject had relative metatarsal protrusion of 2>3=1>4>5; but little certainty can be given to this. The data presented by Bunch and Gross appears to support the use of the high-gear propulsive axis at higher speeds as suggested by Bojsen-Moller and Lameroux. However, it is difficult to draw definitive conclusions, since the study population consisted of only one subject. It is possible that this subject habitually used this propulsive mechanism, irrespective of forward velocity. Moreover, no measures were taken from beneath the fourth metatarsal head.

    Hughes et al. (1991) studied the pattern of pressure distribution under the weight-bearing forefoot in 160 asymptomatic subjects. Peak pressures and contact times as a proportion of stance phase were calculated for each metatarsal head. The longest contact time occurred under the third metatarsal head followed by second and fourth, then the first and the fifth. Examination of peak pressures revealed the highest peak pressures to be under the second metatarsal head. The next highest pressure was beneath third metatarsal head then the first, the fourth; with the fifth showing the lowest loading.

    Hughes et al. subdivided the data by image analyses of plantar pressure patterns into four groups:
    Medial: feet with the highest pressure medially.
    Medial/ central: feet with equal pressure across the first and second metatarsal heads.
    Central: feet with highest pressure centrally (beneath the second / third metatarsals).
    Central/ lateral: feet with high central and lateral pressure but relatively low pressure under the first metatarsal head.

    They believed that short duration loading beneath the fifth metatarsal head was indicative of propulsion through the transversely orientated high-gear propulsive axis. Similarly, it was thought that short first and long fifth metatarsal head loading times were indicative of oblique axis, low-gear propulsion. On this basis, Hughes et al. reported that the medial group employed the high-gear propulsive axis, while the central / lateral group used the low-gear propulsive axis. They reported that the two central groups could not easily be classified as to whether they adopted the high or low-gear propulsive axis. However, they suggested that the pressure profiles pointed towards use of the high-gear axis by the medial central group and low-gear axis by the central group; but there were no obvious differences in contact times between these two groups. Hughes et al. stated that a relatively high medial load is associated with a valgus or pronated forefoot and a relatively high lateral load with a varus/ supinated forefoot. Thus, it seems that high-gear propulsion may be associated with forefoot valgus and low-gear propulsion with forefoot varus. Further research is required to detect the accuracy of these observations.

    Hughes et al. theorised that variation in the metatarsal arc configuration may determine which axis is used by an individual. Moreover, that the habitual adoption of one propulsive axis over the other, in association with certain metatarsal arc configurations may be key determining whether pathology ensues or not. They provided no data to support this hypothesis.



    STRUCTURAL VARIATION IN THE METATARSAL ARC & ITS RELATIONSHIP WITH FOOT PATHOLOGY
    “The longer the metatarsal, the greater the excursion at its head. This increased motion increases the instability of the metatarsophalangeal joint and also the chances for abnormal movement” (Janis and Donick 1975).
    Morton (1930) believed that a short first metatarsal was congenital and contended that short or hypermobile first rays were dysfunctional and would pronate the foot and, thus, lead to deformity. Morton also maintained that when weightbearing stresses become concentrated upon the second metatarsal as a result of first ray dysfunction, enlargement and lengthening of the second metatarsal occurred in response to the increased force acting upon it, increasing the length differential between the first and second metatarsals. Stott et al. (1973) supported this conjecture.
    Wolff’s law (1884) states that “Every change in the use or static function of bone causes a change in its internal form and architecture as well as alterations in its external formation and function, according to mathematical laws” (Brahm 1988). If second metatarsal lengthening does occur as Morton (1930) maintained, it seems likely to be in accordance with Wolff’s law.
    Cimmino (1982) studied the relationship between relative metatarsal length and radiographic density of the second metatarsal head in 100 feet. He reported that those feet with a short first metatarsal had a "statistically significant greater number of dense metatarsals". He maintained that this indicated a response to the shorter first metatarsal. This study does go some way to support Morton's conjecture. However, the determination of metatarsal head density was qualitative and subjective, with no criteria defined. Moreover, Cimmino did not provide any statistical analyses of the data.
    Henenfeld reported how variation in the structural arrangement in the metatarsal arc could influence propulsive function and result in pathology. He believed that variation in the relative lengths of the metatarsals resulted in transference of the role of pivot from the second metatarsal. Henenfeld theorised that a short first metatarsal would increase the angulation in the medial pivotal axis leading to over-use and eventual disruption of this axis. He reported that a short second metatarsal would transfer the role of pivot to the third metatarsal; that this would not result in dysfunction providing the second metatarsal is longer than the first. However, if the second metatarsal is the same length or shorter than the first, the medial pivotal axis is disrupted. Henenfeld reports that short or overlong third, fourth or fifth metatarsals disrupt the lateral pivotal axis. He maintained that a long first metatarsal would only permit the foot to pivot laterally. In this case, the first metatarsal takes the role of pivot and is subsequently prone to pathology. Henenfeld contended that disruption in the propulsive function of the forefoot due to the structural anomalies outlined, resulted in overloading of the metatarsal heads and hyperkeratotic lesions in a predictable manner.
    Sansone (1956) believed that metatarsal length discrepancies resulted in "variant" metatarsal arcs. He maintained that variant metatarsal arcs resulted in abnormal weight-flow and thus, forefoot pathology. On the basis of this observation he devised the Law of forefoot weight distribution: "The arc of the metatarsus parabola deviates directly with any inconsistence in the metatarsal lengths and the regular weight distribution patterns follow accordingly. This can result in one of the following types of forefoot imbalance:
    (1) Anterior forefoot medial imbalance.
    (2) Anterior forefoot lateral imbalance
    (3) Combination anterior forefoot medial and lateral imbalance."
    Sansone (1956) went on to present clinical findings of feet displaying various "variant" metatarsal arcs, their associated symptoms and treatment regimes based upon clinical padding, but presented no data to support his conjectures.
    Barnett (1956) evaluated the effect of metatarsal length variation on forefoot loading in 26 subjects. It was reported that pressure beneath the first metatarsal head increased as a function of first metatarsal length, but that there was no corresponding change in the pressure beneath the second metatarsal head.

    Viladot (1962) described three basic forefoot patterns, each exhibiting specific differences in relative metatarsal protrusion:
    1: the Greek pattern 2>3>1>4>5
    2: the Egyptian pattern 1>2>3>4>5
    3: The square pattern 1=2=3=4>5.
    He claimed that the Greek pattern is the anatomical pattern most likely to predispose to metatarsalgia due to the long second metatarsal.
    Salathe et al. (1986) modelled the resistance of each metatarsal to vertical displacement under vertical load with the heel on and off the ground. They used 3 simulations for each condition: 1: flexible metatarsals, rigid joints, 2:rigid metatarsals, flexible joints, 3: flexible metatarsals, flexible joints. The results of these simulations demonstrated that the 2nd and 3rd metatarsals had greatest resistance to vertical load, under both heel-up and heel-down conditions. The model was based on a foot that displayed a metatarsal formula of 2>3>1>4>5. Salathe et al. stated that the greater the resistance to vertical load, the greater the share of the load borne by that metatarsal, but made no mention of the effect of metatarsal length. It is difficult to draw definitive conclusions from this work, since the results were based on mathematical simulations, the validity of the conclusions drawn are therefore dependent upon the models accuracy.
    Robertson et al. (1986) provided more conclusive evidence of a relationship between relative metatarsal length lengths and vertical load. In a study of 50 dorsoplantar X-rays of asymptomatic feet, relative metatarsal protrusion and posterior displacement of the hallucal sesamoids were measured. These measurements were then correlated with vertical loads beneath the first and second metatarsal heads obtained from a force plate. Shortening of the metatarsal was shown to decrease the load on the first metatarsal (P= 0.001) and to increase the load on the second metatarsal (P=0.014). The posterior displacement of the sesamoids was not significant. The results of Rogers and Cavanagh (1989) support these findings. Rodgers (1995) believed that the increase in second metatarsal loading in association with the Morton foot-type predisposed to pressure related pathology beneath the second metatarsal head.

    THE METATARSAL ARC & SUBTALAR JOINT ROTATIONAL EQUILIBRIUM...

    Perhaps I'll come back to this in the next posting... ;)

    Sorry for the lengthy post, hope some of you enjoy it.
     
  6. High low gear experiment

    Here's a nice little high/ low gear experiment for you all to try.

    1. Put your best foot forward.
    2. Go onto tip toes on this foot, such that you are loading met heads 2-4(5). In other words load your low gear axis.
    3. Transfer your weight to met heads 1 & 2 so that you transfer from low to high gear.

    Question: what motion does your foot undergo in order to achieve this transfer?
     
  7. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    Simon - thanks for the above - it makes this a valuable thread!
    Its not a very fair test, as first ray plantarflexion (which is what happens late in stance) is how "weight flow" moves medially to load the "high gear"
     
  8. OK, But I'm not the first one to use static/ quasi dynamic tests to extrapolate to dynamic function ;)

    So lets see what happens during gait:

    The pink line in the images is a transverse plane representation of the STJ axis as detected using the STJ axis locator (the ant. and post. markers have been connected using paint.)

    In the low gear figures the axis is seen tom move laterally, in the high gear- medially. This fits with the weight flow seen during gait. Norm Murphy once said that the direction of CoP movement matches the directional change of the STJ axis- this seems to fit. Also interesting that in the case Craig presented above, the Left foot (using high gear) is more pronated than the right.
     
  9. I tried to upload attachments to go with this....seem to have failed.

    Got to go prep some casts now (on a Bank Holiday Sunday :( ) will try again later.
     
  10. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    We have no way of knowing if that is a coincidence or if its important. Since using the SiliconCoach and doing close-ups with the digital video from behind (like the pictures above) I have, anecdotally, seen no pattern between rearfoot motion and the use of the oblique or transverse axis. We are collecting data on this and also plantar pressure patterns, so will have hard data by end of year.
     
  11. Try again...

    The pink line in the images is a transverse plane representation of the STJ axis as detected using the STJ axis locator (the ant. and post. markers have been connected using paint.)

    In the low gear figures the axis is seen to move laterally, in the high gear- medially. This fits with the weight flow seen during gait. Norm Murphy once said that the direction of CoP movement matches the directional change of the STJ axis- this seems to fit. Also interesting that in the case Craig presented above, the Left foot (using high gear) is more pronated than the right.

    I like the plantarflexion of the 1st ray explanation for the weight flow; which muscle is used to achieve this and what is its action at the STJ?
     

    Attached Files:

  12. Craig,

    Would be interested in your thoughts on the Hughes et al. study I quoted earlier:

    Hughes et al. (1991) studied the pattern of pressure distribution under the weight-bearing forefoot in 160 asymptomatic subjects. Peak pressures and contact times as a proportion of stance phase were calculated for each metatarsal head. The longest contact time occurred under the third metatarsal head followed by second and fourth, then the first and the fifth. Examination of peak pressures revealed the highest peak pressures to be under the second metatarsal head. The next highest pressure was beneath third metatarsal head then the first, the fourth; with the fifth showing the lowest loading.
     
  13. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    I have not looked at Hughes paper for a very long time, but not sure if anything there is contradictory to what Bojsen-Mollor was suggesting.... the fourth and fifith showing the lowest loading is certainly consistent with weight flow going medially when forefoot propulsion forces are high. As both of BM's axes involve the 2nd met and if the transfer of weight "pivots" about the 2nd met, then I would suspect load is highest on 2nd, which is what Hughes said.
     
  14. Bruce Williams

    Bruce Williams Well-Known Member

    Simon;
    my apologies for only skimming your paper, and thanks for the files of the feet. Could you explain your point once more for me though? I"m a little confused on what you are saying in regards to the pictures adn to your CoP reference from Norman Murphy. I'd like to try to understand how you think the pressures from your pictures would be the same/different from a pressure mapping perspective.
    Also, regarding Craigs' pictures especially with the left foot more pronated. It's not the position of the STJ or RF that Craig is referencing, but the position of the loading of the metaheads. I'm sure you realize that, but it is important to the discussion. It is a bit unfortunate that neither of you have offered a sagittal view of the exact same moments in gait as the transvers and frontal views you offered respectively. I feel that the sagittal view would offer a lot of extra evidence adn perspecitive towards the discussion.
    Regardless, if the CoP - CoF is staying lateral to the 1st and 2nd mpj's this is commonly in association with BM's low gear gait pattern, and in my experience not assistive in the plantarflexion of teh 1st met adn extension of the hallux. Redux I"m sure, but just trying to clarify some things.
    Respectfully,
    Bruce Williams
     
  15. So that others won't think that I only disagree with the theories of Brian Rothbart, I want to offer that I also think that Bojsen-Moller's (BM's) concepts of high gear-low gear are very weak. However, they are not quite yet in the snake-oil weakness class. ;)

    Simon Spooner and I have discussed BM's concepts a few years ago and our work with the STJ axis locator has given both of us some additional insight to BM's concepts that suggest that the metatarsal parabola plays some role in foot function. Here are some problems with the theory of the high gear-low gear axis of BM:

    1. There is no mechanical reason why the center of pressure (CoP), or what Craig has called "weight transfer", needs to go from lateral to medial during propulsion. The CoP does not need to move toward the opposite foot to have normal propulsive mechanics. This is because it is the spatial movements of the center of mass (CoM) relative to the feet that is important in determining gait efficiency. Therefore, as long as the GRF vector that is acting on the propulsive foot is "pushing the CoM" toward the contralateral foot, effective acceleration of the CoM toward the contralateral transfer will occur from the interaction of the ground with the propulsive foot.

    2. BM's theories totally ignore that there are different dorsiflexion stiffnesses of the metatarsal rays that will be very important in determining whether the forefoot exerts a supination moment or pronation moment on the subtalar joint (STJ) during the latter half of stance phase. For example, decreased medial column dorsiflexion stiffness may lead to increased late midstance pronation which may cause propulsion off the 1st and 2nd metatarsal heads (what BM calls "high gear") due to the late midstance pronation that occurs. In this case, BM's "high gear pushoff" would indicate gait abnormality.

    3. The summation of moments acting across the STJ during the latter half of stance phase which are partly determined by the location of the center of pressure (CoP) on the forefoot, the spatial location of the STJ axis, the magnitue of supination moment (or pronation moment) from the Achilles tendon along with the angle of gait of the individual will largely determine whether the individual will propel off their 1st and 2nd rays (what BM calls "high gear") or propel off their 2nd through 5th rays (what BM calls "low gear"). The shape of the metatarsal parabola is likely to be, at best, a very minor player in how the individual selects to propel off of their forefoot.

    4. The transverse plane rotations of the pelvis above the foot during late midstance and propulsion demand that STJ supination and external tibial rotation should occur so that things like abductory twist won't occur. STJ supination should cause increased GRF on the lateral metatarsal heads whereas abnormal STJ pronation should cause increased GRF on the medial metatarsal heads. These STJ moments are described in #3.

    5. By the time the metatarsal parabola has any effect on the foot (i.e. once the heel has lifted off the ground) the individual has already "decided" how they will move their foot through the last few milliseconds of the remainder of the propulsive phase of gait. In other words, the shape of the metatarsal parabola simply is only able to generate its slight effect on foot mechanics in the last few few milliseconds of the stance phase of gait, where it probably has little influence on the gait cycle as a whole.

    My opinion, therefore, is that the shape of the metatarsal parabola is not even in the top ten factors that detemine how the CoP moves during propulsion. It is a factor, but a very weak one that hardly deserves mention in my book.
     
  16. efuller

    efuller MVP

    Problems with "Gear" theory.

    Body weight or center of mass is a different concept than center of pressure. In the right foot the center of pressure is more lateral. (In the left foot, in propulsion, the lateral metatarsal heads are not even in contact with the ground so the center of pressure has to be more medial in the left foot.) I can't remember which of Winters' papers had an excellent explanation of weight transfer. In that paper he showed that the center of gravity (the transverse plane projection of the center of mass) was always between the two feet. Gravity acts downward on the center of mass. (Assume single limb stance) Ground reaction force acts upward at the center of pressure on the foot. So, when the center of gravity is medial to the center of pressure a force couple will be created that will cause the body to fall toword the swing limb side (medial to the stance limb). So, when the center of pressure is more lateral the body will fall faster toward the opposite limb rather than slower as is implied above.

    Just because you have a longer lever arm does not mean a faster velocity of push off. An erroneus assumption of constant angular velocity has been made. With high gear push off ground reaction force has a longer lever arm to resist ankle joint plantar flexion. So much greater force would have to be present in the tendon, with long gear push off, to have the same angular velocity as a short gear push off. We do not know Achilles tendon tension, so we cannot conclude that high gear is automatically faster. A real world example. Get on your bicycle pointed up a slight incline and put the bike in the lowest gear and in the highest gear and start pedalling. In the high gear you might not be able to move the pedals because the resistance is so high. This may be the case for the foot. In the lowest bike gear you will certainly, be able to move the pedals, but you may not be able to go very fast. As you try different gears, you may find one that is optimal for speed. We don't know whre the "gearing" of the foot is in relation to optimal speed production.
     
  17. efuller

    efuller MVP

    Does the gait cause the pain or vice versa?

    Does the gait cause the pain or does pain cause the gait? I could make an arguement in this case that the pain causes the gait.

    What we really need to know is whether the symptoms increase when he supinates (more lateral load) in static stance or do they increase when he pronates (more medial load) in static stance? He could be choosing to use his posterior tibial muscle more on the right to avoid excessive medial forefoot pressure and forces.

    Long gear good, short gear bad??? Examine this from the tissue stress approach. I would not want to be the medial column on the left (high gear) foot. His entire body weight would be on the 1st and second metatarsals if the other foot was still in swing. I have seen feet where this happens. This is a lot of load for these structures. If the Achilles tendon had more force in it because this is long gear push off, all that force would be concentrated on just two metatarsals.

    Explanation of treatment and results. If the above orthosis reduced medial column pain then you would see a medial shift in the center of pressure and more load under the first meatarsal, because the patient would use the posterior tibial muscle less Because he no longer has pain that needs to be avoided. When you add modifications to your orthotic devices and measure changes in location of pressure you cannot know whether the reason you see a change is a purely mechanical effect or a behavioral effect. Pain avoidance is a behavioral effect on gait.

    Eric Fuller
     
  18. But the longest duration fo loading was under met head 3 and second highest peak was under met head 3. Regardless of this, the point I wanted you to realise is that all of these 160 subjects were asymptomatic regardless of propulsive strategy.
     

  19. My point is this: I don't think BM's theories are correct. Secondly, In the case Craig presents and in other discussions of this concept not least in Howard's work, "low gear" propulsive strategy is seen to be a "bad thing" and "high gear" is seen to be "good". I just don't think you can draw that conclusion, they are just different propulsive strategies. It's a bit like supination good, pronation bad- It's not as clear cut as that. This is evidenced to an extent by the Hughes et al. study in which regardless of the propulsive strategy observed, the subjects were (at the time) free from pathology and pain. This fits with our research which has shown that individuals may adopt one or the other propulsive strategies from one step to the next, it is not a case of only using one strategy every step, regardless of the presence of pathology or not.

    The pictures show that this individual can adopt either propulsive strategy. When he adopts a low gear strategy his STJ is supinating; when he adopts a high gear strategy his STJ is pronating. This seems at odds with certain theories. But as I said, pronation bad, supination good is not necessarilly an accurate view. Norm and I had a discussion once (in Montreal I think) about how you can use pressure plate technology to "track the STJ axis" his point was that the axis will be moving in the same direction as observed in the CoP. That is if the CoP is moving medially, so to will the axis. If you view the pictures again although this was performed with a pedobarograph it is easy to understand that, for example, in the high gear sequence the CoP must be moving medially, as too is the axis.

    I do realise the point Craig was making, but we have heard in the past how fnhL causes foot pronation and we have also heard how foot pronation causes fnhl. We also have a theory which suggests that fnhl results in low gear propulsion or vice versa. From my own observation (and those of others) as weight is shifted more onto the medial column in response to pronation the force required to establish 1st mtpj dorsiflexion increases, so you may predict that the force required to establish dorsiflexion in the 1st MTPJ of this individual should be higher in the left foot than right foot, but despite this the left foot was seen to adopt a high gear strategy and the right a low gear strategy.
     
  20. Craig didn't like this test, although I'm not sure that the transfer from low gear to high gear observed in gait is achieved by a different mechanism (you've still got to elevate the lateral border of your foot), I've modified it slightly.

    So try this:
    1. Put your best foot forward.
    2. Go onto tip toes on this foot, such that you are loading met heads 2-4(5). In other words load your low gear axis.
    3. Now swing your trailing leg forward to a heel strike position (to simulate a step)
    4. If you transfered from low gear to high gear what motion did your foot undergo during this? Pronation or supination?

    Pronation right?
     
  21. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    Rather than think in terms of high gear/low gear axes for the case above, what about the first ray is just dorsiflexed and the windlass is not working on the symptomatic right foot ??? The orthotics used were really only aimed at restoring that function.
     
  22. Not sure you can draw that conclusion either. Do the toes dorsiflex?
     
  23. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    As the first met is "relatively" dorsiflexed --> MPJ is less dorsiflexed --> windlass less effective.
     
  24. Bruce Williams

    Bruce Williams Well-Known Member

    Simon;
    Thanks for answering my questions.
    1. Craig's example is very different than yours.
    2. lateral STJ axis is one thing, and also decided non-weightbearing in most instances.
    3. Lateral CoF is not a good thing if the CoF stays lateral at the mpj's!

    This last point is what Craig is trying to make I think. The foot must re-supinate from the midfoot to the mpj's, and if it does not then you get low-gear propulsion and no windlass function and no mpj extension.

    Your examples are not indicative of what Craig is showing in his examples. Also, your line of the STJ axis is not fully indicative of where the CoF would be either.

    I hope this makes things a little more clear.
    Cheers
    Bruce
     
  25. I have no problem with the term less effective, just didn't think you could say "not working".
     
  26. I don't recall suggesting that they were the same.

    Sorry Bruce but I don't know what you are trying to say here. Re-phrase please??

    I think in isolation the position of the centre of pressure or centre of force tells us little. I think you need to define the position of the CoP relative to the joint axis (axes). So saying the CoF is lateral doesn't mean a whole bunch, lateral to what?

    In my example the STJ is seen to undergo pronation with high gear propulsion and supination with low gear propulsion- you seem to be ignoring this Bruce.

    Bruce if the STJ axis is shifting medially then there must be a net pronation moment about the joint, this can be from either extrinsic or intrinsic forces. For an extrinsic force to create a net pronation moment the CoP must be lateral to the axis. I never said my STJ axis line was indicative of were the centre of force would be- I think you are trying to read too much into my throw away line about what Norm Murphy said which was that the CoP moves in the same direction as the axis.

    Bruce this has never been unclear in my mind, but if it helps you feel better then thats fine ;)
     
  27. Bruce Williams

    Bruce Williams Well-Known Member

    Simon;

    If I understand the process correctly, the determination of the STJ axis is traditionally done in a non-weight bearing position. The CoF progression is determined from a dynamic functional foot, not a static non-weightbearing foot.

    Quote:Originally Posted by Bruce Williams
    3. Lateral CoF is not a good thing if the CoF stays lateral at the mpj's!
    Quote: Simon
    I think in isolation the position of the centre of pressure or centre of force tells us little. I think you need to define the position of the CoP relative to the joint axis (axes). So saying the CoF is lateral doesn't mean a whole bunch, lateral to what?

    The CoP progression line as drawn in the F-scan software shows all points as measured as the step progresses. As compared to your pink STJ axis line, the two would not match up in most instances with either foot. You intimated that Norman Murphy said they could or would often correspond. I think that will rarely happen as the CoF line will often start mid to medial heel, move lateral under the 4-5th mets and midfoot and then swing medial towards the 1st and 2nd metaheads and out the hallux or 2nd toe. This will not correspond to any normal STJ axis I've seen you or Kevin draw. So, a lateral CoF progression would remain lateral in the forefoot area as I said above. If it ends up in the region of what BM considers high-gear propulsion, this would be a normal CoF progression. If it stays in the low-gear areas, sub mets and toes 3-5 then we have a serious problem, just as Craig has been suggesting.


    Quote:
    Originally Posted by Bruce Williams
    This last point is what Craig is trying to make I think. The foot must re-supinate from the midfoot to the mpj's, and if it does not then you get low-gear propulsion and no windlass function and no mpj extension.
    Quote: Simon
    In my example the STJ is seen to undergo pronation with high gear propulsion and supination with low gear propulsion- you seem to be ignoring this Bruce.

    Not ignoring it anymore than you are ignoring Craig's points on his example picture. The point is that the forefoot or medial column is supinating in high gear propulsion Simon, though it appears that it is indeed pronating. This is what is supposed to happen as written by pretty much every text I've been privy to. When your example of low-gear propulsion shows the foot supinating, but the forefoot or medial column pronating, this is usually considered an inferior type of gait style. From my experience of utilizing F-scan and video gait analsysis, it is inferior.
    The point I'm trying to make here, as I have many times before is that the STJ axis principle does not apply well to function of the mpj's and the necessary CoF progression patterns that I see daily and weekly in practice.
    I greatly appreciate the pronation and supination moment terminology used to describe these processed., and thank you and Kevin K. and Eric for helping me to undersand them better. But, it does not apply universally to the foot, especially in this matter. Certainly not as you have described your example.

    Quote:Originally Posted by Bruce Williams
    Your examples are not indicative of what Craig is showing in his examples. Also, your line of the STJ axis is not fully indicative of where the CoF would be either.
    Quote: Simon
    Bruce if the STJ axis is shifting mediallythen there must be a net pronation moment about the joint, this can be from either extrinsic or intrinsic forces. For an extrinsic force to create a net pronation moment the CoP must be lateral to the axis. I never said my STJ axis line was indicative of were the centre of force would be- I think you are trying to read too much into my throw away line about what Norm Murphy said which was that the CoP moves in the same direction as the axis.

    How does an axis shift? The moments may shift but not the axis itself does not correct?
    If the CoF is higher lateral to the STJ axis, higher extrinsic forces, then the foot should be pronating. I think that is what you said above. But, I know from experience that the CoF is going to be higher lateral to the STJ axis on your Low-gear example and therefore the foot will be pronating again, according to your example and STJ axis theory. So what you said above about the foot pronating in high gear can't be correct according to what you wrote.
    Root, Valmassy, Subotnick, etc all state that the foot must re-supinate after heel lift and as the foot advances into propulsion. Are you suggesting that this is not true?
    I'm not sure what you are trying to say Simon, hence my first and second posts. Glad it is at least clear in your mind :D
    Bruce
     
    Last edited: May 1, 2006
  28. Bruce, Simon and Colleagues:

    Bruce, let me clarify the importance of moments in regard to the mechanical analysis of the joints of the foot and lower extremity.

    Regardless of whether the clinician understands the importance of how the moments acting across the subtalar joint (STJ) determine the kinematics of the STJ during both the stance phase and swing phase of the gait cycle, the STJ moments do apply universally in determining STJ motion in all cases of human feet. Motion is determined by moments, period. Another way of saying this is that just because an individual does not understand STJ moments as they occur during the contact, midstance or propulsive phases of gait, does not also mean that these moments do not occur or are not important to gait function.

    If the clinician does not understand the concepts of STJ moments and therefore does not understand that they are the key in determining whether the STJ is accelerating or decelerating in a pronation direction, acclerating or decelerating in a supination direction or remaining in a static position, then the clinician will be lost when they are trying to explain and understand how motion or stability occurs at the STJ, even during propulsion. These same concepts of rotational forces determining rotational motion at joints, when applied to the other joints of the foot, whether they be the talo-navicular joint, 5th metatarsal-cuboid joint or first metatarsophalageal joint, can also be used to develop a more complete understanding of foot function in all phases of gait.

    What I think Simon is trying to point out, and excuse me Simon if I am wrong, is that even though the F-scan will show the excursion of the center of pressure (CoP) on the plantar foot, this excursion of the CoP is meaningless for determining STJ moments if you don't also know the spatial location of the STJ axis at the same instant of gait.

    For example, let's say that a clinician experienced in the use of the F-scan system says that the CoP should be plantar to the 2nd metatarsal head at a certain phase of gait. However, how does this clinician know that normal STJ moments are being produced by ground reaction force across the STJ axis if they don't also know where the STJ axis is within space at that same instant in time? The answer...they don't know. If the STJ axis is 5 cm medial to the 2nd metatarsal head at that instant in gait, then there will be a large STJ pronation moment occurring due to the CoP being located "normally" at the 2nd metatarsal head. If, on the other hand, the STJ axis is 3 cm lateral to the 2nd metatarsal head at that instant in gait, then there will be a fairly large STJ supination moment occurring due to the CoP being located "normally" at the 2nd metatarsal head. Therefore, the location of the CoP on the plantar foot is worthless for determining the magnitude and direction of STJ moments from ground reaction force unless one also knows the spatial location of the STJ axis at that instant in time during gait.

    To aid in determining the STJ axis spatial location during gait, Simon and I are introducing a clinical instrument called STJ Axis Locator in the next issue of JAPMA (Spooner SK, Kirby KA: The subtalar joint axis locator: A preliminary report. JAPMA, In Press, 2006). The search for the "holy grail" of finding the spatial location of the STJ axis in live subjects is being further explored by my collaboration in cadaver research with the Penn State Biomechanics Department that will hopefully lead to a method to fairly accurately determine the spatial location of the STJ axis in live subjects without bone pins being drilled into the talus and calcaneus (Lewis GS, Kirby KA, Piazza SJ: Determination of subtalar joint axis location by restriction of talocalcaneal joint motion. Gait and Posture, In Press, 2006). Without these gains in knowledge in STJ spatial location, tracking of CoP location on the plantar foot during gait will be useless in understanding the kinetics of STJ function during the stance phase of walking and running gait.
     
  29. Bruce STJ axial position has "traditionally" been determined non-weightbearing. However, in the images I posted the STJ axis was being tracked in weightbearing gait using an instrument called the Subtalar Joint Axis Locator.

    The pink line was added post video capture by joining the anterior and posterior exit point markers of the axis locator. Thus the pink line is a transverse plane projection of the STJ axis in gait. It is NOT nor did I ever say it was the position of the CoP!!! Please re-read my posts... What I said is that Norm Murphy said if the CoP was MOVING MEDIALLY so too was the STJ AXIS. This does not mean they are in the same position, just that they are travelling in the same direction. I can say this for a fourth time if it helps.

    Normal CoP progression in which environment?; at what gait speed?; pivoting and changing direction? Bruce life isn't as simple as that even BM held this view. Moreover, how do you explain the Hughes et al. data which showed many subjects, being asymptomatic and yet apparently using "low-gear". Where is the published data to support your contention here?

    Kevin seems to have addressed the other points you make, but if it helps I can go through them one more time when I get home from work tonight.
     
  30. Thanh

    Thanh Welcome New Poster

    Bruce,

    Is it possible that during transition from low gear to high gear, the STJ remains supinated to allow external rotation of the tibia whilst the MTJ undergoes pronation about the longitudinal axis, which locks up the calcaneocuboid joint to further stabilise the forefoot during propulsion?
     
  31. Bruce Williams

    Bruce Williams Well-Known Member

    The problem with that is that the STJ is pronated in midstance and for the heel to now lift off the groun, moving into active propulsion, the STJ must now supinate. According to Kevin K and Simon, we need a supination moment to get us to this point and that would require a force medial to the STJ Axis.
    The only way that I see this happening is if 1) the 1st ray dorsiflexion stiffness high (stable 1st ray) 2) the 1st ray is allowed to plantaflex with minimal restriction (use of a cutout or kinetic wedge modification) and 3) the peroneas longus functions as it should and keeps the 1st metahead against the ground - hence allowing high gear propulsion, and a functioning windlass.
    4) would be re: the calcaneocuboid joint locking up - that would be done either with a high dosrsiflexion stiffness of the lateral rays 4and 5 or with a FF valgus post 3-5 or reverse morton's extension etc.
    So, we kind of end up back where Craig started right?
    respectfully;
    Bruce
     
  32. Bruce Williams

    Bruce Williams Well-Known Member

    Quote: Simon
    [What I said is that Norm Murphy said if the CoP was MOVING MEDIALLY so too was the STJ AXIS. This does not mean they are in the same position, just that they are travelling in the same direction. I can say this for a fourth time if it helps.]

    Please say it a few more times for me Simon, it makes me hot! ;)
    So once again I ask you and Kevin, is the Axis moving as you have now said several times?

    Quote: Simon
    [Normal CoP progression in which environment?; at what gait speed?; pivoting and changing direction? Bruce life isn't as simple as that even BM held this view. Moreover, how do you explain the Hughes et al. data which showed many subjects, being asymptomatic and yet apparently using "low-gear". Where is the published data to support your contention here?]

    Ah yes, I was wondering how long it would take for you to ask me to provide published data! :rolleyes:
    Sorry Simon, never read the Hughes paper, and from Craig's quote he didn't seem to feel it mattered to the discussion. I'd have to read it myself to know for sure. I can say this much about the data of Hughes, I would completely agree that many patient's functioning in Low Gear would and could be asymptomatic. Would this not also be true if they were functioning with severely medially displaced STJ Axis? :rolleyes:

    Seriously though. I respect your STJ axis theory and I feel it has added tons to where we are going with foot biomechanics (bx) is that what the abreviation is for? Not sure.
    But, you need to explain how to get a higher supination moment in the forefoot area, like I did in ThanH's post.
    Like it or not, many will feel that the best way to get a higher supination moment in the FF is to use a varus post not just at the heel, but all the way to the 1st mpj like Rothbart!
    Craig has suggested another way, which is to add a FF valgus post, which works as well, and even better with a 1st ray cutout/kinetic wedge etc.
    Cheers;
    Bruce
     
  33. Bruce:

    Let me comment and add to your reasons why STJ supination may occur during late midstance and propulsion:

    1) First ray dorsiflexion stiffness is high (This would tend to increase the ground reaction force (GRF) plantar to the first metatarsal head which would tend to shift the center of pressure (CoP) more medially and thereby increase the STJ supination moment.)

    2) The first ray is allowed to plantarflex with minimal restriction (This will be caused by an increased STJ supination moment from some other source or by a normal to higher medial longitudinal arch height. However, once the hallux dorsiflexion starts normally occuring because of these factors, the first ray plantarflexion that results will shift the CoP medially which will increase the STJ supination moment.)

    3) The peroneus longus functions as it should (The peroneus longus causes a STJ pronation moment due to its lateral position to the STJ axis but it also functions to increase the first ray dorsiflexion stiffness which will tend to shift the CoP medially which will, in turn, cause an increase in STJ supination moment. However, the net change in STJ moments because of these counteropposing moments from peroneus longus contractile activity is probably in favor of a slight increase in STJ pronation moment.)

    4) The calcaneo-cuboid joint locking up (I don't really know what "calcaneo-cuboid joint locking" means. "Calcaneo-cuboid locking", along with "midtarsal joint locking" is terminology we should now discard since it can't be precisely defined. However, it is true that if the lateral column is bearing sufficient weight in late midstance on the 4th and 5th metatarsal heads there will be an increased STJ pronation moment due to the more lateral positioning of the CoP. Surprisingly, however, this may produce increased STJ supination and increased ankle plantarflexion during propulsion and increased duration of propulsive phase of gait. This paradoxical result of an increase in GRF on the lateral column causing more STJ supination during propulsion is probably due to the gastrocnemius-soleus complex having increased magnitude and duration of contractile activity during propulsion since the presence of adequate GRF plantar to the 4th and 5th metatarsal heads allows this increased contractile activity of the gastrocnemius-soleus complex without concomitantly causing lateral instability of the foot during propulsion.)


    Other factors that may increase STJ supination moment and/or decrease STJ pronation moment during late midstance and propulsion:

    A) Increased contractile activity of the posterior tibial, flexor digitorum longus, flexor hallucis longus, gastrocnemius and/or soleus muscles.

    B) Decreased contractile activity of the peroneus brevis muscle.

    C) More medial positioning of the CoP in the forefoot.

    D) More lateral positioning of the STJ axis.

    E) More medially directed GRF vector such as is caused by genu valgum deformity (Van Gheluwe B, Kirby KA, Hagman F: Effects of simulated genu valgum and genu varum on ground reaction forces and subtalar joint function during gait. JAPMA, 95:531-541, 2005).

    And finally, Bruce, yes, the STJ axis is continually moving in space relative to the plantar foot during the gait cycle (Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001). The STJ axis translates medially and internally rotates with STJ pronation and translates laterally and externally rotates with STJ supination. The three dimensional motions of the STJ axis closely follows the three dimensional motions of the talar neck (i.e. anterior exit point of STJ axis) relative to the posterior-lateral calcaneus (i.e. posterior exit point of STJ axis).

    I believe that many of the observations that and you and Howard Dananberg have made and have lectured on can be integrated quite nicely with the STJ axis-rotational equilibrium theory as I have tried to demonstrate above with my comments.
     
  34. efuller

    efuller MVP

    Are we in agreement on definition of windlass function?

    I'm not quite sure what is meant by not working. Or not working as well. A function of the windlass is to add dorsiflexion stiffness to the first ray. Another function is to create a supination moment at the STJ, and possibly create a supination motion. I could theorize more functions, but I will talk about these. In the picture of the right foot the first met head is off of the ground and the STJ is in a much more supinated position. The functions, that I just stated, are not needed in this foot. There is redundancy in the foot and the function of dorsiflexion stiffness is, in the right foot, now needed in the lateral column. The foot is in a quite supinated position and a supination moment from some other source must have been present to get it into this position. The windlass may not be "functioning" in the right foot but it does not need to when the foot is in the position that it is in.

    Eric
     
  35. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    What I meant by not working is what you said - ie if you look at the picture of the right foot during propulsion (and ignore all the high gear/low gear stuff), the first MPJ of that foot is not dorsiflexing fully, so windlass not fully established ... but take your point that it may not need to be (but the foot was symptomatic).
     
  36. Bruce Williams

    Bruce Williams Well-Known Member

    Eric;
    Just because the foot may be in a somewhat supinated position it does not mean that the foot is propulsing optimally or without pain.

    As Simon pointed out, the foot is actually pronating when the hallux is fully dorsiflexed and the windlass is fully engaged and the foot is functioning in high gear propulsion.

    The supinated position of the foot in the picture is still in a low gear propulsion mode and will not be functioning optimally and is primed for tissue stress over time.

    Cheers.
    Bruce
     
  37. Bruce, Craig, Eric and Colleagues:

    Looking at Craig's 14 y/o patient makes me think that this lad has midfoot pain that is made worse by subtalar joint (STJ) pronation and its secondary effects on the midtarsal/midfoot joints and the pain is made better by STJ supination. In addition to the mechanisms suggested by Craig and others, I would also offer that this patient is walking with a more supinated gait pattern in propulsion (evidenced by the low gear push-off) due to pain in his foot. This abnormal gait pattern, or antalgic gait pattern (i.e. limp) may have secondarily, over time, caused his sacroiliac and low back pain. Once the proper orthosis was made for him that generated sufficient external STJ supination moment on the foot and he no longer needed to generate internal STJ supination moments to have his foot be less painful, the orthosis not only improved his pain but also improved his gait.

    The point that Eric was making regarding the windlass is a good one. If the patient is so supinated in late midstance and propulsion that propulsion is occurring off the 2nd-5th digits, then the windlass will not be fully functioning. In addition to what Eric said, if the foot is pronating at the STJ in late midstance but has good STJ axis location and good medial longitudinal arch (MLA) height, then the windlass will probably function normally, even though the STJ is pronating abnormallly in late midstance. However, if the STJ is pronating abnormally in late midstance but has a medial STJ axis location and a low MLA height, then functional hallux limitus will likely result and reduced windlass function may occur.

    The possible explanations for the exact mechanical scenario in this 14 y/o boy's foot is, of course, made much more complex when a pain avoidance behavior (i.e. antalgic gait) is used during gait. An antalgic gait pattern makes gait examination techniques, whether visual, via pressure-sensing insoles/mats, force plates or 2D or 3D gait analysis much more difficult to interpret since normal muscular contractile activity and temporal patterns are not occurring. Therefore, I don't think that we can be certain of why this child is walking the way he his, since there are many possibly explanations given the limited information presented.
     
  38. efuller

    efuller MVP

    Where is the stress?

    Both the right foot and the left foot are primed for tissue stress. The left foot will have excessive load on the medial forefoot and the the right foot will have excessive load laterally after heel lift. From the pictures, if the patient continued to walk this way then I would expect medial column pain in the left foot and lateral column pain in the right foot. The windlass activivation does not magically make the foot immune to stress. In fact if there is a high pronation moment at the time of high medial weight bearing, the windlass will not create enough supination moment to cause motion. This would lead to high stress within the structures of the windlass.

    Bruce just becaue the foot is pronated does not mean that it is propulsing optimally and without pain.

    In my opinion, optimum push off would have even pressure across the metatarsal heads. Of course, there are exceptions to this.

    Eric Fuller
     
  39. musmed

    musmed Active Member

    ? yes ? No

    Dear Craig

    There is a very valid osteopathic saying that allies to EVERYONE who deals with another.

    Tight joints ache Loose joints PAIN. ie Hypermobile joints pain and hypOmobile joints ache. Did anyone ask if the other foot ached? I bet NOT and I would like to bet that the joint mobility of both feet was NOT looked at!

    PAul Conneely
    www.musmed.com.au
     
    Last edited by a moderator: May 28, 2006
  40. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    There was no history, present or current of any pain, aches or discomfort in the more pronated foot (I kept probing and asking as I felt as though there should have been). I would normally compare joint motions in both feet and would have noted any difference at the time, but its been a while since I seen this boy, so do not really recall.
     
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