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Biomechanics of the cavus foot

Discussion in 'Biomechanics, Sports and Foot orthoses' started by NewsBot, Apr 5, 2016.

  1. NewsBot

    NewsBot The Admin that posts the news.


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    Shock attenuation properties at heel strike: Implications for the clinical management of the cavus foot
    Charlene Grech, Cynthia Formosa, Alfred Gatt,
    Journal of Orthopaedics; Volume 13, Issue 3, September 2016, Pages 148?151
  2. My guess is that the accelerator on the calcaneus measured absolute acceleration in all directions, but I haven't read the paper to know for sure.
  3. NewsBot

    NewsBot The Admin that posts the news.

    Shock attenuation properties at heel strike: Implications for the clinical management of the cavus foot.
    Grech C, Formosa C, Gatt A
    J Orthop. 2016 Mar 31;13(3):148-51
  4. NewsBot

    NewsBot The Admin that posts the news.

    Morphology of the Hindfoot in Pes Cavus
    A Weightbearing 3D CT Study

    Timo Schmid et al
    Foot & Ankle Orthopaedics September 2016 – December 2016 vol. 1 no. 1
  5. Beccapod

    Beccapod Member

  6. efuller

    efuller MVP

    Anyone have this paper or more info on joint surface vectors. What is a joint surface vector? It would be very interesting to compare joint surface anatomy found with 3d imaging to motion of the joint in the subtalar joint. Cahil in the 60's proposed the idea of the posterior and middle facets of the STJ being surfaces of cones. Cones have an axis that could be the axis of the STJ. This could provide an anatomical basis for the location of the STJ axis relative to the talus and calcaneus.
  7. Craig Payne

    Craig Payne Moderator

    Unfortunately there is not a full text on this as it is a conference abstract from the AOFAS mtg.
  8. wdd

    wdd Well-Known Member

    Did the study include ages of the participants?

    I ask because it is highly likely that even in idiopathic cases the same cavoid foot changes dramatically over a life time. Some of the changes will be associated with "natural" growth, disease progression, soft tissue and osseous adaptions, to structural and functional history, superimposed disease and probably a lot of things that haven't crossed my mind.

    Anyway, one of the common features of pes cavus that doesn't seem to be mentioned much and which might have significant effect on the progression of the condition is the presence of a lateral longitudinal arch?

    The lateral border of the foot normally gives significant stability to the foot. The ten percent or so of you who have cavoid feet could try balancing on one foot and comparing your ease and facility for doing so with someone who has no lateral longitudinal arch (all else being equal).

    I have often wondered if an easy, simple and useful early treatment (in appropriate cases) might be to create a device that simply filled in the lateral arch, preferably with the foot in a "neutral position" (whatever that means), creating lateral stability.

    I suppose that one of the assumptions I am making is that at least in idiopathic cases one of the causes of disease progression comes from the need to further invert the foot, in an attempt to create lateral stability, which further increases the height of the medial arch and plantarflexion of the first ray amongst other things.

    Back to the above study. Unless the ages of the participants are taken into account like is not being compared to like?

  9. Cavus feet (i.e. high medial-arched feet) are truly an interesting type of foot which I still find fascinating even after over three decades of practice. I don't know that the presence of the lateral longitudinal arch in a cavus foot means anything more than these feet have an increased calcaneal inclination angle on weightbearing.

    One of the primary biomechanical issues with the cavus foot is that these feet tend to have a laterally deviated subtalar joint (STJ) axis. The talar head and neck are positioned directly over the calcaneus in the cavus foot (instead of pointing medially in the flat foot with a medially deviated STJ axis) so that the talar head (and STJ axis) points directly toward the central aspect of the forefoot. This lateral STJ axis position increases the magnitude of external STJ supination moment and decreases the magnitude of external pronation moment from ground reaction force (GRF) when compared to a foot with a normal STJ axis spatial location.

    As a result, during weightbearing activities, the STJ will tend to supinate excessively in the cavus foot (with a lateral STJ axis) unless this STJ supination moment from GRF is counterbalanced by some other source of STJ pronation moment that prevents over-supination of the foot. The central nervous system (CNS) of the individual with a lateral STJ axis and cavus foot will recognize that, in order to keep the forefoot plantigrade, and to prevent supination ankle injuries, that it must increase the efferent output to the only two muscles which can produce significant internal STJ supination moment: the peroneus brevis and peroneus longus muscles. The symptoms that are likely to occur from this increased muscular activity of the peroneals in the lateral STJ axis/cavus foot include: 1) peroneal muscle fatigue, 2) peroneal tendinitis and/or 3) peroneal tendinopathy.

    One relatively simple way for the foot-health clinician to decrease the efferent output from the CNS to the peroneal muscles during weightbearing activities is to increase the external STJ pronation moment from GRF acting on the plantar foot. This may be accomplished with some type of valgus wedging plantar to the rearfoot, midfoot and/or forefoot which redirects GRF more laterally and increases the external STJ pronation moment during weightbearing activities. Once the CNS recognizes that the STJ no longer wants to supinate at the STJ with each step with the in-shoe valgus wedging in place, the CNS will decrease the efferent output to the peroneals in order to conserve metabolic energy since, now, instead of the peroneal muscles being required to generate STJ supination moment to avoid injury and keep the forefoot plantigrade, the in-shoe valgus wedging is providing the STJ pronation moment, but now from external to the foot (i.e. via the laterally-directed GRF of the in-shoe valgus wedging).

    The above is a fairly simple mechanical analysis of how cavus foot structure can affect the mechanics of gait. The foot-health clinician that wants to increase their expertise in clinical biomechanics and foot orthosis therapy should understand these biomechanical principles completely if they desire to better help their patients with cavus feet, and their related biomechanical pathologies.


    Kirby KA: Methods for determination of positional variations in the subtalar joint axis. JAPMA, 77: 228-234, 1987.

    Kirby KA: Rotational equilibrium across the subtalar joint axis. JAPMA, 79: 1-14, 1989.

    Kirby KA: Biomechanics of the normal and abnormal foot. JAPMA, 90:30-34, 2000.

    Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001.

    Fuller EA, Kirby KA: Subtalar joint equilibrium and tissue stress approach to biomechanical therapy of the foot and lower extremity. In Albert SF, Curran SA (eds): Biomechanics of the Lower Extremity: Theory and Practice, Volume 1. Bipedmed, LLC, Denver, 2013, pp. 205-264.
  10. efuller

    efuller MVP

    In feet with a high lateral arch you often see pain and callus under the metatarsal heads. It's simple physics. The lateral arch does not contact the ground so there is smaller area of contact. Body weight is the same. Pressure is Force/Area. The force is the same, but the area over which that force is spread is smaller, so there will be higher pressures. These feet do really well with a device that increases the load to the central part of the lateral arch. Increasing load in one location will reduce it in another.

    I agree with Kevin that most, but not all of cavus feet, will have laterally deviated STJ axes. The lateral axis is the cause of the instability. In this case, the definition of instability is the tendency to invert. And as Kevin described, you will see an increased use of the peroneal muscles.

    In order for the laterally deviated axis foot to balance without muscular activiation, the center of pressure has to be under the STJ axis. What this means is that the force x distance for the area on the lateral side of the axis has to equal the force x distance for the area on the medial side of the axis. With a lateral STJ axis, the area lateral to the axis will tend to have a smaller distance from the axis, so the forces there will have to be higher when the foot is balanced. Conversely, the forces on the medial side of the axis will be smaller. So, in stance there will be much less upward force on the first metatarsal head and this could contribute to less dorsiflexion, more plantar flexion of the first ray. And, as Kevin pointed out, with the lateral axis the peroneus longus muscle will tend to be more active. That's two reasons that you might see increase in the medial arch height, over time with cavus feet.

  11. wdd

    wdd Well-Known Member

    "I don't think that the presence of the lateral longitudinal arch in a cavoid foot means anything more than these feet have an increased calcaneal angle of inclination on weight bearing".

    Does that mean that the lateral border, in a normal foot, doesn't offer a significant structural stability to the foot and reduces the need for pronatory muscle function during weight bearing?

    "Once the CNSrecognises that the foot no longer wants to supinate at the STJ with the in shoe valgus wedging the CNS will reduce the efferent output to the peroneal in order to conserve metabolic energy......."

    It's probably a pretty niave question but doesn't the same principal apply without the valgus wedge, i.e. A reduction in the efferent output to the STJ supinators would also conserve metabolic energy?

    This is assuming that even with the lateral deviation of the STJ axis there is still, without any muscle function, a pronatory moment.

    Last edited: Jan 22, 2017
  12. wdd

    wdd Well-Known Member

    "These feet do really well with a device that increases the load to the central part of the lateral arch".

    Filling in the lateral arch with a sufficiently dense material would be one way of doing that?

    Loading all rather than just the "central part of the lateral arch" would minimise pressure increase within the tissues of the lateral arch?

  13. efuller

    efuller MVP

    What do you mean by structural stability? If you mean likelihood of suffering an inversion ankle sprain then any ground reaction force lateral to the STJ axis will tend reduce the likelihood of an inversion sprain. Upward ground reaction force on the styloid process will, in the vast majority of feet create a pronation moment at the STJ.

    It depends on the foot. Those feet with a laterally deviated STJ axis will tend to supinate at the STJ if no other factors are present. People don't walk well when their feet supinate toward their end of range of motion in the direction of supination. These people will tend to use their peroneal muscles to prevent supinating toward the end of range of motion of the STJ. On the other hand people with average or medially positioned STJ axes will tend to pronated toward the end of motion in the direction of pronation. Most people can walk relatively well when their foot is pushed toward the end of range of motion in the direction of pronation. These people will not need to use their peroneal muscles as much as the people with the laterally deviated STJ axis. So, it is not a question of conservation of energy, but instead a question of certain muscles having to work harder, in lateral STJ axis feet, to prevent ankle sprains. The valgus wedge will increase pronation moment from the ground so that the peroneal muscles don't have to work as hard.
  14. efuller

    efuller MVP

    When the lateral arch is high enough so that styloid process does not touch the ground, the location of noticed increased stress is often the fifth metatarsal head. There is also an increase in bending moment on the lateral column, but the more commonly seen problem is pain at the fifth metatarsal head.

    When I said central part of the lateral arch I meant from just behind the met head to just anterior to the weight bearing area of the calcaneus. My use of the term the central part of the lateral arch may have been misleading. This foot type is where custom orthotic devices that have the same shape as the lateral arch of the foot would do much better than a OTC orthotic with a flat lateral arch. When the top of the orthotic has the same shape as the loaded foot, ground reaction force will be more evenly distributed along the length of the foot.

  15. Another important point regarding the laterally deviated STJ axis/cavus foot is that, one must remember, during late midstance and propulsion, the prime mover is the gastrocnemius-soleus (GS) muscles. Since the Achilles tendon passes medial to the STJ axis, then a strong internal STJ supination moment is generated by contractile activity of the GS muscles during late midstance and propulsion.

    Now, if there is already too much external STJ supination moment coming from GRF acting on a foot with a laterally deviated STJ axis during late midstance and propulsion, when combined with the internal STJ supination moment from GS muscle contractile activity, we have a definite problem: a tendency for this excess STJ supination moment to cause over-supination or an inversion ankle sprain.

    The GS muscle activity during late midstance and propulsion means that, during these phases of walking, that the center of pressure (CoP) acting on the plantar foot must be lateral to the STJ axis (i.e. to create an external STJ pronation moment) in order to counterbalance the internal STJ supination moment from GS muscle activity. In other words, the ground must be trying to pronate the foot at the STJ during late midstance and propulsion in order for the STJ to supinate at a slow enough velocity that still keeps the forefoot plantigrade without over-supinating.

    If the CNS detects that over-supination is going to occur during late midstance and propulsion, it will do two things, 1) increase efferent output to the peroneal muscles to increase the internal STJ pronation moment to counterbalance the excessive STJ supination moment, and 2) decrease the efferent output to the GS muscles to decrease the internal STJ supination moment being generated by the GS muscle contractile activity, which is clinically seen as a shortened propulsive phase of gait.

    This all comes back to the principle of rotational equilibrium that states that the only way to ensure constant rotational velocity of supination is that the STJ supination and pronation moments (i.e. both external and internal) must exactly equal each other. In other words, too much supination can be just as bad as too much pronation. About time podiatrists start learning this lesson and quit worrying about trying to supinate all their patient's feet with orthoses.
  16. wdd

    wdd Well-Known Member

    Kevin and Eric thanks for your responses.

    Another couple of questions.

    Is there still considered to be a neurological deficit associated with pes cavus? I remember reading, at least twenty years ago, that more severe cases were always associated with a measurable neurological deficit and that there was a presumption that in those cases where no conduction deficit could be measured this was more likely to be due to the relative insensitivity of the measuring equipment than the absence of deficit. Is pes cavus always associated with atrophied/smaller lower leg musculature either generally or just of the peroneals.

    Is anything of the cavoid deformity reflected in the hands and/or arms?

  17. efuller

    efuller MVP

    I'm not sure about the neurological deficit. About 20 years ago I was reading that very thing in a textbook and I decided to look at that question. I looked up the citation that was used to support that assertion and the citation was very weak. That may have been one lazy author who did not track down a better citation. Or that one bad citation may be the source of an old doctors tale about the association between cavus and neurological deficits. One other anecdote. When I was teaching a group of students were doing a presentation on Charcot Marie Toothe and they came up with a picture of an actual patient. They repeated what it said in the book about CMT having a cavus foot. The video they had showed someone with some obvious muscle weakness and a flat foot. The point is that rotational equilibrium still applies in the face of muscle weakness. Perhaps in feet with more lateral STJ axes and muscle weakness you will see more of a cavus deformity develop and with more medial STJ axis you will see more planus deformity. Again, this is just arm chair theorizing.

    My sense is that there are a lot of cavus feet out there without any neurological deficit. Of course that is said without careful study.

    I haven't looked at hand anatomy enough to say if there is hand shape that correlates with cavus feet. There are some hand deformities related to muscle weakness.


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