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What is Subtalar Joint Axis and Rotational Equilibrium (SALRE) Theory?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kevin Kirby, Nov 22, 2010.


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    I thought it may be helpful to start a new thread so that those of you who are less familiar with Subtalar Joint Axis and Rotational Equilbrium (SALRE) Theory may hear about it from its author (Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001).


    First of all, let's start with the question:

    What is SALRE theory?

    1. SALRE theory uses the basic physics principle of rotational equilibrium at the subtalar joint (STJ) to mechanically describe how alterations in spatial location of the STJ axis may have an effect on the kinetics of the STJ.

    2. SALRE theory proposes that medial STJ deviation will increase the magnitude of external STJ pronation moments caused by the action of ground reaction force (GRF) and will increase the magnitude of internal STJ pronation moments caused by muscle/tendon tensile forces and ligamentous tensile forces. SALRE theory also proposes that lateral STJ deviation will increase the magnitude of external STJ supination moments caused by the action of GRF and will increase the magnitude of internal STJ supination moments from muscle/tendon tensile forces and ligamentous tensile forces.

    3. SALRE theory provides a coherent mechanical explanation of how alterations in the structure of the forefoot relative to the rearfoot and rearfoot to leg within the transverse and frontal planes (i.e. congenital, acquired, surgical or traumatic alterations) may have an effect on the kinetics of the STJ.

    4. SALRE theory provides a coherent mechanical explanation for how certain pathologies such as posterior tibial tendon dysfunction, peroneal tendinopathy, sinus tarsi syndrome, and chronic lateral ankle instability, to name a few, may develop over time in patients with medial and lateral STJ axis deviation.

    5. SALRE theory provides a coherent mechanical description for how foot orthoses may cause alterations in external STJ supination and pronation moments acting on the foot during weightbearing activities.

    6. SALRE theory provides a coherent explanation for the clinical observation that there is a large inter-individual variation in the resistance of the foot to external STJ supination and pronation moments from externally acting forces such as from custom foot orthoses or during manual examination tests (e.g. supination resistance test).

    7. The spatial location of the STJ axis in the weightbearing foot is the reference position for SALRE theory. The determination of STJ neutral position, heel bisections or forefoot to rearfoot relationship is not necessary in SALRE theory to gain a better understanding of the kinetics of the STJ.


    Now lets go to the second question:

    What is SALRE theory not?

    1. SALRE theory is not a theory that describes the method of treatment that should be used for patients with mechanically-based foot and lower extremity pathology. However, SALRE theory can be used, along with tissue stress theory, to help guide the clinician toward more effective foot orthosis design and mechanical treatment by allowing the clinician to better understand the kinetics of the STJ.

    2. SALRE theory does not specifically describe the biomechanics (i.e. kinematics and kinetics) of the other joints of the foot and lower extremity. However, SALRE theory may be used to better understand the biomechanics of the other joints of the foot and lower extermity.

    3. SALRE theory is not meant to be the final answer or only theory of foot function that describes the complex biomechanics of the foot and lower extremity. Rather, SALRE theory is meant to be a stepping stone toward the development of a more complete understanding of foot and lower extremity biomechanics so that the clinician may make better treatment choices for their patients with mechanically-based foot and lower extremity pathology.

    Hope this helps better explain what my current thoughts are on SALRE theory.
     
  2. David Smith

    David Smith Well-Known Member

    Kevin

    SALRE is a statement of physics and as such its principle is unequivocal: I believe however that some or even many do not quite get the concept of balance of forces and moments, so I have written the following:

    On the thread 'is SALRE a single axis theory'? Robert made the point that ‘The forces (and moments) about the STJ axis are always balanced’. This is entirely correct and it may be that Robert is among the few who understand that concept.

    I have put forward the concept before that force and moments in any mechanical system are always in equilibrium but this has not been well received since it goes against the more intuitive concept of net unbalance of moments and forces that is more usually taught and talked about. In other words that there is a force or moment acting at one side of the mechanism (or equation) that causes movement because of a lack of opposing force or moments. This is ok as a reductionist learning method but ultimately lacks robustness and leads to misunderstanding in more complicated scenarios of mechanical actions such as in the biological model.

    The SALRE model will work perfectly well when explained in terms of unbalanced force and moments but I believe becomes even clearer when using the concept of constant equilibrium.

    The reason that equilibrium does not seem to work to some people is because they leave inertia out of the equation. This means there must be imbalance.
    E.G. A force acting on a body causes acceleration, which to most people means motion in the direction of the force but the concept of motion is not entirely correct. The term is used therefore 'unbalanced force' acting on a body causes acceleration of that body i.e. there is nothing pushing back to stop the motion in the direction of the force. This ignores 'INERTIA': INERTIA is a body's (any body/lump of stuff with mass) resistance to change in motion, which is a crucial consideration and here's why:

    The inertia produces a resistance to an applied force i.e. an equal and opposite reaction, which is consistent with and fulfils Newtons 3rd Law of motion. ‘EVERY action has an equal and opposite reaction’.

    So if we consider two bodies with the same volume but one is lead, with a large mass and the other is polystyrene with a relatively very small mass. We apply a force to each that will accelerate them at the same rate. Since force = mass x Acceleration and therefore acceleration = force / mass, the force required to be applied to the polystyrene is much less than the lead.
    In both cases, if we consider inertia, the forces in the system are in equilibrium (balanced not unbalanced) even though there is motion.

    This can produce confusion, since if the forces are balanced how can there be motion. This is because inertial force is not an external force; it is an internal force in terms of internal to the body of interest. Only external forces can act to change the motion of a body if that body is a closed system and the reference of motion is external to that body.

    So to get back to the feet and the STJ: the mass of the foot is very small relative to the forces applied to it, therefore its inertia is relatively small also. As explained with the lead - polystyrene example; if a force is applied to a small mass it will not need to be very large to achieve a high acceleration.

    Therefore if a certain foot of interest was able to freely move without constraints about the STJ, i.e. it has no muscle or ligament attachments, then the maximum force that could be applied to that foot would be directly proportional to its inertia, which is a force equivalent but equal and opposite to its mass x the acceleration.
    So unless the acceleration was huge the force applied would be very small.

    Now take the same foot and add in / replace the muscle and ligament attachments (MLA). Imagine for simplicity that the force, in this case GRF, acts on side and plantar to the STJ and the replaced MLA act on the other. You now have a push, pull of forces about a fulcrum scenario.

    The MLA force can resist the GRF, how much they resist determines how great the GRF is and how great the GRF is might determine how much the MLA resistance force is. Ironically, since I said it is important to consider inertial force, the inertial force can be virtually ignored here since it a relatively very small force. I.E. the mass is small and now because the MLA force is applied in opposition to acceleration by GRF the net acceleration id very small. Small mass x Small acceleration = Small force.

    This means that at any time (as Robert so perceptively pointed out) the forces and moments acting about the STJ are balanced. They are a balanced between GRF and MLA force (and their lever or moment arms, which I'll come to shortly) and small inertial forces
    .
    Of course active MLA are not just on one side opposite the GRF they are on all sides. Therefore the force acting on one side of the STJ might be GRF plus some MLA forces and all forces acting must be considered in the final equation of tissue stress.

    To get an accurate estimate of the forces acting within the muscles and ligaments it is necessary to know the lever or moment arm lengths. Forces required for equilibrium are directly proportional to the length of moment arm. Therefore the position of the STJ axis relative to the MLA is crucial in determining the stress within a certain tissue. Also accurately defining the forces in the tissues, i.e. the stress, allow us to design a suitable intervention.

    It seems to me then that SALRE is a reliable and robust principle to apply to any problem solving of tissue stress and resulting pathology.

    Regards Dave
     
  3. Should do. It took you about 2 hours to expalin it to me in that Bloody awful traffic jam around the M25 if memory serves ;).


    SALRE, for me, is above all a way of thinking.

    I think the progress of biomechanics can be considered a series of "quantum leaps" in understanding.

    Prior to Root, from what I can see in the literature, biomechanics was uniquely about foot shapes and postures. Flat feet and non flat feet and such. The huge advance I believe Root made, and this is as relevant today as it was then, was to consider the foot not as an amorphous and homogenous blob, but as a series of interconnected and interdependant joints. The simple fact that in a "fallen arch" the problem may be in a structure which is not even IN the arch.

    Quantum leap.

    SALRE, for me, is the next quantum leap because it builds on root to take it to the next level. SALRE takes the concept of movement at joints and refines it to the internal and external forces. The idea of force and movement / posture (or kinetics / kinematics if you prefer) being considered separately. My favourite thought experiment, and for me one of the most applicable clinically, is number 7 This game me hours of head scratching but then when the penny finally dropped it caused a profound shift in the way I thought.

    SALRE is of course, all the things which Kevin describes. But none of those are, for me, the most important aspects. The original root orien and Weed text caused a fundamental shift in thinking which has remained beyond the point at which the detail of the model has been reconsidered (as Root predicted it would be). SALRE, IMHO, will be remembered in 50 years for creating the next shift in thinking from movement to physics, and I don't doubt that this too will be enlarged and improved upon.

    So whilst all the things Kevin describes are true, for me the real truth of SALRE is not in those specifics wherin it describes what we think about how physics works within the foot...

    Its where it teaches us HOW to think about how physics works in the foot.

    I maintain, however, that it would be better received if it had an acronym which was easier to say.
     
  4. Thanks Dave and Robert for the kind comments.

    Now for a little early history of the development of Subtalar Joint Axis Location and Rotational Equilibrium (SALRE) theory.

    1984: Idea for palpating plantar aspect of heel to determine when to use anti-pronation features on orthoses was first learned from Dr. John Weed during a private discussion with him in the hallway at CCPM during my Biomechanics Fellowship.

    1984: Started palpating feet of all students and patients during Biomechanics Fellowship and then started extending palpation into plantar forefoot to determine midtarsal joint (MTJ) axis locations.

    1985: Discovered that all feet had straight line of STJ axis on plantar foot, with no effect from MTJ axes.

    1985: Made discovery that medial STJ axes were associated with pronation-related symptoms and lateral STJ axes were associated with supination-related symptoms.

    1985: Came to conclusion that Blake Inverted Orthosis produced observed supination effects by shifting ground reaction force (GRF) medial to STJ axis.

    1985: Came to conclusion that medial heel supination moment is needed to counterbalance lateral forefoot pronation moment from GRF in order to allow normal foot posture and normal gait function.

    1985: Invented "supination resistance test" as method by which to approximate the tensile force which was necessary from the posterior tibial muscle in order to supinate the foot. Invented "maximum pronation test" in order to find an easier method by which to determine whether foot was maximally pronated or not maximally pronated and how many degrees the foot is from the maximally pronated position.

    1986: Wrote and submitted first paper to JAPMA on biomechanical importance of spatial location of STJ axis that included methods by which to determine STJ axis spatial location. Paper was eventually published in 1987 (Kirby KA: Methods for determination of positional variations in the subtalar joint axis. JAPMA, 77: 228-234, 1987).
     
  5. Deborah Ferguson

    Deborah Ferguson Active Member

    Kevin,David and Robert

    Thanks for the clear and concise explanation of SALRE. Sometimes my brain is awash with different theories and this makes it difficult to apply practically and directly to patients at the coal face. Brilliant.

    Thanks once again
    Deborah
     
  6. Kevin you have often described the/a light bulb moment was when reading :

    Van Langelaan E. J. van, A Kinematical Analysis of the Tarsal Joint an Radiographic Study. Acta Orthopaedica Scandinavica Suppl #204. 1983. Vol. 54.

    Ive had many some from throw away lines on here and the last from Isaacs which took me 6 months and reading

    In-Shoe Pressure Measurement and Foot Orthosis Research: A Giant Leap Forward or a Step Too Far? Simon K. Spooner, David K. Smith, and Kevin A. Kirby J Am Podiatr Med Assoc 2010;100 518-529

    re friction vectors for the penny to drop. I have a copy of Van Langelaan and find it a very taxing read, just wondering if you could expand on the importance of this paper/book
     
  7. efuller

    efuller MVP

    Reading Van Langelaan's paper was a pivotal moment for me for several reasons. Some of those reasons are important in historical context of 1986. At that time I was thoroughly indoctrinated in Neutral position biomechanics. Everyone around me accepted it as dogma.

    Van Langelaan pointed out the definition of axis of motion. Some people still don't get that an axis of motion is an imaginary line that describes motion of one part to another. (What's not in the Van Langelaan paper is that you can use that imaginary line to calculate joint moments given some restrictions.) For some joints the axis of motion is followed quite closely and for others there are an infinite number of possible axes of motion even though you measure one at a time. Some people still think that it is the imaginary line that determines the motion, when it's really the motion that determines the imaginary line.

    Another important point that was in Van Langelaan was the systematic literature review of the joints of the foot. He pointed out that lining up of the axes of the cc and tn joints was misquoted from the original paper in following papers and did not make sense. At the time, we were taught the "rigid/lever mobile adapter function of the midtarsal joint occurred because of the lining up of the axes of the joints of the midtarsal joint. This allowed me to question what I was taught, which was very important in my personal development.

    These points shouldn't be new to people on the arena, becasue I, and others, have been saying them for years. That paper is where I learned it.

    Eric
     
  8. Here is a brief history of Subtalar Joint Axis Location and Rotational Equilibrium (SALRE) Theory:

    1984: Idea for palpating plantar aspect of heel to determine when to use anti-pronation features on orthoses was first learned from Dr. John Weed during a private discussion with him in the hallway at CCPM during my Biomechanics Fellowship.

    1984: Started palpating feet of all students and patients during Biomechanics Fellowship and then started extending palpation into plantar forefoot to determine midtarsal joint (MTJ) axis locations.

    1985: Discovered that all feet had straight line of subtalar joint (STJ) axis on plantar foot, with no effect from MTJ axes.

    1985: Made discovery that medial STJ axes were associated with pronation-related symptoms and lateral STJ axes were associated with supination-related symptoms.

    1985: Came to conclusion that Blake Inverted Orthosis produced observed supination effects by shifting ground reaction force (GRF) medial to STJ axis.

    1985: Came to conclusion that medial heel supination moment is needed to counterbalance lateral forefoot pronation moment from GRF in order to allow normal foot posture and normal gait function.

    1985: Invented "supination resistance test" as method by which to approximate the tensile force which was necessary from the posterior tibial muscle in order to supinate the foot. Invented "maximum pronation test" in order to find an easier method by which to determine whether foot was maximally pronated or not maximally pronated and how many degrees the foot is from the maximally pronated position.

    1986: Wrote and submitted first paper to JAPMA on biomechanical importance of spatial location of STJ axis that included methods by which to determine STJ axis spatial location.

    October 1986: First Precision Intricast newsletter written and published.

    May 1987: First paper on STJ axis location published. (Kirby KA: Methods for determination of positional variations in the subtalar joint axis. JAPMA, 77: 228-234, 1987).

    1987: First realized that maximally pronated position of STJ created special circumstance within the range of motion of STJ. When external STJ supination added to foot, STJ supination motion occurred. However, when external STJ pronation moment was added to foot when STJ was maximally pronated, no STJ motion would occur. Physics principle of rotational equilibrium was added to concept of STJ location in order to better explain the kinetics of the STJ. I came to realize that STJ rotational equilibrium provided mechanical explanation for sinus tarsi syndrome in feet with medially deviated STJ axes.

    1988: Paper on rotational equilibrium of the STJ written and submitted for publication to JAPMA.

    January 1989: First paper on rotational equilibrium of STJ published. (Kirby KA: Rotational equilibrium across the subtalar joint axis. JAPMA, 79: 1-14, 1989.)

    1990: Asked by Steven DeValentine, DPM to co-author, along with Don Green, DPM, a chapter in his book on conservative treatment of children's flatfoot deformity. Spent two months reading every available paper on flatfoot that was available.

    1990: Started experimenting with medial heel skive positive cast modification with Paul Rasmussen at Precision Intricast orthosis lab in Lodi, California. I felt that the medial heel skive would be a much simpler way to add STJ supination moment to a foot with a foot orthosis without performing the more extensive positive cast modifications required by Blake Inverted Orthosis, while also still maintaining original medial longitudinal arch shape of foot.

    1991: Wrote chapter with Don Green on children's flatfoot treatment. Invented the term "orthosis reaction force" (ORF) to describe how foot orthoses alter the plantar location and magnitudes of GRF in both traditional and Blake inverted Orthoses for children with medially deviated STJ axes. Provided first written description of my supination resistance and maximum pronation tests. Provided first written description of how foot orthoses may be less efficient at "controlling pronation" due to a medially deviated STJ axis. Chapter submitted for publication.

    1991: Medial heel skive technique perfected after a year of trial on my own patients. Paper on medial heel skive technique written and submitted for publication to JAPMA.

    August 15-19, 1991: Auckland, New Zealand. First international lecture where I presented concepts of STJ axis location and the effects of STJ axis location and rotational equilibrium on foot orthosis function.

    1992: Dr. DeValentine's book published. (Kirby KA, Green DR: Evaluation and Nonoperative Management of Pes Valgus, pp. 295-327, in DeValentine, S.(ed), Foot and Ankle Disorders in Children. Churchill-Livingstone, New York, 1992.)

    April 1992: Paper on medial heel skive technique published in JAPMA. (Kirby KA: The medial heel skive technique: improving pronation control in foot orthoses. JAPMA, 82: 177-188, 1992.) Won Journal of American Podiatric Medical Association's Scholl Award for Outstanding Paper Published in 1992.

    1996: Eric Fuller, a former student, former Biomechanics Fellow and close friend of mine, describes to me how center of pressure on the plantar aspect of the foot may be used to further simplify the calculation of STJ moments relative to STJ axis determinationmethods. I initially don't think the idea is so good, but with further explanation from Eric, I believe he is onto something very important.

    June 1997: First Precision Intricast newsletter book is published which contains more detailed clinical discussions on clinical importance of STJ axis location. (Kirby KA: Foot and Lower Extremity Biomechanics: A Ten Year Collection of Precision Intricast Newsletters. Precision Intricast, Inc., Payson, Arizona, 1997.)

    1999: Invited to write article for JAPMA on normal and abnormal foot function for JAPMA. Idea of importance of STJ axis location to normal and abnormal foot function more fully described.

    January 2000: Paper on biomechanics of normal and abnormal foot published in JAPMA. (Kirby KA: Biomechanics of the normal and abnormal foot. JAPMA, 90:30-34, 2000.)

    2000: Wrote and submitted for publication a more complete description of SALRE theory using the concepts of STJ spatial location, STJ rotational position, and rigid body/costraint/nonconstraint mechanisms for publication in JAPMA. Paper was reviewed by two reviewers, initially criticized by both reviewers as being too long.

    January 3, 2001: Made first drawing of preliminary design of subtalar joint axis locator (STJAL) and sent it to Simon Spooner , PhD, after private e-mail discussions with Simon on the research possibility of such a device.

    2001: Invited by Department of Mechanical Engineering at UC Davis to participate in biomechanical study of knee joint loads during seated cycling. Measured STJ axis location in 23 cyclists and found that STJ axis location was important in determining knee joint loading forces in cyclists. Trish Ruby was master's candidate doing research along with Maury Hull, PhD, her advisor. David Jenkins, DPM and I did measurements on subjects.

    2001: Dr. Spooner makes prototype STJAL and then travels to Sacramento to do initial radiologic investigation on two subjects of feasibility of using such a device to track STJ axis spatial motions non-invasively.

    October 2001: Paper on SALRE theory published in JAPMA. (Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001.) Won the Journal of American Podiatric Medical Association's Scholl Award for Outstanding Paper Published in 2001.

    2002: Paper on significance of STJ axis location on knee joint loads during seated cycling published in Journal of Biomechanics. (Ruby P, Hull ML, Kirby KA, Jenkins DW: The effect of lower-limb anatomy on knee loads during seated cycling. J Biomech, 25 (10): 1195-1207, 1992.)

    November 2002: Second book of Precision Intricast Newsletters is published with discussion on SALRE theory and incorporating SALRE theory into Tissue Stress Theory. (Kirby KA: Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002.)

    2004: First met Steve Piazza, PhD, Neil Sharkey, PhD, and Greg Lewis (PhD student) from Penn State Biomechanics Lab at biomechanics meeting in Los Angeles. We all discussed Steve and Greg's cadaver experiments with mathematical optimization techniques for location of STJ axis which was first described by Ton Van Den Bogert and Benno Nigg. They invited me to Penn State to lecture to their biomechanics students and do experiments using fresh-frozen cadaver specimens on accuracy of STJ axis location palpation method. First discussions on concept that talus may be immobilized relative to tibia with constant ankle joint dorsiflexion moments in experimental apparatus occurred at this time.

    April 2005: Greg Lewis presented first paper on our new non-invasive method to determine STJ axis spatial location by placing markers only on tibia and calcaneus.
    (Lewis GS, Kirby KA, Piazza SJ: A motion-based method for location of the subtalar joint axis assessed in cadaver specimens. Presented at 10th Anniversary Meeting of Gait and Clinical Movement Analysis Society in Portland, Oregon. April 7, 2005.)

    September 2005: Paper cowritten with Tom Roukis, DPM, on using STJ axis palpation method to better determine optimum calcaneal position during medial slide osteotomy of calcaneus surgery is published in JAPMA. (Roukis TS, Kirby KA: A simple intraoperative technique to accurately align the rearfoot complex. JAPMA, 95:505-507, 2005.)

    November 2005: Research paper on significance of genu valgum on STJ moments, coauthored along with Belgian biomechanists, Bart Van Gheluwe, PhD, and Friso Hagman, PhD, is published in JAPMA. (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.)

    May 2006: Coauthored paper with Simon Spooner on STJ axis locator is published in JAPMA. (Spooner SK, Kirby KA: The subtalar joint axis locator: A preliminary report. JAPMA, 96:212-219, 2006.)

    February 2007: Eric Fuller, DPM, and I coauthor and submit chapter titled "Subtalar Joint Equilibrium and Tissue Stress Approach to Biomechanical Therapy of the Foot and Lower Extremity" in book (that has not yet been published). The chapter uses SALRE theory and Eric's Tissue Stress Theory to describe mechanical explanation behind orthosis treatment using a combination of both SALRE and Tissue Stress theories.

    2007: Paper with Penn State Biomechanics Lab on new method to determine STJ spatial location in live subjects published in Gait and Posture. (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.)

    January 2009: Third book of Precision Intricast newsletters published with chapter on biomechanics on STJ axis location. (Kirby KA: Foot and Lower Extremity Biomechanics III: Precision Intricast Newsletters, 2002-2008. Precision Intricast, Inc., Payson, AZ, 2009.)

    2009: Collaborative paper from NIH and Penn State Biomechanics Labs using fast MRI scans of live subjects confirms accuracy of new non-invasive method of determining STJ axis spatial location is published in the Journal of Biomechanics. (Lewis GS, Cohen TL, Seisler AR, Kirby KA, Sheehan FT, Piazza SJ: In vivo tests of an improved method for functional location of the subtalar joint axis. J Biomechanics, 42:146-151, 2009.)

    2009: Two papers from Javier Pascual Huerta, PhD, and his Spanish colleagues are coauthored and published in JAPMA. These experiments studied effects of frontal plane orthosis wedging on static and dynamic response of subjects to such wedges. SALRE theory is used to help explain experimental findings from the two studies. (Pascual Huerta J, Ropa Moreno JM, Kirby KA: Static response of maximally pronated and nonmaximally pronated feet to frontal plane wedging of foot orthoses. JAPMA, 99:13-19, 2009; Pascual Huerta J, Ropa Moreno JM, Kirby KA, Garcia Carmona FJ, Orejana Garcia AM: Effect of 7-degree rearfoot varus and valgus wedging on rearfoot kinematics and kinetics during the stance phase of walking. JAPMA, 99(5):415-421, 2009.)

    Hope this brief history of the creation and development of SALRE theory is helpful for those of you who are interested.
     
  9. I believe I first read Van Langelaan's thesis when I was in my Biomechanics Fellowship at CCPM in 1984-1985. I think I told Eric Fuller about Van Langelaan's thesis, since he was one of my students at the time, but maybe he can correct me if I'm wrong.

    You have to understand, Michael, that Van Langelaan's paper was the first research study to determine that the STJ axis was a bundle of axes and not a hinge axis as we had been taught at CCPM. Therefore, these ideas were quite revolutionary for 1985.

    In 1985, when I was 28 years old, I was the Biomechanics Fellow learning from the likes of Ronald Valmassy, Chris Smith, John Weed, Jack Morris, Lester Jones, Richard Blake and John Marczalec. Basically, at that time, everything that was taught at CCPM was Root theory. Since I was still just developing my palpation technique for locating the STJ axis on the plantar foot and was trying to figure out whether there was or was not any mechanical importance to the STJ axis location, I had many questions that needed answers. Unfortunately, there wasn't a single person that I knew, including my biomechanics professors, that could give me much help with the path I was going down since I was the first person to go down the path of trying to find a correlation of STJ axis location to foot function. This was a difficult and lonely journey that only a person that has experienced it themselves can completely understand.

    To put it bluntly, at that time at CCPM, Root theory was king. And since it was the prevailing dogma at the time, I had to keep many of my opinions to myself since I didn't want to rock the boat at CCPM while I was still a Fellow. In fact, if you tried to teach something new that wasn't Root theory during that era, you were looked down upon....just ask Eric Fuller. He experienced it first-hand many times after I went into private practice in 1985 while he stayed on to teach Biomechanics after his Biomechanics Fellowship.

    Also, as Eric stated, the literature review was excellent in Van Langelaan's paper. He made some excellent points about the older STJ research studies, basically poking holes in the older research and pointing out how innaccurate it probably was.

    In addition, the next paper to follow from the same PhD advisor (Antony Huson) using the same testing apparatus, was done by Benink two years later which looked at the "tarsal index" and the force required to supinate the foot by externally rotating the tibia (Benink, RJ: The constraint mechanism of the human tarsus. Acta Orthop Scand, 56: (Suppl) 215, 1985). This paper was also very important in reinforcing the idea that supination resistance will change with differences in foot structure.

    On a final note, I must give probably the most credit to Benno Nigg and his early books and papers that greatly influenced my thought process on the mechanical importance of STJ axis location from 1984-1986 when I was working on my first paper on methods of STJ axis determination. I am attaching a few drawings from one of Benno's books (Nigg, B.M. (ed.). Biomechanics of Running Shoes. Human Kinetics Publishers, Inc., Champaign, Illinois, 1986) that I devoured at that time in my career. These images are still deeply etched into my memory as being some of the most influential images that helped alter my opinion as to importance of STJ axis spatial location on foot function.
     

    Attached Files:

  10. David Wedemeyer

    David Wedemeyer Well-Known Member

    Does anyone have the Van Langelaan study to share? I may have read it but it doesn't ring a bell and its not in my folder. Thanks
     
  11. I´ll try it´s 10.8 mb 248 pages of reading pleasure. Check your inbox in a little while.
     
  12. Petcu Daniel

    Petcu Daniel Active Member

    It can be downloaded from: http://informahealthcare.com/toc/ort/54/s204

    Daniel
     
  13. I find it very interesting that the Subtalar Joint Axis and Rotational Equilibrium (SALRE) theory has attracted so much attention from those individuals in podiatry who want to promote their own pet "theories". Since I have absolutely no financial interest in SALRE theory, then whether SALRE theory succeeds or fails as a theory really will not affect me in any way.

    The ideas of rotational equilibrium can be used in any joint of the foot or lower extremity to better understand the kinetics of that joint. I have written and lectured on rotational equilibrium at the metatarsophalangeal joints, midtarsal joint and ankle joint and find this mechanical approach to the foot to be extemely valuable in understanding not only how joint movement occurs, but also how joint stability occurs in the human foot.

    One of the most interesting things about rotational equilibrum across the subtalar joint (STJ) is that, to my knowledge, there is no other joint that has such a large interindividual variation in spatial location relative to the plantar foot than the subtalar joint. It is for this reason why I feel that understanding the biomechanics of STJ spatial location is extremely important for developing a better appreciation for the very signficant effect it can have on foot function during weightbearing activities.

    SALRE theory, very simply put, looks at how the primary inversion-eversion joint axis of the foot, the subtalar joint (STJ) axis, affects the kinetics of the foot and lower extremity. The reason I chose to more critically analyze the STJ, rather than the other joints of the foot, was because, during my training at the California College of Podiatric Medicine (CCPM) as a student and Biomechanics Fellow from 1979-1985, the "oblique midtarsal joint" and "longitudinal midtarsal joint" axes were thought to be of critical importance to foot function with the STJ only being taught to be important to allow normal eversion and inversion of the foot during gait and allow the foot to adapt to uneven terrain. The inclination angle of the STJ axis was also mentioned by the biomechanics professors at CCPM as being important in determining the ratio of frontal plane to transverse plane motion betwen the calcaneus and the tibia during weightbearing activities. However, there was no mention of medial or lateral deviation of the STJ axis during my four years as a student at CCPM.

    In my initial experimentations with STJ palpation in feet during 1984-85, I became excited with the potential for further analyzing the mechanical importance of STJ axis spatial location because many feet that I examined had obviously asymmetrical foot and gait function, but the Root-style measurements I made on these feet showed no significant asymmetries between feet. What I started noticing was that the feet with pronation-related symptoms had medially deviated STJ axes and the feet with supination-related sympoms had laterally deviated STJ axes. To me, this was very exciting because it provided me with a mechanically coherent explanation of why feet with obviously asymmetrical foot function may have been functioning asymmetrically, even though the Root-style measurements I had made on them told me they should be functioning symmetrically.

    These observations were a revelation to me since I always was interested in wanting to know why the feet that I was examining were functioning the way that they did. My problem at the time, was that no one else seemed to understand the importance of STJ axis location other than myself. Therefore, I felt obligated, for my profession, to explore these important observations of STJ axis location over the next few years so I could attempt to write intelligently about my findings in peer-reviewed journals. In this way, I hoped that, over time, other scientists could explore my ideas further to see if they were supported or refuted by their own research.

    What I find most interesting about the podiatrists who complain the most about SALRE theory, is that they are also the podiatrists who seem to want an "easy-in" to being considered experts in podiatric biomechanics. They have not authored or co-authored any peer-reviewed journal articles, they have done no research themselves, and they always have a financial interest in seeing their own "theories" are promoted above all others. The basic fact with these people is that they simply don't want to spend all the time and do all the hard work that is required to do research and get papers published in peer-reviewed journals. So they spend more of their time attacking other theories in straw-man fashion, rather than providing coherent mechanical analyses as to why their "theories" should be considered to be any more valid or useful than other theories.

    When all the dust has settled from these discussions, hopefully the most logical and mechanically coherent theory will prevail. Until then, I will continue to work with my colleagues around the world to build further on the knowledge-base of foot and lower extremity biomechanics with the goal of improving the evaluation and treatment of mechanically-related foot and lower extremity pathologies by foot-health professionals.
     
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