Kevin A. Kirby, DPM

Kevin A. Kirby, DPM We provide the most advanced podiatric care to our patients with an emphasis on the biomechanics of the foot and lower extremity.
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Dr. Kevin Kirby graduated from the California College of Podiatric Medicine in 1983 and completed his first year surgical residency at the Veteran’s Administration Hospital in Palo Alto, California. He spent his second post-graduate year doing the Fellowship in Podiatric Biomechanics at CCPM where he also earned his MS degree. Dr. Kirby has authored or co-authored 27 articles in peer-reviewed journals, has authored or co-authored five book chapters, and has authored five books on foot and lower extremity biomechanics and orthosis therapy, all five of which have been translated into Spanish language editions. He has invented the subtalar joint axis palpation technique, the anterior axial radiographic projection, the supination resistance test, the maximum pronation test and the medial heel skive and lateral heel skive orthosis techniques. He has also created and developed the Subtalar Joint Axis Location and Rotational Equilibrium Theory of Foot Function and has co-developed the Subtalar Joint Equilibrium and Tissue Stress Approach to Biomechanical Therapy of the Foot and Lower Extremity. He has lectured internationally on 33 separate occasions in China, Spain, Belgium, New Zealand, Australia, England, Dominican Republic and Canada over the past 23 years on foot and lower extremity biomechanics, foot orthoses, and sports medicine. He has also lectured extensively throughout the United States. Dr. Kirby is a member of the editorial advisory board for the Journal of the American Podiatric Medical Association and a manuscript reviewer for the Journal of Biomechanics, Journal of Foot and Ankle Surgery, Medicine and Science in Sport and Exercise, Journal of Foot and Ankle Research and Journal of Sports Sciences. He is currently an Adjunct Associate Professor in the Department of Applied Biomechanics at the California School of Podiatric Medicine and has a full time podiatric biomechanics and surgical practice in Sacramento, California.

02/03/2026

Biomechanics Terminology for the Modern Podiatrist: Pressure

In this 13-minute video, I review the definition and units used to describe "pressure". My discussion on this important topic discusses how "pressure" is different than "force". I also give some real-life practical examples of how high pressures can injure the tissues of our body. In addition, the technology used to measure plantar pressures of the foot is introduced along with how foot orthoses can be used to reduce pathologies caused by high pressures, such as plantar ulcerations, plantar calluses and foot pain at bony prominences of the plantar foot are also reviewed.

02/01/2026

Biomechanics Terminology: Stress, Strain and an Introduction to Tissue Stress

In this 16-minute mini-lecture, I discuss how stress and strain are defined, the different types of stress, and why rthe concept of "tissue stress" is such an important concept for all podiatrists and foot-health professionals to understand. In this lecture, I review the different types of stress including: axial stress, compression stress, tension stress, torsional stress, bending stress and shear stress. In addition, I discuss how axial and eccentric loads on long bones can cause both tension stress and compression stress within their cortical walls. Included also is a description of how differences in metatarsal cross-sectional thickness can prevent or lead to metatasal stress fractures.

The "stress-strain curve" derived from materials testing machine experiments are introduced along with the concept of tissue stiffness and elastic and plastic deformations. A complete understanding of the stress/strain behaviour of the tissues of our feet and lower extremities is the key to gaining a better appreciation of why injuries to the foot and lower extremity occur and how best to treat these injuries with custom foot orthoses and other therapies.

01/31/2026

Biomechanics Terminology for the Modern Podiatrist: Moments

In this lecture on modern biomechanics terminology, I review the concept of rotational force, or "moment" (i.e. "moment of force"). Moments can be either external, generated by external forces acting on the foot, such as ground reaction force, or internal moments, such as that generated within the body by muscle, tendon, ligament or fascial tension forces.

Moments can either accelerate rotation (i.e. angular acceleration) in the direction of the moment, decelerate rotation in the direction opposite to the direction of the applied moment and can also act in equal and opposite directions across a joint axis to help stabilize a joint.

Newton's second law of motion can be used as the guiding principle to help explain how muscle moments, along with gravitational acceleration and ground reaction forces, help us produce the motions necessary to performs all types of sports activities and other weightbearing activitites. In addition, examples of moments acting across the ankle joint and subtalar joint are used within my presentation to further give practical examples of how alterations in direction and magnitudes of internal and external moments affects foot and ankle biomechanics. Muscle testing is also mentioned within the presentation in regards to how "muscle strength" is not exactly what we are testing when clinically assessting "muscle strength" in our patients, but rather we are clinically assessing joint moments produced by the tension force within the muscle/tendon complex when we are testing "muscle strength" clinically.

01/30/2026

Biomechanics Terminology for the Modern Podiatrist: Force

It is vitally important that podiatrists, and other foot-health professionals, have a firm grasp of the meaning of standard physics and engineering terminology so that they can better understand the biomechanical function of the human foot and lower extremity. Without a good understanding of these terms and their meaning, the health professional will be left with only a superficial understanding of the complexities of foot and lower extremity biomechanics and foot orthosis therapy.

In this lecture on the term "force" and what it means, and doesn't mean, in physics and biomechanics, I discuss how force is defined, the different types of force, the four components of a force vector, what forces can do to objects and the specific example of ground reaction force and force plates. In addition, in this 14-minute presentation, I review what the difference is between "external force" and "internal force" and why axial and eccentric loading forces are important in understanding musculoskeletal injuries.

A better appreciation of forces is the key to becoming an expert in the treatment of patients with mechanically-related foot and lower extremity pathologies. Over the next few days, I will be posting up other lectures on "Biomechanics Terminology" in order to not only introduce the meaning of these important biomechanical terms, but to also refresh the memory of those who may have learned about these terms in the past.

Biomechanics Terminology and Concepts: Rotational EquilibriumIt is often helpful to review basic physics terminology and...
01/28/2026

Biomechanics Terminology and Concepts: Rotational Equilibrium

It is often helpful to review basic physics terminology and concepts so that a better understanding of foot and lower extremity biomechanics may be obtained by the podiatry student and resident, practicing podiatrist and foot-health specialist. In this post, I want to review the very important physics concept of rotational equilibrium.

When a force acts across an axis of rotation, it creates a "rotational force" or "torque" or "moment of force" or, more simply, "moment". Within the field of biomechanics, the term being used for a rotational force is "moment" which is term I will use in the subsequent discussion.

To calculate the magnitude of moment being created across an axis of rotation, both the magnitude of applied force acting perpendicular to the axis of rotation must be known and the distance from the point of application of that force to the axis of rotation must also be known. This distance from the point of application of force to the axis of rotation is known, in biomechanics, as the "moment arm" or, in lay terms, the "lever arm" of that applied force. Then, moment (M) is equal to the perpendicular force (F) times the moment arm (L) or M= F x L.

Within our bodies, moments can accelerate and decelerate motion and also cause increased stability within our joints of the foot and lower extremity. Increasing moments will tend to cause motion in the direction of the moment. For example, an increase in ankle joint dorsiflexion moment will tend to cause ankle joint dorsiflexion motion and an increase in ankle joint plantarflexion moment will tend to cause ankle joint plantarflexion motion.

One of the most important physics and biomechanics concepts in understanding how joint motion and joint stability are produced within the human body is the concept of "rotational equilibrium". What then does the concept of rotational equilibrium mean?

Rotational equilibrium simply means that the moments acting in one direction across an axis of rotation are exactly counterbalanced by moments acting in the opposite direction across that axis of rotation. For example, in the case of the subtalar joint (STJ), rotational equilibrium will only occur when the STJ pronation moments are exactly equal in magnitude to the STJ supination moments.

I first applied the concept of rotational equilibrium across the STJ axis within the medical literature in my paper from 37 years ago (Kirby KA: Rotational equilibrium across the subtalar joint axis. JAPMA, 79: 1-14, 1989). Then 12 years later, I combined the concept of STJ rotational equilibrium with STJ axis spatial location to better explain the kinetics of the STJ (Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001).

A children's playground toy of a see-saw can be used to better illustrate the concept of rotational equilibrium. In my illustration, on the left side of the see-saw board, a weight of 200N is acting at a perpindicular distance of 2.0 m (2.0 m moment arm) from the axis of rotation of the see-saw which, in turn, produces a 400 Nm counter-clockwise moment across the see-saw axis. On the right side of the see-saw board, a weight of 100N is acting at a perpendicular distance of 4.0 m (4.0 m moment arm) from the axis of rotation of the see-saw which, in turn, produces a 400 Nm clockwise moment across the see-saw axis.

In this illustration, the see-saw is balanced, and not moving, positioned in a horizontal position. How can the see-saw board be balanced, not be rotating and be stable even though the forces acting on either side of the see-saw board across it's axis of rotation are unequal? This is because the different lengths of moment arms for each weight creates exactly equal counter-clockwise and clockwise moments. In other words, the see-saw only will only balance in a horizontal position when rotational equilibrium is established across it's axis of rotation and the counter-clockwise moments and clockwise moments are exactly equal in magnitude.

Rotational equilibrium also means that there is no net acceleration across the axis of rotation and/or there is a constant rotational velocity. Rotational velocity is more commonly known as angular velocity in physics and biomechanics. Therefore, when a joint is seen to be stable, and not moving, since it's angular velocity is equal to 0, then we know that rotational equilibrium is present in that joint.

For example, if you are standing in a stable positionon both feet, and your ankle joint is not dorsiflexing or plantarflexing, then your ankle joint's angular velocity is equal to 0. But more importantly, because we now understand the physics concept of rotational equilibrium, you will now be able to very confidently state that your ankle joint must be in rotational equilibrium and all the ankle dorsiflexion moments must exactly equal all the ankle plantarflexion moments at that instant in time.

Rotational equilibrium can also exist if the joint is rotating at a constant angular velocity. This physics fact is derived from Newton's First Law of Motion which states that an object at rest stays at rest, and an object in motion stays in motion with the same velocity, unless acted upon by a net external force. For example, if the elbow joint is flexing at a constant 5 degrees/second then it also will be said to be rotational equilibrium since no net elbow flexion angular acceleration is acting at the joint.

Rotational equilibrium in the see-saw illustration below is due to the static nature of the see-saw, meaning it is balanced in a horizontal position, with an angular velocity and angular acceleration equal to 0. We can also say that the see-saw is stable or has been stabilized due its rotational equilibrium.

If, however, additional weight is added either to the left or right side of the see-saw, then the see-saw will undergo angular acceleration in the direction of rotation of the larger applied moment. Understanding how joint motion is produced from a joint position of static rotational equilibrium (i.e. static equilibrium) is important for any podiatrist or foot-health clinician that hopes to become an expert in foot and lower extremity biomechanics.

01/26/2026

Walking Biomechanics - Phases of Gait

Below is a slow-motion video of a young woman walking.

Uploaded from Daniel Leary at https://www.youtube.com/watch?v=73pLODfIRUY

The phases of walking gait can be clearly seen in this slow-motion video. The phase of walking gait when the foot in on the ground is called "stance phase" while the phase of walking gait when the foot is off the ground is called "swing phase.

Stance phase begins when the heel first contacts the ground at the point of gait known as "heel contact", which is also the beginning of the "contact phase" of walking. Contact phase then ends as the forefoot becomes fully loaded by ground reaction force (GRF) at "forefoot loading".

Forefoot loading also marks the beginning of the "midstance phase" of walking gait at the center of mass (CoM) of the body passes from posterior to anterior relative to the planted foot. Midstance phase then ends at "heel off" which occurs the instant thaty the heel lifts from the ground.

"Propulsive phase" then begins at heel off and ends at "toe off". Toe off occurs at the instant the toes lift away from the ground and the foot loses contact with the ground. Therefore, the beginning of the stance phase of walking is heel contact, with the end of stance phase being toe off. Swing phase begins at toe off and ends at heel contact.

Note that during walking, the CoM rises in early stance phase to reach its maximum height above the ground at the middle of midstance, when the CoM is directly over the planted foot. The CoM then falls forward from the middle of midstance to reach its lowest level relative to the ground at the instant of heel off of the stance phase foot and heel contact of the contralateral foot. The raising and lowering of the CoM relative to the ground during walking gait is directly opposite to the raising and lowering of the CoM which occurs during running gait.

In walking gait, the CoM is at its highest level relative to the ground at the middle of midstance when the CoM is directly over the foot while, during running, the CoM is at its lowest level when the CoM is directly over the foot. Therefore, the kinetic and potential energy exchanges of walking gait is the exact opposite of the kinetic and potential energy exchanges of running gait in the bipedal human.

Walking is often modeled as an "inverted pendulum" due to the cyclical path of the CoM "swinging" over the planted foot with each walking step. The rising CoM stores potential energy during the first half of stance phase due to the increased height of the CoM relative to the ground. Then, after the middle of midstance of walking, the CoM falls downward, gaining kinetic energy during the last half of stance phase to the gradually accelerating CoM which reaches its lowest level of potential energy at heel off. In this way, metabolic energy is conserved during walking by this cyclical movement of the CoM over the planted foot with each walking step, using as an inverted pendulum as the energetic model.

In addition, the metabolic efficiency of walking gait is signficantly improved by the construction of the human foot. The construction of the longitudinal arch of the human foot, being able to flatten slightly is essential during early midstance phase to absorb impact energy and allow for adaptation of the forefoot to terrain surface irregularities. In addition, the increase in contractile activity within the powerful gastrocnemius-soleus-Achilles tendon complex, in combination with the corresponding increase in tension force within the plantar ligaments and plantar fascia during late midstance, creates increased longitudinal arch stiffness during late midtance, resulting in a foot that can become a more "rigid lever" during propulsion, also increasing the metabolic efficiency of walking (Kirby KA: Longitudinal arch load-sharing system of the foot. Revista Española de Podología, 28(2), 2017).

01/26/2026

Low-Dye Strapping for Plantar Fasciitis and Plantar Arch Pain

Low-Dye strapping was invented by Ralph W. Dye, DSC, and was first described in the medical literature in the Journal of the National Association of Chiropodists-Podiatrists and Pedic Items in November 1939 (Dye RW. A Strapping: The Journal of the National Association of Chiropodists-Podiatrists and Pedic Items, November 1939. Journal of the American Podiatric Medical Association. 2007 Jul 1;97(4):282-284).

Low-Dye strapping is a tape-strapping technique that is widely used within the podiatric profession, and other foot-health professions, as a method to help support the longitudinal arch of the foot and treat plantar arch pathologies. In the video below, I am shown demonstrating one of the most common techniques for application of a Low-Dye strapping to the foot. Typical low-Dye strapping involves using 1" and 2" cloth adhesive tape to apply a tension-load-bearing strapping system to the plantar longitudinal arch of the foot.

Low-Dye strapping, by preventing excessive longitudinal arch flattening and elongation, reduces the tension force within the plantar fascia and other plantar tension load-bearing structures of the plantar foot, such as the plantar intrinsic muscles and plantar ligaments. Low-Dye strapping may be used in conjunction with custom foot orthoses to decrease the pain with weightbearing activities within the tension load-bearing structures of the plantar foot, including the plantar fascia, plantar ligaments and plantar intrinsic muscles.

The 1" and 2" cloth adhesive tape that I most commonly is a porous cloth adhesive tape generally used in sports applications which is easily torn by hand. Ideally, the skin of the plantar foot should be cleaned with isopropyl alcohol before taping to increase tape adhesion. In addition, a "pre-tape spray" containing a skin adherent greatly helps the tape stay adhered tightly to the skin for a longer period of time.

https://www.amazon.com/Cramer-Tuf-Skin-Athletic-Kinesiology-Gymnastics/dp/B0001DK33U/ref=sr_1_1_sspa?crid=1L6QRHXPQ8NJV&dib=eyJ2IjoiMSJ9.MrPGriz-_82IcfFy9RhbGZ9rdlS2cHafYjsWGodMoS4iZLya73eD9xjsy-o-Z9lJvMOSGe9_8FTtMOpojf6Rt8zEfENKMjgMgNEswX1SoAjrIeI7ZfaVJegCH2vicn6rpM7tzen5w-HfDTkFIPJqhW561u9-mFEEH9olnS3L3O48uAbXf204CuzkVjhHflX_Lr3J1-7u4sqWec5nSccxJKTx9kXis859E4bA_sRb_6jMC1-8eRN90KVrGqyw5DUdkaUsyxiFj569sTK8Xz8CMMytH7scEE9xg_WWtsYUGyg.V-PqD2uvzJWgUkBmguu-CtB4yK7hcbrhpyOgY5IhgAI&dib_tag=se&keywords=pre%2Btape%2Bspray%2Badhesive%2Bsports&qid=1769407350&sprefix=pre%2Btape%2Bspray%2Caps%2C266&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1

Alternatively, K-tape, a more expensive alternative to cloth adhesive tape, which is more stretchy than cloth adhesive tape, can also be used in the same fashion and is generally easier for the patient to apply. However, K-tape will generally produce a lesser effect on reducing the tension load on the plantar fascia and other tension load-bearing structures of the longitudinal arch than with cloth adhesive tape since it stretches much more than cloth adhesive tape (Kirby KA: Longitudinal arch load-sharing system of the foot. Revista Española de Podología, 28(2), 2017).

01/25/2026

Transverse Plane Rotations of the Pelvis and Lower Extremity During Walking

In the animation that I created below, the transverse plane rotations of the pelvis and lower extremity are illustrated. Please note that the transverse plane rotations within the pelvis correspond to the motions of one leg swinging forwads and the opposite limb in stance phase moving backwards relative to the pelvis.

These transverse plane rotations of the pelvis in the bipedal human are thought to not only increase the metabolic efficiency of walking gait but also help increase the length of the walking stride (Inman VT, Eberhart HD. The major determinants in normal and pathological gait. Jbjs. 1953 Jul 1;35(3):543-558). It is because of these necessary transverse plane rotations of the pelvis and lower extremity during human bipedal walking that the gait phenomenon of "abductory twist" can occur in some individuals with excessive subtalar joint pronation moments during the late midstance phase of walking gait.

01/25/2026

Transverse Plane Elastic Strain Energy Storage and Release within Hip During Walking

In this video, I am demonstrating how the hip joint can store and release elastic strain energy within the transverse plane. Understanding that the ligaments, muscles and tendons that cross the hip joint can both store and release elastic strain energy within the transverse plane during walking is fundamental to realizing why the gait phenomenon of "abductory twist" occurs in some individuals.

In a subject that is lying completely relaxed in a supine position, manually rotating the hip into an internally rotated position and then releasing the lower extremity shows how the hip joint may store and release transverse plane elastic strain energy. When the capsular ligaments, muscles and tendons that cross the hip joint are stretched by internal hip rotation, these soft tissue structures will store elastic strain energy, which is a form of potential energy.

When the limb is suddenly released, the stored elastic strain energy is converted into kinetic energy that causes a rapid external rotation of the thigh, leg and foot due to rapid shortening of these ligaments and muscles. This storage and release of transverse plane elastic stain at the hip is an important contributor to the gait phenomenon known as "abductory twist", where rapid external rotation of the foot occurs at the time of heel off in individuals where the hip has been excessively internally rotated during the late midstance phase of gait by excessive pronation of the subtalar joint.

Elastic strain energy is also an important energy-conservation mechanism in many forms of animal locomotion, including running and jumping in the bipedal human, galloping in horses and running in dogs and cats, hopping in wallabies and kangaroos, to name just a few examples. The storage and release of transverse plane elastic strain energy within the hip of the bipedal human has not been scientifically studied before to my knowledge, but may also be an energy-conserving mechanism in the walking and running human.

01/24/2026

Is There Any Harm to Long-Term Use of Foot Orthoses?

One of most frustrating proclamations about foot orthoses that I see being spread on the internet by certain health professionals is that “long-term use of foot orthoses causes the feet to become weak”.

Unfortunately, there seems to be a number of health professionals with little experience in custom foot orthosis therapy who, for some odd reason, believe that most foot pathologies can be corrected by foot strengthening exercises. Because of their ignorance of custom foot orthosis biomechanics and therapy, these health professionals end up sowing confusion not only for the patients that wear custom foot orthoses, but also for other medical professionals who advise patients on custom foot orthosis therapy.

The bottom line is that the statement, “long-term use of foot orthoses causes the feet to become weak” is not supported by any available scientific research. In addition, that statement is also contrary to my personal experience of wearing custom foot orthoses for the past 45 years and making prescription foot orthoses for patients over the past four decades. After having treated tens of thousands of patients with custom foot orthoses, I can say, quite categorically, that custom foot orthoses do not weaken the feet or legs over time.

In fact, I have never seen a single patient among these tens of thousands of patients I have treated with custom foot orthoses develop weak foot or leg muscles over time by wearing foot orthoses. On the contrary, I have seen the muscles of the feet and legs of many of my patients become stronger with the use of custom foot orthoses since well-made foot orthoses, over time, will frequently allow the individual to exercise with more intensity and with greater duration of activity, and with less pain, so that both their foot and leg muscles can become stronger.

An analogy with the use of prescription eyeglasses helps drive home the point. Do eye doctors tell their patients to only wear their prescription eyeglasses for a certain amount of time and then, after they start seeing better and with less blurred vision and eye strain, tell them to “wean” themselves off of their prescription eyeglasses by doing daily eye exercises? Of course not.

Experienced eye doctors tell their patients to continue wearing their prescription eyeglasses as long as their eyeglasses continue to work since these prescriptive medical devices are the simplest and most therapeutically effective method by which to relieve their blurred vision and eye strain. They don’t tell their patients to quit wearing their prescription eyeglasses after a period of time, and start doing eye exercises due to some strange concern about their patients developing “weak eyes” over time due to their eyeglasses.

In much the same way, experienced podiatrists and foot-health professionals who are well-trained in foot orthosis biomechanics and therapy will tell their patients to continue wearing their prescription foot orthoses as long as their orthoses continue to work since they know that these prescriptive medical devices are the simplest and most therapeutically effective method by which to improve both their gait abnormalities and the mechanically-related symptoms of their feet and lower extremities. They don’t tell their patients to quit wearing their prescription foot orthoses after a period of time, and start doing foot strengthening exercises due to some unwarranted worry about their patients developing “weak feet” over time due to their custom foot orthoses.

The therapeutic need for prescription eyeglasses is due to abnormalities within the internal structure of the eyes. Likewise, The therapeutic need for prescription foot orthoses is due to abnormalities within the internal structure of the feet. Prescription eyeglasses have no more chance of changing the internal architecture of the eyes over time than do prescription foot orthoses have a chance of changing the internal architecture of the feet over time. No amount of eye strengthening exercises will change the internal structure of the eyes and no amount of foot strengthening exercises will change the internal structure of the feet.

Prescription eyeglasses modify the light rays entering the eye so that the patient’s eyes can function better and so they can have less eye strain and have less blurred vision. In much the same way, prescription foot orthoses modify the ground reaction forces on the plantar foot by changing the magnitudes, location and timing patterns of those forces so that the patient’s feet can function better, and the patient can perform their daily weightbearing activities with less pain and more comfort.

Therefore, when you hear or see another podiatrist or health professional make the statement that foot orthoses cause “foot weakness” and “should only be worn for a short period of time to avoid foot weakness”, please ask them for references for their statements. They won’t have any references to support their claims. Why? Because the notion that long-term use of foot orthoses causes foot weakness is, simply, not true.

Prescription foot orthoses, when made correctly, are some of the most useful and least problematic therapies to treat many mechanically-based pathologies of the feet and lower extremities. The podiatrist, or foot-health professional, that has good competence and expertise in custom foot orthosis therapy can be a great benefit to their medical community due to the positive impact that their well-made custom foot orthoses can have on the lives and health of the people of their communities.

01/23/2026

Abductory Twist

Abductory twist is a sudden abduction motion of the foot (i.e. heel moving medially relative to the forefoot) at the time of heel-off during walking gait. Abductory twist is a relatively common gait abnormality that occurs due to the external rotation motion of the pelvis above the foot during late midstance not being matched by corresponding subtalar joint supination and tibial external rotation during late midstance.

As a result of this "mismatching" of the speeds of transverse plane rotations of the pelvis and lower extremity and speed of subtalar joint supination during late midstance, the resultant increase in elastic strain energy occurring within the muscles, tendons and ligaments of the hip, knee and lower extremity will be resolved into this rapid medial movement of the heel at the time of heel-off, or abductory twist.

The sudden medial movement of the heel at the instant of heel off occurs due to the frictional forces between the heel of the foot and the ground being suddenly released after heel-off occurs and, as a result, no longer being able to revent external rotation motion of the foot relative to the ground. The best example of an abductory twist is seen in the last few steps of the left foot in this slow motion video.

Abductory twist is not a pathology that spefically needs to be treated, but, rather, is a clinicial finding of an abnormal gait pattern which may lead to pathologies in the future. Basically, abductory twist indicates that there are excessive subtalar joint pronation moments during late midstance that may, over time, create foot and lower extremity biomechanically-related pathologies.

Van Langelaan's 1983 Research Showed That Midtarsal and Subtalar Joint Axes are "Bundles of Axes", and Not Immovable "Hi...
01/22/2026

Van Langelaan's 1983 Research Showed That Midtarsal and Subtalar Joint Axes are "Bundles of Axes", and Not Immovable "Hinge-like" Axes that are Fixed in Space

The video below shows the anterior and lateral views of the cadaver foot-lower leg preparations that Van Langelaan used in his 1983 research that discovered multiple "bundle of axes" in both the midtarsal joint and subtalar joints (Van Langelaan EJ: A kinematical analysis of the tarsal joints: An x-ray photogrammetric study. Acta Orthop. Scand., 54:Suppl. 204, 135-229, 1983).

Van Langelaan (shown in the photo below with me holding his thesis) was the first to use more modern methods of measuring joint axes. His research disproved the long-held podiatry myth that there are two, rigidly-fixed midtarsal joint axes, the longitudinal and oblique MTJ axes. Van Langelaan's PhD adviser was Anthony Huson, MD, PhD, who has given permission to use his videos for teaching.

Note, on the anterior view of the foot, how large the talo-navicular transverse plane motions are when compared to other joints of the foot. Also note, on the lateral view, how the talus and tibia rotate together as part of the leg within the transverse plane, while the calcaneus, navicular, cuboid and rest of the midfoot joints all seem to rotate much more as a unit within the frontal plane.

This "torque-convertor" function of the human foot allows the transverse plane motions of the hip, knee and tibia that normally occur during gait and other weightbearing activities to be translated into frontal plane motions of the foot, allowing the foot to remain planted on the ground during the stance phase of gait.

[Video courtesy of Anthony Huson, MD, PhD]

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