immobilize

IS ‘SUBTALAR NEUTRAL’ SKIINGS’ HOUSE OF CARDS?

If you purchased custom footbeds for your ski boots or had your ski boots custom fit you may have been told that your foot was placed in subtalar neutral and that this created the strongest position of the bones of the foot and leg for skiing. Neutral in this context refers to a neutral configuration of the subtalar joint of the ankle/foot complex.

As best I can recall, the term subtalar neutral began to emerge in the ski industry about 1978. The authoritarian manner in which it was presented and promoted suggested that it was science-based and supported with evidence that conclusively demonstrated superior performance. But I never saw or heard any explanation as to how subtalar neutral could create the strongest position for skiing of the bones of the foot and leg and I have still not seen such an explanation.

Back in 1978, I didn’t even know what the subtalar joint was. I couldn’t envision how the bones of the foot and leg could be maintained in a specific configuration while foam was injected into a liner around the foot and leg or through some other custom fit system. But in spite of the lack of even a theory to support the premise of subtalar neutral as creating ideal biomechanical alignment of the bones of the foot and leg for skiing the premise seemed to be readily accepted as fact and quickly became mainstream. By the time The Shoe in Sport (which questioned the principles on which the plastic ski boot is based) was published in 1989 (1987 in German), neutral subtalar was firmly entrenched in the narrative of skiing.

In my US Patent 4,534,122 (filed on December 1, 2013) for a dorsal support system that I called the Dorthotic, I had unkowingly tried to fix the subtalar joint in a static position as evidenced by the excerpt below from the patent:

The system of the invention applies significant pressure to the dorsal (upper) surface of the foot over the instep, including the medial and lateral aspects thereof, and hence to the bones of the mid-foot to substantially prevent these bones from moving relative to each other.

Note: The prior art refers to the current paradigm in existence.

The objective of the dorsal support system was to immobilize the joints of the bones below the ankle in conjunction with the joints of the bones of the midfoot while allowing unrestricted dorsi-plantarflexion of the ankle joint within it’s normal range of motion. But the significant medial (inner) pressure applied by the  system to the bones of Podborski’s foot below his ankle made it difficult for him to stand and balance on one foot with the system in a ski boot shell even on the concrete floor of my workshop. Removing the offending structure from the dorsal support system quickly resolved the issue by allowing his foot to pronate. This made me aware that structures that impede supination did not appear to create issues. This insight raised the possibility of a fit system based on selective constraint applied to specific aspects of the foot and leg as opposed to what I termed indiscriminate (general) constraint.

Even though at the time that I wrote my US Patent No, 5,265,350 in February of 1992 I still did not comprehend the mechanism behind the claimed superior performance associated subtalar neutral, I knew enough to know that attempting to fix the subtalar joint in any configuration in a ski boot would interfere with, or even prevent, a skier from balancing on one foot.

Here is what I said in the patent:

The prior art refers to the importance of a “neutral sub-talar joint”. The sub-talar joint is a joint with rotational capability which underlies and supports the ankle joint.

………………….the prior art which teaches, in an indirect manner, that the ideal function for skiing will result from fixing the architecture of the foot in a position closely resembling that of bipedal function, thus preventing monopedal function (balance on one foot on the outside ski).

I later discovered that the above statement came close to the truth.

I also discussed the issue of subtalar neutral in my post NO NEUTRAL GROUND (2.) published on September 1, 2014. But I did not learn about the origins of subtatar neutral and especially the intense controversy surrounding it in professional circles until recently when I came across a discussion on Root and his subtalar neutral theory in an online podiatry forum.

The Origin of Subtalar Neutral

Merton’s Root’s subtalar joint neutral theory was first described in the textbooks, Biomechanical Examination of the Foot, Volume 1. – 1971 (Root, Orien, Weed and Hughes) and Normal and Abnormal Function of the Foot – 1977 (Root, Orien, Weed). The basic premise of Root’s subtalar neutral theory is that a neutral position of the subtalar joint (which Root defined as existing when the foot was neither supinated or pronated), is the ideal position of function in static (two-footed bipedal, erect) stance and in gait where the subtalar neutral theory posited that the foot was pronated in the first half of the stance phase then transitioned through neutral in mid stance to become supinated in the latter half of the stance phase.

Root’s paradigm proposes that the human foot functions ideally around the subtalar joint’s neutral position and that deviations from this ideal position are deformities.

What Root really said

Root and his associates never stated that the joints of the foot should be immobilized in subtalar neutral. The reference to static in subtalar neutral as the ideal position of function in static stance pertained to a subject standing in place in an erect bipedal stance on a flat, level, stable surface with the weight apportioned between the two feet. In this static stance the Root subtalar neutral theory posited that the subtalar joint should rest in neutral. Root and his associates never stated, implied or suggested that the joints of the foot should be configured and immobilized in subtalar neutral. Further, Root and his associates made no reference, of which I am aware, to the application of subtalar neutral to activities other than static stance and gait. Critrics have asserted that a subtalar neutral position in static stance is neither normal or ideal. In defining subtalar joint neutral as normal, Root’s theory implied the existence of abnormal pathologies in the feet of the majority of the world’s population.

The lack of evidence

Critics of Root and his associates “Eight Biophysical Criteria for Normalcy” claim the criteria was nothing more than hunches, that these conjectures were accepted as fact, when, in reality, there was no experimental data or research to support them and that the eight criteria were neither normal or ideal.

 The STJ neutral position problem

One of the early critics of Root and his associates was Kevin Kirby, DPM. He is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt College in Oakland, Ca.

Kirby observed a large error range in determining STJ neutral position on the same foot from one examiner to another. In unpublished studies done during his Biomechanics Fellowship at the California College of Podiatric Medicine, Kirby found that the Biomechanics Professors were +/- 2 degrees (a 4 degree spread) and the podiatry students were +/- 5 degrees (a 10 degree spread)  in determining STJ neutral position.

Subtalar neutral appears to be what amounts to a knife edge between pronation and supination where neutral is the border or transition point between the two states. Unless the subtalar neutral position can be precisely and consistently identified, it is impossible to know whether the subtalar joint is pronated or supinated.

The future of subtalar neutral in skiing

Too many times theories of how the human foot functions and therefore how mechanically inducted foot problems are treated have been presented as if they were facts. The dogmatic adherence that sometimes ensues from such an approach has frequently stifled the evolution of foot mechanics. This has been particularly apparent in the field of podiatry which has been dominated by the Root paradigm. (4.)

The long standing controversy and growing challenges mounted against the credibily of Root’s subtalar neutral theory has significant implications for the continued promotion of subtalar neutral in skiing as providing the strongest position of the bones of the foot and leg.

It may eventually be shown to be unfortunate that Root’s influential textbooks were published at a time when the ski industry was attempting to come to terms with the skier/boot interface issues associated with the new paradigm created by the rigid shell plastic ski boot.

In my next post, I will discuss what a ski boot should do for the user or perhaps, more a case of what a ski boot shouldn’t do.


  1. Root ML, Orien WP, Weed JH, RJ Hughes: Biomechanical Examination of the Foot, Volume 1. Clinical Biomechanics Corporation, Los Angeles, 1971
  2. https://wp.me/p3vZhu-Bv
  3. Are Root Biomechanics Dying: Podiatry Today, March 27, 2009
  4. Foot biomechanics- emerging paradigms: Stephen F Albert, 4th Congress of the International Foot and Ankle Biomechanics (i-FAB) Community Busan, Korea. 8-11 April 2014

 

FEATURE POST: THE EMERGING REVOLUTION UNDERFOOT

There is a rapidly emerging convergence of electronic wearable technologies such as CARV, in ski boot digital sensor technology, and sport performance equipment. This years ISPO dedicated a large space to this segment with the larger mobile phone companies all showing concepts and apps.

There is a similar convergence emerging on the science front with attention increasingly focussed on the human foot as rapidly evolving micro-sensor technologies allow the study of metrics associated with foot function such as arch height and specific muscle activity. These technologies enable users to look inside footwear and study its effect on the foot that have previously been hidden out of sight and free from investigation and scrutiny. In due time, some of the premises that form the cornerstone of knowledge in skiing, such as the foot functions best in skiing when its joints are immobilized in a ski boot and, the ski boot is a handle that is used to apply force to a ski, will be scrutinized, revealed and discredited as fabricated nonsense.

THE EMERGING REVOLUTION UNDERFOOT

CARV IN BOOT DIGITAL SENSOR TECHNOLOGY

CARV – The world’s first wearable that helps you ski better. – https://carv.ai

Notch – 3D Motion Sensor Technology captures movements and shares and replays them in 3D in any modern browser – https://wearnotch.com

The equivalent of DNA, as an investigative tool with which to study the effects of footwear on the human foot, has arrived.

 

 

BOOT-FITTING 101: THE ESSENTIALS – SHELL FIT

In this post, I am going to discuss the process I follow to assess what I call the essential foot to shell clearances. This is a 2-step process.

Step 1 – Establish the clearances between the structures of the foot and the inner wall of the boot shell required for the foot to function.

Step 2 – Establish the physical connections between discrete restraint force transfer areas of the foot and the inner walls of the boot shell required for the effective force transfer to the ski, for containment of the foot required to support the processes of balance and for the coupling of the foot to specific mechanical references in the boot shell related to the running surface of the ski.

As a prelude to discussing shell fit, it is necessary to point out that a major shift is occuring in the area of focus on the human foot.

Until recently, most discussions on the human foot have focussed almost exclusively on the rearfoot; the ankle complex, the tibial-talar and sub-talar joints, ankle dorsiflexion and plantarflexion, ankle mobility, inversion, eversion, etc. This limited focus has been at the expense of an appreciation and understanding of the role of the forefoot and the complex lever mechanism that enables the first MTP joint to apply large forces to the ground. A study (1) published in 2004 commented:

The plantar aponeurosis (plantar fascia) is known to be a major contributor to arch support, but its role in transferring Achilles tendon loads to the forefoot remains poorly understood.

 Fascia is a sheet or band of fibrous tissue such as lies deep to the skin or invests muscles or various body organs.

The most plausible reason why the role of the  plantar aponeurosis in transferring Achilles tendon loads to the forefoot is poorly understood is that it has not been given much attention until recently.  

The above cited study concluded:

Plantar aponeurosis forces gradually increased during stance and peaked in late stance.

The almost exclusive focus of attention on the rearfoot has led to assumptions about the function of the foot as a system which are only now being called into question and found to be erroneous or invalid. One result is the erroneous assumption that the arch of the human foot is weak and collapses under the weight of the body. This has spawned a lucrative market for custom made arch supports intended to provide what is perceived as needed support for the arch of the foot.

In boot-fitting, the process of fascial tensioning, in which the height of the arch decreases and the forefoot splays, has been misinterpreted as an indication of a collapsing (implied failure) of the arch due to its inability to support the weight of the superincumbent body during skiing maneuvers. This has led to an almost universal perception and acceptance in skiing of custom arch supports as essential foundations for the foot and the most important part of a ski boot.

The Fascial Tension/SR Stance Connection

Plantar aponeurosis forces peak in late stance in the process of fascial tensioning where they act to maximally stiffen the foot in preparation for the application of propulsive force to the ground. When fascial tensioning of the plantar aponeurosis peaks, forward rotation of the shank is arrested by isometric contraction of the Achilles tendon. This is the shank angle associated with the SR Stance.

Immobilize – Support – Stabilize

Discussions of foot function in the context of the foot to shell clearances necessary for foot function and especially fascial tensioning, tend to be obscured by a consistent, persistent narrative in the ski industry spanning decades that the foot should be supported, stabilized and immobilized in a ski boot. Foot splay, associated with fascial arch tensioning, is viewed as a bad thing. Efforts are made to prevent foot splay with arch supports and custom formed liners in order to the fit the foot in the smallest possible boot size in the name of optimizing support.

In the new paradigm that exists today, the foot is increasingly viewed in the context of a deeply-rooted structure. In the design and fabrication of footwear, attention is now being directed to the accommodation of the  fascial architecture  and the importance of fascial tensioning as it pertains to the science of the human lever mechanism of the foot.

Fascial Tensioning and the Human Foot Lever

Fascial tensioning is critical to the stiffening of the foot for effective force transmission and to foot to core sequencing.

The body perceives impact forces that tend to disturb equilibrium as vibrations. It damps vibration by creating fascial tension in the arches of the foot and the lower limb. Supporting the structures of the foot, especially the arch, diminishes both the degree and speed of fascial tensioning to the detriment of the processes of balance and the ability to protect the tissues of the lower limbs through the process of damping of impact forces.

Dr. Emily Splichal has an excellent webinar on The Science of the Human Lever – Internal Fascial Architecture of the Foot as it pertains to foot to core sequencing – https://youtu.be/_35cQCoXp9U

The DIN Standard is Not a Foot Standard

A major problem for the human foot in a ski boot is the DIN standard toe shape. DIN stands for ‘Deutsches Institut für Normung’ which means ‘German Institute of Standardization’.

The DIN toe shape creates a standard interface for bindings. In a strong, healthy foot, the big toe or hallux should be aligned straight ahead on the center axis of the boot/ski. But as an interface for the human foot, the DIN standard toe shape of a ski boot is the equivalent of a round hole for a wedge-shaped peg.

The graphic below shows a photograph of a foot overlaid over a photograph of the ski boot for the same foot. The outline of the wall of the boot is shown in red. Even though the length of the boot shell is greater than the length of the foot, the big toe will be bent inward by the wall of the shell using the one finger space behind the heel shell length check.

screen-shot-2017-02-09-at-3-55-38-pm

The Importance of Foot Splay

The progressive fascial tensioning that occurs as CoM advances over the foot transforms foot into a rigid lever that enables the plantar foot to apply force the ground or to a structure underneath the plantar foot such as a ski or skate blade. Forefoot splay is important to the stiffening of the forefoot required for effective plantar to ground force transfer.

Ski boot performance is typically equated with shell last width. Performance boots are classified as narrow. Such boots typically have lasts ranging from 96 mm to 99 mm. Narrow boots are claimed to provide superior sensitivity and quick response, implying superior control of the ski.

The outside bone-to-bone width shown in the photo below is not quite 109 mm. The boot shell has been expanded. The 2 red arrows show the 5th and 1st toe joints (metatarsophalangeal joint or MTP joint). A prime hot spot in less than adequate shell width in the forefoot, is the 5th MTP joint. Even a minimal liner will narrow the boot shell width by 3 to 4 mm.

mt-width

Shell Check: Start Point 

I start with a skier standing in both boot shells with the insole in place from the liner then have them claw each foot forward in the shells using their toes until they can just feel the wall of the shell with the outside (medial) aspect of the big toe when they wiggle the toe up and down. If there is a finger space behind the heel, the shell is in the ball park.

A second check is made with the skier standing on one foot. Some allowance for the correct alignment of the big toe  can be made by grinding the inside of the shell where it is forcing the big toe inward. When fully weighted, a fascially tensioned forefoot will splay approximately 3 mm for a female and 5 mm for a male.  The ball shaped protrusion of the 5th MTP joint is typically almost directly below the toe buckle of a 4 – buckle boot.

Once a skier can stand on one foot in each shell with adequate space for normal foot splay, the rear foot can be checked for clearance. The usual sources of problems are the inside ankle bone (medial malleolus) and the navicular and/or the medial tarsal bone. A good way to locate the prime areas of contact is to apply a thick face cream or even toothpaste to the inside ankle bones then carefully insert the foot into the boot shell, stand on it to make contact with the shell, then carefully remove the foot. The cream will leave tell tale smears on the boot shell which can then be marked with a felt pen.

Getting Step 1 successfully completed can involve alternating back and forth between forefoot and rearfoot clearance. Until, both areas are right, full normal foot splay may not occur. Step 2 is done in conjunction with liner modifications which can be a process in itself and is often the most problematic aspect of creating an environment in a ski boot that accommodates and supports foot function especially fascial tensioning.


  1. Dynamic loading of the plantar aponeurosis in walking – Erdemir A1, Hamel AJ, Fauth AR, Piazza SJ, Sharkey NA  – J Bone Joint Surg Am. 2004 Mar;86-A(3):546-52.

US PATENT 5,265,350 ON PRONATION

Here is what I said in my US patent (since expired) that I wrote in January 1991 and filed on February 3, 1991 about the existing philosophy in ski boots (aka – the prior art)

“The inventive technology disclosed by the present application, as will be described in more detail below, teaches the importance of accommodating and enhancing both bipedal and monopedal function by providing for freedom of medial movement of the inside ankle bone. This is in direct contrast with the prior art which teaches, in an indirect manner, that the ideal function for skiing will result from fixing the architecture of the foot in a position closely resembling that of bipedal function, thus preventing monopedal function. 

The prior art refers to the importance of a neutral sub-talar joint. The sub-talar joint is a joint with rotational capability which underlies and supports the ankle joint. The sub-talar joint is substantially “neutral” in bipedal function. That is to say that the foot is neither rolled inward or rolled outward.

If the foot can be substantially maintained in a neutral position with the arch supported and with a broad area of the inner aspect of the foot well padded, there will exist a good degree of comfort. Such a state of comfort exists because the foot is not able to roll inward (pronate) to a degree where significant mechanical forces can be set up which would allow it to bear against the inner surface of the boot shell. In effect, this means that initiation of the transition from a state of bipedal to a state of monopedal function, is prevented. This transition would normally be precipitated by an attempt to balance on one foot. If the foot is contained in a neutral position, traditional supportive footbeds (arch supports) are quite compatible with the mechanisms and philosophies of the prior art.

COMMENT: The objective of the conventional ski boot, whether intended or not, is to make skiing exceedingly difficult. Towards this end, the objective is comfort. A ski boot that renders the lower limbs dysfunctional can be very comfortable while at the same time making skiing exceptionally difficult. Although a priority, comfort in itself does not necessarily equate with good balance and control in skiing.

Problems arise when the foot is attempting a transition from a state of bipedal stance to monopedal stance. If the transition to monopedal stance or function can be completed without interference from the structures of the ski boot, all is fine and well. However, if the transition is allowed to proceed to a point where the mechanics associated with the monopedal function can establish significant horizontal forces, and the further movement of the foot is blocked before the transition can be completed, the skier will experience pain and discomfort at the points where the inner aspect of the foot bears against the structures of the footwear. This is the situation experienced by a majority of the skiers with prior art footwear. It is at this point where arch supports, if employed, also begin to cause discomfort. It should be noted that it is the normal tendency of the foot to pronate when weight bearing on one foot.

Footbeds (arch supports) may work in conventional boots (which traditionally do not allow natural biomechanics or movement of the foot to occur), but in a boot which accommodates and supports natural leg and foot articulation and function, arch supports can be detrimental.

When the foot attempts to pronate inside the ski boot, it is often the case that the ankle bone will come to bear against the inner surface of the boot shell. When contact of this nature occurs, pain and other related complications usually result. Since the consensus of those skilled in the art of ski boot design and modification is that pronation or the rolling inward of the foot is detrimental, and, thus, undesirable, provision is not made to allow for such movement. Rather, the structure of the footwear is intended to resist or even prevent it.

Thus, the problem with existing footwear arises due to the dynamic nature of the architecture of the foot. When the wearer is standing with the weight equally distributed between left and right feet so that the centre of mass of the wearer is manifesting itself in the centre between the feet, the architecture of the wearer’s foot assumes a specific configuration. As the wearer begins to shift his weight towards one foot so that the other foot bears proportionately less weight, the wearer’s centre of mass moves over the medial aspect of the weighted foot so as to assume a position of balance.

In order for this movement of the wearer’s centre of mass to occur, the architecture of the weighted foot must undergo a progressive re-alignment. Existing footwear does not adequately anticipate this re-alignment of the architecture of the foot and thus such footwear inhibits the wearer’s ability to assume a balanced position.”

While I am working on the video cited in my last post I will do a post next that describes how to assume a pronated position on one the foot and what it feels like.

THE MYTH OF PRONATION AND THE COLLAPSING ARCH

If you purchased a pair of ski boots or had work done by a boot-fitter you may have been told that your feet pronate and that this will cause your arch leg to collapse creating a myriad of problems including a lack of control and especially an inability to effectively transfer energy. You may have also been told that your foot functions best in skiing when it is immobilized, preferably in a neutral position, one that completely prevents pronation. All of the preceding are myths. But more than simply being untrue, they are potentially dangerous. ‘Pronation is bad’ is nothing more than a good story; one that most people buy into simply because they have no idea of what pronation is. So they tend to assume that the store clerk or boot-fitter actually knows what they are talking about.

When I first started modifying ski boots in 1973 in an attempt to help my own skiing I bought into the pronation is bad story after reading an article in a running magazine about how over-pronation (an invented term) was causing injuries in runners. The article implied that the human feet, far from being a marvel of complex engineering, are riff with problems like ‘pronation‘  that require corrective devices such as footbeds or prescription orthotics to make feet function properly. This made sense to me at the time, but only because of what I didn’t know. After reading the story in the running magazine, I had what I thought was an epiphany; ‘If foot defects can cause a myriad problems in running, imagine what havoc they must be wreaking in skiing’. Thinking I was on to something, I had prescription orthotics made for my wife and myself by a sports podiatrist. Later, I began making custom footbeds for ski boots. In the 1970s, I was one of the few boot-fitters in world making custom footbeds. And while the response of the majority of skiers I made them for was overwhelmingly positive there was one problem, my own custom footbeds didn’t work for me. In fact, footbeds and prescription orthotics made skiing much more difficult for me than insoles with no arch support. Unfortunately, the pronation is bad story caught on. Soon the evils of over-pronation morphed into the evils of pronation period; any and all pronation was bad and should be stopped or at least greatly restricted.

As Mark Twain quipped, “It ain’t what you know that gets you into trouble. It’s what you know for sure that just ain’t so”. For the past 30 years most of the world has known for sure that pronation is bad. Now a study published this month (1) confirms what I and others have maintained for years, not only is pronation not a predisposition to injury but there are significantly less injuries in those whose feet pronate.

Far from being a bad thing in skiing, pronation is the key to setting up the over-centre mechanism that makes the forces of skiing work for you instead of against you. So what is pronation?

In future posts I will explain what pronation is and why it is essential to sound ski technique and the ability to balance on the outside ski.


1.  British Journal of Sports Medicine (http://bjsm.bmj.com/content/early/2013/06/12/bjsports-2013-092202.abstract?sid=3e90eba8-f3ca-46f7-88e0-d8a28f83b729)

Sources of the story on the Danish study include:

A Popular Myth About Running Injuries – New York Times
http://well.blogs.nytimes.com/2013/06/26/the-myth-of-pronation-and-running-injuries/?_r=1

Speciality running shoes may not reduce injuries – Health – CBC
http://www.cbc.ca/news/health/story/2013/06/27/running-shoes-injuries.html

ENERGY TRANSFER: DO WE REALLY WANT THIS?

When talking about ski boots, the big buzz word in the industry is energy transfer. According to the experts, the better the boot, the more energy it will transfer inferring that transferring energy is both desirable and beneficial. But is it? And what is meant by energy transfer? It is not clear what the objective of energy transfer is or how it relates to effecting control of a ski.  As far as I know, no one has offered an explanation. Yet it is consistently stated as the broad objective of a ski boot. In addition, there seems to be consensus among the experts that the foot functions best when it’s joints are immobilized in the ski boot. Presumably this would serve to maximize energy transfer.

Definitions

  • energy |ˈenərjē|noun ( pl. energies ) – Physics, the property of matter and radiation that is manifest as a capacity to perform work (such as causing motion or the interaction of molecules).
  • transfer |noun |ˈtransfər|  – an act of moving something or someone to another place.

It follows from the above definitions that energy is a general capacity to perform work with no particular sense or control over the process. Therefor, energy transfer is the act of moving energy from one place to another. If energy transfer is the primary function of the ski boot as the experts seem to agree on, then the boot will act to transfer energy from the skier to the snow surface. In accordance with Newton’s Third Law, the snow will transfer an equal and opposite amount of energy back to the boot. Where does this energy go? Up the vertical column of the body.

What follows is an excerpt from a letter of support offered by G.Robert Colborne for my nomination for the Gold Medal in Applied Science & Engineering in the 1995 British Columbia Science & Engineering Awards. Dr. Colborne’s area of expertise is the human lower limbs in particular quantifying mechanical moments of force (ergo; torques) around the joints of the lower limb, and the mechanical power generated or absorbed by the muscle group crossing these joints. At the time he wrote his letter, Dr. Colborne was the assistant Professor of Anatomy at the University of Saskatchewan, Canada

“Recent considerations of safety in skiing highlight the importance of dissipating (NB; preventing the transfer of energy) ground  reaction forces (i.e.; snow reaction forces) through the joints of the foot and ankle, which are multi-axial and able to absorb significant energy without sustaining injury. The next more proximal joint (ergo; closer to the torso) is the knee, and this structure is implicated all too often in skiing injuries, where forces are transmitted (ergo; energy is transferred) by rigid boots that restrict ankle and foot movement”.

  • dissipate |ˈdisəˌpāt|verb1 [ no obj. ] disperse or scatter: the cloud of smoke dissipated.• (with reference to a feeling or other intangible thing) disappear or cause to disappear:

Dr. Colborne went on to state:

“Mr. MacPhail’s design enables toe musculature of the lower limb to absorb these forces before they are directed (ergo; transferred) into the ligaments of the knee, thus protecting these relatively stiff tissues from injury.”

In summary, the lower limbs protect the knee by dissipating ground reaction forces through the joints of the foot and ankle. The stated objective of the ski boot is to immobilize the joints of the foot and ankle and transfer energy. Where doe the transferred energy manifest itself? in the knee joint. There are other implications of restricting movement of the joints of the foot and ankle that I will discuss in future posts.

KNEE INJURIES – PART 2

When I started skiing in 1970, the buzz was all about the new safety bindings. Debates raged in magazines and ski shops over which binding was the best as in the safest. After years of skiing being perceived as dangerous because of the incidence of broken legs, a new era had arrived with the introduction of a generation of sophisticated bindings. This created the perception that it was finally safe to go out play on the ski hills. But as the sound of snapping leg bones faded into the background it was replaced by an even grimmer sound; the popping of knee ligaments, in particular, torn ACLs. Before the introduction of the rigid plastic ski boot, few skiers had ever heard of an ACL. That was about to change.

It was about the time that I started working with National Ski Team members in 1977 that I began to hear of racers suffering knee injuries. Knee injuries seemed to start with a trickle. I can’t even recall hearing of a recreational skier suffering one. Like most skiers, I believed that the new bindings had addressed the injury issue. Even after knee injuries started to increase in frequency I thought it only a matter of time before refinements would be made to ski bindings and that this would be the end of them. As the popping of ligaments got more frequent, panic seemed to set in in the industry. Skiing had entered a period of vigorous growth. The last thing it needed was a good news, bad news story as in, “The good news is that the rigid plastic boot has made skiing easier. Now for the bad news…..”. As best I can recall, it was around 1980 that a team of spanish orthopaedic surgeons published a study linking the introduction of the rigid plastic boot to knee injuries noting that the incidence appeared to be rising in lock-step with sales of the boot. A classic problem-solving strategy is to go back to the time when a problem first emerged and look for anything that changed. In this case, the most significant change was in the boot. Meantime, those with expertise in biomechanics were pointing out that by stiffening the ankle the boot was sending the forces of skiing upward to the relatively weak knee.

In retrospect, it seemed like it should have been obvious that encasing the foot within what amounts to an orthopedic splint would act to transfer force up the leg. It’s ironic, if not erroneous, that the industry, even today, talks about the boot transferring energy to the ski as if this were the end game of skiing. The reality is that unless the ski industry has repealed Newton’s Third Law (which is doubtful), if a skier were to transfer energy to anything through the boot it would be through the stack of equipment between the sole of the boot to the source of Ground (or Snow) Reaction Force at the snow. This being the case, according Newton’s Third Law which states; “For every action there is an equal and opposite reaction”, the snow will transfer an equal amount of energy through the stack of equipment back up the skier’s leg to the knee. The issues are way more complex than a simple transfer of energy. But I will start with the simple and obvious then build from here.

The question is, “Given the established reputation of skiing as being a dangerous sport prior to the introduction of the rigid plastic ski boot and the fact that skis attached to the foot and leg act as force multipliers, did anyone consider the implications of trying to immobilize the foot and leg within a rigid plastic ski boot?”