THE KNEE INJURY MECHANISM PARADOX


In response to a feature article, ‘Busted knees and broken legs’, that ran recently in one of Whistler’s weekly newsmagazines, I wrote the letter to the editor that follows below.

As seems typical of articles on the subject of knee injuries, the take home message to the reader is that most knee injuries are caused by skier error.  Skiers fall improperly or try to pull themselves forward from a sitting back position. This creates what is called a drawer shift mechanism that pulls the femur back against the tibia at the knee joint rupturing the ACL. While this mechanism is definitely a factor, as Tone Bere of the Oslo Sports Trauma Research Center noted, knee injuries do occur before a fall or without a racer falling after a knee injury is sustained. When a knee injury does occur before a fall, the knee injury invariably causes the fall. This was also noted in the paper I cited in my post GS AND KNEE INJURIES – CONNECTING THE DOTS – https://skimoves.me/2014/05/29/gs-and-knee-inju…necting-the-dots/

Articles such as the one that appeared in the Whistler newsmagazine, also infer that progress has been made in equipment and that skiing is much safer than it was decades ago. This position is contradicted by studies such as Bere’s that found that 1 in 3 WC racers are injured each year. What I have never seen mentioned in any consumer article on ski injuries, is the fact that not only has the modern plastic ski boot never undergone any product safety testing intended to determine the effect on the consumer that I am aware of, but that plastic boot was cited by a number of preeminent authorities in the Shoe in Sport, published in 1987, as being unphysiologic and not designed along anatomical principles.

In the Shoe in Sport, Dr. E. Stussi,  Member of GOTS – Chief of Biomechanical Laboratory ETH, Zurich, Switzerland, commented,

The increasing stiffness of the flexion joint of the boot decreases the ability of the ankle to compensate for the load and places the entire load on the knee. Improvements in the load acting on the ankle make it biomechanically very likely that the problems arising in the rather delicate knee joint will increase.

Dr. med. H.W. Bar, Orthopedics-Sportsmedicine, member of GOTS, Murnau, West Germany, commented,

Investigations by Pfeiffer have shown that the foot maintains some spontaneous mobility in the ski boot. Thus the total immobilization by foam injection or compression by tight buckles is unphysiologic. Only in the case of major congenital or post traumatic deformities should foam injection with elastic plastic materials be used to provide a satisfactory fixation of the foot in the boot.

In effect, the comments of experts in the field such as Dr. E. Stussi, Dr. med. H.W. Bar, Professor  Dr. M. Pfeiffer, were putting the industry on notice that design of the plastic ski boot was problematic.

Seth Masia provides an excellent overview of the ‘anything goes so long as it sells’, marketing approach of the ’70s in his article,  Almost Hits, Mostly Misses, Skiing Heritage 2005 – Google books

A copy of The Shoe in Sport was given to me in 1988 by two German radiologists who were both keen skiers. They were aware of the deficiencies of the conventional boot and had witnessed the injuries. They heard that I was working on a new ski boot design and offered their assistance in designing a boot based on principles of functional anatomy. As the University of Ottawa papers noted, technologies did not exist prior to 1997 that enabled the study of the effects of a ski boot on a user during actual ski maneuvers.  In going forward with the ski boot project in 1991, I was aware of the issues raised in Shoe in Sport. Given that I was starting from a clean sheet of paper so to speak,  if I could not overcome the problems and produce a design based on principles of functional anatomy, one that would be supported and even endorsed by accredited scientists, I could not go forward. I had to get it right. Otherwise, there was no point in proceeding.

The problem for the industry is that I not only succeeded, but the Birdcage studies identified key markers of ski control and balance that can easily be put into algorithm that can assess sound ski technique and be applied to teaching softwares that guide skier learning. In the last 5 years, the introduction of small motion and force sensors has exploded. Used in conjunction with a smartphone app, technologies are now possible that will not only capture and interpret the exchange of forces between the foot of a user and the snow, but act in the capacity of a black box or flight recorder in acquiring a digital record of all events associated with an injury. I foresaw this possibility back in 1991.

As my letter to the editor says…………………..

THE TRUTH IS OUT THERE

In response to the cover feature Pique ran Jan. 21 I wanted to share that in 2013, PhD candidate, Tone Bere of the Oslo Sports Trauma Research Center, asked in Mechanisms of injuries in World Cup alpine skiing” (March 2013), why one out of every three elite alpine skiers is injured during the five month ski season.

Bere’s research found that ACL injuries that occur before a fall, or without falling, develop rapidly due to high skiing speeds and that there is no single solution that will prevent them.

This is due to the presence of phantom torques on the outside leg of a turn that can bend and rotate the leg and shear off the ACL far faster than current binding technologies can detect, let alone react to.

The predisposition of a skier to knee sprains is exacerbated by the fact that tightly-fitted rigid plastic ski boots transfer the forces of skiing up the leg to the knee. The tighter, more precise the fit, the greater the transfer of forces from the ski to the knee.

Prior to the widespread acceptance of the new rigid, plastic ski boot in the early ’70s, knee injuries in skiing were rare. Broken legs occupied centre stage. The introduction of the safety release binding changed that. But the jubilation from the dramatic decline in broken legs had barely subsided when a worse problem began to emerge — severe knee sprains, especially to the ACL.

Contrary to what many believe, there has never been support in sound principles of science for the idea of clamping the foot and leg in what amounts to an orthopedic splint and then attaching a large lever to the boot and applying stress to it.

When the authoritative Shoe In Sport was published in 1987, preeminent experts raised red flags about the effect of the new ski boots on knee injuries. Dr. M. Pfeiffer of Institute for the Athletic Science spoke from the literal epicenter of the ski world at the University of Salzburg when he said, “The ski boot and its shaft must be adapted to the technical skill of the skier, and the technical skills of the skier must be adapted to the preexisting biomechanical functions of the leg and the foot.”

His comments were intended to spur the development of a ski boot designed along anatomical principles, a goal that remains to be achieved even today.

Meantime, Dr. E. Stussi, member of GOTS, chief of Biomechanical Laboratory ETH stated, “Improvements in the load acting on the ankle (meaning a tighter fitting boot) make it very likely that the problems arising in the rather delicate knee joint will increase.” In other words, Dr. Stussi stated that if the industry kept improving the fit of ski boots, knee injuries would increase.

But the industry kept right on improving the fit of the ski boot and knee injuries increased exactly as Dr. Stussi had predicted. Rather than heed the warnings of experts like Dr Stussi and Dr. Pfeiffer, the industry represented the perfect fit, as the Holy Grail with the apparent end objective of transferring 100 per cent of the potentially injurious forces of skiing to the knee,

In 1991, at the request of Canada’s most successful alpine skier, Steve Podborski, I agreed to try and develop a new ski boot. But I agreed on the condition that we would do the prudent and responsible thing, engage scientists with the appropriate expertise to provide oversight and guidance.

My mission was to develop a ski boot that made skiing easier, but more important, made skiing safer. Podborski had competed and won in 1980 on some of the world’s most difficult downhill courses mere months after reconstructive knee surgery using an innovative in-boot technology I had invented. It reduced the stress on his knee to the point where he could compete and win whereas that was impossible with a conventional boot. I knew I was headed in the right direction.

But I wanted accredited experts to confirm that I was. Our company, spent close to $140,000 on studies intended to prove or disprove my theory. The studies proved my theory to be correct.

In 1995, I was nominated for the gold medal in the categories of applied science and engineering in the B.C. Science and Engineering Awards by the industrial technology advisor to the National Research Council of Canada. In order to go forward, a nomination must garner support from a candidate’s peers in the field. In his letter of support, Dr. Robert Colborne, assistant Professor of Anatomy at the University of Saskatchewan, an expert in the human lower limbs, said the following.

“Recent considerations of safety in skiing highlight the importance of dissipating ground reaction forces through the joints of the foot and ankle, which are multi-axial and able to absorb significant energy without sustaining injury.

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

In his letter of support, Alex Sochaniwsky, P. Eng., the biomedical engineer who designed the research vehicle, wrote the software (where none existed) and conducted the studies said,

The design and development strategies used by David MacPhail are very holistic in nature, placing the human system as the central and most critical component in the biomechanical system. His intent is to maximize human performance and efficiency, while foremost preserving the well-being and safety of the users and minimizing biomechanical compromises.

That is where I drew a line in the snow in 1991, “foremost preserving the well-being and safety of the users.”

I am still waiting for others to join me.

David MacPhail