BioMechanics 101 & 102

The sources and statistics vary, but they all agree that well over ninety percent of the population over pronates. With this being said, and with literally hundreds if not thousands of articles directly linking excessive pronation to dozens of Biomechanically induced Musculo-Skeletal Pathologies and Syndromes throughout the entire kinetic chain, correctly made foot orthotics provide great patient care as well as to act as a profit center to dramatically increase both in house referrals and your practice’s bottom dollar.

However it goes without saying that inconsistent results, unhappy patients and seeing a patient twelve times to “adjust the orthotics” or sending the orthotics back to the lab countless times does not qualify as good patient care or as a profit center as you end up with frustrated patients and you personally “eat” the inevitable costs of wasted time, additional shipping and the “free” visits that end up costing you a ton of money.

For those of you who want the simple nuts and bolts of our philosophy, the “short version” is directly below. And for those of you who wish to get a more in depth view point of our philosophy, the “long version” will be in available just after the “short version” text below.

The Actual Biomechanics: "The Short Version"

A very simple overview of the gait cycle is as follows:

Gait is divided into stance and swing phase, approximately 60% and 40% respectively.
Stance phase is divided into three phases: heel strike, midstance and push off or propulsive phase. Although mid stance is longer than heel strike and propulsive phase, each phase is about 1/3 of the total stance phase.
As your heel strikes the ground it should be slightly supinated or inverted. Supination means locked bones and stability as opposed to Pronation which means unlocked bones and a relative instability. So, when you strike the ground, you want to land on a solid, steady platform or foundation. This is why striking the ground in some supination is desirable.
As you progress through heel strike and enter midstance (which begins when the forefoot hits the ground), the foot naturally begins to pronate which initiates the unlocking of the joints of the foot to provide shock absorption and the ability to adapt to uneven terrain. Some pronation is not only good, but is in fact a very necessary action for proper function.
Near the end of midstance, you ideally want the foot to begin to supinate again to prepare for the push off phase. Push off or propulsive phase begins when the heel comes up off the ground while the “balls of the foot or metatarsal heads remain on the ground. It would make sense that you would want to push off of a “rigid lever” as opposed to an unlocked and therefore unstable foot. So this is why it is desirable for the foot to once again supinate.
In summary, you strike the ground in some supination (rigid locked stable foot), you pronate during midstance (unlocked foot, mobile adaptor for shock absorption), and you supinate when to push off or propulse yourself forward (rigid locked stable foot).

Now, with the above in mind, when the patient’s arch or arches excessively collapse or “over pronate”, whether symmetrically or asymmetrically two major things occur which by themselves or in combination cause all of the aches and pains listed in the “more orthotic indications” section of this web site...

The first is that when the patient’s arch or arches pronate excessively, the collective joints of the foot unlock. Although some pronation and unlocking of the joints is necessary for normal shock absorption and function, pronating excessively causes these joints to remain unlocked way too long into the stance phase of gait. As the patient’s center of gravity and full weight shifts over the unlocked foot in midstance, the foot has no chance to re-supinate to become the “rigid lever arm” to propulse off of as the patient’s weight maintains the unlocked foot in full pronation. In essence, this results in the patient “pushing off” an unlocked and unstable foot which allows the ground to manipulate the entire foot adversely resulting in:

Pathologic boney damage from abnormal shearing forces and physical pathologic boney contact that ultimately leads to various sites of Osteoarthritis in the both the forefoot and rearfoot.
Stretched and torn ligaments, tendons leading to dozens of conditions such as bunions, hammer toes, heel and arch pain and many more “biomechanically induced musculo-skeletal pathologies” along the entire kinetic chain.

The second thing which occurs is that, in many patients, a significant and excessive internal rotation of the entire lower extremity is generated from this excessive pronation. In essence, when the arch drops, the talus rotates medially. To the degree that the talus rotates medially, the tibia in turn also rotates medially. This excessive internal tibial rotation can place undue stress and torque at the knee, causing ligament and meniscus tears as well as various knee compartment syndromes and patella tracking problems. Additionally, in many cases the excessive generated internal torque is transferred to the femur which, when it internally rotates excessively, the femoral head translates posteriorly, inducing an anterior pelvic tilt and an increased lumbar lordosis. This is a well documented and major cause of both hip and lower back pathology that we see each and every day in our practice.

On a closing note, this brief overview did not touch on one major point; symmetry vs. asymmetry. This is to say that when the patient pronates symmetrically or both arches collapse equally or to the same degree, you most times do not have the added complication of limb length discrepancy. Conversely, the patient who pronates differently, stands and walks with one foot more externally rotated than the other, has an uneven arm swing etc…, you can be very sure that this patient will have the added complication of at least a functional limb length discrepancy.

The ramifications of either a “functional” limb length discrepancy or a true “structural” limb length discrepancy are covered in our “BioMechanics 102” section. But let is suffice to say that in either case, the difference in leg length adds a tilting component to the already detrimental effects of the excessive torque along the entire kinetic chain and you end up grossly with some degree of “shearing of the two halves of the body.” A quick example and a blanket statement because of this phenomena is “any one with SI joint pain or instability, unless it is due to direct trauma or birth defect, is functioning with a limb length discrepancy.”

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