Biomechanics and shoe wear

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Alternatives to pressure systems?

<ADMIN NOTE> This topic has been split off from In-Shoe Pressure Systems </>

Those of us with small clinics and no academic role, will not come across these systems. Can memory foam be used in a similar way? Obviously we will not gauge timing parameters, but would it enlighten us in relation to contact pressures? Does an old worn insole give as much info? What about the outsole?


On another biomechanical topic, we all get those patients that say "I wear out the outside of my footwear (heels)". It is normal to heel strike with the heel(STJ) slightly supinated? How and when is this deemed pathological? Is there anybody out there that can give me a short biomechanical and lay answer. Does a hard inverted heel strike invite a hard abrupt rear-foot collapse during midstance?

 

Atlas, what is your real name anyway???

Memory foam can not be used for in-shoe or out of shoe pressure analysis.

I use a worn insole to show patients the pressures that their feet create on their shoe insoles to try to reinforce to them about how their abnormal plantar pressures may be causing pain. Nothing expensive or high tech, but certainly quick and very meaningful to many patients.

Outersole wear is quite different since this will predominatly occur only at the location on the shoe sole when the foot strikes the ground and where the foot leaves the ground (i.e. those times of highest velocity of the shoe sole relative to the ground and ,therefore, the times of highest abrasion of the outersole).

In addition to subtalar joint (STJ) rotational position at the time of heel strike, the angle of gait also will greatly affect location of shoe wear since this determines the angle of the foot at heel strike. A more abducted angle of gait will show heel wear more laterally. A more adducted angle of gait will show heel wear more medially.

The magnitude of STJ pronation moment will be increased with a harder durometer lateral heel midsole, with a more laterally flared heel sole and with a more medially deviated STJ axis since these all increase the pronation moment arm for ground reaction force (GRF) at initial heel contact to cause a STJ pronation moment. An increased magnitude of GRF of heel contact may, in general, occur due to increased walking or running speed or to an increase in body weight.

 

Hi Atlas

One extremely layman’s view here.

The reasons for a person striking the ground more lateral on the heel than what we might consider normal vary enormously. It may be because of foot orientation but it can just as easily be hip, femoral of Tibial causes that underlie it. I would even go so far as to say some social groupings can contribut to it!

The more lateral the foot strikes the more prolonged the moment for GRF to load the lateral foot. Equally the more externally rotated the low limb is I suspect there is greater tendency for rear and midfoot collapse (if STJ MTJ allow it). A person with good STJ movement and marked Forefoot Supinatus is more likely to develop overcompensation not only at the STJ but quite noticeably at the MTJ (particularly between early heel lift and push off, for my money the most vulnerable part of gait). If this foot is of a more supinated type then the tendency for lateral instability occurs especially if eversion moments at the STJ are limited (quite often my experience in looking at these people).

In either case there is the added issue of how they obtain forward progression in the saggital plane. Both in the collapsed Rear and midfoot case together with the marked external rotation and more supinated foot case I see a tendency towards Adductory heel whip (more so with the restricted STJ movement) with early heel lift ( to make up for lack of easy flexion of the knee in the saggital plane).

The over compensating STJ MTJ person can develop a tendency to momentary high velocity internal rotation of the knee at this point. The over supinated person can develop the tendency to a momentary, high velocity external rotation, hyperextension at the knee with a momentary lateral drift of the low limb at the same time.

Looking forward to being reminded about how lay a person I am.

Cheers
Ian

 

The more lateral the ground reaction force (GRF) on the posterior aspect of the heel of the shoe, the longer will be the pronation moment arm across the subtalar joint (STJ) axis. There is not necessarily more "prolongation" or increased duration of GRF causing a pronation moment.

If there is a net STJ pronation moment then the STJ will pronate if pronation range of motion if available in the foot. However, a maximally pronated STJ can still be laterally unstable during gait, in other words, show a tendency toward supination instability. Even though the STJ rotational position does affect the midtarsal joint (MTJ) the STJ rotational position is not the sole determinant of MTJ function during gait.

Whether there is excessive MTJ "collapse" or not will be determined largely by many factors other than whether the STJ is in a pronated position or neutral position or a 3 degree pronated from neutral position. Other factors that govern whether the medial arch will "collapse" are as follows:

1. Ligamentous tensile stiffness of plantar aponeurosis and plantar ligaments of medial metatarsal rays.
2. Strength and firing pattern of plantar intrinsic muscles of the medial arch.
3. Strength and firing pattern of peroneus longus, posterior tibial, flexor digitorum longus and flexor hallucis longus muscles.
4. Magnitude of GRF acting on each medial metatarsal rays.
5. Geometry of osseous components of medial longitudinal arch.

Since abductory twist is caused by a STJ pronation moment occuring when a STJ supination moment should be occurring, then any structural deformity or functional problem that causes excessive STJ pronation moments during late midstance may cause an abductory twist.

Forward progression of an individual within the sagittal plane occurs in all walking gait patterns. In order to walk with "normal gait", certain biomechanical criteria must be met in the foot and lower extremity, structurally and functionally, to allow this normal gait to occur. This is why abnormal gait is so prevalent within the human population: it only takes a small deviation from the biomechanical criteria that are required for normal gait for the individual to develop an abnormal gait pattern.

 

Originally Posted by Atlas
>Those of us with small clinics and no academic role, will not come across these systems. Can memory foam be used in a similar way?

There is a significant difference between static analysis and dynamic analysis, so the simple answer would be, no.

>Obviously we will not gauge timing parameters, but would it enlighten us in relation to contact pressures?

Without the time space parameters, it is meaning less. This would be like seeing all the frames of a video shown on one screen all at the same time. It would be impossible to follow the narrative. Some patterns of recognition may appear and educated guesses made but these would be fraught with error.

>Does an old worn insole give as much info? What about the outsole?

Insole will give a texturalised indication of the foot insole interphase and this can be illuminative. Polished surfaces would indicate movement between the surfaces, and scorch marks (dark discolouration) would locate points of prolonged high sheer. However still meaningless without the time space parameters. Many would make educated guesses for pattern recognition, which would be better than nothing.

Outsole wear represents the interface between the outer surface of the shoe and the ground. With shoes, which are close fitting and compatible with the foot, the wearmarks would be similar to the foot, inside. If the shoe was bigger or not compatible with the foot it protect then the outerwear would be less of a mirror. Two simple examples to illustrate this point, a person wearing someone else’s well worn shoes, the wearmarks would be incompatible and the wear under snow shoes would be different to the wear at the foot insole interface. When the same person from the beginning wears good fitting shoes the wear marks are a true sheering impression of the foot segments of stance phase.


Three-dimensional appearance of the shoe does provided interesting data, which is ironically more intricate and complex than pressure or force analysis currently, does. However scientists relate better to that they can measure and single and two-plane analysis offers simpler models. These are by themselves, incomplete but the best technology we have. To the Sherlock Holmes of shoes yes much could be deducted. Watson, but this may irritate the pure scientist, who prefers inductive thought. Shoe analysis is fertile ground for the seasoned practitioner. A nice party trick is to observe the wearmarks on the plantar surface of the heel. Starting at the lateral posterior border you can follow though the stance phase and identify the pendulum swing of the STJ demonstrated by the single plane erosions on the material and match these to the tri-plane actions of the STJ. Abduction is seen at the anterior aspect of the heel , dorsiflexion demonstrated by the wear marks on the medial anterior component and eversion also seen in the medial lateral depression of the heel corner (medial side.) This area corresponds to the medial grind off area on the heel elevated foot orthoses. This will give a reasoned model of the leg and rearfoot and when combined with the wear patterns of the lateral to medial forefoot another set of information to related to stance phase activity right up to toe off. Bi-lateral comparison can be made and reasonable assessment of the ankle can follow. The sagittal analysis is easily confirmed by the sheer wear on the shoes. All this information can act as a valuable cross check with an objective assessment of signs and symptoms from the patient. When inconsistance arises then the clinician suspicions become more acute. The first question to ask under these circumstances would be “Are these your shoes?”

On another biomechanical topic, we all get those patients that say "I wear out the outside of my footwear (heels)". It is normal to heel strike with the heel (STJ) slightly supinated?

What is normal? A foot about to bear weight prefers a stable lower leg and gravity determines the thust of heel strike needs to be damped down, otherwise the muliarticular segment would be quickly destroyed. The pendulum action of supination pronation, synchronises this via open and closed chain motion. Ideally an inverted heel (supinated STJ) can achieve this state.

How and when is this deemed pathological?

If the action of the stj is no longer opening and closing chain motion at he right time for weight transference. Temporary delays may be over come by compensation such as prolonged pronatory phases late into propulsion. Over dependency may result in repetitive stress injuries due to pathomechanical changes.

Does a hard inverted heel strike invite a hard abrupt rear-foot collapse during midstance?

No, because other factors need to be involved.

Cameron
Hey, what do I know?