PAGE 2
Shoes
and Athletic Injuries:
Analyzing Shoe Design, Wear Pattern, and
Manufacturers’ Defects
  By Bruce Wilk, PT, OCS/William Gutierrez, PT, OCS, ATC

As the push-off phase of running is approached, the foot supinates in order to become a rigid lever and propel the body for­ward, So in essence, the foot initially coils to absorb the body’s weight then recoils to propel the body onto the other foot(15).

Thus, if the foot rolls in excessively, the subject is a pronator. Pronators tend to roll medially throughout the lower extremity during the stance phase. They also tend to have a more supple, shock absorbing foot. The drawback to this type of foot is that more power will be nec­essary during push off. When looking at old shoes of a pronator they deform medially. The medial arch of the midsole is compressed, and there is extensive wear at the lateral aspect of the heel and at the medial forefoot. The prona­tor may also have low arches. Therefore, while it is important for the foot to have good shock absorption, athletes with pronated feet also need shoes which emphasize control of the rear foot.

Research has shown that shoes construct­ed with soft materials in the soles and uppers, or shoes that are broken down on the medial aspect, may allow a medial roll of the foot and ankle during stance(16). Clarke, and cowork­ers(17), noted that shoes with a soft midsole and no heel flare allow the greatest amount of pronation, while shoes with hard midsoles and a 30 degree flare allowed the least pronation.

Supination is on the opposite end of the spectrum from pronation. If the foot rolls out excessively, the subject is a supinator. Supinating feet do not absorb shock well, and their shoes should provide adequate cushioning for the lateral edge of the foot. Tell-tale signs of shoe wear in a supinator include old shoes that tilt laterally, laterally compressed midsoles, and soles that are overly worn along the lateral edges. Supinators usually have high arches.

Thus, selecting a running shoe that will adequately support a runner’s lower limb anato­my and biomechanics can be quite complex, as documented in several sources(18,19).

Shoe Variety

The way people run varies considerably, and a shoe that’s right for one person can cause another blisters, musculoskeletal strains, or joint

inflammation. Twenty years ago, the only criteria for buying sneakers was ensuring that the toes didn’t jam against the end of the toe box. Today, however, shoe design has become sophisticated with a wide variety of choices available. It has become neces­sary for physical therapists, and other health care specialists, to assess foot biomechanics and running style in order to provide the patient with help­ful information in choosing the cor­rect shoe.

 

Checking Feet

It is important to determine if a patient is a pronator or a supinator. This can be done by drawing a line bisecting the Achilles tendon and the calcaneus's. The alignment of these marks is evaluated with the patient standing. If the calcaneal line tilts medially then the foot has a tendency to pronate. Conversely, if the cal­caneal line tilts laterally then the foot has a ten­dency to supinate(20).

Another clinical technique used to deter­mine foot posture is to palpate the talar dome. This is done with the patient standing. If the talus is more palpable medially, then the foot is in a pronated position. If the lateral aspect of the talus is more palpable, the foot is in a supinated position.

 

Wear of Shoes

A running shoe, when placed on a flat level surface, should not be biased medially or lateral­ly. The main purpose of the shoe is to hold the foot stable. It should be constructed so its upper, midsole and outsole are firmly attached (Figure 1). The uppers, heel counter and the sole should be straight. The shoes should not rock from side to side and the shock absorbing pockets should resist collapsing under load. Defective or worn out shoes which don’t hold feet in a neutral position may accentuate a pre­existing musculoskeletal imbalance (i.e. exces­sive pronation or supination). This may lead to unnecessary aches and pains and, if not treated, a more serious or permanent injury.

 

The importance of carefully inspecting run­ning shoes for manufacturer’s defects before purchase, and regular checks for uneven or

excessive wear throughout the life of the shoe can not be overemphasized. The following guidelines will help the athlete avoid buying defective running shoes and max’ prevent unnecessary injuries.

The shoe should be glued together secure-lv. Test this by holding the shoe and trying to pull the upper part of the shoe away from the midsole, and the midsole from the outsole (Figure 2). Any separation will weaken the shoe’s support.

The upper part of the shoe should he glued straight into the sole. Test this by putting the shoe on a level surface and inspect the hack of the shoe (Figure 3A). The heel counter should appear even, and should not lean to the right (Figure 3B) or left, A brand new shoe that leans medially or laterally could cause injury. especially if there is a large asymmetry~ between each shoe of a pair.

The sole of the shoe should be level to the surface on which the shoe is resting. Test this b~’ checking that the medial and lateral aspect of the heel is even when resting on a flat, level sur­face (Figure 4Aand B). Compare each shoe indi­vidually, then compare the right to the left shoe for symmetry. An asymmetry of two millimeters can tilt the shoe in or out significantly.

Test for asymmetry by applying a down­ward medial and a downward lateral force to

               A                    B 

Figure 3: A)    The medial (a) and lateral (b) vertical dis­tances      are equal on the left shoe,

Figure 3: A)   Dotted lines show a 90 (goniometric.) angle formed between the center of the heel counter and a horizontal line through the middle of the midsole of the shoe. B)   Dotted lines show the right, outward lean of the upper  shoe because it is glued into the midsole at a lateral angle.

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