Shoe wear, or the way your shoes show wear, can often hold much meaning, yet can also be very ambiguous. One of the first things to do is compare both shoes and look for asymmetry in wear; this will reflect asymmetry of function. There may be difference or inequality in leg length, foot pronation, muscle strength, or rotation.
Before discussing abnormal wear patterns, we first must determine what is considered normal. A shoe with a normal wear pattern indicates that you land on the outside of your heel with your weight moving quickly along the outer side of your foot (not causing much noticeable wear). As weight is transferred between the first and second metatarsal heads, you may see a wear spot just behind the first and second toes. This is where you take off into your next step. Faster runners those running sub -7:30's will have a third wear spot at the tip of the shoe.
Outer heel wear or rearfoot strikers: The point of initial contact with the ground is usually the place showing the most wear. Some outer heel wear could actually be normal; most people have wear here. However, when it becomes excessive, it usually suggests overpronation.
Possibly due to a pigeon-toed gait which would make this area the initial point of contact with the ground. The heel counter is bent inward, and the medical part (inside) of much of the sole shows wear. This pattern also can suggest severe pronation. The best way to tell is by really looking at the foot in addition to the shoe.
A lot of forefoot wear and little heel wear usually indicates forefoot strike, which the shoes of many fast sprint and middle distance runners will show. Uneven wear, or wear below the second or third metatarsal area, may indicate a supination.
Morton's foot (short 1st metatarsal) and excessive pronation. The indicated metatarsal may be at high risk for a stress fracture. Middle of the sole or lateral sole wear in general may reflect a high-arched, under-pronated foot. Medial sole wear with a bent counter and a medial shift of the upper foot, probably indicates severe excessive pronation.
With excessive pro-nation, heel counters may bend inward; with under pronation they may tilt to the outside. There are some situations in which the outside tilt of the heel counter and lateral shift (to the outside) of the upper may indicate severe excessive pronation.
The uppers of your running shoe may likewise tilt inward (with a hyperpronated foot) and outward (with an underpronated foot). There may be holes by the toes or by the big toe alone. This could mean that the shoe you're wearing is too shallow or too short at the front of the foot. There should be a thumb's width between the tip of the shoe and the toes. Also, if the big toe makes a bump in the shoe less that 1/2" from the tip, the shoe is probably too short.
So, pay attention to your shoes! What you wear and how they are wearing can do more for injury prevention than you might think.