Running Injuries and the Shape of the Foot- Pronation:
A very interesting aspect of orthopedics is the predictability of injury. Patterns exist in nature, and a correlation is often seen between the shape of one's foot and the injuries one may encounter. "Experience" then becomes nothing more than pattern recognition: the realization that certain types of foot alignment predispose to specific types of problems. Of course there are exceptions, and the following examples represent generalizations only.
Most runners are familiar with the term "pronation". This describes a foot that is flat. In other words, the arch is minimal, or even absent. A pronated, or flat, foot, can be rigid or flexible. Rigid means that the deformity is fixed or constant, and independent of weight-bearing. A flexible flat foot presents only with weight bearing, and the arch is restored when weight is off the limb. The function of the arch is two fold: shock-absorption and energy-storage, and it acts similarly to the leaf spring of a car. The arch is supported by many small ligaments and by the posterior tibial tendon, which serve to maintain and control the arch.
The only other fact that is essential to understand is that a relationship exists between the normal "controlled collapse" of the arch with weight-bearing and rotation of the lower leg. This occurs through the complex series of joints between the leg and foot. In short, the greater the tendency toward pronation (the greater the flexibility and flattening of the arch), the greater the rotation of the lower leg. This is the basis for many of the overuse injuries that correlate with the pronated foot.
Thus, rotation of the leg that occurs with each and every step, can produce torsional, or twisting, forces on the soft tissues that attach to various parts of the leg. If excessive, one may develop patellar tendinitis, or shin splints, for example. Furthermore, rotation of the lower leg also affects the alignment and motion of the patella, which can produce pain in and around the patella, called "patellofemoral syndrome". The focus therefore, is controlling pronation by supporting the arch of the foot, in addition to treating the symptoms and problems above the foot. Often, simply using a more supportive shoe, one which incorporates some type of "motion control", or arch buttress, will do the trick. Another option is a supportive insert ("arch support"), i.e.- an orthotic. It is useful to check the shoe first, as it is easy to buy the wrong type. Custom orthotics can be expensive. Over-the-counter varieties are much cheaper, and can be useful as a short-term trial.
Running Injuries and the Shape of the Foot- Supination:
Several issues ago, the concept of foot shape and injury correlation was introduced. The pronated foot is a "flat foot", one with a diminished, arch. Recall that the function of the arch is two fold: shock-absorption and energy-storage. The arch is supported by many small ligaments and by the posterior tibial tendon, which serve to maintain and control the arch. Furthermore, the greater the tendency toward pronation (the greater the flexibility and flattening of the arch), the greater the rotation of the lower leg. This is the basis for many of the leg overuse injuries that correlate with the pronated foot.
The opposite of the pronated or flat foot is the supinated, or high-arched foot. The chief characteristic of the high arch is its rigidity. It lacks the controlled collapse characteristics of the normal arch. Without this flexibility and collapse, there is reduced capacity for shock-absorption and cushioning. In addition, there is decreased energy-storage without the controlled arch collapse of the supinated foot. It has been shown that more than 50% of the energy absorbed with arch collapse is retransmitted to the limb with toe-off. Hence, the supinated foot is a less-efficient, stiffer, less cushioned foot, relative to its opposite.
Remember that the pronated foot transmits torsional (twisting) forces upwards within the limb secondary to the complex biomechanics of the ankle and other joints of the hindfoot. The supinated foot then, by virtue of its stiffness, confers little rotation, as there is minimal arch collapse, but rather transmits direct impact forces up the leg. Unfortunately, just as the twisting forces of the pronated foot can contribute to injury, so too can the direct waves of concussion transmitted by the supinated, high-arched foot. However, these forces are more likely to produce high impact type injuries.
Injuries most likely to occur because of impact transmission most commonly include stress fractures. These may include sites such as the tibia (lower leg), and neck of the femur (hip). These pounding forces may even effect more distant locations such as the sacroiliac joints of the lowest portion of the back and pelvis, and the lumbar spine (low back). Symptoms may include running related leg, knee, groin, and low back pain. Whether these forces can actually contribute to arthritis of the knee, hip and spine is debatable. Evidence is controversial (see below web site for archived discussion of running and arthritis).
Just as orthotics may be helpful to the injured pronator, they may also benefit the supinator. Extra cushioning is essential in this type of foot. Usually, this involves the use of shock-absorbing inserts, for example, viscoelastic substances, commercially available at most running stores. Certain shoes are designed with extra padded soles for the same function. These shoes utilize a variety of substances including closed-cell midsoles, air chambers, and gel pads within the heel. The effectiveness of these substances is variable.
In summary, it is useful to know the type of foot architecture one must live and run with, in order to select the correct shoe type, and to avoid and recover from injuries. The pronated foot needs arch support to control excessive arch collapse and limit the rotational forces transmitted upwards within the leg. The supinated foot needs cushioning to compensate for the lack of arch collapse and shock-absorption, with excessive axial forces passed upstream.
Finally, excessive pronation and supination represent the extreme ends of the spectrum, the "toe regions", or small ends of the population curve. Most feet are in between, with average, or relatively "normal" arches.
Dan Wnorowski, M.D.