Shin splints, shoes, and the posterior tibial tendon:
One of the most common troublesome conditions that can plague the runner is "shin splints". This entity classically presents as pain on the inside of the shin bone (tibia), usually in a longitudinal distribution (up and down the leg), typically in the lower third. It is often bilateral. I most commonly see this problem in runners with a history of sudden increases in training mileage or intensity, those that run on the same side of the slanted shoulder of the road, or those with a change in footware.
Every runner has a unique foot, and the arch of the foot is especially variable. The arch of the foot can be high and rigid (the "cavus" foot), or low and flexible (the "flat foot"). Furthermore, the flat foot, though most often flexible, can be fixed, or rigid. It is the flexible flat foot ("pes planus", or "pronation"), that contributes to the shin splint problem.
The arch of the foot is made up of a column of bones much like the architectural "Roman arch". These bones are arranged apex upward, and tethered together by a series of ligaments that bind and support the bones. But like any structure, the arch may be prone to fatigue and collapse. Therefore, the muscles and tendons that help support the arch are extremely important. The main muscle-tendon unit that supports the arch is the posterior tibial tendon. As it's name implies, it originates from the back (posterior) of the tibia, traverses behind the medial malleolus (bump on the inside of the ankle), and attaches near the apex of the arch to help support it.
Shoes are also very important and will be the focus of this discussion, as they relate to the shin splint problem. We all have heard the importance of "supportive shoes", but what does this really mean? For the runner with flatfoot tendency, or with a "tired arch", support means a cushion in the shoe, or some sort of "motion control" component engineered into the shoe design which serves to prop up the arch. The motion the shoe is supposed to control is pronation, or simply, collapse of the arch during stance phase (with weight-bearing). This usually means stiffening the area directly adjacent to ad beneath the arch (tough plastic buttresses are common, or a different material in the outer sole beneath the arch). Sometimes special insoles will do. This can make a big difference in avoiding arch overuse, strain, and collapse.
So what does this have to do with shin splints? A supportive shoe is very important in the feet of those with flexible flatfoot, i.e.- pronators, to prevent fatigue of the arch, and hence, stretching and fatigue of the posterior tibial tendon. Overuse of the posterior tendon can present as either a tendinitis, or shin splints. The symptoms vary from pain in the arch, pain behind or below the medial malleolus, or along the inner shin. Swelling may sometimes be present. Treatment is aimed at reducing inflammation (ice, medication, etc.), resting the inflamed tissue (decreased mileage, avoiding the cambered side of the roads, etc.), and supporting the arch, and secondarily, the posterior tibial tendon (shoe modifications).
A word of warning. If pain persists despite these conservative modifications, one must consider the possibility of more serious injury, such as tibial stress fracture, or posterior tibial tendon tear. Also, numbness in the foot is not typical, and suggests other problems, as well. If in doubt, get it checked out!
Dan Wnorowski, M.D.