The term shin splints usually applies to pain in the front of the leg, occurring anywhere between the ankle and the knee. However, it can also refer to pain in the inner side of the lower leg. The pain in both of these areas is usually initiated by walking, running, or jumping. In extreme cases one can have pain in these areas while just standing still.
The main cause of these injuries is pronation. This is a biomechanical defect of the foot that is sometimes responsible for pain in the foot, ankle, leg, knee, hip, and lower back.
When pronation is present, the muscles overwork in an attempt to maintain the foot in a normal alignment with the leg. When this normal alignment is not maintained, then the foot becomes unstable.
This instability of the foot cause more stress on the leg muscles. This continued "overusage" by the leg muscles will cause pain, swelling, tears within the muscle, and eventually the muscle will tear away from the shin, or stress fractures will occur.