Introduction to Shin Splints
The term shin splints is a lay term that is often used to refer to many painful conditions of the (lower) leg. However, most often it refers to a periostitis (inflammation of the periosteal lining) of the tibia caused by excessive pulling forces from musculature that attaches into the periosteum of the tibia.
Shin splints can be divided into anterior shin splints and posterior shin splints. In anterior shin splints, the musculature involved is located in the anterior compartment of the leg, most often the tibialis anterior, and the pain is experienced anteriorly. In posterior shin splints, the musculature involved is located in one or both posterior compartments of the leg, most often the tibialis posterior in the deep posterior compartment or the soleus in the superficial posterior compartment, and the pain is experienced posteriorly. Shin splints is also known as tibial stress syndrome.
Shin splints is effectively caused by excessive use of the musculature of the leg. With each contraction of the involved musculature, the pulling force of the contraction is transferred to the tibial attachment, placing tensile (pulling) stress on the periosteum. If the tensile forces overcome the ability of the periosteum to absorb those forces and/or overcome the regenerative ability of the periosteum, tibial periostitis occurs. If shin splints becomes more severe, it can also result in tearing of the periosteum and of the tendinous fibers of the involved musculature.
The most common form of shin splints is anterior shin splints and most often this condition involves the tibialis anterior. The tibialis anterior is a dorsiflexor of the foot at the ankle joint. During the gait cycle when walking (or running), if the person first contacts the ground with their heel (termed “heel strike”), then their foot is dorsiflexed upon contact. This means that the tibialis anterior is isometrically contracted at the instant of heel strike, just as the shock force from striking the ground travels up the body. The combination of the tautness of the contraction plus the ground reaction shock force places a great tensile stress at the tibial attachment, possibly resulting in periosteal inflammation and tearing. As the foot continues through the gait cycle from heel strike to midstance, the tibialis anterior transitions from isometrically contracting to eccentrically contracting to control the plantarflexion descent of the foot to the ground. This continues the stress load upon the tibialis anterior and therefore its tibial attachment. Anterior shin splints can also involve the other dorsiflexors of the anterior compartment: extensor digitorum longus (and associated fibularis tertius) and extensor hallucis longus. Therefore periostitis of the fibula as well as irritation and inflammation of the interosseus membrane are also possible with anterior shin splints.
The most common cause of anterior shin splints is any sport/activity that involves running, especially for long distances. Running on a hard surface such as asphalt or concrete is particularly difficult because the shock force from hitting the ground is greater. Most often, shin splints will occur when a person either first starts running or when they increase too quickly the mileage that they run.
Another causative factor for anterior shin splints is overpronation of the foot, specifically a supple flat foot which causes the arch to collapse (overly evert) when weight bearing. This tends to increase the tensile (pulling) force of the tibialis anterior at the periosteum of its tibial attachment for three reasons. When walking or running, if the foot excessively everts, the tibialis anterior (an invertor) is overly stretched, increasing its tautness and therefore its tensile pulling force at its tibial attachment. Further, it is more likely to eccentrically contract and be overworked in an attempt to prevent the excessive eversion/collapse of the arch, also increasing its tensile force upon the periosteum. Finally, the overstretch increases the likelihood of activating the muscle spindle stretch reflex, thereby causing chronic tightness of the tibialis anterior and therefore increased tensile forces at the periosteum of the tibia.
As with anterior shin splints, posterior shin splints is essentially a periostitis from overuse/contraction of musculature. Posterior shin splints can involve any posterior compartment musculature, whether it is in the superficial posterior compartment or the deep posterior compartment. The muscles most often involved are the tibialis posterior in the deep compartment or the soleus in the superficial compartment. Because all muscles that cross the ankle joint posteriorly do plantarflexion, posterior shin splints is usually caused by activities that require repetitive plantarflexion of the foot; for example dancing or playing basketball.
Beyond the causes listed above, tightness of or myofascial trigger points in the involved musculature also predispose the client/patient to the development of shin splints because the increased tone equates to increased tensile force upon the periosteum at the osseous attachments.