Shin Splints - Causes and Epidemiology

Causes and Epidemiology

Shin splints, known as medial tibial stress syndrome (MTSS), can usually be attributed to overloading the muscles of the lower extremities or to biomechanical irregularities. Muscle imbalance, including weak core muscles, can cause lower-extremity injuries, and inflexibility and tightness of the gastrocnemius, soleus, and plantar muscles (commonly the flexor digitorum longus) may contribute, as well. Increasing activity, intensity, and duration too quickly leads to shin splints because the tendons and muscles are unable to absorb the impact of the shock force as they become fatigued; also, the tibial bone-remodeling capabilities are overloaded. The pain associated with MTSS is caused from a disruption of Sharpey's fibres that connect the medial soleus fascia through the periosteum of the tibia where it inserts into the bone. With repetitive stress, the impact forces eccentrically fatigue the soleus and create repeated tibial bending or bowing; thus, contributing to MTSS. The impact is made worse by running uphill, downhill, on uneven terrain, or on hard surfaces. Improper footwear, including worn-out shoes can also contribute to shin splints. Risk factors for developing MTSS include:

• Excessive pronation at subtalar joint
• Excessively tight calf muscles (which can cause excessive pronation)
• Engaging the medial shin muscle in excessive amounts of eccentric muscle activity
• Undertaking high-impact exercises on hard, noncompliant surfaces (ex: running on asphalt or concrete)

While MTSS is the most common name, other conditions often overlap as causes including compartment syndrome and stress fractures. Females are 1.5 to 3.5 times more likely to progress to stress fractures from shin splints. This is mostly due in part to females having a higher incidence of diminished bone density and osteoporosis. Shin splint pain is described as a recurring dull ache along the posteromedial aspect of the distal two-thirds of the tibia; the difference in stress fracture pain is that it is typically localized to the fracture site and is more proximal than the pain caused by MTSS. Studies have found that they may cause death.

People with flat feet are especially prone to shin splints. Bio-mechanically, over-pronation is the common cause for medial tibial stress syndrome. It involves excessive inward rolling that causes tibial twisting and overstretching of the lower extremity muscles. Having poor form, such as leaning forward or backward too much, as well as running with toes pointing outwards all contribute to the causation of shin splints.

Medial tibial stress syndrome is the most prevalent form of shin splints and can affect a broad range of individuals. It affects mostly runners and accounts for approximately 13% to 17% of all running-related injuries. High school age runners see MTSS injury rates of approximately 13%. Aerobic dancers have also been known to suffer from MTSS, with injury rates as high as 22%. Military personnel undergoing basic training see lower MTSS injury rates between 4% and 6.4%.