Medial tibial stress syndrome (MTSS), commonly known as shin splints, is an overuse injury.

Causes / typical injury mechanism: MTSS is thought to arise as a result of a combination of repetitive muscle contractions and stress on the tibia. It is usually seen in individuals who participate in activities that include running, jumping, and prolonged walking. There is often a recent history of increased activity load and high-impact exercise.

Classic history and presentation: MTSS presents as lower leg pain located near the posteromedial tibia. Symptoms will typically begin soon after starting exercise and become less intense as exercise is continued. In more severe cases, the pain will persist after exercise has stopped and may be present with normal daily activities. Occasionally, there will be mild swelling near the posteromedial border of the tibia at the site of pain.

Prevalence: MTSS is one of the most common causes of exercise-induced lower leg pain. Often seen in athletes and military recruits, it accounts for 14%-20% of running-related injuries and is seen in up to 35% of military recruits.

Risk factors: Risk factors include female sex, increased body mass index, increased navicular drop (a measure of foot pronation and arch height), increased plantarflexion range of motion, increased external rotation of the hip, and prior history of MTSS.

Pathophysiology: Repetitive contractions of the tibialis posterior, flexor digitorum longus, and soleus muscles apply tension to the tibial periosteum, causing inflammation. Additionally, repetitive bending or bowing of the tibia can cause bone fatigue and microtrauma.