Causes / typical injury mechanism: Tibial stress fractures result from repetitive microtrauma of the tibia caused by repeated running or jumping.

Classic history and presentation: Tibial stress fractures most commonly occur in athletes, specifically those in running and jumping sports, and military trainees. Patients classically complain of gradually increasing pain and tenderness in the shin with physical activity. By presentation, many patients are unable to perform their aggravating activity and may report pain even at rest.

Prevalence: There is little data on the prevalence of stress injuries in the general population. Prevalence is greater in high-impact activities like running sports. Some reports indicate that up to 20% of elite runners may suffer from some sort of stress fracture. Incidence in National Collegiate Athletic Association (NCAA) athletic populations is reported at around 5.7 stress fractures per 100 000 athletic encounters, although this rate is significantly higher in women's running sports (> 20 / 100 000). The tibia is implicated in between 20% and 60% of stress injuries, depending on the sport and level of play.

• Age – Tibial stress fractures often present in young, active patients but may occur in patients of all ages.
• Sex / gender – Evidence suggests that stress fractures are more common in women than men.

Risk factors: The greatest risk factor for stress fractures is prior history of a stress fracture. Exposure to intensive training regimens, particularly with a recent increase in intensity, and training on hard surfaces or in hard-soled footwear are considered extrinsic risk factors for tibial stress fractures. Some data has also shown associations with lower muscle and bone mass of the lower leg, small bone size, foot abnormalities, and hormonal or nutritional imbalances. The classic triad for stress fractures in female athletes consists of eating disorders, amenorrhea, and osteoporosis.

Pathophysiology: Tibial stress fractures are thought to result due to abnormal repetitive loading of the tibia, resulting in increased bone resorption relative to bone synthesis. Over time, this results in microtrauma within the bone that eventually leads to a continuous cortical discontinuity that is then considered a stress fracture.

Grade / classification system: Stress fracture grading is based on MRI imaging:

• Grade 1: Shows periosteal edema on fat-suppressed T2 imaging.
• Grade 2: Also includes increased signal intensity within the marrow cavity or along the endosteal surface on fat-suppressed T2 imaging.
• Grade 3: Periosteal and marrow edema are visible on both T1 and T2 imaging.
• Grade 4: A fracture line is visible on T1 and T2 imaging.