Stress fractures refers to a common injury that results from overuse. This is typically seen in the lower extremities, although stress fractures have also been reported in the upper extremities and ribs. The tibia, metatarsals, fibula, and navicular bones are at the greatest risk for stress fracture, while less common locations are the femur, pelvis and sacrum. Stress fractures are caused by repetitive loading of the bone, which eventually wears down over time, leading to a fracture. This differs from the typical fracture in that it is not preceded by an acute traumatic event, but rather shows a progressive increase in pain of the lower extremity during exercise and activity. This injury is commonly noted among athletes and military recruits.
Normal bone remodeling occurs when increased load is applied to the bone: the microdamage from the stressors is repaired through the physiologic process of bone remodeling. A stress fracture occurs when the microdamage occurs at a rate that exceeds the bone remodeling, causing a progressive injury. People suffering from conditions that weaken the bone, such as osteoporosis, are more prone to stress fractures.
Athletes that have a history of increasing or changing intensity of athletic activity are also more prone to developing this condition. Three factors have been identified in increasing one’s risk for stress fractures: an increase in the applied load, an increase in the number of applied stresses, or a decrease in the surface area of the applied load.
Stress fractures are often underdiagnosed, as they may not show up on X-rays for the first two to four weeks after the injury has occurred. The initial radiographic findings may be nonspecific, indicating local periosteal reaction, or endosteal cortical thickening. The low sensitivity of X-rays makes other imaging techniques preferred. Technetium-99m bone scanning has been shown to detect stress fractures as early as 72 hours, although it may mistakenly detect other conditions, such as infections or bone growth. Magnetic resonance imaging (MRI) scans have also been useful in detecting stress fractures, and have greater sensitivity than normal X-rays.
There are four grades of stress fractures based on radiologic findings:
- Grade 1 fractures appear normal on X-rays, but have a poorly defined area on bone scan
- Grade 2 fractures appear normal on X-rays but have a more intense area on bone scan
- Grade 3 fractures reveal a discrete line on X-ray, and a sharp area of uptake on bone scan
- Grade 4 fractures reveal fracture or periosteal reaction on X-ray, and a more intense localized transcortical uptake on bone scan
The treatment of stress fractures involves decreased activity and immobilization. Patients are usually advised to decrease activity for four to six weeks, followed by a progressive and gradual return to normal intensity. The use of leg braces and crutches has been shown to speed the healing and return to normal training. Typically rest over this period of time gives the body more than enough time to heal the fracture through normal bone remodeling, although in some specific cases, there is a risk for non-union.