A Stress Fracture is a fracture caused by repeated axial or rotational forces on bone.
There is initial periosteal edema. As this progresses, there is progressive marrow involvement leading to eventual break in the cortex. Bone callus formation occurs later. American Journal of Sports Medicine-1995
Data is varied as is the distribution. Two thirds of all stress fractures are in the lower extremity according to a 1998 German study.
Stress fractures comprised 20% of all overuse injuries over a two year period.
Stress fractures by site: Tibia-46%, Navicular-15%, Fibula-12%
Dennell, et. al. in 1996 published a study that showed that while Tibial Stress Fractures occurred most commonly in long distance runners, foot stress fractures occurred most commonly in Track and Field Athletes.
In a 1996 Australian Sports Medicine Study, the most frequent sites were: Metatarsal(42), Tibia(36), Fibula(30), and Navicular(26). In that same study, the frequency of stress fractures in sports was: Track and Field(54), Distance Running(35), Dance(32) and Australian Football(14). In that same study, the frequency of types of Stress Fractures by sport was: Track and Field:navicular, tibia, metatarsal in that order; Distance running: tibia, metatarsal, fibula in that order.
Stress Fractures are mainly an overuse injury. Too Much, Too Soon, Too Fast! Muscular fatigue in the athlete will cause increased bone strain that may contribute to the formation of the stress fracture. Muscles exert a protective effect during contraction by reducing bending strains on cortical bone surfaces.
Extrinsic factors include sudden change in activity or training program, equipment(shoe gear, etc.), running surface and type of sporting activity.
Intrinsic factors include anthropometry, range of motion, gait patterns, muscle loading pattern and bony alignment of the extremity. They also include flexibility deficits or ligamentous laxity, poor physical conditioning, and lower relative muscle strength. Another intrinsic factor in female athletes is menstrual disorders with no history of eating disorder.
There is most often a clinical diagnosis in the private practice setting. Treat it as a stress fracture until the x-rays prove otherwise. This usually means a very detailed history and physical exam correlated with initial x-ray findings and follow-up x-ray findings. X-ray is 40-75% accurate. Accuracy is dependent on: age of the stress fracture, location of the stress fracture within the bone and the specific site. The Tibia is the most difficult, while the fibula and metatarsal are a little easier. Other diagnostic tools for stress fractures include therapeutic ultrasound (highly sensitive), tuning fork (low tech), Technetium three phase bone scan (most sensitive, but very non-specific), CT scan, and MRI.
Early detection, Rest and Immobilization are key to best treatment. Typical stress fracture healing time is 6-8 weeks for most sites. The Tibia can take as much as 6-16 months. Typically the fibula will heal in 6-12 weeks. The Navicular will usually take as much as 12 weeks or more and may require fixation. The 5th Metatarsal will take 6 weeks or longer with weightbearing. As for the other lesser Metatarsals, the 2nd Metatarsal usually takes 4-6 weeks, while the 3rd and 4th Metatarsals take 4 weeks.
Personal experience in the treatment of many athletes, professional and amateur, has shown that the use of flexible and semi-rigid functional orthotics in athletes has significantly decreased the incidence of stress fractures of the lower extremity. This finding has been upheld by numerous studies done by the military on personnel in training.