Stress fracture

Tumor biology and incidence
Stress fractures are injuries that result from overuse.  They are typically associated with muscle fatigue leading to decreased support of bony architecture.   An estimate of the incidence of stress fractures in athletes and military recruits is 5-30%. 
Age
Stress fractures may occur in people of all ages.
Gender
Females experience stress fractures more frequently than males.  This is especially true for females suffering from the "female athlete triad" - amenorrhea, disordered eating, and osteoporosis. 
Presentation
Patients with stress fractures present with pain that increases with activity and decreases with rest.  The pain also may occur at an earlier point in each subsequent workout.  Patients also frequently complain of night pain.  There is also typically one specific spot that feels more tender than any other area on the same bone. 
Physical findings
The primary finding on physical exam is pain upon palpation of the affected area.  The pain may also be reproduced by having the patient load the affected bone.
Plain films
Early in the process of developing a stress fracture, there may be no significant findings on X-ray.  After several weeks a periosteal reaction may be seen.  Further along in the disease process, one may see an area of cortical lucency suggesting a nonhealing stress fracture. 
Site
Greater than half of all stress fractures occur in the lower extremity.
Size
Stress fractures may occur in various sizes depending on the length of the disease process and the affected bone. 
Tumor effect on bone
The effect on the bone is to cause a separation within the cortex that is incomplete, typically only occurring on one cortex. 
Bone response to tumor
As with the typical response of bone to fracture, there is a periosteal reaction and thickening of the cortex while remodeling is occurring. 
Cortex
The cortex is typically thickened compared to the cortex at a distant site in the same bone.
Soft tissue mass
There is typically no soft tissue mass associated with stress fractures.
Bone scan
A bone scan is considered to be positive if focal isotope uptake occurs in the area of clinical interest on the 3^rd phase of the scan.  If there is no uptake, a stress fracture is not likely present.  The isotope uptake may occur prior to clinical symptoms and may persist after symptoms have resolved. 
CT Scan
CT scans facilitate visualizing the bony architecture and seeing the extent of the stress fracture. 
MRI
MRI is able to show bone marrow edema and periosteal reaction associated with this pathologic process in addition to the subclinical extent of disease. 
Differential Diagnosis
Fracture, Osteomyelitis, Bone metastases, Osteoid osteoma, Exertion-related compartment syndrome, Bone contusion, Shin splints (medial tibial stress syndrome, tibial traction periostitis).
Natural history
Typically a stress fracture may occur with the onset of a new training regimen or beginning as a new military recruit.  The pain will continue to increase with each subsequent workout, usually occurring earlier in each workout.  After seeking medical consultation, the patient will be recommended to rest and stop participating in the offending activity.  Once a period of rest has been completed, the pain should begin to subside and subsequently the patient may resume prior activities. 
Diagnosis and treatment
The primary treatment is rest, usually for 4-12 weeks.  NSAIDs and other analgesics may be used to limit pain.  A healthy diet including calcium and Vitamin D should be maintained.  Bisphosphonates may be prescribed if there is a lack of healing noted after 2-3 months of rest. 
Complications
Complications may include avascular necrosis, nonunion, malunion, posttraumatic arthrosis, and continuous pain. 
Recommended Reading
1.         Stress Fracture.  Jonathan C. Reeser. http://www.emedicine.com/pmr/TOPIC134.HTM

2.        Stress Fracture.  AAOS.  http://orthoinfo.aaos.org/topic.cfm?topic=A00112

3.      Stress Fractures. Mayo Clinic.  http://www.mayoclinic.com/health/stress-fractures/DS00556