Femoral neck stress fractures are overall uncommon injuries. Stress fractures are generally stratified into high or low risk, based on probability of propagation to a displaced fracture or nonunion. Femoral neck stress fractures are always considered high risk. Most studies concentrate on athletes and military recruits, but they can also occur in the elderly population. Stress fractures can be subdivided into fatigue fractures (normal bone exposed to repeated stress) or insufficiency fractures (normal stress is applied to abnormal bone). Fatigue fractures are caused by overuse and generally considered in younger and active patients who participate in sports or activities that require repetitive weight-bearing activity (eg, long-distance runners). Insufficiency fractures generally occur in the elderly population and can be caused by low-energy mechanisms such as a ground level fall or even ambulation in some cases. 

Causes / typical injury mechanism: Increase in normal activity level leading to repetitive stress to the femoral neck in younger, active patients. Ground level falls are causative low-energy trauma in elderly patients.

Classic history and presentation: The condition will present as an insidious onset of pain about the groin and hip. Patients may cup their hand around the affected hip when asked for the location of their pain (C-sign). Pain is generally activity related in the early stages and will usually resolve with rest. As the condition progresses, patients may experience pain with any weight-bearing activities. It is common in runners and highly committed athletes who endorse prolonged levels of high activity or endorse increased frequency, duration, or intensity of activities. Also consider in an elderly patient with persistent hip pain.

Prevalence: This is an uncommon condition and prevalence is not well established, but it seems to affect females more than males.

Risk factors: Female athlete triad (hypothalamic amenorrhea, anorexia / insufficient energy availability, and osteoporosis), sudden increase in activity level, change in training surface, change in footwear, inadequate recovery time between training sessions, osteoporosis, vitamin D deficiency, metabolic bone disorders (osteomalacia and Paget disease of the bone), high serum cortisol levels / chronic steroid use.

Pathophysiology:

• Fatigue fractures – Microscopic cracks that occur with repetitive loading. With continued repetitive loading, small hairline cracks may extend and can eventually result in a cortical fracture. Femoral neck stress fractures are generally divided into compression and tension sided. Inferior medial femoral neck fractures are considered compression side (weight-bearing will cause fracture site to compress) and generally heal without surgical intervention. Superior lateral femoral neck fractures are tension sided (weight-bearing will cause fracture site to distract) and will generally need operative intervention.
• Insufficiency fractures – Similar mechanism as fatigue fractures, except the bone is abnormal (ie, osteoporotic) and normal forces can cause microscopic cracks and eventually lead to fracture.

Related topic: femoral neck fracture