Femoral Neck Stress Fracture

Updated: Oct 28, 2022
  • Author: Scott D Flinn, MD; Chief Editor: Sherwin SW Ho, MD  more...
  • Print
Overview

Background

Stress fractures are a problem in various populations including runners and military trainees. [1, 2, 3] These fractures can occur with as little as 2-3 weeks of training, be very mild, causing only minimal changes to the bone which eventually heals, or they may progress to a complete fracture that requires surgical fixation. Although rare, poor outcomes may occur in the form of nonunions or avascular necrosis. Certain stress fractures have a higher risk of poor outcome, including anterior tibial and femoral neck stress fractures (FNSFs).

(See also the articles Femoral Head Avascular Necrosis [in the Sports Medicine section], Avascular Necrosis, Femoral Head and Stress Fracture [in the Radiology section], and Stress Fracture [in the Physical Medicine and Rehabilitation section], as well as Risk Factors for Bone tress Injuries: A Follow-up Study of 102,515 Person-Years and Total Hip Arthroplasty in the Older Population on Medscape.)

FNSFs (see image below) are some of the most difficult injuries to diagnose. The pain associated with such an injury may be poorly localized in the hip and may be referred to the thigh or back. Physical examination findings are not very specific for this injury, and diagnostic radiographs in the form of x-ray films, bone scans, and/or magnetic resonance images (MRIs) are often necessary. [4] Failure to diagnose FSNFs may lead to catastrophic consequences, including avascular necrosis of the femoral head and the need for a hip replacement in otherwise healthy young individuals. [5, 6, 7] A high index of suspicion in the appropriate risk populations is the key to diagnosing and treating FNSFs.

Radiograph showing a tension-side, completed femor Radiograph showing a tension-side, completed femoral neck stress fracture.

(See also the article Femoral Neck Stress and Insufficiency Fractures.)

For patient education resources, see the Foot, Ankle, Knee, and Hip Center; Breaks, Fractures, and Dislocations Center; and Sports Injury Center, as well as Broken Leg and Total Hip Replacement.

Next:

Epidemiology

United States statistics

Stress fractures may develop in up to 15% of runners and military trainees. [3] Of those patients who develop stress fractures, about 5-10% of the fractures are in the femoral neck. [8] Stress fractures on the compression side (the inferior aspect) of the femoral neck are more common than stress fractures on the tension side (the superior aspect).

Previous
Next:

Etiology

Improper training is the most obvious cause for a stress fracture. Increasing the duration, frequency, and/or intensity of training too quickly does not allow for proper bone and supporting muscle adaptation, resulting in microscopic damage to the bone, which cannot be healed quickly.

In the military population, trainees who have initially lower levels of fitness and higher body mass indexes are at an increased risk of stress fractures. [1]  A history of a previous stress fracture is also a risk factor for a recurrence. In addition, coxa vara has been associated with an increased risk of FNSF. [9]  Finally, a study on male US Marine Corps recruits showed a higher risk of stress fracture with low body weight and small femoral diaphysis. [10]

Other hypothesized risk factors for FNSF include improper footwear, leg-length discrepancies, and a change of the running surface.

Females with the female athlete triad (ie, disordered eating, menstrual dysfunction, premature osteoporosis) are also at increased risk for stress fractures. (See also the article Female Athlete Triad.)

Young women who perform weightbearing exercise regularly can increase the bone density of their femoral neck. [11]

Plebes undergoing training at the US Naval Academy who had significant weight loss and smaller muscle mass were associated with a much higher incidence of stress fracture than their fitness-matched cohorts. [3]

A study by Goldin et al suggested that femoral neck stress injury patients have a higher incidence of bony abnormalities associated with pincer impingement, including coxa profunda and acetabular retroversion, however, further studies are needed to evaluate this relationship. [12]

Previous
Next:

Functional Anatomy

The femoral neck lies between the femoral head and femoral shaft, demarcated by the greater and lesser trochanters. Weight-bearing forces from the trunk cause a compressive force on the inferior aspect of the femoral neck, whereas the superior aspect is subject to tensile forces. [6, 13] The blood supply to the femoral head runs through the femoral neck; thus, an FNSF may disrupt the blood supply to the femoral head and cause avascular necrosis of the femoral head. [6]

Previous
Next:

Sport-Specific Biomechanics

The load of the runner's body weight is transmitted down the lower extremities through the bones and may exceed 3-5 times the body weight in the femoral neck during running. Muscles help to absorb forces and distribute load, especially the gluteus medius. The weight of the trunk and upper extremities applies compressive forces to the inferior aspect of the femoral neck. Conversely, tensile forces act upon the superior aspect of the femoral neck. These forces become important in the prognosis and management of the stress fracture. A sudden reduction in weight and lower muscle mass combined with daily training was associated with an increased risk of FNSF in US Naval Academy plebes. [3]

Previous
Next:

Prognosis

FNSFs are often difficult to diagnose. The patient's history of increasing hip pain while running and physical examination findings of pain upon internal and/or external rotation of the hip or pain upon single-leg standing should arouse clinical suspicion of an FNSF. (Note: Single-leg hopping on the affected leg may complete the fracture and should be highly discouraged.)

The patient should be restricted to crutches, non-weight bearing or touchdown weight bearing, if it causes no pain. Perform further investigation, including radiography, bone scanning, and/or MRI. A missed FNSF that was originally diagnosed as bursitis or tendonitis, with the patient allowed to return to sports, only to have the patient snap the femoral neck and eventually require an artificial hip, is obviously not the desired outcome. A completed displaced FNSF has about a 25% chance of having a poor outcome even with surgical fixation; thus, diagnosing these injuries before completion of the fracture is essential.

In a retrospective study of stress injuries involving basic combat trainees, Shaw et al found that 58% of service members who had a FNSF treated surgically subsequently left military service because of the injury. [14]

Complications

Nondisplaced compression-side FNSF appears to have no increased long-term risk for avascular necrosis of the femoral head or osteoarthritis for these patients. [15]

Compression-side nondisplaced FNSFs may recur and become displaced, especially if the patient is returned to activity too quickly. Displaced tension-side FNSFs have complications that include avascular necrosis of the femoral head and need for total hip arthroplasty (THA). Complete displaced FNSFs are associated with complications such as nonunion, osteonecrosis of the femoral head, and long-term disability. [16]

Previous