eMedicine Specialties > Sports Medicine > Hip

Femoral Neck Stress Fracture

Scott D Flinn, MD, Medical Director, Directorate for Primary Care, Primary Care, Naval Medical Center San Diego
Contributor Information and Disclosures

Updated: Nov 7, 2007

Introduction

Background

Stress fractures are a common 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, and cause 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 eMedicine 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 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.

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

For excellent patient education resources, visit eMedicine's Foot, Ankle, Knee, and Hip Center; Breaks, Fractures, and Dislocations Center; and Sports Injury Center. Also, see eMedicine's patient education articles Broken Leg and Total Hip Replacement.

Frequency

United States

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).

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, 9} 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

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

Clinical

History

• Runners and military trainees develop stress fractures as the duration, frequency, and intensity of weight-bearing activities is increased. Furthermore, changes in running surfaces, such as from a flat surface to hills, or carrying a pack may increase the risk of stress fractures.
• The patient reports a gradually worsening deep, achy pain in the hip, groin, or thigh.
• Usually, pain initially occurs after an activity. As the stress of training continues, pain occurs during training and becomes more intense.
• Unless the form of the activity is modified, the pain gradually worsens over a few weeks to the point where the patient is unable to walk without pain.
• Continued activity will probably result in completion of the stress fracture.

Physical

• Physical examination reveals the patient to have an antalgic gait.
• Unlike many other stress fractures, it is not possible to palpate the femoral neck and determine the presence of the usual bony tenderness of a stress fracture. However, hip palpation may suggest another diagnosis, such as a hip flexor strain, if pain is present at the anterior inferior iliac spine and upon hip flexion. Other possible diagnoses include greater trochanteric bursitis, adductor strain, or a pubic ramus stress fracture. (See also the eMedicine articles Trochanteric Bursitis [in the Sports Medicine section], Adductor Strain [in the Physical Rehabilitation and Medicine section], and Pelvic Fractures [in the Orthopedic Surgery section].)
• Pain at the extremes of passive range of motion (ROM), especially external and internal rotation, is the most sensitive sign for stress fractures.
• Pain that is associated with log rolling, axially loading a supine patient (heel tap), and with single-leg standing or hopping also suggests a stress fracture. (Note: Performing a single-leg hopping test in a patient with a potential FNSF is risky and may cause completion of the stress fracture; this practice is not advised.)

Causes

• 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.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 eMedicine article Female Athlete Triad.)
• Young women who exercise regularly can increase the bone density of their femoral neck.
• 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

References

• Femoral Head Avascular Necrosis
• Femoral Neck Fracture
• Groin Injury
• Hip Dislocation
• Hip Fracture
• Hip Pointer
• Hip Tendonitis and Bursitis
• Iliopsoas Tendinitis
• Osteitis Pubis
• Piriformis Syndrome
• Sacroiliac Joint Injury
• Slipped Capital Femoral Epiphysis
• Snapping Hip Syndrome

• Foot, Ankle, Knee, and Hip Center
• Breaks, Fractures, and Dislocations Center
• Sports Injury Center
• Broken Leg Overview
• Broken Leg Causes
• Broken Leg Symptoms
• Broken Leg Treatment