eMedicine Specialties > Orthopedic Surgery > Hip

Femoral Neck Stress and Insufficiency Fractures

Author: Michael S Wildstein, MD, Associate Professor of Orthopaedic Surgery, Charleston Veterans Affairs Medical Center; Attending Physician, Wildstein Spine Center, PA
Coauthor(s): H Del Schutte, Jr, MD, Associate Professor of Orthopedic Surgery, Department of Orthopedic Surgery, Medical University of South Carolina
Contributor Information and Disclosures

Updated: Mar 4, 2009

Introduction

Femoral neck stress fractures are a common cause of hip pain in select populations. Chronic, repetitive activity that is common to runners and military recruits predisposes these populations to femoral neck stress fractures. These injuries must be differentiated from insufficiency fractures, which, although similar in appearance and presentation, result from an entirely different pathophysiology and occur in a different population.

History of the Procedure

The first description of femoral neck stress fractures in the literature was published by Asal in the German Arch für Klinische Chirurgie, in 1936. Since that time, numerous articles have recognized these fractures as difficult entities to treat. In 1963, Ernst recorded what was at the time the largest series of femoral neck fractures and described the resulting disability in military servicemen.¹ Although the geneses of acutely traumatic fractures are different from those of stress fractures, the treatments are similar

Since the first descriptions of the vascular anatomy of the femoral neck, orthopedists have recognized the importance of prompt reduction of femoral neck fractures in preventing avascular necrosis (AVN) of the femoral head. Closed reduction and impaction of the fracture parts, followed by immobilization in a spica cast application, with the injured extremity in internal rotation, was adopted by numerous orthopedists of the time. However, it was not until 1931 that the first methods of internal fixation were publicly described by Smith-Petersen.² The medical community was hesitant to accept internal fixation, but this method of treatment nonetheless came into wide use and remained so until the 1970s.

Seven years after Smith-Petersen introduced internal fixation, Moore described a multiple-pin fixation technique, which was followed shortly thereafter by the Thompson femoral endoprosthesis. The varied methods of treatment sparked great debate over whether replacing the entire femoral head or simply fixing the neck fracture was more beneficial. The idea that impacting fracture fragments was the key aspect in healing led to the development of the Pugh nail and the Richards screw, in the 1950s and 1960s. Both of these modalities are designed around a sliding fixation process whereby fracture fragments can compress against each other.

Finally, Judet described another method of treatment that has not been practiced widely but still deserves mention: the quadratus femoris muscle pedicle graft. With this technique, a vascularized bone graft is placed across the posterior femoral neck and into the femoral head to prevent the complication of AVN.

Problem

The femoral neck area is subjected to large compressive and sheer forces associated with ambulation. Even in the most sedentary individual, the daily cyclic loading of the hip and femoral neck produces high stresses on the bony trabeculae in this anatomic region. In long-distance runners and other high-performance athletes, the forces across the femoral neck are multiplied exponentially because the athletes' training regimens place tremendous physical burdens on this relatively small bridge of bone, which connects the femoral head to the diaphysis.

The greatest physical symptom that stress fractures manifest is pain in the hip, groin, or anterior thigh. Such pain can severely limit an athlete's ability to train, compete, and, ultimately, ambulate if the problem progresses undiagnosed. The ultimate result of an untreated stress fracture can be a complete fracture (possibly displaced) of the femoral neck. Even isolated, this injury could be devastating to a performance athlete. The sequelae of this fracture include avascular necrosis of the femoral head and fracture nonunion, both of which can adversely impact athletic careers.

Frequency

Femoral neck stress fractures occur most commonly in 2 subsets of the population. Elite distance runners,^3,4,5,6,7 military recruits, and dancers constitute the first group.⁸ The true prevalence of fractures in this group is difficult to pinpoint because such patients with hip pain and femoral neck stress fractures who never present to a physician and whose fractures go on to heal spontaneously are never identified. Data from several military hip fracture studies by Stoneham and Morgan, in Britain, and Volpin and colleagues, in Israel, place the prevalence at 0.2-4.7% in patients without a history of a single traumatic episode.^9,10 The prevalence of stress fractures in the general population may be surmised to be far less than that demonstrated in these 2 groups.

The second group comprises hypoestrogenic (postmenopausal) women and individuals with pathologic entities resulting in osteopenia (eg, osteoporosis, Paget disease, hyperparathyroidism). Fractures in this group are termed insufficiency fractures, because bone quality is insufficient to support the diurnal physiologic demands placed on it.

Femoral neck stress fractures in children are exceedingly rare and should be far down on the list of differential diagnoses, behind such conditions as slipped capital femoral epiphysis, Legg-Calve-Perthes disease, infection, and transient synovitis. There are only 5 reports of this entity in the English literature to date. While Blickenstaff and Morris claimed in a 1966 article to have found only compression-sided stress fractures of the femoral neck in children, Lehman and Shah reported on a tension-sided stress fracture in a child of 14 years.^11,12

Etiology

Femoral neck stress fractures in young, otherwise healthy individuals are related to the inability of bony trabeculae weakened by osteoporosis to withstand physical stresses. Unusually high physical demands on normal bone over the long term can lead to mechanical failure of the bone trabeculae. The phenomenon is seen with exercise beyond the point of muscle fatigue,¹³ alterations of ground reactive forces that yield abnormal stress patterns in bone, and increased muscular contractions. Contrast this with insufficiency fractures of the femoral neck, which are the result of normal stresses of everyday activity placed on structurally compromised bone. Thus, insufficiency fractures occur in individuals who have concomitant metabolic derangements, such as hyperparathyroidism and renal failure, or menopause.¹⁴

At least 1 example of a crossover group exists: amenorrheic female athletes. Because of their lack of body fat, female distance runners often temporarily halt their menstrual cycle. As a result, they become hypoestrogenic and, therefore, physiologically similar to postmenopausal females.

Estrogen is an essential factor in the development and maintenance of bone strength; in its absence, bones become brittle and osteopenic. This places these female athletes in a sort of double jeopardy, producing characteristics that contribute to stress fractures and causing a background hypoestrogenic state that predisposes these women to insufficiency fractures.

Pathophysiology

A closer look at the genesis of a stress fracture in the femoral neck reveals that the damage manifested on the physical level derives not from a traumatic event per se but rather from a metabolic derangement. Bone initially responds to increased mechanical loading by increasing resorption. Resorption is normally counterbalanced by an equal but opposite, osteoblast-mediated metabolic repair. Under situations of extraordinarily high levels of training, such as those faced by military personnel and elite athletes, bone resorption begins to exceed the bone's capacity to remodel. Additionally, pharmacologic (glucocorticoids), nutritional (vitamin D and calcium deficiency), and other (postmenopausal, hyperparathyroid) states can adversely affect osteoblasts' ability to keep pace with osteoclastic resorption. If this metabolic imbalance persists, microfractures develop that eventually weaken bone to the point of a complete fracture.

Presentation

Presentation and examination

Although femoral neck stress fractures are relatively uncommon in the general population, they must be part of any thorough physician's differential diagnosis for an athlete presenting with anterior hip or groin pain. A history of insidious hip or groin pain that is directly related to an increase in the level or duration of athletic activity and that is relieved by rest is typical. Early diagnosis is often difficult because of the lack of an identifiable traumatic event, which tends to dissuade primary care physicians from obtaining radiographs. Even the astute physician ordering hip films upon first presentation may overlook this diagnosis because fracture callus is not evident early in the process. A bone scan may be helpful in cases in which suspicion is high but radiographic findings are equivocal. The higher degree of sensitivity of bone scanning is useful in detecting stress fractures and other forms of periosteal injury without complete fracture.

In patients presenting with hip pain and negative findings during the initial workup, obtaining plain radiographs of the ipsilateral knee also should be considered. Referred pain along the course of the anterior branch of the obturator nerve may manifest as ipsilateral hip pain and should be in the clinician's differential diagnosis, especially in younger patients.

Magnetic resonance imaging (MRI), while costly, offers increased specificity in the detection of stress fractures. The importance of early detection cannot be underestimated, because the interval between the onset of symptoms and the diagnosis often dictates whether an injury can be treated with rest and protected weightbearing or if surgical intervention is required to reduce a displaced neck fracture.

Case study

A 29-year-old male had spent 6 months training for a marathon by running approximately 45 miles/wk. He mentioned to one of his fellow runners that he had recently noticed a mild ache in his right groin. On the advice of his friend, the man took a few days off from running, and the pain resolved without further treatment. While running in the marathon the following week, he developed the same ache, which not only persisted but also increased so greatly that he had to cease running at mile 14. He was driven home by a friend; upon arrival at his house, he was unable to bear weight on the right leg. At his friend's insistence, the man traveled to an emergency department, where he was seen by a physician. No films were obtained at that time, because the patient had a full, painless range of motion; he was instructed to take ibuprofen and was sent home without a walking aid.

The following day, the patient went to his primary care physician and obtained a referral to a physiotherapist. Following 3 weeks of therapy, he was still unable to comfortably bear weight. He returned to the emergency department one night the following week because his pain had persisted. The patient was told to ice the groin and was given a prescription for a cyclooxygenase-2 (COX-2) inhibitor, but he did not receive a radiograph. The patient continued his physiotherapy for an additional 3 weeks without improvement of his symptoms, at which time his primary care physician referred him to a local orthopedic surgeon.

Upon physical examination, the patient had approximately 1.5 cm of shortening on the affected side, with severely limited range of motion at the hip. A radiograph confirmed a basicervical fracture of the femoral neck, with a neck-shaft angle of 90°. An MRI suggested the development of a fibrous nonunion.

The patient was taken to the operating room for open reduction and internal fixation. A subtrochanteric osteotomy for correction of the varus deformity of the femoral neck also was contemplated, but gentle traction restored enough neck-shaft angle to permit placement of a dynamic hip screw (DHS). Six months postoperatively, the fracture was thought to be sufficiently healed to allow unprotected weightbearing. At 8 months postoperatively, the patient had resumed low-impact activities, such as cycling and swimming. After more than 3 years, he had resumed recreational running without difficulty.

This case is classic in its presentation. A young male distance athlete with insidious onset of hip pain, which was likely a stress fracture of the femoral neck, went undiagnosed despite several visits to the doctor. Only after obtaining appropriate imaging studies was the truly serious nature of the patient's symptoms revealed.

Indications

In 1965, Devas instituted a classification scheme for fatigue fractures, based on prognosis and radiographic appearance.¹⁵ His system split stress fractures into compression and transverse (tension) types. Compression fractures are the less serious of the 2 and are seen most frequently in younger adults. These fractures are considered stable and may be treated with several days of rest followed by a period of protected weightbearing. Nonoperative management of these fractures necessitates frequent radiographs because late displacement, a potentially catastrophic complication, has been reported in the literature.

In select instances, if athletes with a known compression-type fracture continue to participate in strenuous activities, the lesion may progress to the level of the superior femoral neck and become a complete and, in the worst instance, displaced femoral neck fracture. Situations in which a physician may elect to prophylactically treat a compression-type fracture expectantly include those in which patients experience metabolic bone processes that weaken the femoral neck's structural properties.

Transverse fractures, by contrast, are more commonly seen in the elderly population and carry a 10-15% possibility of displacement, with subsequent avascular necrosis (AVN) of the femoral head. A displaced femoral neck is one of the few true orthopedic emergencies, owing to the disastrous outcomes associated with AVN. Transverse fractures appear on an internally rotated anteroposterior (AP) radiograph as a crack at the superior femoral neck. One can see sclerosis of the underlying bone, along with cortical deficiency. Over a period of days to weeks, these fractures may become complete, and callus formation may become evident over time.

Surgical treatment is warranted for all stress fractures that have progressed to a transverse fracture of the femoral neck. The question then becomes which treatment procedure is more beneficial to the patient. The orthopedist may choose either internal fixation or arthroplasty. The decision-making process should include consideration of the patient's bone quality, life expectancy, physiologic status, and overall activity level. However, the main factor in deciding which type of repair to undertake should be the likelihood of revision surgery being needed in the future for a failed arthroplasty. For most younger individuals in otherwise good health, this means internal fixation of the fracture is warranted.

Indications for hemiarthroplasty include such factors as pathologic bone, rheumatoid arthritis, renal failure or other chronic illness, and limited lifespan.

In the elderly population, osteoporosis becomes increasingly prevalent, resulting in decreased bone fatigue strength. When bone fails under physiologic loads in this population, it may be termed an insufficiency fracture. The differentiation between stress and insufficiency fractures lies in the bone's capacity to resist fracture under physiologic strains.

Relevant Anatomy

Vascular

The femoral head derives its blood supply from 3 terminal arterial branches. The lateral epiphyseal artery (an ascending branch off of the medical femoral circumflex artery of the profunda femoris) is the predominant source of blood flow, and its distribution to the head is largely skewed toward the subchondral bone of the femoral articular cartilage. Two accessory arteries supply the remaining 10% of femoral head circulation. These minor arteries are the inferior metaphyseal artery (the ascending branch of the lateral femoral circumflex artery) and the medial epiphyseal artery of the ligamentum teres. The latter vessel originates from the obturator artery. The vascular anatomy of the femoral neck is especially important because fractures of this region can have devastating effects on the already tenuous blood supply to this area. The severity of the vascular disruption generally correlates with the degree of displacement of the fracture.

Bone

By midadolescence, the femoral epiphysis is usually closed, providing a reasonable anatomic picture of the femoral head and neck. The neck-shaft angle, which is approximately 130°, is relatively constant between the sexes. Femoral anteversion is estimated at 10.4° and remains unchanged even after skeletal maturity is reached. A fairly large synovial membrane encloses the femoral head and a good portion of the anterior femoral neck. The greater trochanter, a large, posteriorly located, bony prominence, serves as the major attachment for the external rotators; it also provides a definitive surgical landmark for the insertion of numerous femoral internal-fixation devices.

Contraindications

In general, nondisplaced, compression-type femoral neck fractures are relative contraindications to surgery. In contrast, tension-type stress fractures demand surgical treatment because they have a high propensity for fracture displacement. Contraindications to surgical fixation of a tension-type femoral neck fracture are few because this is one of the few true orthopedic surgical emergencies. If a displaced femoral neck fracture occurs, the very real possibility of disruption of blood supply to the femoral head makes surgery necessary. Absolute contraindications include a medically unstable patient who would be unable to tolerate the stress of surgery and anesthesia. If initial operative fixation is not obtained and osteonecrosis ensues, the patient, when stabilized, will require a hemiarthroplasty as definitive treatment.

• Search for CME/CE on This Topic »