Femoral stress fractures in adults

INTRODUCTION — The femur, as the largest bone in the body, has dozens of muscle origins and insertions [1]. As such, it is prone to stress injury at several locations. Stress injury (including stress reaction and stress fracture) denotes gradual structural compromise (from edema to frank cortical fracture) due to training overload. Stress fractures may be incomplete or complete, and either non-displaced or displaced. Femoral neck stress fractures are considered high-risk for complications, particularly displacement; whereas, femoral shaft stress fractures are low-risk.

This topic is focused on overuse stress injury of the femur in physically active individuals, and will discuss patterns of femoral stress fractures (both epidemiologic and patho-anatomic), examination findings, radiographic assessment, and treatment. Insufficiency fractures in older adult patients, acute traumatic femur fractures, stress fractures generally, and other specific stress fractures are reviewed separately. (See "Overview of common hip fractures in adults" and "Midshaft femur fractures in adults" and "Overview of stress fractures" and "Stress fractures of the tibia and fibula".)

EPIDEMIOLOGY AND RISK FACTORS — Femoral stress fractures (FSF) are uncommon. In case series, they comprise between 1 and 25 percent of all stress fractures [2-6]. While the exact overall incidence is not known, the observational studies reporting a higher incidence likely include more athletes participating in distance running [7]. While smaller series report that FSF are more common in military trainees than athletes (as a percentage of stress fractures) [8,9], studies with larger numbers show comparable rates in both groups (ranging from 1 to 7 percent of all stress fractures) [10,11]. In most studies, femoral neck injuries are more common than femoral shaft stress fractures [6,8-10], although this finding is not consistent [11,12].

Overuse FSF have been diagnosed in patients from age five [13] to physically active adults in their 50s and 60s [2,14]. The large majority of published studies involve athletes and military recruits in their late teens and early 20s [15], and most subjects are male.

FSF are most commonly associated with running [2,3,12]. A systematic review of the risks for femoral stress fractures identified two well-established factors: female gender and previous history of stress fracture [16]. Female athletes and female military recruits are thought to be at higher risk for FSF due to lower body mass and lower bone mineral density than males. Those with amenorrhea or poor aerobic fitness prior to starting military training are at particular risk [17,18]. FSF also occur in those who are overweight with limited participation in sports [19]. (See "Functional hypothalamic amenorrhea: Pathophysiology and clinical manifestations".)

A number of other factors have been associated with stress fractures generally (table 1). Although not all of these are specifically associated with femoral stress fractures, many are worthy of attention, including the following [7]:

●Low level of physical fitness

●Sudden increases in the volume and intensity of physical activity

●Diet poor in calcium; poor bone health

●Poor biomechanics (see "Overview of stress fractures", section on 'Risk factors')

While evidence remains limited, some experienced clinicians consider dynamic femoral anteversion and genu valgum to be additional biomechanical risk factors for femoral neck stress fracture. Leg length inequality, which is associated with recurrent stress fracture at other sites (eg, tibia, fibula, metatarsal) [20], has been implicated in hip and pelvis fractures in multiple case reports. If leg length inequality results in an abnormal running gait, the resulting increase in the load placed on the hip is likely to increase stress across the femoral neck and the risk of stress fracture. Leg length inequality has been described as mild when less than 3 cm but may have biomechanical consequences in athletes such as runners [21].

CLINICAL ANATOMY — The most common femoral stress fractures (FSF) involve the femoral neck and the proximal femoral shaft (figure 1 and figure 2). Other FSF that have been described (in order of decreasing frequency) include injuries to the distal femoral shaft, supracondylar and condylar regions, and femoral head [8,9,22].

●Femoral neck stress fractures may occur on the superolateral (tension side) or inferomedial aspect (compression side) of the femoral neck (figure 3). The former are considered high-risk stress fractures, as the risk for complications is greater. The tenuous blood supply to the femoral head is a key factor in the relatively high risk for complications (figure 4 and figure 5). This is discussed separately. (See "Overview of common hip fractures in adults", section on 'Anatomic considerations'.)

The patho-anatomy predisposing to femoral neck stress injuries remains unclear. The fracture is associated in some studies with coxa vara (a decreased medial angle between the femoral head and shaft (figure 6)), but this is not a consistent finding [8,23,24].

●Femoral shaft stress fractures occur most often at the proximal posteromedial cortex. This is the location for the insertion of the adductor brevis (figure 7 and figure 8) and the origin of the vastus medialis (figure 9 and figure 10). The repetitive forces exerted against the femur when these muscles contract may play a role in the development of these fractures [8,9,22,25].

●Distal femoral shaft stress fractures are less common but can be seen medially or laterally [8].

●Stress fractures of the supracondylar and condylar regions [26-29], femoral head [30-33], and lesser trochanter [34] have been described but are uncommon [8,9,22].

MECHANISM OF INJURY — Overuse stress fractures, regardless of location, share a common underlying mechanism of injury. Local bone metabolism becomes imbalanced due to the stress of repeated workloads, and bone formation cannot compensate adequately for increased bone resorption. This causes bone edema and micro-fracture. These may in turn propagate and create frank cortical disruption (lucent lines on plain radiograph). This pathologic process can result in complete (trans-cortical) and even displaced fractures [9,35]. Muscle fatigue may contribute to this process. If muscle functioning is impaired from fatigue, its protective role in controlling motion and decreasing shock with impact is lost, thereby imparting greater stress to bone [36].

CLINICAL PRESENTATION AND EXAMINATION

History — Overuse femoral stress fractures (FSF) of all types result from over-training, most often running. The patient may give a history of training of long duration (eg, distance running over many months or years), a recent increase in training volume or intensity, or a change in the type of training (eg, addition of hill runs) [22]. FSF are most common in athletes and military trainees. Females and those with low body mass index are at increased risk [16,18]. Clinicians should inquire about amenorrhea and any history of stress fracture, which are associated with increased risk. (See "Overview of stress fractures", section on 'Diagnosis'.)

It is important to inquire about medication use, as several drugs are associated with an increased risk of hip fracture, although not specifically with femoral stress fractures. These medications include glucocorticoids, bisphosphonates, and proton pump inhibitors, when these are used chronically. (See "Osteoporotic fracture risk assessment".)

Common presentations for particular injury types include the following:

●Femoral neck stress fractures typically present with vague anterior groin pain that develops or worsens with exercise or prolonged standing [36,37]. Runners preparing for a marathon commonly develop such pain during the training phase that involves runs longer than two hours. More experienced runners often experience such pain when they attempt to run back-to-back marathons with insufficient recovery time between races.

●Femoral shaft stress fractures present with deep aching pain in the thigh. While not focal, pain most often develops in the medial portion of the proximal third of the thigh. Pain increases with activity and may radiate to or even predominate in the knee.

●Distal femoral stress fractures are more likely to elicit complaints of tenderness over the distal femur or pain that radiates into the knee.

With either type of fracture, the patient cannot tolerate high-impact activities such as running [9,22].

Although FSF are uncommon, clinicians should be aware of these conditions because delayed diagnosis of femoral neck injuries can lead to permanent disability [37,38]. (See 'Complications' below.)

Examination findings — Patients with a femoral stress injury may demonstrate an antalgic gait. Due to the muscle bulk around the femoral neck and shaft, it is difficult to palpate a stress fracture in these locations. Because of this difficulty, and because FSF are uncommon, there is frequently a delay in diagnosis of several weeks or more, which increases the risk of complications [37,39].

Patients with a femoral neck stress fracture may experience pain when the hip is placed at the end-points of its range of motion (eg, full internal rotation), or less commonly hip motion may be restricted, particularly internal and external rotation or flexion (especially if the fracture has displaced). Femoral shaft stress fractures typically allow normal hip motion, but resisted hip flexion or knee extension (and possibly resisted hip adduction) may elicit pain.

Special tests for particular injuries include the hop test and the fulcrum test. The hop test is thought to be a sensitive but non-specific maneuver for identifying lower extremity stress injuries, including femoral neck stress fractures. The patient is instructed to hop repeatedly on the symptomatic leg. Inability to perform repeated hops or worsening groin pain marks a positive test [8,9,12]. The hop test may also be used to help assess femoral shaft stress fractures. With these injuries, pain experienced while hopping localizes to the thigh rather than the groin. (See "Overview of stress fractures", section on 'Physical examination'.)

The fulcrum test is used to assess possible stress fracture of the femoral shaft [4,40,41]. In this test, the patient sits at the edge of an exam table and the examiner places one of their forearms, radius side up, under the painful thigh of the patient (picture 1 and movie 1). Then the examiner pushes down on the patient's knee with their free hand. The test is repeated as the examiner moves the "fulcrum" arm proximally along the underside of the patient's thigh and repeats downward pressure at the knee. Pain and reproduction of the patient's symptoms suggest a femoral shaft stress injury at the site of pain. Although not rigorously studied, the fulcrum test is thought by many sports medicine specialists to be a useful and accurate technique for identifying femoral shaft stress injury [8,9,22,42].

Distal femoral stress fractures (ie, supracondylar and condylar injuries) are uncommon and manifest point tenderness at the site of injury. Although such fractures can cause referred pain at the knee, the knee joint examination is unremarkable [8,26].

DIAGNOSTIC IMAGING — Plain radiographs, including standard views of the hip, femur, and knee, are the first studies obtained when a femoral stress fracture (FSF) is suspected. When pain is limited to the groin, knee studies are typically not necessary. If plain radiographs demonstrate a stress fracture, the diagnosis is made and no further imaging is necessary (image 1 and image 2) [15,36]. However, plain radiographs of a FSF are usually normal for approximately three to four weeks following the start of symptoms, and a femoral stress reaction may cause symptoms for long periods without visible pathology on a plain radiograph [2,9,25,43,44]. Therefore, normal plain radiographs cannot definitively rule out a femoral stress injury.

Magnetic resonance imaging (MRI) is the study of choice when definitive diagnosis of a FSF is required (image 3 and image 4 and image 5) [7,32,45,46]. A systematic review reported the sensitivity of MRI for lower extremity stress fracture to range from 68 to 99 percent, which was superior to any other modality [45]. Reported specificities varied widely among studies. Imaging shows that most FSF are transverse, but longitudinal stress injuries can occur [47]. MRI can identify femoral stress reactions as well as stress fractures. The MRI grade of stress reaction can be used to predict recovery time [48,49].

Although nuclear scintigraphy (bone scan) has been used in many of the studies of FSF, the radiation exposure entailed and the increasing availability and decreasing cost of MRI have made this modality largely obsolete [4,9,25].

Anecdotal reports suggest that ultrasound may be useful for diagnosis in select patients (eg, thin distance runners), but there is no high quality evidence supporting this approach and further study is needed.

DIAGNOSIS — Definitive diagnosis of a femoral stress fracture (FSF) is made by imaging study, usually plain radiograph or magnetic resonance imaging (MRI). Initial clinical suspicion for the diagnosis is based on the history, which generally involves a recent increase in training volume or intensity, most often in runners or military recruits, and suggestive physical findings, such as positive hop and fulcrum tests. However, the history may be limited and examination findings unclear. Plain radiographs are often non-diagnostic, particularly during the early stages of injury. Often, MRI is required to establish the diagnosis and to distinguish between stress fractures of the proximal shaft and the femoral neck. (See 'Clinical presentation and examination' above and 'Diagnostic imaging' above.)

DIFFERENTIAL DIAGNOSIS — Femoral stress injuries share features with many other lower extremity pathologies [9,22]. The differential diagnosis of hip and groin pain, thigh pain, and knee pain are reviewed in detail in the separate UpToDate topics listed immediately below.

●Hip pain – (See "Approach to hip and groin pain in the athlete and active adult" and "Approach to the adult with unspecified hip pain".)

●Anterior, medial, and posterior thigh pain – (See "Quadriceps muscle and tendon injuries", section on 'Differential diagnosis' and "Adductor muscle and tendon injury", section on 'Differential diagnosis' and "Hamstring muscle and tendon injuries", section on 'Differential diagnosis'.)

●Knee pain – (See "Approach to the adult with knee pain likely of musculoskeletal origin" and "Approach to the adult with unspecified knee pain".)

Alternative diagnoses of particular importance when considering the diagnosis of femoral stress fracture are discussed here:

●Femoral neck stress fracture – The differential diagnosis for these fractures includes the following:

•Femoroacetabular injury: These injuries include femoroacetabular impingement, labral tear, and osteochondral injury. Such conditions often manifest some mechanical component (eg, catching, locking, blocking), whereas femoral neck fractures generally do not. When a definitive diagnosis must be made, magnetic resonance imaging can be obtained.

•Hip flexor tendon injury: Patients with tendinitis or tendinopathy involving the proximal rectus femoris tendon generally have reproducible point tenderness at the tendon origin at the anterior inferior iliac spine, and pain is exacerbated by flexing the muscle against resistance. Less commonly, pain arises deep in the upper thigh at the attachment of the reflected head of quadriceps (rectus) femoris. Hip flexor injuries involving the iliopsoas tendon (which are common among dancers) may cause pain more localized to the upper medial thigh, mimicking the pain of a femoral shaft stress fracture. The hop test can help distinguish between tendon injuries and fractures, as initiating the hop causes pain but landing does not with tendon injuries. When a definitive diagnosis must be made, magnetic resonance imaging can be obtained.

•Hip osteoarthritis (OA) and femoral head avascular necrosis (AVN): The insidious onset and characteristics of pain associated with hip OA and AVN are similar to those of femoral neck stress fractures, but imaging studies distinguish between these conditions. On examination, hip motion typically shows greater limitations with OA or AVN compared with a femoral neck stress fracture. If plain radiographs are insufficient, magnetic resonance imaging (MRI) can be performed to establish a definitive diagnosis. (See "Clinical manifestations and diagnosis of osteoarthritis" and "Treatment of nontraumatic hip osteonecrosis (avascular necrosis of the femoral head) in adults".)

•Other conditions: Other hip conditions are rarely confused with a femoral neck stress fracture. Some, including sacroiliac joint dysfunction, piriformis syndrome, hip external rotator tendinopathy, greater trochanteric pain syndrome, and inguinal conditions (hernia, nerve entrapment) may mimic stress fracture symptoms, primarily pain radiating to the groin. However, such cases are uncommon. The differential diagnosis and approach to groin pain in athletes is reviewed separately. (See "Approach to hip and groin pain in the athlete and active adult".)

●Femoral shaft stress fractures – The differential diagnosis for these fractures includes the following:

•Quadriceps, adductor, or hamstring muscle strain or contusion: Patients with strains or contusions of thigh musculature typically give a history of discreet trauma. Focal pain is reproducible with muscle palpation or resisted contraction. If necessary, MRI can distinguish between a stress fracture and these musculotendinous injuries. (See "Quadriceps muscle and tendon injuries" and "Adductor muscle and tendon injury" and "Hamstring muscle and tendon injuries".)

•"Thigh splints": This is an uncommon periostitis analogous to "shin splints" (medial tibial stress syndrome). The patient with thigh splints (femoral periostitis) complains of a deep aching in the thigh, but the pain is more diffuse than that associated with a stress fracture [50]. If necessary, MRI can distinguish between a stress fracture and thigh splints.

•Osteoid osteoma, and less commonly osteoblastoma, cause hip and groin pain that can mimic a stress fracture. Nocturnal pain and relief with nonsteroidal antiinflammatory drugs (NSAIDs) are characteristic of osteoid osteoma. However, even with plain radiographs and MRI evaluation, these conditions may be difficult to differentiate from stress fracture. New MRI criteria may make identification of osteoid osteoma more accurate [51-53]. (See "Nonmalignant bone lesions in children and adolescents", section on 'Osteoid osteoma'.)

●Nerve injury – Peripheral nerve entrapment can cause pain at any number of sites in the groin or thigh that mimics pain from a FSF. Such nerve entrapments may include the ilioinguinal nerve and pudendal nerve for groin pain, obturator nerve for medial groin/thigh/knee pain, and lateral femoral cutaneous nerve for anterolateral thigh pain (ie, meralgia paresthetica). (See "Overview of lower extremity peripheral nerve syndromes".)

●Neoplasm and infection – Neoplasm (particularly bone sarcoma) and infection should be considered in patients, especially younger patients, complaining of generalized hip, thigh, or knee pain, particularly if there is no history of trauma or overuse, pain persists at rest or at night, or there are associated constitutional symptoms or signs (eg, fever, sweats). (See "Osteosarcoma: Epidemiology, pathology, clinical presentation, and diagnosis".)

INDICATIONS FOR ORTHOPEDIC CONSULTATION OR REFERRAL — If a plain radiograph or magnetic resonance imaging (MRI) confirms the presence of a tension-side (ie, superolateral cortex) femoral neck stress fracture, the patient should be made non-weight bearing and referred to an orthopaedic surgeon within 24 hours. If the fracture is displaced, immediate referral is needed. If there is a compression-side (ie, inferomedial cortex) femoral neck stress fracture, the patient should follow strict non-weight-bearing precautions for the affected extremity and be evaluated by an orthopedist or sports medicine specialist within 72 hours.

Primary care clinicians who have experience in stress fracture management can provide definitive care for all other types of femoral stress fractures (FSF). Otherwise, the patient should be told to remain non-weight-bearing on the affected extremity and referred to a sports medicine specialist or an orthopedist within one week.

Delayed union for femoral shaft stress fractures is uncommon, but if this occurs, the patient should be referred to an orthopaedic surgeon on a routine basis. Likewise, displacement of a femoral shaft or supracondylar stress fracture at the time of diagnosis or during healing is extremely uncommon, but immediate referral should be made to an orthopedic surgeon if this occurs.

MANAGEMENT

Basic initial care — If there is reasonable clinical suspicion for a femoral stress fracture, make the patient non-weight-bearing on the affected extremity until the diagnosis is ruled out. Provide basic analgesia as needed. Generally, acetaminophen is sufficient. Nonsteroidal antiinflammatory drugs (NSAIDs) may delay fracture healing, but this has not been demonstrated in stress fractures. Nevertheless, we prefer to avoid NSAIDs if possible. (See "Nonselective NSAIDs: Overview of adverse effects", section on 'Healing of musculoskeletal injury'.)

As part of the initial work-up, we generally obtain a serum vitamin D concentration. (See 'Follow-up care and prevention' below and "Stress fractures of the tarsal (foot) navicular", section on 'Follow-up care and prevention'.)

Femoral neck stress fracture treatment — Treatment for femoral neck stress fractures depends upon the location and characteristics of the fracture. Tension (superolateral) side fractures are considered emergency conditions because of the risk of disrupting the blood supply to the femoral head, and these are immediately referred to an orthopedic surgeon (figure 3). Compression (inferomedial) side fractures are more stable and amenable to surgical or non-surgical management. No prospective trials comparing approaches to the treatment of femoral neck stress fractures have been published, and the treatment approaches outlined below are based upon available observational evidence and our clinical experience.

Tension (superolateral) side fracture — If a tension side femoral neck fracture is complete or displaced (figure 3), immediate orthopedic consultation is required, as these injuries typically require emergency surgery with open reduction as needed and internal fixation. Complete non-displaced tension side fractures are also treated surgically on an urgent basis. Following surgery, the patient is typically non-weight-bearing for six weeks, followed by protected-weight-bearing for six weeks [8,9,15,37].

Debate is ongoing about the best treatment for incomplete tension side femoral neck stress fractures without displacement. Most orthopedic surgeons in the United States recommend surgery [15,36]. For athletes who desire to return to sport as quickly as possible and for any patient for whom compliance is in question, we suggest surgical treatment, assuming the patient is willing to accept the risks associated with surgery (eg, infection). However, in the large majority of cases, non-displaced tension side fractures heal completely with non-surgical management involving strict non-weight-bearing. This has been shown in multiple observational studies with large numbers of patients and lengthy follow-up [23,54]. Before determining treatment, the patient and clinician should discuss the relative risks and benefits of each approach.

If the patient elects non-surgical management, institute bed rest for one to two weeks followed by strict non-weight-bearing with crutches for an additional four to eight weeks [23]. Weekly plain radiographs should be obtained for the first four to six weeks to monitor fracture healing and position, followed by bimonthly radiographs until 12 weeks out from initiation of treatment. Should radiographs show displacement or extension of the fracture, or inadequate healing, the patient should be referred to an orthopedist, as surgery is likely to be necessary. The following table outlines a basic rehabilitation program for patients who are otherwise healthy but have sustained an uncomplicated, incomplete, tension-side femoral neck stress fracture (table 2).

Compression (inferomedial) side fracture — Compression side femoral neck stress fractures (figure 3) can generally be managed successfully without surgical intervention. Multiple observational studies suggest that, if non-displaced, these fractures heal well with non-weight-bearing ‒ none of the 154 patients managed conservatively in the studies referenced developed complications or required subsequent surgery [23,54]. However, some surgeons recommend surgical intervention if the fracture line traverses more than 50 percent of the femoral neck [15].

We suggest this initial approach to treatment:

●Strict non-weight-bearing for the affected extremity with crutches for two weeks.

●Thereafter, advance weight-bearing as tolerated, ensuring that the patient remains completely pain-free. If pain develops, the patient resumes non-weight-bearing with crutches for an additional two weeks.

●At four to six weeks, resume full weight-bearing if pain-free.

●Concomitant with advancing to full weight-bearing, the patient may begin stationary cycling, swimming, or aqua-jogging (ie, running in a swimming pool) if they can do so completely pain-free.

●Obtain weekly radiographs through week four of treatment to monitor fracture healing and potential complications (eg, propagation, displacement).

●Obtain radiographs at 6 weeks, 8 weeks, and 12 weeks to ensure continued healing.

●The basic rehabilitation program outlined in the following table may be used for patients who are otherwise healthy but have sustained an uncomplicated, incomplete, compression-side femoral neck stress fracture (table 3).

Femoral shaft stress fracture treatment — The treatment of femoral shaft stress fractures is non-surgical but a wide variety of approaches have been used. For uncomplicated femoral shaft stress injuries, we suggest this approach to treatment:

●Symptomatic phase (three weeks) – Patient remains non-weight-bearing for the affected extremity, using crutches for three weeks.

●Asymptomatic phase (three weeks) – Patient resumes full weight-bearing on the affected leg. The patient may begin swimming and strength training with the unaffected leg, but no strength training or impact activities (eg, running) that involve the affected leg are permitted.

●Basic phase (three weeks) – Training advances and may begin to include the affected leg, but using light weights only. Running in a straight-line (ie, no sharp turns or cutting permitted) may be done every other day, but volume must start low and is advanced in small steady increments.

●Resumption phase (three weeks) – Gradual return to longer-distance running and sport-specific training. The following table outlines a basic rehabilitation program for patients who are otherwise healthy but have sustained an uncomplicated, incomplete femoral shaft stress fracture (table 4).

Plain radiographs should be obtained approximately every three weeks, prior to advancing to the next phase. Provided the patient is otherwise healthy, doing well clinically, and proceeding through the stages of rehabilitation without problems, clinicians may choose to increase the interval between radiographs up to every five to six weeks in order to reduce radiation exposure.

Throughout this treatment program, the hop test and fulcrum test are performed at the end of each phase. If the patient is symptomatic, they do not advance to the next phase, but rather resume the beginning of the current treatment phase.

This approach is drawn from a prospective study of seven elite athletes who followed a four-step algorithm of 12 weeks total duration. All athletes returned to their pre-injury participation levels and none developed a recurrence during a 48 to 96 month follow-up [55]. Reasonable alternative programs undoubtedly exist, but no prospective trials comparing approaches to the treatment of femoral shaft stress fractures have been published, and approaches vary widely. Treatment programs described in case series range from simply decreasing running mileage (but allowing continued running!) [40], to stopping running but allowing full weight-bearing [2], to limited weight-bearing [4,22,56], to a period of non-weight-bearing until radiographs show evidence of healing [15,25].

Condylar and supracondylar femoral stress fracture — Published evidence pertaining to the management of condylar and supracondylar femoral stress fractures is limited to case reports. Based on this limited evidence and our clinical experience, we suggest that these injuries be treated in the same manner as femoral shaft stress injuries.

Unproven therapies — A number of alternative therapies have been proposed for the treatment of fractures, but none has shown clear benefit in the treatment of femoral stress fractures. (See "General principles of definitive fracture management", section on 'Adjunctive therapy for fracture healing'.)

FOLLOW-UP CARE AND PREVENTION — A history of stress fracture is an important risk factor for reinjury [16]. Therefore, it is important to address any correctable intrinsic or extrinsic risk factors. Interventions may include the following [15,18]:

●Vitamin D and calcium supplementation for patients with vitamin D insufficiency or low bone density. (See "Vitamin D deficiency in adults: Definition, clinical manifestations, and treatment".)

●Nutrition assessment for patients with low body mass index or possible inadequate caloric intake.

●Resistance training program (eg, weightlifting) for patients with inadequate strength or muscle endurance.

●Biomechanics assessment and instruction for runners and others with high-risk running gait or movement patterns.

●Change in running surface and/or running shoes, if these may be contributing to injury risk. (See "Running injuries of the lower extremities: Risk factors and prevention", section on 'Running shoe design'.)

General recommendations and further discussion of the prevention of stress fractures are provided separately. (See "Overview of stress fractures", section on 'Prevention'.)

Military personnel, particularly new recruits, sustain femoral stress fractures (FSF) at relatively high rates, and prevention measures are a subject of on-going research. These issues are reviewed in detail separately. (See "Overview of stress fractures", section on 'Prevention in military, police, and first responders'.)

For military personnel, as well as athletes, following formal scripted training regimens, program modifications and greater awareness of FSF on the part of coaches and training staff has been shown to decrease injury rates [23,39,57]. In a 20-year observational study of Finnish military conscripts, the incidence of displaced femoral neck stress fractures was cut in half by instituting an educational program for medical officers and training instructors on the prodromal symptoms of FSF [39]. For new military recruits, improving pre-training physical fitness levels with running, jumping, and resistance exercises builds bone density and muscular endurance, and thereby likely decreases the risk for FSF [15].

COMPLICATIONS — Of the different types of femoral stress fractures, the risk of significant complication is greatest for displaced femoral neck fractures. Observational studies with follow-up over a number of years report significant morbidity for patients with femoral neck fractures that were displaced at the time of initial diagnosis [37,39]. Complications included delayed- or non-union, osteonecrosis of the femoral head, shortening of the femoral neck, and early-onset osteoarthritis. Because all displaced fractures began as femoral neck stress reactions, and then progressed to non-displaced stress fractures, these complications can be viewed as potential complications for any femoral neck stress injury. Of note, over 90 percent of these patients had prodromal symptoms prior to the fracture displacement, emphasizing the importance of early diagnosis and appropriate treatment.

The major potential complication of femoral shaft stress fractures is propagation of the fracture line, which ultimately may lead to a complete fracture with possible displacement. While femoral shaft stress fractures are at low risk for complications, complete fractures (grade 4) usually require surgical intervention.

General complications associated with all types of fractures are reviewed separately. (See "General principles of fracture management: Early and late complications".)

RETURN TO WORK AND SPORT — Other than those with displaced femoral neck stress fractures, it is rare for a patient with a femoral stress fracture (FSF) to have any limitations upon returning to sport or demanding physical work.

Once the patient has completed one of the treatment plans described above, is pain free, and their plain radiographs demonstrate appropriate healing, they may gradually resume full sport and work activity over two to eight weeks, depending on the severity of the initial injury [9,55]. For athletes, returning to impact activities (eg, running) on an every-other-day basis for one to two months after treatment of a FSF reduces the chance of recurrence [2]. Swimming and cycling are exercises that help maintain aerobic fitness with less impact than running [12].

ADDITIONAL INFORMATION — Several UpToDate topics provide additional information about fractures, including the physiology of fracture healing, how to describe radiographs of fractures to consultants, acute and definitive fracture care (including how to make a cast), and the complications associated with fractures. These topics can be accessed using the links below:

●(See "General principles of fracture management: Bone healing and fracture description".)

●(See "General principles of fracture management: Fracture patterns and description in children".)

●(See "General principles of acute fracture management".)

●(See "General principles of definitive fracture management".)

●(See "General principles of fracture management: Early and late complications".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: General fracture and stress fracture management in adults" and "Society guideline links: Lower extremity (excluding hip) fractures in adults" and "Society guideline links: Acute pain management".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: How to use crutches (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Epidemiology and risk factors – Femoral stress fractures are uncommon overall but appear to occur most often in runners and military recruits. The incidence is increased among those with a history of stress fracture and females. Other risk factors include poor physical fitness, sudden increases in training volume or intensity, and poor bone health. (See 'Epidemiology and risk factors' above.)

●Clinical anatomy and mechanism – Femoral neck stress fractures may occur on the superolateral (tension side) or inferomedial aspect (compression side) of the femoral neck (figure 3). The former are considered high-riskwith a greater risk for complications. (See 'Clinical anatomy' above and 'Mechanism of injury' above.)

Femoral shaft stress fractures occur most often at the proximal posteromedial cortex. Femoral stress fractures occur when bone formation cannot compensate adequately for increased bone resorption caused by demanding workloads.

●History and physical examination – Many patients with overuse femoral stress fractures describe one of the following:

•Training of long duration (eg, distance running over many months or years)

•Recent increase in training volume or intensity

•Recent change in type of training (eg, addition of hill runs)

Patients may demonstrate an antalgic gait. Those with a femoral neck stress fracture may experience pain when the hip is placed at the end-points of its range of motion (eg, full internal rotation); those with a femoral shaft stress fracture demonstrate normal hip motion, but resisted hip flexion or knee extension (and possibly resisted hip adduction) may elicit pain. Special tests for particular injuries include the hop test and the fulcrum test (picture 1), which are described in the text. (See 'Clinical presentation and examination' above.)

●Diagnostic imaging – Plain radiographs, including standard views of the hip, femur, and knee, are the first studies obtained when a femoral stress fracture is suspected. When pain is limited to the groin, knee studies are typically not necessary. If plain radiographs demonstrate a stress fracture, the diagnosis is made and no further imaging is necessary. However, plain radiographs are typically normal for approximately three to four weeks following the onset of symptoms, and a femoral stress reaction may cause symptoms for long periods without visible pathology on a plain radiograph. Magnetic resonance imaging (MRI) is the study of choice when definitive diagnosis is required. (See 'Diagnostic imaging' above and 'Diagnosis' above.)

●Differential diagnosis – Femoral stress injuries share features with many lower extremity pathologies. The differential diagnosis of hip and groin pain, thigh pain, and knee pain are reviewed in detail in separate UpToDate topics. Alternative diagnoses to consider include:

•Femoral neck stress fracture – Femoroacetabular injury; hip flexor tendon injury; hip osteoarthritis; femoral head avascular necrosis.

•Femoral shaft stress fracture – Quadriceps, adductor, or hamstring muscle injury; femoral periostitis; osteoid osteoma.

•Other considerations – Nerve entrapment; infection; neoplasm

●Indications for orthopedic referral – If a plain radiograph or MRI confirms the presence of a tension-side (ie, superolateral cortex) femoral neck stress fracture, the patient should be referred to an orthopaedic surgeon within 24 hours. If the fracture is displaced, immediate referral is needed. If there is a compression-side (ie, inferomedial cortex) femoral neck stress fracture, the patient should be evaluated by an orthopedist or sports medicine specialist within 72 hours. Other indications for referral are discussed in the text. (See 'Indications for orthopedic consultation or referral' above.)

●Management – If there is reasonable clinical suspicion for a femoral stress fracture, the patient should be made non-weight-bearing on the affected extremity until the diagnosis is determined. Further treatment depends upon the location and type of fracture. Fractures at high risk of complications (eg, tension-side femoral neck stress fracture) are generally treated surgically. Treatment for the common types of femoral stress fractures amenable to non-surgical management, including basic rehabilitation programs, is described in the text. As part of management, any predisposing risk factors (eg, low vitamin D, low bone density, inadequate muscle strength, poor running mechanics) should be addressed. (See 'Management' above.)

●Complications – Of the different femoral stress fractures, the risk of significant complication is greatest for displaced femoral neck fractures. Potential complications include delayed- or non-union, osteonecrosis of the femoral head, shortening of the femoral neck, and early-onset osteoarthritis. (See 'Complications' above.)