Chapter 21: Stress Fractures

Timothy L. Miller, Christopher C. Kaeding

Chapter Outline

Historical Perspective

Stress fractures of bone, also known as fatigue fractures or march fractures, are common and troublesome injuries in athletes and nonathletes alike. Originally described by Breithaupt21 in unconditioned Prussian military recruits in 1855, they typically occur in individuals who perform repetitive tasks and, therefore, result from an overuse mechanism.32,84 Stress fractures are not a single consistent entity. They occur along a spectrum of severity which can impact treatment and prognosis.64,65,67 Not only does the extent of these injuries vary, but the clinical behavior of these injuries varies by location and causative activity.18,19 
Traditionally, stress fractures have been predominantly regarded as occurring in the weight-bearing bones of the lower extremities. Here the repeated stresses of running and jumping are the typical precipitating activity.3,57,85 However, as awareness of potential overuse injuries of the upper extremity has increased, so has the diagnosis of stress fractures in the upper extremity.6,11,12,24 This chapter is meant to provide general guidance on the causes, risks, classification, and treatment of stress fractures. It should be borne in mind that no two stress fractures behave exactly alike. Treatment protocols should be individualized to the patient, the causative activity, the anatomical site, and the severity of the fracture. A treatment algorithm employed by the authors is presented later in this chapter. 

Pathophysiology

Stress fractures are a material fatigue failure of bone.10,62,68 These stress injuries result from an overuse mechanism. Repeated episodes of bone strain can result in the accumulation of enough microdamage to become a clinically symptomatic stress fracture.62,75 Fatigue failure of bone has three stages: Crack initiation, crack propagation, and complete fracture. Crack initiation typically occurs at sites of stress concentration during bone loading.74 Stress concentration occurs at sites of differential bone consistency such as lacunae or canaliculi.74 Initiation of the microcrack alone is not sufficient to cause a symptomatic fracture. In fact, crack initiation is likely important for bone health because, when coupled with the reparative response, it is the first step in bone remodeling. It may serve to increase bone density and strength. Crack propagation occurs if loading continues at a frequency or intensity above the level at which new bone can be laid down and microcracks are repaired. Propagation, or extension of a microcrack, typically occurs along the cement lines of the bone. When propagating parallel to the cement lines, microcracks expand more rapidly than when propagating perpendicular to cement lines.65 Continued loading and crack propagation allows for the coalescence of multiple cracks to the point of becoming a clinically symptomatic stress fracture.68,74 If the loading episodes are not modified or the reparative response increased, crack propagation can continue until structural failure or complete fracture occurs.15,65 
Any stress or load causes some strain of or deformation to bone, and any strain of bone results in some microdamage.62,92 Since in vitro bone appears to have no endurance limit (a strain level below which a material may be loaded an infinite number of times without failure), with continued loading, microdamage will continue to occur and accumulate until complete fracture occurs.10,132 Fortunately, in vivo bone has a reparative healing response to microcracks. Bone metabolic units (BMUs) traditionally known as “cutting cones” respond to repair microcracks.74,119 Healthy bone is in homeostasis between microcrack creation and repair. If the healing response cannot stop crack propagation, a fatigue failure results. Propagation of a microcrack to a size of 1 to 3 mm is believed to be large enough to become symptomatic.68,137 Through the adaptive process of remodeling, bone is able to respond to crack initiation and propagation such that the loaded bone is strengthened in preparation for future loading.82 This positive adaptive response is known as Wolff’s law and is an essential part of bone health.62,68 

Risk Factors

A variety of biologic and mechanical factors are thought to influence the body’s ability to remodel bone and therefore impact an individual’s risk for developing a stress fracture. These include, but are not limited to sex, age, race, hormonal status, nutrition, neuromuscular function, and genetic factors. Other predisposing factors to consider include abnormal bony alignment, improper technique/biomechanics, poor running form, poor blood supply to specific bones, improper or worn-out footwear, and hard training surfaces.13,38,75 
The key modifiable risk factors in the development of overuse injuries of bone relate to the preparticipation condition of the bone and the frequency, duration, and intensity of the causative activity. Without preconditioning and acclimation to a particular activity, athletes are at significantly increased risk for the development of overuse and fatigue-related injuries of bone.53,89,117 

The Neuromuscular Hypothesis

Muscle contraction can have both provocative and protective effects on fatigue failure of bone.62,68 Muscle contraction results in internally generated compressive, tensile, and/or rotational stresses on bone. In this way muscle contraction creates microdamage. An example of this “internal” loading of bone would be the rotational strain placed on the humerus during the throwing motion. Yet neuromuscular function can also be protective of the skeleton by facilitating the distribution of externally applied loads. Since the late 20th century, it has been widely accepted that neuromuscular conditioning plays a significant role in enhancing the shock absorbing and energy dissipating function of muscles to the ground reaction forces occurring during impact loading. This neuromuscular function is able to decrease the amount of energy being directly absorbed by the bones and joints.62 Thus, as muscles fatigue they are less able to dissipate the applied external forces, allowing for more rapid accumulation of microtrauma to the bone.65 Muscle fatigue may be a collaborative culprit in the development of stress fractures in overtrained athletes and military recruits. 

General Treatment Principles

Stress fractures are the result of the loss of the normal balance between the creation and repair of microcracks in bone. Treatment principles include an evaluation of both sides of this equation. In order to decrease the creation of microcracks one must evaluate the patient’s training regimen, biomechanics, and equipment. In order to maximize the patient’s biologic capacity to repair microcracks, one must evaluate the general health of the patient, including nutritional status, hormonal status, and medication use. The clinician should be aware of the female athletic triad which is the interaction and frequent coexistence of disordered eating, amenorrhea, and stress fractures in female endurance athletes.13,37,38,55 

Stress Fracture Versus Insufficiency Fracture

There is a subtle difference between stress fractures and insufficiency fractures. Both are the result of the loss of balance between the creation and repair of microdamage in bone. A stress fracture is generally felt to be the result of high loads placed on relatively normal bone, whereas an insufficiency fracture is the result of normal loads placed on bone with impaired healing capacity.74 Insufficiency fractures are typically seen in elderly females. An example would be a metatarsal fatigue fracture in a household ambulator. 

Diagnosis

Clinical Presentation

Pain that is initially present only during activity is common in patients presenting with a stress fracture. Symptom onset is usually insidious, and typically patients cannot recall a specific injury or trauma to the affected area. If activity level is not decreased or modified, symptoms persist or worsen. Those who continue to train without modification of their activities may develop pain with normal daily activity and potentially sustain a complete fracture.37 Physical examination reveals reproducible point tenderness with direct palpation of the affected bone site. There may or may not be swelling or a palpable soft tissue or bone reaction. 

Imaging

Plain x-rays are usually negative early on in the course of a stress fracture, especially in the first 2 to 3 weeks.5,31,134 Two-thirds of initial x-rays are negative, but half ultimately prove positive once healing begins to occur making standard radiographs specific but not sensitive.23 
Even after healing has begun to occur, radiographic findings can be subtle and may be easily overlooked if the images are not thoroughly scrutinized.47,135 Likewise, diagnostic ultrasound imaging has not been shown to be reliable for diagnosing stress injuries of bone.107 
Bone scintigraphy has been shown to be nearly 100% sensitive for stress injuries of bone, but with lower specificity than magnetic resonance imaging (MRI).59,115 Bone scan-negative, but MRI-positive stress fractures have been reported.73 Especially useful for tarsal, femoral, pelvic, and tibial plateau stress fractures, bone scans are usually positive in all phases of a triple-phase technetium scan (angiogram, blood pool, delayed). This allows for easier differentiation of stress fractures from periostitis, or medial tibial stress syndrome (shin splints), as periostitis is often negative in the angiogram and blood pool phases and positive in the delayed image phase. Periostitis has also been shown to have a more diffuse distribution along the medial border of the tibia as opposed to a focal “hotspot” indicating a stress fracture.28,138 
In the clinical setting, the greatest value of bone scintigraphy is to allow early diagnosis of stress injuries.39,133 Bone scans will often demonstrate increased uptake in the affected bone 1 to 2 weeks before radiographic changes occur (Fig. 21-1). Given that uptake on bone scan requires 12 to 18 months to normalize, often lagging behind the resolution of clinical symptoms, bone scans are less helpful for guiding return to activity and/or sports participation.69,102,108 This, then, makes them less useful in the clinical setting for determining prognosis or assessing clinical union of the fracture. 
Figure 21-1
X-ray (A), bone scan (B), and T2-weighted MRI (C) images of a 23-year-old distance runner with left proximal tibia pain.
 
Arrow indicates area of increased T2 signal on MRI. This correlated with the area of the patient’s pain. All images were obtained within a 5-day period.
Arrow indicates area of increased T2 signal on MRI. This correlated with the area of the patient’s pain. All images were obtained within a 5-day period.
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Figure 21-1
X-ray (A), bone scan (B), and T2-weighted MRI (C) images of a 23-year-old distance runner with left proximal tibia pain.
Arrow indicates area of increased T2 signal on MRI. This correlated with the area of the patient’s pain. All images were obtained within a 5-day period.
Arrow indicates area of increased T2 signal on MRI. This correlated with the area of the patient’s pain. All images were obtained within a 5-day period.
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Single photon emission computed tomography (SPECT) scan is a more specific nuclear medicine scanning technique than planar bone scan. Using analysis of the metabolic rate of cells, it is especially helpful in detecting stress fractures of the vertebral pars interarticularis (Fig. 21-2), pelvis, and femoral neck.26 
Figure 21-2
Single-photon emission computed tomography bone scan demonstrating increased contrast uptake at the site of bilateral L4 pars interarticularis stress fractures in a 15-year-old female gymnast.
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Computed tomography (CT) delineates bone well and is useful when the diagnosis of a stress injury is difficult, particularly in the case of tarsal navicular stress fractures (Fig. 21-3) as well as those of the vertebral pars interarticularis or linear stress fractures. CT scanning is useful for demonstrating evidence of healing by clearly showing the periosteal reaction and the absence of a discrete lucency or sclerotic fracture line.20,26,31,50 It is also helpful in determining if the fracture is complete or incomplete.98,126 
Figure 21-3
High-risk stress fracture.
 
A: CT example of a high-risk tarsal navicular stress fracture in a competitive dancer. B: After 3 months of nonoperative treatment, the fracture shows minimal signs of interval healing and has developed a nonunion.
A: CT example of a high-risk tarsal navicular stress fracture in a competitive dancer. B: After 3 months of nonoperative treatment, the fracture shows minimal signs of interval healing and has developed a nonunion.
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Figure 21-3
High-risk stress fracture.
A: CT example of a high-risk tarsal navicular stress fracture in a competitive dancer. B: After 3 months of nonoperative treatment, the fracture shows minimal signs of interval healing and has developed a nonunion.
A: CT example of a high-risk tarsal navicular stress fracture in a competitive dancer. B: After 3 months of nonoperative treatment, the fracture shows minimal signs of interval healing and has developed a nonunion.
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MRI is the most sensitive and specific imaging study available to evaluate stress injuries of bone.59,73,118 This imaging modality has demonstrated superior sensitivity and specificity over bone scan and CT for associated soft tissue abnormalities and edema and may delineate injury earlier than bone scan.59,115 MRI has been used more frequently recently as the primary diagnostic tool for stress fractures. Its sensitivity is similar to that of a bone scan; however, it is much more precise in delineating the anatomic location and extent of injury.7,73,77 
Typical MRI findings on T2 sequences include a band of low signal corresponding to the fracture line, surrounded by diffuse high signal intensity representing marrow edema.4 Though expensive, it has the additional benefit of identifying soft tissue injuries. In summary, MRI is highly useful clinically for the diagnosis of many stress fractures, especially if used by musculoskeletal radiologists familiar with specific imaging protocols.7,118 

Classification/Grading

Stress fractures are classified in multiple ways but most commonly by the size of the fracture line seen on imaging, the severity of pain or disability, the biologic healing potential of the particular injury or location, the natural history of the particular fracture, or some combination of these parameters.7,39,66,67,109 The classification of stress fractures as either “high risk” or “low risk,” has been suggested by multiple authors.18,19,22 High-risk stress fractures have at least one of the following characteristics: Risk of delayed union or nonunion, risk of refracture, and significant long-term consequences if they progress to complete fracture.19,65 Table 21-1 shows a list of anatomic locations considered high risk for stress fractures. This distinction allows clinicians to quickly determine if they can be aggressive or conservative with the decision to return an athlete to training or competition. 
 
Table 21-1
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Table 21-1
Anatomic Sites for High-risk Stress Fractures65
  •  
    Femoral Neck (Tension Side)
  •  
    Patella (Tension Side)
  •  
    Anterior Tibial Cortex
  •  
    Medial Malleolus
  •  
    Talar Neck
  •  
    Dorsal Tarsal Navicular Cortex
  •  
    Fifth Metatarsal Proximal Metaphysis
  •  
    Sesamoids of the Great Toe
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In addition to knowing the classification of whether a stress fracture is high risk or low risk as determined by its anatomic site, the extent of the fatigue failure or “grade” of the stress fracture is also needed to completely describe the injury and make appropriate treatment plans.37,6567 As described above, stress injuries to bone occur on a continuum from simple bone marrow edema (stress reaction) to a small microcrack with minor cortical disruption to a complete fracture with or without nonunion. The management of bony stress injuries should be based on the location and grade of the injury. These two details give us the amount of damage that has accumulated and whether it is a high- or low-risk injury. A combined clinical and radiographic classification system developed by the authors of this chapter is shown in Table 21-2. This system has shown high inter- and intra-observer reliability among sports medicine and orthopedic clinicians.66 This chapter will later present a recommended treatment algorithm based on this classification system. Figures 21-421-7 show examples of the grades of stress fracture severity based on this classification system.66 
Figure 21-4
 
(A, B): T2 MRI examples of Kaeding–Miller Type I and Type II stress fractures of the tibia in a collegiate lacrosse player. The right tibial stress reaction was symptomatic with pain in this patient (Type II). The increased signal intensity in the left tibia representing a stress reaction was asymptomatic at the time of presentation (Type I).
(A, B): T2 MRI examples of Kaeding–Miller Type I and Type II stress fractures of the tibia in a collegiate lacrosse player. The right tibial stress reaction was symptomatic with pain in this patient (Type II). The increased signal intensity in the left tibia representing a stress reaction was asymptomatic at the time of presentation (Type I).
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Figure 21-4
(A, B): T2 MRI examples of Kaeding–Miller Type I and Type II stress fractures of the tibia in a collegiate lacrosse player. The right tibial stress reaction was symptomatic with pain in this patient (Type II). The increased signal intensity in the left tibia representing a stress reaction was asymptomatic at the time of presentation (Type I).
(A, B): T2 MRI examples of Kaeding–Miller Type I and Type II stress fractures of the tibia in a collegiate lacrosse player. The right tibial stress reaction was symptomatic with pain in this patient (Type II). The increased signal intensity in the left tibia representing a stress reaction was asymptomatic at the time of presentation (Type I).
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Figure 21-5
Kaeding–Miller Type III stress fracture of the fifth metatarsal in a 28-year-old male marathon runner.
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Figure 21-6
Kaeding–Miller Type IV stress fracture of the humeral shaft in baseball pitcher/football quarterback.
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Figure 21-7
Kaeding–Miller Type V stress fracture of the ulnar shaft in a 35-year-old female who used crutches for 6 weeks following an ankle fracture.
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Table 21-2
Kaeding–Miller Stress Fracture Classification System
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Table 21-2
Kaeding–Miller Stress Fracture Classification System
Grade Pain Radiographic Findings
(CT, MRI, Bone Scan, or x-ray)
I Imaging evidence of stress fracture
No fracture line
II + Imaging evidence of stress fracture
No fracture line
III + Nondisplaced fracture line
IV + Displaced fracture (>2 mm)
V + Nonunion
 

Note: Shown is a combined clinical and radiographic classification system for stress fractures that has shown high intra- and inter-observer reliability.

 

Kaeding, C, Miller T. The comprehensive description of stress fractures: A new classification system. J Bone Joint Surg Am. 2013;95:1214–1220.

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High-Risk Stress Fractures Versus Low-Risk Stress Fractures

Low-risk stress fractures include the femoral shaft, medial tibia, ribs, ulnar shaft, and first through fourth metatarsals, all of which have a favorable natural history. These sites tend to be on the compressive side of the bone, and respond well to activity modification. A low-risk stress fracture is less likely to reoccur, develop nonunion, or have a significant complication should it progress to complete fracture.18 
High-risk stress fracture locations are noted in Table 21-1. Not only do fractures at these anatomical sites have a predilection to progress to complete fracture, delayed union, or nonunion, have a refracture, or have significant long-term consequences should they progress to a complete fracture, but they also often have worsening prognosis if they have a delay in diagnosis. A delay in treatment may prolong the patient’s period of complete rest of the fracture site and potentially alter the treatment strategy to include surgical fixation with or without bone grafting. Due to their location on the tension side of the respective bones, these fractures possess common biomechanical properties regarding propagation of the fracture line. In comparison to low-risk stress fractures, high-risk stress fractures do not have an overall favorable natural history. With delay in diagnosis or with less aggressive treatment, high-risk stress fractures tend to progress to nonunion or complete fracture, require operative management, and recur in the same location.19,94 

Management of High-risk Stress Fractures

Treatment decision making for high-risk stress fractures should be based on radiographic findings with less consideration given to symptom severity. The immediate goal of treatment of a high-risk stress fracture is to avoid progression and get the fracture to heal. Typically this requires either complete elimination of loading of the site or surgical stabilization. Ideally while the fracture is healing, one works to avoid deconditioning of the athlete while minimizing the risk of a significant complication of fracture healing.37,64 While overtreatment of a low-risk stress fracture may result in unnecessary deconditioning and loss of playing time, undertreatment of a high-risk injury puts the athlete and indeed all patients at risk of significant complications. Understanding the classification and grade of stress fractures and their implications is the key to providing optimal care to all patients with a high-risk injury. 
The presence of a visible fracture line on a plain radiograph in a high-risk stress fracture should prompt serious consideration of operative management. Depending on injury classification, patients with stress injuries in high-risk locations may require immediate immobilization and/or restriction from weight-bearing activities with close monitoring. If an incomplete fracture is present on plain films with evidence of fracture on MRI or CT in a high-risk location, immobilization and strict nonweight bearing is indicated. Worsening symptoms or radiographic evidence of fracture progression despite nonoperative treatment is an indication for surgical fixation. All complete fractures at high-risk sites should receive serious consideration for surgical treatment. In summary, surgical fixation should be considered for high-risk stress fractures for several reasons. These include expediting healing of the fracture to allow earlier return to full activity as well as to minimize the risk of nonunion, delayed union, and refracture. Finally, surgical intervention may be necessary to prevent catastrophic fracture progression such as in the case of a tension-sided femoral neck fracture.17,19 

Return to Sports Participation

Generally in athletes, return to play should only be recommended after proper treatment and complete healing of the injury. As previously mentioned, high-risk stress fractures have a significantly poorer prognosis when they progress to complete fracture as well as having more frequent complications. Because of the significant complications associated with progression to complete fracture, it is not recommended that an individual be allowed to continue to participate in their activity with evidence of a high-risk stress fracture.64 Complete rest, including weight-bearing restrictions, with or without immobilization or operative management is commonly required.37 
The majority of early stress reactions at high-risk sites heal with nonoperative management.19 A period of absolute rest to eliminate the individual’s symptoms and gradual return to training with activity modification is suggested for early stress reactions at high-risk sites.9 Return to play decision making for a low-grade injury at a high-risk location should be predicated on the patient’s compliance level, healing potential, and risk of worsening of the injury. A key difference between a low-grade stress fracture at a high-risk location versus a low-risk location is that with the low-risk site the athlete or patient can be allowed to continue to train or otherwise be active, whereas the high-risk site needs to heal prior to full return to activity. 
Regardless of the grade and location, the risk of continued participation should be discussed with each athlete, and the management of each fracture should be individualized. Cross-training while resting from the inciting activity allows maintenance of cardiovascular fitness while decreasing stresses at the healing fracture site.37,60 Return to participation should be a joint decision between the physician, athletic trainer, coach, and athlete. 

Management of Low-risk Stress Fractures

Low-risk stress fractures may be treated nonoperatively with relative rest and activity modification. Decision making should be based in part on symptom severity. Those who experience enough pain to limit function should be treated with relative, if not complete, rest.37 As the treatment algorithm in Figure 21-8 suggests, if the fracture does not heal or if symptoms persist beyond 4 to 6 weeks, the options for treatment are immobilization with restriction from weight-bearing or operative intervention. Those patients with a low-risk stress fracture who present with pain but have no functional limitation may continue their activities as tolerated using symptoms as a guide. The decision to continue activity despite the presence of a low-risk stress fracture and titrate the volume of activity to a low pain level can be made after a discussion with the patient of the possible progression to complete fracture with this approach. This approach is acceptable, if the risk and consequence of progression to complete fracture are acceptable to the patient due to the importance of their continuing their activity. If the goal is not to continue activity, but to heal the low-risk stress fracture, then rest to a pain-free level is required. The acceptable level of activity will differ among patients and may include discontinuation of only the aggravating activity, discontinuing all training activities, or placing the patient on a non–weight-bearing status. Unless otherwise contraindicated, a patient may be permitted to cross-train during this time with cycling, swimming, or aqua-running to maintain fitness as long it does not cause pain at the stress fracture site. As with high-risk stress fractures, close follow-up of these patients is necessary to assure compliance with activity restrictions and prevent fracture progression to a higher-grade injury. 
Figure 21-8
Recommended treatment algorithm for stress injuries of bone.
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Low-grade stress injuries at a low-risk site have a better prognosis for time to recovery than a higher-grade injury at the same low-risk site.7,18 The difference in treatment of these two levels of severity, then, has to do with the expected time of treatment, the required degree of activity modification, and the need for immobilization. The goal of treating injuries with this level of severity is to decrease the repetitive stress at the fracture site enough to allow the body to restore the dynamic balance between damage and repair. This may include decreasing the volume and intensity of activity, equipment changes, technique changes, or cross-training. One benefit to such a strategy is that the individual typically does not suffer a substantial loss of conditioning while still allowing his or her body to repair the bone injury. If pain intensifies and activity modification alone is inadequate for healing, treatment should be intensified to include complete rest, immobilization, or surgical intervention (Fig. 21-8). 

Return to Sports Participation

Despite advances in imaging and our understanding of stress fracture behavior, return to activity decisions continue to challenge sports medicine practitioners. Many factors need to be discussed with the athlete or patient. None of these considerations is more important than assessing and explaining the risks of continued participation, particularly in the setting of an ongoing injury. All patients should understand the risk of noncompliance with the treatment plan; this is especially true for high-risk stress fractures. A treatment plan should be tailored to the individual’s athletic and personal goals with a thorough discussion of the risks and benefits of continued participation.8,60,64,91 
In the treatment of low-risk stress fractures, the point in the competitive season at which the injury is diagnosed is often a major consideration for return to play. Athletes at the end of a competitive season or in their off season, often desire to be healed from their stress fracture before resumption of competition or preseason training.64 For these individuals, the treatment plan should include relative rest and activity modification to a pain-free level. In contrast, athletes in mid-season with low-risk stress fractures often desire to finish the season and pursue treatment for a cure at a later time.37 Low-risk stress fractures will usually heal by limiting the athlete to a pain-free level of activity for 4 to 8 weeks.24 Gradual increase in activity can begin once the athlete is pain free with activities of daily living and when the site is nontender.24 

Upper-Extremity Stress Fractures

Stress fractures most commonly occur in the lower extremity as a result of the impact loading of walking, running, or jumping.84 However, individuals performing repetitive tasks with the upper extremity and those who require upper extremity weight bearing may develop stress injuries of bone (Figs. 21-6 and 21-7). Upper-extremity stress fractures account for less than 10% of all stress fractures, and are commonly found in throwing athletes and rowers.63,129 In recent years, there has been increased attention focused on upper-extremity stress fractures, and case reports of these injuries have increased. The great majority of these stress injuries are considered low risk and usually require only activity modification to heal. Repetitive torsion, weight bearing, and muscle contraction overload of bone must be considered when evaluating these injuries. Any repetitive overhead athlete or laborer complaining of the nontraumatic onset of pain in the upper extremity, with a normal examination and the presence of pain only with the repetitive activity should be considered as having a possible stress fracture.63 
In the shoulder girdle, arm, forearm, and wrist, strain is generated by the rotational torque of swinging or throwing, as well as by the tension or compression generated by muscle contraction.130 A third mechanism of creating bone stress in the upper extremity is repetitive axial loading. Sinha et al.116 reviewed 40 stress fractures of the ribs and upper extremity. They noted that individuals performing weight-bearing activities of the upper extremity (gymnastics, cheerleading) developed all their stress fractures distal to the elbow, indicating that with such activities significant bony overload occurs in the distal upper extremity as opposed to the proximal portion. 
As mentioned previously, the majority of upper-extremity stress injuries respond well to nonoperative treatment with rest and activity modification. One of the few stress fractures of the upper extremity that may require surgical intervention is the olecranon stress fracture in a competitive thrower. Though this injury has the potential to heal with conservative management, when a stress fracture line (Grade 3 injury) is discovered in a throwing athlete’s olecranon process, internal fixation is the ideal treatment.2,41,112 

Vertebral, Pelvic, and Sacral Stress Fractures

Spondylolysis, or a stress fracture of the pars interarticularis region of the posterior elements of the vertebrae, occurs most commonly in patients performing repetitive hyperextension of the spine (gymnasts, cheerleaders, divers, weight lifters), and is a common cause of pediatric low back pain.77 The L4 and L5 levels are most commonly affected. Patients present with the insidious onset of low back pain ultimately with complaints of significant back spasms. This injury is often misdiagnosed as lumbar strain. Short periods of rest may temporarily relieve pain, but return to activity typically results in immediate exacerbation of symptoms.25,77 
On examination, affected individuals may have clinical hyperlordosis in addition to pain with palpation over affected vertebral levels, and exquisite pain and muscle guarding with one- and two-leg standing trunk extension.25 Pain may also be elicited by trunk rotation and extension, prone hip extension, and prone trunk extension. Neurologic evaluation is usually normal but occasionally the patient may have associated radiculopathy.77 
On radiographic evaluation, x-rays have low sensitivity for stress fracture of the pars interarticularis.25 Anteroposterior, lateral, and bilateral oblique views should be obtained. If positive, the classic defect of a “collar” on the neck (pars interarticularis) of the “Scotty dog” is seen on oblique views. X-ray imaging however has fallen out of favor in recent years because of low sensitivity and high radiation exposure. A SPECT scan has a greater sensitivity and is becoming the gold-standard test for diagnosis of a pars interarticularis stress fractures77 (Fig. 21-2). A thin-cut CT scan (1.5- to 2-mm cuts) may additionally aid in determining the extent and age of a stress fracture in this area. Furthermore, a combination of SPECT and CT findings may help determine the likelihood of healing and may help define the treatment protocol.77 
The treatment protocol for stress fractures of the pars interarticularis is somewhat controversial. Initially, activity modification and avoidance of lumbar hyperextension is recommended. If symptoms persist, a nonrigid brace such as a corset may be applied. After 2 to 4 weeks of rest and bracing, patients should begin a regimen of physical therapy which includes trunk stabilization, core strengthening, and lumbar spine flexibility exercises.77 If pain is still present by 4 weeks, a thoracolumbosacral orthosis (TLSO) or low-profile rigid antilordotic Boston brace should be considered to unload posterior elements and prevent hyperextension. Treatment should be continued until the patient is symptom-free. Complete healing, however, may take as long as 3 to 6 months, and a repeat axial-cut CT scan may be considered to assess the amount of healing.25 
Return to play may be as early as 8 weeks if the patient remains pain free at rest, in hyperextension, and while performing aggravating activities.25 Surgical fixation may be considered if the patient continues to experience persistent pain despite rigid bracing, especially if neurologic symptoms are present or progressive.77 

Pelvis and Sacrum

Stress fractures of the pelvis and sacrum are uncommon and typically involve the pubic rami. These injuries occur most often in women, military recruits, long-distance runners, or joggers after increases in duration, frequency, or intensity of impact-loading exercise.55 Patients with stress fractures of the pubic rami present with insidious pain in the inguinal, perineal, or adductor regions that is relieved by rest. Sacral stress fractures present with vague, poorly localized pain in the gluteal or groin area.42 Therefore, a high index of suspicion must be maintained. 
On physical examination, patients may demonstrate an antalgic gait, tenderness over the pubic rami, or an inability to stand unsupported on the affected side. Patients with a sacral stress fracture may also demonstrate pain with hip flexion, abduction, and external rotation in addition to increased pain when asked to hop. These patients usually will have normal hip and spine range of motion but complain of deep groin pain at the extremes of hip motion. 
X-rays are initially negative in most cases of both pelvic and sacral stress fractures.25,42 Later in the healing process callus may be present on plain films. Bone scan or MRI is usually necessary for early diagnosis. Treatment requires cessation of running and jumping activities, protected weight bearing, and relative rest lasting from 6 weeks to 8 months. An initial brief period of nonweight bearing may be necessary based on the patient’s pain level. Surgery is not typically necessary if the fracture is diagnosed in a timely manner. 

Lower-Extremity Stress Fractures

Femur

Stress injuries and fatigue fractures may occur at a variety of sites in the femur. The most commonly involved areas are the shaft, the intertrochanteric region, and the neck. As mentioned previously, the tension or superior side of the femoral neck is a high-risk site for fracture propagation. Here, a missed or delayed diagnosis significantly increases the patient’s risk for a potentially catastrophic complete fracture. 

Femoral Neck

Seen most frequently in runners, dancers, and military recruits, the diagnosis of a femoral neck stress fracture is often delayed for 5 to 13 weeks.43,61,89 Unlike femoral shaft stress fractures, which are low risk and therefore heal with activity modification, femoral neck fractures are high-risk injuries.19,36 Tension-sided femoral neck stress fractures possess the greatest risk for fracture progression.19,36 The diagnosis requires a high degree of suspicion and usually occurs in runners with vague hip or groin pain. Examination will likely reveal an antalgic gait, pain with palpation in the groin, hip, or anterior thigh as well as pain at the extremes of hip range of motion.40,42,48,49 Subtle limitation of flexion and internal rotation may also be present with or without a positive log roll test.87 
Confirmation of the diagnosis usually requires bone scan and/or MRI. The radiographic appearance lags behind symptoms and may not be evident until some healing has occurred.61 X-rays have a high false-negative rate. Bone scan or SPECT scans have proven useful for early diagnosis, but false negatives have been reported up to 12 days after symptom onset.26 MRI is becoming more popular and is a sensitive study identifying early marrow edema, which typically resolves in 8 to 12 weeks.59,115 
Femoral neck stress fractures require aggressive management with inferior cortex fractures requiring restricted weight bearing for 6 weeks or longer.40,42,48,49 Weekly radiographs should be obtained until the patient can walk pain free with a cane. Return to play or other vigorous activity may be delayed up to 2 years.114 We believe tension-sided stress fracture is an indication for surgical fixation with parallel screws or a sliding hip screw device.131 If no displacement is present, some authors have advocated bed rest as the first-line treatment without immediate surgery.9 Regardless, recognition of the tension-sided femoral neck stress fracture and immediate appropriate treatment is of utmost importance to prevent complete fracture, nonunion, and the potential development of femoral head osteonecrosis.40,42,48,49 

Femoral Shaft Stress Fractures

Stress fractures of the femoral shaft are diagnosed most commonly in runners, in particular female runners, with the most common location being the junction of the proximal and middle thirds of femoral shaft.55,101,123 As with most stress injuries of bone, the history often reveals a recent increase in frequency, intensity, or duration of a repetitive activity. Pain with running then progresses to pain with activities of daily living and functional limitation. Examination is positive for an antalgic gait with normal knee and hip range of motion. Pain with palpation may be present at the anterior thigh with hopping on the affected leg reproducing the pain. The fulcrum or “hanging leg” test involves having the patient seated on an examination table with the leg hanging freely. A three-point bending force is then applied to the thigh with the edge of the table being used as a fulcrum. Pain elicited is indicative of a stress fracture. As with most stress injuries plain x-rays are typically negative early in the course of the injury. Fracture callus and a radiolucent fracture line usually appear 2 to 6 weeks after symptom onset. Bone scan or MRI may be necessary for an early diagnosis. 
Nonoperative treatment of femoral shaft stress fractures is usually successful. First-line interventions include protected weight bearing with crutches for 1 to 4 weeks depending on symptom severity and radiologic grade of the injury. Activity modification with cross-training during this time period allows maintenance of aerobic fitness, skill, and strength. If the patient is pain free with day-to-day activities at 2 weeks, a rehabilitation program with low-impact exercise may be initiated. Time to full recovery varies, but has been reported as 5 to 10 weeks from diagnosis with return to full athletic participation at 8 to 16 weeks. 

Knee and Lower Leg Stress Fractures

Patella

Patellar stress fractures are rare but troublesome injuries occurring most often in basketball players, soccer players, and high jumpers.65,122 Risk factors for a tension-sided (anterior cortex) stress fracture of the patella are flexion contracture and/or harvest of a patellar tendon graft for ACL reconstruction.122 The patient’s history reveals anterior knee pain, worse with jumping. The key diagnostic features are point tenderness to palpation of the anterior patella and increased pain with resisted knee extension.65 Radiographic studies may show fracture lines in longitudinal or transverse directions, but these must be differentiated from a bipartite or tripartite patella.122 A bone or MRI scan identifying bone edema can clarify the diagnosis. 
Due to the distractive forces of the extensor mechanism, transverse fractures are prone to displacement. Nondisplaced fractures are treated in a hinged knee brace with the knee in full extension for 4 to 6 weeks, followed by progressive range of motion and quadriceps rehabilitation. 
Displaced fractures should be treated with open reduction and surgical fixation.65 Fractures in a longitudinal direction occur most often at the lateral patellar facet, and if displaced, the lateral fragment may be excised. Case series have reported that acute nondisplaced fractures can heal with immobilization and relative rest, but open reduction and internal fixation is recommended for chronic or displaced fractures. 

Tibial Shaft Stress Fractures

Stress fractures of the tibia represent 20% to 75% of all stress fractures in athletes.8,16 To effectively treat stress injuries at this anatomical site, a distinction must be made between medial tibial stress syndrome (shin splints), a compression-sided stress fracture, and a tension-sided stress fracture. The most predominant type is a low-risk posteromedial cortex (compression side) stress fracture with the much less common type being the high-risk “dreaded black line” of the anterolateral cortex of the central shaft (Fig. 21-9A).54,128 Most commonly occurring in running sports such as soccer, track, and field, basketball or ballet, the pain occurs initially after activity. Pain later develops during running and progresses to eventually affect activities of daily living. On examination, there is localized pain with point tenderness at the anterior or medial tibia. Edema, palpable periosteal thickening, and pain with percussion may also be present. A “tuning fork test” may be performed to elicit pain if a high pretest probability is present but is generally not performed due to a high false-negative rate and limited availability of the proper equipment.81 
Figure 21-9
 
A: Case example of a 23-year-old female college soccer player with chronic anterior tibial pain and stress fracture of the anterior tibial cortex (arrow). B: Final treatment required operative fixation with a statically locked intramedullary rod. Cortical thickening remains evident 6 months post surgery.
A: Case example of a 23-year-old female college soccer player with chronic anterior tibial pain and stress fracture of the anterior tibial cortex (arrow). B: Final treatment required operative fixation with a statically locked intramedullary rod. Cortical thickening remains evident 6 months post surgery.
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Figure 21-9
A: Case example of a 23-year-old female college soccer player with chronic anterior tibial pain and stress fracture of the anterior tibial cortex (arrow). B: Final treatment required operative fixation with a statically locked intramedullary rod. Cortical thickening remains evident 6 months post surgery.
A: Case example of a 23-year-old female college soccer player with chronic anterior tibial pain and stress fracture of the anterior tibial cortex (arrow). B: Final treatment required operative fixation with a statically locked intramedullary rod. Cortical thickening remains evident 6 months post surgery.
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X
X-rays may be positive if symptoms have persisted for 4 to 6 weeks. Bone scan often demonstrates focal fusiform uptake, which differs from the linear uptake seen with medial tibial stress syndrome.28,39 MRI is more useful for grading and providing a prognosis for return to play (Figs. 21-1 and 21-4A,B).46 
Treatment should initially involve steps to control pain and limit, if not completely discontinue, running or jumping activities. The use of crutches, immobilization, and limited weight bearing may be necessary depending on symptom severity and fracture classification.83,134 If the fracture is diagnosed early, it frequently may be treated by limiting practice activities but still participate in competitions. Once pain free, cross-training with low-impact or nonimpact aerobic training may begin and be used to supplement training during a gradual return to running. Compression-sided injuries may take 2 to12 weeks to heal. Tension-sided injuries achieve faster return to play with intramedullary (IM) rod fixation (Fig. 21-9B).27,128 The options for treatment of injuries in this location include 4 to 6 months of rest, bone grafting, electrical stimulation, or IM nailing.65 If a patient or athlete desires to resume training for sports at the same or increased intensity, IM nailing is usually recommended.105 

Medial Malleolus

Stress fractures of the medial malleolus are relatively rare and are usually associated with running and jumping sports.95,113 They are inherently unstable and prone to nonunion.104 A high index of suspicion is the key to their early recognition as patients typically present with the insidious onset of medial ankle pain that is increased with exercise and relieved by rest. Physical examination reveals medial malleolar tenderness to palpation and an effusion of the ankle joint. It is important to also evaluate the patients for any predisposing factors that may contribute to stress overloading in the area such as foot or lower limb alignment.95,113 Varus alignment in particular, can cause medial overload.93 On x-ray, the fracture line extends vertically or horizontally from the medial articular surface of the tibial plafond. 
Treatment of an incomplete fracture requires no weight bearing and immobilization with gradual rehabilitation in low-demand individuals. In high-demand athletes and those who wish early return to sports participation, a more aggressive approach may be warranted. Complete fractures require treatment with open reduction and malleolar screw fixation. As with traumatic ankle fractures, most patients return to full activity by 6 to 8 weeks postoperatively. Nonunion of a medial malleolar stress fracture requires bone grafting and screw fixation.104 

Fibula

Stress fractures of the fibula are also rare given the limited amount of weight-bearing stress borne by this bone. The most common location is in the distal third of the diaphysis just proximal to the distal tibiofibular syndesmosis. It may be associated with overpronation and a valgus hind foot.88 Patients typically present with lateral leg and ankle pain with mild swelling and may have a notable limp. Point tenderness can be elicited by palpation of the bone or by performing a syndesmosis squeeze test. Recommended initial treatment is weight bearing as tolerated in a protective fracture brace, followed by gradual return to activity once pain and swelling have resolved. With early diagnosis, athletes may return to participation after 3 to 6 weeks of rest.18 Complete healing occurs within approximately 8 to 12 weeks. 

Stress Fractures of the Foot

Calcaneus

Calcaneal stress fractures occur most commonly in long-distance runners and military recruits from repetitive loading of the heel with weight-bearing activities. Patients present with the insidious onset of diffuse heel pain with running that may be increased by toe walking or during the toe-off phase of running. Examination reveals edema and a positive “heel squeeze” test. This is performed by compressing the body of the calcaneus between the palms of both hands. Increased pain with hop testing may also be present. 
Plain x-rays become positive after 2 to 4 weeks. At that time a sclerotic line with callus perpendicular to the trabecular lines of the calcaneal tuberosity may be visualized. Bone scan and MRI usually demonstrate increased reactive bone in this region as well, confirming the diagnosis. Initial treatment is to decrease activity and use cushioned heel inserts until symptoms have improved and healing is evident radiographically. The use of a cast or brace and a brief period of nonweight bearing may be necessary if ambulation is painful. The estimated time to return to sports participation is 3 to 8 weeks. 

Tarsal Navicular

Previously thought to be uncommon, navicular stress fractures are now frequently recognized in jumping and running athletes.14,29,30,58,79 This is a high-risk stress fracture.19,65,78 Patients present with vague midfoot and medial arch symptoms of insidious onset often leading to delayed diagnosis110,125,126 and the final diagnosis may be delayed from 2 to 7 months.71,126 On examination, patients report tenderness at the “N spot” (the dorsal aspect of the navicular), but pain may be diffuse rather than localized. Continued weight-bearing activity may delay the healing process, resulting in progression to a complete fracture or nonunion. Therefore, midfoot pain in a running or jumping athlete requires a high index of suspicion and early aggressive management. 
Since most fractures occur in the sagittal plane and in the central third of the dorsal navicular cortex, x-rays are usually negative.86 It has been proposed that this site has a poor blood supply predisposing the bone to stress-related injury.56,96 This region has also been correlated with the plane of maximum shear stress during a combination of plantar flexion and pronation.34,52,72 Associated foot anomalies that may predispose a patient to this type of fracture include a short first metatarsal, a long second metatarsal or a calcaneonavicular coalition.98,125,126 
Bone scan can confirm the diagnosis, but CT (Fig. 21-3) or MRI may be necessary to determine the exact location and extent of the fracture and the amount of healing or to diagnose a nonunion.86 The key to a successful outcome in treating this injury is early diagnosis with aggressive treatment.111 Current literature supports nonsurgical treatment of incomplete fractures and no weight bearing is recommended in a cast for 6 to 8 weeks followed by gradual rehabilitation.97,100,125 Upon return to play the use of orthotics should be considered if a bony abnormality or poor biomechanics are present.72 
The decision to surgically treat a navicular fracture has typically been ascribed to fractures that are complete and/or show evidence of sclerosis at the margins.86 Surgical fixation with or without bone grafting is suggested for those in whom nonsurgical management has failed.45,70,71,100 Because of the poor blood supply to the region where the fracture occurs, it is crucial to immobilize the fracture site after surgery and until radiographic healing has occurred.98 

Metatarsal Stress Fractures

First through Fourth Metatarsals

Stress fractures of the first through fourth metatarsals are generally considered low-risk injuries. Excluding the fifth metatarsal, first metatarsal stress fractures make up 10% of all metatarsal stress injuries and are associated with overpronation during running. The remaining 90% are distributed between the second, third, and fourth metatarsals.44 Stress injuries to these bones are associated with running over 20 miles/week. Pes planus deformity increases the impact stress to the medial four metatarsals. In runners, most injuries occur in the distal shaft. However, in ballet dancers, fractures may occur proximally and often involve the medial border of the second metatarsal due to weight bearing in the en pointe position. Patients present with localized pain and swelling in the absence of trauma and report symptom onset after an increase in training intensity. Close inspection of the foot may reveal low arches, overpronation while running, and point tenderness over the involved metatarsal. Pain is often exacerbated with inversion of the foot.44 
Weight-bearing AP, lateral, and oblique radiographs should be obtained. In dancers with second metatarsal pain, internal and external oblique radiographs of the foot may be necessary to fully evaluate the involved bone. Treatment involves rest and the use of a stiff-soled shoe or fracture boot to decrease bending stresses across the midfoot.44 Gradual reconditioning with progression of repetitive loading such as pool running progressing to cycling, then land running is recommended in athletes to maintain cardiovascular fitness and prevent progression of the injury. Once the fracture has healed, orthotic devices should be prescribed if abnormal bony alignment or foot biomechanics are present. In dancers, proximal second metatarsal stress fractures may progress to nonunion and must be aggressively managed with casting or fracture bracing until radiographic healing is present (usually 6 to 8 weeks). 

Fifth Metatarsal

The proximal fifth metatarsal is considered a high-risk site for stress fracture. Because of the poor blood supply to the affected area, both stress injuries and traumatic injuries are prone to nonunion.1,120,121 Figure 21-10 demonstrates the three zones of the proximal fifth metatarsal. Zone I represents the tuberosity; zone II the watershed or avascular area at the metaphyseal–diaphyseal junction.116 Zone III represents the proximal diaphysis. Fractures occurring in zone II have the greatest risk for delayed healing due to the limited vascularity of this site.1,120,124 Occurring commonly in basketball players and runners, these injuries present with the insidious onset of lateral foot pain that is worse during and after running or jumping activity.120 Pain steadily worsens if the causative activity is continued. Not uncommonly an acute fracture occurs following days to weeks of antecedent pain. On clinical evaluation, point tenderness is present directly over the fracture.124 Plain x-rays usually show sclerotic change around the fracture site (Fig. 21-5). Bone scans are only occasionally necessary for diagnosis, but bone scan or MRI may be employed if an occult fracture is suspected. 
Figure 21-10
Illustration demonstrating the three zones of the proximal fifth metatarsal.
 
Zone I, tuberosity; Zone II, watershed (avascular) zone at the metaphyseal–diaphyseal junction; Zone III, proximal diaphysis.124
Zone I, tuberosity; Zone II, watershed (avascular) zone at the metaphyseal–diaphyseal junction; Zone III, proximal diaphysis.124
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Figure 21-10
Illustration demonstrating the three zones of the proximal fifth metatarsal.
Zone I, tuberosity; Zone II, watershed (avascular) zone at the metaphyseal–diaphyseal junction; Zone III, proximal diaphysis.124
Zone I, tuberosity; Zone II, watershed (avascular) zone at the metaphyseal–diaphyseal junction; Zone III, proximal diaphysis.124
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Treatment for stress fractures of the proximal fifth metatarsal, as with all high-risk anatomical sites, should be aggressive.33,35 In nonathletes, a short-leg non–weight-bearing cast or fracture brace for 6 to 8 weeks is recommended. Longer immobilization may be required if no radiographic evidence of healing has occurred during that time period.33 Because of the potentially prolonged healing time and risk of refracture or nonunion following conservative treatment, there is now a greater tendency to use surgical fixation as the primary treatment.51,76,80,90 This tendency is shared by the authors of this chapter. 
In high-demand athletes, IM screw fixation with a 4- or 4.5-mm cannulated screw permits faster return to play since casting alone in this population has been shown to have a high failure rate.99,103 If nonunion is not present, bone grafting usually is not necessary at the time of IM fixation. Weight bearing should be initiated 7 to 14 days postoperatively, with training progressing to full unrestricted activity over 9 weeks. Return to sports activities is expected at approximately 3 to 9 weeks postoperatively in patients with zone II or III fractures.126 A risk, however, remains for fracture nonunion and fatigue failure of the screw.136 

Sesamoids

Sesamoid stress fracture is a rare and difficult diagnosis to make. This injury must be differentiated from sesamoiditis, bipartite, and tripartite sesamoids, hallux rigidus and a painful soft tissue callous.127 The medial sesamoid is most frequently involved. Because most of the body’s weight is transferred through the medial aspect of the first metatarsal during the toe-off phase of activity, the medial sesamoid receives both tensile and compressive stresses.65 Patients with this injury typically present with pain localized to the plantar surface of the first metatarsal head which is worse upon weight bearing and during the toe-off phase of the gait cycle. Pain on palpation, pain with resisted active great toe plantarflexion, and pain over the sesamoids with stretch into full dorsiflexion of the first metatarsophalangeal joint are positive indicators on physical examination.127 Diagnosis of sesamoid stress fracture by x-ray is challenging, if not impossible, when the fracture is nondisplaced. Additional imaging, including bone scan or MRI, is often required to identify marrow edema and differentiate stress fracture from a bipartite sesamoid. 
Conservative treatment with 6 weeks of non–weight-bearing cast immobilization to prevent dorsiflexion of first ray is the recommended initial treatment.65 Unloading of the first metatarsal head is the primary goal. Consideration should also be given to the use of orthotic devices in the shoe after casting. Complete resolution of this fracture and its symptoms may take as long as 4 to 6 months.88 Surgical excision is recommended for delayed union or chronic pain.106 Removal of the entire medial sesamoid may, however, result in weakening of the flexor hallucis brevis insertion on the proximal phalanx, resulting in the great toe drifting into valgus. Partial sesamoidectomy has been suggested as an alternative to complete sesamoidectomy to effectively resolve symptoms and maintain normal mechanics of the great toe.65 Surgery is considered to be a last resort and generally should be avoided in athletes. 

Prevention of Stress Injuries

Prevention is the ideal treatment of stress injuries of bone. An assessment of the athlete’s risk should be made at preparticipation evaluations, especially in those with a history of previous stress fractures.37,64 Correction of amenorrhea in females and calcium and Vitamin D supplementation is recommended in addition to general nutritional optimization. If biomechanical abnormalities are encountered, the use of appropriately designed orthotic devices should be considered as an initial corrective measure. However, gait analysis, appropriate running form, and technique changes may be necessary to prevent future injuries. 

Summary

The diagnosis of a stress fracture is usually straightforward if a high index of suspicion is maintained and the proper imaging studies are obtained. They are common injuries particularly in endurance athletes and military recruits. The authors’ classification system for stress fractures characterizes these injuries based on the patient’s symptoms as well as their position on a radiographic continuum of severity. Our recommended treatment algorithm further stratifies these injuries as either high risk or low risk based upon the biomechanical environment in which they are located. High-risk stress fractures are primarily loaded in tension, have a poor natural history, and commonly require surgical intervention. Low-risk fractures are most often those loaded in compression, have a better prognosis, and are unlikely to progress to complete fracture. The goal of this algorithm is to provide clinicians with general guidelines for the management of stress fractures based on recent literature findings and the authors’ clinical experience. It should not be interpreted as a set of rigid rules for treatment. Stress fracture management should be individualized to the patient taking into consideration injury site (low risk vs. high risk), grade (extent of microdamage accumulation), the individual’s activity level, competitive situation, and risk tolerance. 

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