What is a stress fracture?

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A stress fracture is a partial or complete fracture of a bone caused by repeated mechanical stress that is lower than the stress required to fracture the bone during a single loading event (Fredericson et al., 2006).

Unlike an acute fracture, most stress fractures develop gradually through repetitive overload and/or overuse, when mechanical stress exceeds the bone’s capacity to remodel and adapt, allowing microdamage to accumulate (Vasiliadis, 2017).

Bone stress injury (BSI) is the broader term for the spectrum from low-grade stress reactions to bone fractures. A stress fracture therefore represents a more advanced injury within the BSI spectrum (George et al., 2024).

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The process can be summarised as:

Repetitive loading → accumulated microdamage → bone stress injury → progressive structural damage → stress fracture

In runners, repetitive lower-extremity loading places particular stress on bone. The tibia is the most commonly affected site, although the metatarsals, tarsal navicular, femur and pelvis can also be affected (George et al., 2024).

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Stress fracture vs bone stress injury:

BSI is the broader term, encompassing the spectrum from stress reactions to fractures. A stress fracture is a fracture resulting from repetitive loading and represents a more advanced stage of the BSI spectrum (Fredericson et al., 2006; George et al., 2024).

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How common are stress fractures in runners?

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Stress fractures and BSIs are common in physically active populations, particularly in sports involving repetitive loading such as running. However, reported figures vary according to the population and whether the measurement refers to BSIs, stress fractures, running injuries, or anatomical distribution.

Up to 95% of BSIs in athletes occur in the lower extremities, with the tibia being the most common location (George et al., 2024).

An annual BSI incidence of up to 21.1% has been reported in track and field athletes, while more than one-third of female cross-country and long-distance runners have been reported to experience lower-extremity BSIs (George et al., 2024).

A systematic review reported an overall BSI incidence of 9.7% in female athletes and 6.5% in male athletes (George et al., 2024).

Among competitive high-school runners, tibial BSI had a reported lifetime prevalence of 41% in females and 34% in males (Tenforde et al., cited in George et al., 2024).

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Stress fractures as a proportion of running injuries

Lower-extremity stress fractures account for approximately 80–90% of all stress fractures and represent 0.7–20% of sports medicine injuries. In runners, stress fractures have been reported to account for approximately 16% of running-related injuries (Kahanov et al., 2015).

Importantly, 16% does not mean that 16% of runners develop a stress fracture. It refers to the proportion of running-related injuries represented by stress fractures.

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Where do stress fractures occur in runners?

The tibia is the most common site of stress reactions and stress fractures in runners (Kahanov et al., 2015).

One review reported the following distribution:

 

Stress fracture site:

Tibia : 23.6%

Tarsal navicular: 17.6%

Metatarsals: 16.2%

Femur: 6.6%

Pelvis: 1.6%

(Kahanov et al., 2015)

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Other figures reported in the supplied literature include:

• Metatarsals: approximately 20% of lower-extremity stress fractures

• Tarsal bones, particularly the navicular: approximately 20% of stress fractures in runners

• Fibula: approximately 7–12% of all stress fractures

• Pelvis: approximately 1–2% of all stress fractures

• Great toe sesamoids: approximately 0.4% of all running injuries

(Kahanov et al., 2015)

 

How Are Stress Fractures Classified?

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Stress fractures can be classified as low risk or high risk according to their anatomical location and biomechanical characteristics. This classification is important because it can help guide management and rehabilitation (Chen et al., 2013; George et al., 2024; Kahanov et al., 2015).

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What is a high-risk stress fracture?

High-risk stress fractures have a greater potential to:

• Progress to a complete fracture

• Develop delayed union or nonunion

• Require surgical repair

• Require assisted or non-weight-bearing

• Occur on the tension side of the natural biomechanical axis (Chen et al., 2013)

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Common high-risk sites include:

• 5th metatarsal

• Anterior tibia

• Tarsal navicular

• Femoral neck (tension side)

• Patella

• Medial malleolus

• Talar neck

• 1st metatarsal sesamoids

(Chen et al., 2013)

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In runners, the anterior tibia is particularly important. While the posteromedial tibial shaft is considered low risk, stress injuries involving the anterior tibial cortex are considered high risk and may require prolonged non-weight-bearing or surgical fixation because of their higher complication risk (George et al., 2024).

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What is a low-risk stress fracture?

Low-risk stress fractures have a more favourable natural history and generally:

• Respond well to non-surgical management

• Allow unassisted weight-bearing

• Occur on the compression side of the natural biomechanical axis (Chen et al., 2013)

 

Common low-risk sites include:

• Femoral shaft

• Medial tibia

• Fibula

• Ribs

• Ulnar shaft

• Calcaneus

• 1st–4th metatarsals

(Chen et al., 2013)

Kahanov et al. (2015) similarly describe the femoral shaft, medial tibia, fibula, calcaneus and 1st–4th metatarsals as typical low-risk locations.

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Why does low-risk vs high-risk classification matter?

The distinction between low-risk and high-risk stress fractures is important because anatomical location can influence management and rehabilitation (Chen et al., 2013).

High-risk injuries have a greater potential for complete fracture, delayed union or nonunion and may require more protective management or surgical intervention. Low-risk injuries generally have a more favourable natural history and respond well to conservative management (Chen et al., 2013; Kahanov et al., 2015).

For runners, both the grade of the bone stress injury and the risk associated with its anatomical location should therefore be considered (George et al., 2024).

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Low risk vs high risk

LOW RISK: Compression → favourable natural history → conservative management

HIGH RISK: Tension → greater complication risk → more protected management

This classification complements, rather than replaces, MRI grading. MRI grading describes the grade of the bone stress injury, whereas low-risk/high-risk classification relates primarily to the anatomical location and associated risk (George et al., 2024; Kahanov et al., 2015).

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Contributing Factors to Bone Stress Injuries

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Bone stress injuries (BSIs) occur when load-induced microdamage accumulates faster than bone can remodel and repair itself (George et al., 2024).

A key part of BSI management is identifying and addressing the individual factors that may have contributed to the injury, particularly before returning to full training (George et al., 2024). 

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Key contributing factors

These may include:

• Low energy availability (LEA) and Relative Energy Deficiency in Sport (REDs)

• Menstrual health and nutritional deficiencies

• Running biomechanics

• Muscle strength and flexibility deficits

• Training load and mechanical loading (“training errors”)

• Footwear

• Smoking, maturity and participation in distance/endurance running (Kahanov et al., 2015; George et al., 2024)

 

Energy availability and REDs

Low energy availability (LEA), and more specifically REDs, is an important intrinsic risk factor for BSI. REDs describes the physiological and psychological consequences of a mismatch between energy intake and energy expenditure and can affect both female and male athletes (George et al., 2024).

LEA can impair bone health and increase BSI risk. In the literature reviewed by George et al. (2024), amenorrhea and low testosterone were reported in 37% of elite female and 40% of elite male distance runners, with 4.5-fold higher rates of bone injuries than in runners with normal menstruation or testosterone levels.

 

Why do contributing factors matter?

Addressing relevant contributing factors may help reduce recurrence and support rehabilitation. In particular, 60% of the studies reviewed by George et al. (2024) highlighted assessing REDs risk and menstrual health in female athletes.

These factors should be addressed before returning to full training (George et al., 2024).

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Why Are Female Runners More Predisposed to Stress Fractures?

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Female athletes may have a higher risk of stress fractures, with low energy availability, menstrual dysfunction and impaired bone health being important factors.

The Female Athlete Triad describes the relationship between prolonged low energy availability, amenorrhoea, hormonal dysfunction and impaired bone health. It is a significant risk factor for stress fractures in female athletes (Chen et al., 2013). 

A systematic review reported stress fracture incidence of 9.2% in female military recruits compared with 3% in males, and 9.7% in female athletes compared with 6.5% in male athletes (Chen et al., 2013). 

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Other factors associated with stress fracture risk in females include:

• Older age at menarche

• Maternal history of osteoporosis or low bone mineral density

• Greater weekly participation in sport

Stress fractures were nearly twice as common in girls participating in sport for ≥8 hours per week compared with those participating for ≤4 hours per week (Chen et al., 2013). 

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Why does the Female Athlete Triad matter?

Female athletes with a stress fracture should be evaluated for factors associated with the Female Athlete Triad, including dietary intake, weight changes, energy availability and menstrual history. Assessment may also include evaluation of bone mineral density and appropriate nutritional or psychological support (Chen et al., 2013). 

Early identification is important. In adolescent female runners with low bone mass, 90% continued to meet the criteria for low bone mass three years later, highlighting the importance of identifying the Triad and optimising bone health early (Chen et al., 2013). 

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What Are the Symptoms of a Stress Fracture?

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Stress fractures usually develop gradually, rather than suddenly. The most common early symptom is focal pain and tenderness over the affected bone, often occurring towards the end of physical activity (Kahanov et al., 2015; Chen et al., 2013).

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Symptoms may progress through several stages:

Pain after or towards the end of activity → pain during activity → persistent pain during walking or daily activities.

A recent increase or change in training, repetitive exercise, or insufficient recovery may be present in the weeks before symptoms develop (Kahanov et al., 2015; Chen et al., 2013).

 

Common signs and symptoms:

• Gradual onset of pain

• Focal tenderness over the affected bone

• Pain initially occurring after or towards the end of exercise

• Pain that progresses to occur during exercise

• Persistent pain during walking or daily activities as the injury progresses

• Local swelling may be present (Kahanov et al., 2015; Chen et al., 2013)

 

What is found on physical examination?

Physical examination typically identifies localized tenderness over the involved bone, with or without swelling (Kahanov et al., 2015; Chen et al., 2013).

Depending on the suspected anatomical location, specific tests may also be used, including the hop test, fulcrum test and hyperextension test (Kahanov et al., 2015; Chen et al., 2013).

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How Long Does a Stress Fracture Take to Heal?

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The healing time for a stress fracture varies according to the injury site, grade and risk classification. The literature reports healing and return-to-activity times ranging from approximately 4 weeks to 1 year (Kahanov et al., 2015). 

For low-risk stress fractures, the vast majority heal within 8 weeks with conservative treatment, although some may develop delayed or non-union and require surgical intervention (Kahanov et al., 2015). 

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Typical time to weight-bearing activity

Reported average times vary according to the anatomical site and risk classification (Kahanov et al., 2015) :

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