Hairline or stress fractures are tiny cracks on a bone that often develop in the foot or lower leg. The most significant risk for a hairline fracture is playing high impact sports that involve repetitive jumping or running.

Hairline fractures may also occur in the upper limb and are often related to falls or accidents.

Hairline fractures usually develop gradually as a result of overuse, as opposed to larger bone fractures or breaks that are mostly caused by acute traumas, such as a fall. While hairline fractures may heal with sufficient rest, they can be painful and last several weeks.

Anyone who engages in regular physical activity can develop a hairline fracture, especially if the activity involves repetitive movements that put a strain on a bone or a group of bones. The most common treatment approach is rest.

Fast facts on hairline fractures:

  • Hairline fractures can occur from overuse or repetitive activity.
  • They can be hard to notice, but a dull pain often develops over time.
  • Feelings of pain from light to moderate pressure can indicate a hairline fracture.
  • Pain may be reduced using common painkillers, such as paracetamol.
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Continuous strain on a bone may cause hairline fractures.

Bones are rigid in maintaining their structure but have a degree of elasticity that allows them to react to specific movements.

This means that bones can bend slightly to absorb some of the impacts that activities such as running, jumping or walking have on the bone itself or its joint socket.

However, when strain is continuously placed upon a bone, over time, microscopic cracks, known as hairline or stress fractures, can develop.

For example, engaging in long-distance running will expose bones in the lower leg, ankle, and foot to a persistent level of strain that increases over time. Eventually, this stress can cause a hairline fracture to develop.

High impact sports entail the most significant risk of hairline fractures, including:

  • basketball
  • tennis
  • ballet
  • football or rugby
  • track and field sports
  • soccer
  • hockey

Hairline fractures can also develop as a result of sudden or disproportionate changes to the intensity, duration, frequency, or type of physical activity. It is important to remember that these injuries can occur regardless of physical fitness.

Certain factors are associated with an elevated risk of developing hairline fractures, these include:

  • Gender: Hairline fractures are more common in women, particularly those with irregular menstrual cycles.
  • Anatomical abnormalities: Some abnormalities can intensify the strain on particular bones, such as having flat feet or high arches. This can also be exasperated by low quality or worn out footwear.
  • Bone problems: Conditions that weaken bones, such as osteoporosis
  • Previous hairline fractures: A hairline fracture causes the bone to be more susceptible to fractures reoccurring
  • Diet imbalances: Weakened bones can develop from diets that lack nutrients essential to bone health, such as calcium or vitamin D, increasing the risk of hairline fractures occurring.

Symptoms are different from those of a more severe fracture or break when a person often feels a sharp pain immediately.

The pain from a hairline fracture will intensify when the person engages in activities that put a strain on the injured bone. This can inhibit a person’s mobility, which means they will be restricted as to how much weight they can put on the affected area.

Other symptoms may include:

  • swelling
  • bruising
  • tenderness
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Confirmation of a hairline fracture diagnosis may come from an X-ray.

A doctor will do a physical examination first, where they will assess the person’s reaction to pressure on the affected area.

A doctor may confirm the diagnosis using medical imaging techniques including:

  • magnetic resonance imaging (MRI)
  • X-ray
  • nuclear bone scan

Hairline fractures are easily dealt with, but medical attention should be sought immediately to prevent the injury from worsening.

Ignoring a hairline fracture can lead to a more serious fracture or break occurring, which is more difficult to treat.

If not treated or ignored, the hairline may not heal, resulting in a non-union fracture.

The majority of hairline fractures will heal by themselves if the person refrains from activities that put a strain on the affected area.

For the first 24 to 48 hours, a person can help the healing process by elevating the affected area and applying ice where possible. As the swelling decreases and the pain subsides over the first 2 weeks, it is helpful to reintroduce weight-bearing activities gradually.

Staying active helps to stimulate the recovery process, so non-weight bearing activities, such as swimming or cycling, are also encouraged. However, it is essential to avoid high-impact sports or activities that can worsen the injury during the recovery period.

A complete recovery will typically take between 6 to 8 weeks, after which full mobility should be restored.

In some cases, a doctor may recommend protective footwear, a splint, or the use of crutches to minimise strain placed on the fractured bone during movement. In rare cases, a hairline fracture can be severe enough to warrant surgery if it does not heal on its own.

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Wearing insoles may help to reduce the risk of a hairline fracture.

Sometimes, hairline fractures can be difficult to prevent. For example, in those who engage in high impact sports or who have certain conditions, such as osteoporosis.

The risk of a hairline fracture can be broadly reduced by:

  • using high-quality exercise equipment
  • supporting anatomical abnormalities by wearing insoles, for example
  • ensuring changes to the duration, frequency, or intensity of activity are gradual, rather than sudden
  • getting sufficient rest between bouts of exercise
  • eating a healthful, balanced diet, which includes an appropriate amount of calcium and vitamin D
  • not ignoring pains associated with exercise, and seeking medical advice for ongoing discomfort