Bone Stress Injuries in Runners Part 1

The Bone Stress Continuum

Runners are particularly susceptible to stress fractures due to the repetitive and high-impact nature of their sport. Stress fractures occur when bones are subjected to continuous, excessive force that outpaces the bone's ability to heal and adapt. The continuum of bone stress injuries in runners represents the progression of damage that occurs due to repetitive loading and overuse. This continuum includes three stages: bone stress, stress reaction, and stress fracture. Each stage involves increasing severity and potential risk to bone health. 

1. Bone Stress (Initial Stage)

At the earliest stage of bone stress injury, the bone is subjected to repetitive loading but has not yet undergone significant damage. During this phase, bone remodelling is occurring at a normal rate, as the bone experiences micro-damage from activities like running.

• Characteristics: The bone's ability to repair and adapt to stress is still intact. No clinical symptoms such as pain or swelling typically occur at this stage.

• Biomechanics: In runners, this stage is marked by subclinical changes in the bone's microstructure, where bone turnover (resorption and formation) occurs in response to repetitive impact forces. The bone is stressed but does not yet exhibit any visible damage.

• Prevention: Maintaining adequate rest, gradual increases in training load, and good biomechanics are important to prevent further progression into a stress reaction or stress fracture.

2. Stress Reaction (Intermediate Stage)

When bone stress continues and exceeds the bone's ability to repair, a stress reaction occurs. At this stage, the bone begins to show signs of microdamage or irritation that may be seen on imaging (like MRI scans). The bone’s microstructure starts to show changes that indicate a breakdown, but the damage is still limited.

• Characteristics: Athletes may begin to experience pain, typically in the form of dull, localized discomfort that worsens with activity and improves with rest. This pain may not be visible immediately but is noticeable when the bone is loaded. In some cases, this stage can be asymptomatic until imaging detects the changes.

• Biomechanics: At this stage, the bone may show areas of increased bone turnover or "periosteal reaction" (an early sign of bone healing). However, the bone has not yet developed a full fracture.

• Treatment: Rest, modified training, and targeted rehabilitation can help reverse the changes seen in this stage. Managing factors like improper footwear, running technique, and nutritional deficiencies is crucial at this point.

3. Stress Fracture (Advanced Stage)

If bone stress continues unchecked, the bone progresses to the most severe stage, a stress fracture. This is a crack or break in the bone, typically resulting from prolonged overuse. Stress fractures occur when the cumulative effect of repeated stress exceeds the bone's ability to heal.

An MRI showing a fracture line in the tibia

• Characteristics: Stress fractures present as acute pain that is localized to the site of the fracture. The pain persists even during rest and may be associated with swelling, bruising, and tenderness to touch. Stress fractures can often be diagnosed through imaging, such as X-rays, bone scans, or MRI, depending on the location and severity.

• Biomechanics: By this stage, the bone has a visible fracture line or crack, which can range from small micro-fractures to more severe breaks that require medical intervention. In runners, stress fractures are most commonly seen in the tibia, metatarsals, femoral neck, and navicular bone.

• Treatment: Treatment for a stress fracture typically involves immobilization (e.g., using a walking boot or crutches), rest from running, and in some cases, surgery, depending on the location and severity. Recovery can take weeks to months, and during this period, cross-training (low-impact activities) may be suggested to maintain fitness.

Summary of the Continuum:

1. Bone Stress: Microdamage occurs but bone remodeling keeps pace; no symptoms.

2. Stress Reaction: Bone shows microdamage, localized pain may occur, but no fracture yet.

3. Stress Fracture: A crack or break in the bone occurs, pain is persistent, and medical intervention is often required.

   The key to preventing progression from one stage to the next is early detection and appropriate management. Runners must listen to their bodies, modify training loads as needed, and ensure proper nutrition and recovery to prevent the onset of more serious injuries. Early intervention can prevent a simple bone stress issue from developing into a full-blown stress fracture.

Find out more about stress fractures in runners in Part 2: Prevalence, Risk Factors, Prevention and Management