What are Bone Stress Injuries (BSI)?

BSI are overuse injuries commonly seen in runners or active individuals. In normal individuals, when we exercise our bones experience some level of microdamage which is then remodelled. This is a normal process.

When a BSI occurs, the bone remodelling cannot keep up with the level of microdamage and this can form a stress reaction to the bone. BSI can be scaled on a continuum from a stress reaction, stress fracture to complete fracture.

  • Stress reaction: inflammation of the periosteum and marrow oedema, no break of the cortex is seen on scan.
  • Stress fracture: a break in the outer cortex of the bone. The hairline stress fracture usually will not be detected on x-ray scan.
  • Complete fracture: a complete break through the bone, dividing it into two or more.

What causes a BSI?

A BSI does not just occur due to running too much, there are a range of risk factors that can contribute to this type of injury.

This may include:

  • Previous history of BSI: Studies have found that individuals who have had a previous BSI are five times more likely to develop another BSI. This may be due to not addressing previous risk factors.
  • No weight/strength training: A high running load does not improve bone strength. Strength training not only improves muscle strength, but also bone strength by improving bone mineral density. Not incorporating some sort of weight training will increase your risk of BSI.
  • Low BMI: Having low BMI means that you’re more likely to have low bone mass and reduced bone strength. Low BMI may mean that an individual is restricting what they are eating and not getting enough calories to support their activity level. This can lead to low energy availability and can increase risk of BSI.
  • High running volume: Too much load applied to the bone that is not accustomed to that load will increase your risk of BSI. Bones will usually adapt and will remodel over time to progressively higher training loads/volume; however, if this load is increased too quickly, the bone will not be able to withstand the increase and won’t be able to remodel, leading to BSI. In addition, reduced rest can increase risk as the bone has no time for the rebuilding phase to occur. Poor sleep quality can reduce bone health due to alterations in the balance between bone reabsorption and remodelling.
  • Diet –> Low energy availability: Energy availability (EA) is defined as the difference between energy intake and exercise energy expenditure. We require energy not only to exercise, but to also help with hormonal and metabolic processes outside of the demands of exercise. If you have a low EA, this results in altered neurohormonal pathways that may contribute to impaired bone quality and risk of BSI.
  • Menstrual cycle: People who usually menstruate and stop having regular menstrual cycles (amenorrhea) or experience less than 9 cycles a year (oligomenorrhea) have reduced bone mineral density (BMD) and reduced bone strength leading them to be at increased risk of BSI. This is usually due to the reduced hormone circulation and as well as having low energy availability that can coincide with one another. This is usually known as the female triad.
  • Biomechanics: Some movement patterns have the potential to alter the magnitude and/or rate of bone loading. They may also alter the direction in which a bone is loaded and the subsequent distribution of strain within the bone.

How can you prevent BSI?

Addressing some of the modifiable risk factors above (i.e. risk factors that you can change) can help reduce your risk of a BSI. This includes managing your diet, incorporating strength training, and making sure you have adequate rest and sleep.

  1. Diet: It is important that you have a well-balanced diet when exercising and especially when exercising at high volumes. This is to ensure that we have Energy Availability to not only fuel us during exercise, but for other hormonal and metabolic processes that occur day to day.
  2. Strength training: Incorporating strength training into your exercise regime not only helps build muscle strength, but it also helps increase bone strength (by increasing bone mineral density). Studies have shown that increasing your running load will not increase your bone health/strength, and therefore some sort of strength training should be included to help reduce risk of BSI.

Four simple lower limb exercises that you could include to help build strength and improve running performance are the following:

  • Weighted Squats
  • Deadlift
  • Weighted Lunges or Bulgarian split squat
  • Weighted Calf Raises
  1. Adequate rest and sleep: Ensuring that your body has time to rest and recover is very important in reducing your risk of injuries and BSI. You should aim to get 7-9 hours a night to allow your body to recover.

How do you treat BSI and can you return back to running/sport?

Treatment and timeframes for BSI depends on the location, the severity and whether the BSI is deemed low or high risk. Most BSI are low risk, and the following general principles apply for rehab.

Phase 1: Initial Management – reduce load and promote healing.

During this phase, it is important to modify activity and reduce load through the injured bone to allow healing. Depending on the location of the injury, this may include ensuring you don’t put weight through the area and/or wearing a special boot to immobilise the area. It is also important to identify and address any potential risk factors that have led to BSI. Your physiotherapist or other health professional helping you manage your injury can help you with this. Strength training of the opposite leg may continue and cross-training that limits weightbearing through the injured leg may be considered here to maintain physical conditioning.

Phase 2: Mid-stage rehab – load progression

The main goal for this phase is to gradually increase weightbearing through the injured leg and restore muscle function. Continuing strength exercises of adjacent muscles such as calves, hamstrings, quadriceps, and the hip will help prepare the individual for a return to run. A progressive resistance program can be implemented specific to the muscles attached to the affected bone to help with bone growth and build its capacity. Your physiotherapist can help tailor this program to your injury and the goals you have for returning to specific activities in phase 3. Cross-training can continue during this phase.

Phase 3: Return to running/sport

The final phase is returning to running and/or sport. It is important that certain criteria are ticked off before this phase is attempted, and this can usually be determined by a physiotherapist or sports doctor. A physiotherapist will implement a graduated return to running program tailored for you and your goals. Timeframes to return to running/sport vary between the location and type of BSI. It generally takes 6 weeks for bone healing to occur (i.e. phase 2), so it can take around 10-16 weeks to also move through phase 2 and return to sport/performance.

  • Written by Emma Draffin

    Emma is a Physiotherapist who specialises in the treatment of musculoskeletal and sporting injuries. She is particularly passionate about hip and knee injuries and takes great pride in working with clients throughout their entire rehabilitation journey. Emma places a strong emphasis on exercise prescription, complemented by other evidence-based treatment techniques to achieve the best outcomes for her clients.