Bone stress injuries in runners

5 Risk factors leading to Bone stress injuries in runners.

Doug James, Physiotherapist, Podiatrist, Marathoner.

A bone stress injury (BSI) is a painful and debilitating problem that affects runners and athletes. It usually occurs as a result of surges in training loads which often coincides with preparing for a competition or a race. Additionally, we’re finding athletes who had to take time off due to Covid-19 quarantine are at greater risk due to a marked reduction in loading during their isolation, and then an overcompensation when returning to running. Depending on the severity of the BSI, the injury may be season ending, or even career ending. The following article will discuss how BSIs develop and the risk factors associated with them.

How they develop

Bone stress injuries occur when the capacity of a bone is unable to deal with the amount of stress it is subjected to ^[5]. In runners, stress is most commonly generated from running training loads, but any and all physical activity can contribute. If the amount of stress and load is not adequately managed, this can lead to painful fractures developing within the bone. With impact exercises such as running, the bones in our feet, legs, hips and spine undergo stress from compression (jarring from impact when landing), and tension (from muscles absorbing impact, stabilising the body, and creating propulsion). When a healthy bone undergoes sufficient stress that is still within a tolerable level, a process is triggered within the bone to make it stronger. This process involves the removal of part of the bone’s support structure that is then replaced with remodelled and stronger bone.

Symptoms to watch for

In early-stage BSI, symptoms are usually mild – perhaps felt as an ache or light bruising sensation, and might only be felt at the start of physical activity, and/or after the athlete has cooled down. It is thought that at this stage of the injury there is usually only mild damage and a small amount of swelling around the exterior lining of the bone may be evident on MRI. At this stage, the bone’s capacity for loading and stress may be slightly reduced, so caution is needed with any higher risk activities (high-intensity sessions e.g. hills or intervals, or very long runs). If the training load (or other physical activity) continues to stress the bone in its weakened state, swelling within the marrow of the bone begins to develop. At this stage, the injury becomes more uncomfortable during running, but symptoms may still ‘warm up’ as the session continues.

If stress to the bone isn’t reduced sufficiently, the cortical or hard part of the bone begins to degrade and fractures can form within it. By this stage, the injury would be very uncomfortable to run on and is often accompanied by an aching sensation even at rest.

Common BSI sites

80-95% of all stress fractures occur in the lower limbs^[1]. The majority of these lower limb BSI are found in the tibia (shin bone) 33^[2]-55%^[3], metatarsals (long toe bones in the forefoot) 20%^[2], and the remainder in the hindfoot and femur (thigh bone).

Who is at risk

Bone Stress Injuries can account for 50% of injuries sustained by runners and military recruits ^[3]. Female runners are twice as likely as their male counterparts to develop a bone stress injury ^[3]. Aside from being female, there are a number of factors that have been identified as risks for developing a bone stress injury.

Risk factor: Training load

By their nature, a BSI requires stress to develop ^[3]. A rapid increase in training load, particularly in poorly conditioned athletes or those new to running will likely bring about sufficient stress to develop a bone injury. A long history of physical activity is protective ^[6] as this tends to improve bone density over time. Total training volume needs to be monitored over the course of weeks and months to ensure adequate recovery occurs in order for bones to strengthen. For runners that have taken more than 2 weeks off training due to illness and/or quarantine, a gradual return to pre-break levels is advised. Those that are new to running need to be careful if mirroring the training of more experienced runners.

Risk factor: Running technique

Running technique can play a part in the development and likely location of a BSI. Distance runners who land on their heels are more likely to develop a BSI in the tibia. In contrast, sprinters, and runners who land on their forefoot are more likely to develop a metatarsal (toe bones) BSI.

Runners that produce high ground reaction force (impact)^[2,3,4] and had increased rearfoot eversion [4] (rolling in) were more likely to suffer tibial stress fractures. Gait retraining can be beneficial in cases of recurrent BSI but needs to be done carefully due to the risk of injury developing from an unaccustomed running style ^[6].

Risk factor: Footwear

Shoes can play a role in the development of a BSI. It was found that running in old or worn-out shoes increases the risk of BSI^[8]. General footwear industry advice is to replace shoes within 600km of running, but keep in mind that shoes will also degrade over time irrespective of use.

A recent study has proposed that running in maximalist (thickly cushioned shoes such as Hoka^TM) may reduce the risk of tibial stress fractures in female (but not male) runners. By comparison, minimalist (thinly cushioned) shoes were linked to metatarsal stress fractures⁽¹⁰⁾. The use of foot orthotics was found to help reduce the risk of developing BSI in military recruits^[9].

Risk factor: Low energy availability

Tracking the amount of energy you consume compared to your daily energy expenditure can help determine if your body is in an energy deficit. This is where the amount of energy consumed is less than the amount expended. Low energy availability reduces the ability of bone to resist load and/or impairs its ability to repair micro-damage ^[6]. Sustained periods of energy deficit can have negative effects on the body and will compromise performance and recovery. In females, this can lead to disorders in their menstruation cycle ^[6,7].  

Assessing your attitude towards food can help to identify eating behaviours that may result in low energy availability. The Eating Attitudes Test (EAT-26) questionnaire is a simple screening tool that can help flag problematic eating behaviours ^[7]. Athletes that score 20 or higher on this test would benefit from professional guidance. The questionnaire can be found easily on google.

Risk factors: Vitamin D and calcium deficiency

Low vitamin D ^[1] and calcium levels were common findings in athletes that develop BSI [4,5,6]. Ensuring adequate levels via dietary intake or supplementation is an important factor, and a fairly easily achieved goal to help reduce BSI risk. 

• 600 IU of vitamin D daily is suggested for ages 9 to 70 years
• 800 IU of vitamin D daily is recommended for > 71 years or older
• 1300 mg of calcium daily for ages between 9 to 18 years^[11].

Conclusion

Bone Stress Injuries are painful injuries that are best avoided. It is important to be aware of the signs and symptoms of a BSI – particularly if you are new to running, have increased your training (especially after taking more than two weeks off running), and/or are at risk of any of the factors listed above. Developing a considered plan for your training load and recovery is crucial for avoiding this potentially season-ending injury.  If you suspect you have a bone stress injury or have had one in the past, contact the intraining running injury clinic for an assessment and to develop a plan on how best to avoid them in future.

By Doug James – Physiotherapist and Podiatrist at intraining running injury clinic.

References:

1. Alexandra Abbott, Mackenzie L. Bird, Emily Wild, Symone M. Brown, Greg Stewart & Mary K. Mulcahey (2020) Part I: epidemiology and risk factors for stress fractures in female athletes, The Physician and Sportsmedicine, 48:1, 17-24, DOI: 10.1080/00913847.2019.1632158
2. Tavares, J., Jost, T., Drewelow, G., & Rylander, J. (2020). Do maximalist shoes mitigate risk factors for tibial stress fractures better than stability or flexible (marketed as minimalist) shoes? Footwear Science, 12(1), 63–74. https://doi.org/10.1080/19424280.2019.1708977
3. Milner, C. E., Ferber, R. D., Pollard, C. S., Hamill, J., & Davis, I. (2006). Biomechanical Factors Associated with Tibial Stress Fracture in Female Runners. Medicine & Science in Sports & Exercise, 38(2), 323–328. https://doi.org/10.1249/01.mss.0000183477.75808.92
4. Song SH, Koo JH.   Bone Stress Injuries in Runners: a Review for Raising Interest in Stress Fractures in Korea.   J Korean Med Sci. 2020 Mar;35(8):e38. https://doi.org/10.3346/jkms.2020.35.e38
5. Miller, T. L., Kaeding, C. C., & Rodeo, S. A. (2020). Emerging Options for Biologic Enhancement of Stress Fracture Healing in Athletes. Journal of the American Academy of Orthopaedic Surgeons, 28(1), 1–9. https://doi.org/10.5435/JAAOS-D-19-00112
6. Warden A, Davis I, Fredericson M. Management and prevention of bone stress injuries in long-distance runners. J Orthop Sports Phys Ther. 2014;44(10):749e765. https://doi.org//10.2519/ jospt.2014.5334.
7.  Sanderson, S., Raab, S., & Moch, P. (2012). BMI and EAT-26, Predictors for Low BMD? SAGE Open, 2(1), 1–5. https://doi.org/10.1177/2158244012441604
8. Gardner LI, Jr., Dziados JE, , Jones BH, , et al.. Prevention of lower extremity stress fractures: a controlled trial of a shock absorbent insole. Am J Public Health. 1988; 78: 1563– 1567.
9. Snyder RA, , DeAngelis JP, , Koester MC, , Spindler KP, , Dunn WR. and Does shoe insole modification prevent stress fractures? A systematic review. HSS J. 2009; 5: 92– 98. http://dx.doi.org/10.1007/s11420-009-9114-y
10.   Salzler, M. J., Bluman, E. M., Noonan, S., Chiodo, C. P., & de Asla, R. J. (2012). Injuries Observed in Minimalist Runners. Foot & Ankle International, 33(4), 262–266. https://doi.org/10.3113/FAI.2012.0262
11. Institute of Medicine (US) Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. Dietary reference intakes. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. 1997.