Bone stress injuries in runners

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

Bone stress injuries (B.S.I.’s) are a painful and debilitating problem that affects runners and athletes. They usually occur as a result of increased training loads which often coincides with preparing for a competition or a race. Depending on the severity of the B.S.I., the injury may be season ending, or even career ending. The following article will discuss how B.S.I.’s 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 B.S.I.’s, symptoms are usually mild, 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 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 B.S.I.’s 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

B.S.I.’s 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.

5 Risk factors to look out for:

Training load

By their nature, B.S.I.’s require 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. Those that are new to running need to be careful if mirroring the training of more experienced runners.

Running technique

Running technique can play a part in the development and likely location of B.S.I.’s. Distance runners that land on their heel are more likely to develop BSI’s in the tibia. In contrast, sprinters, and runners that land on their forefoot are more likely to develop B.S.I.’s in their metatarsals.

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

Footwear

Shoes can play a role in the development of B.S.I.’s. It was found that running in old or worn out shoes increases risk of B.S.I.’s^[8]. General footwear industry advice is 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 (thick cushioned shoes such at 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⁾. Use of foot orthotics were found to help reduce the risk of developing B.S.I’s in military recruits^[9].

Low energy availability

Tracking the amount of energy you consume compared to your daily energy expenditure can help determine if your body is in 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 impair 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.

Vitamin D and calcium deficiency

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

Conclusion

Bone Stress Injuries are a painful running injury that is best avoided. It is important to be aware of the signs and symptoms of B.S.I.’s – particularly if you are new to running, have increased your training, 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.

Call (07) 3367 3088

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