Bone stress injuries: RISK FACTORS (part 3)

Playing Surface

Playing surface has historically been considered a contributor to BSI risk, with participation on harder surfaces such as asphalt hypothesised to increase loading compared with participating on softer surfaces such as grass, rubber and sand. However, the interaction between playing surface and injury risk is complex. Athletes alter their leg stiffness when running on surfaces of differing compliance in order to maintain a constant vertical excursion of their centre of mass. Leg stiffness decreases when running on stiffer surfaces to normalise GRF magnitude to some extent; however GRF loading rates appear to be systematically increased when running on surfaces that are less compliant. Ultimately, what may be important with regards to BSI risk is whether there has been a recent change in running surface that an athlete has yet to become accustomed to. Changes may include increased participation on:

1) Less compliant surfaces, which may increase bone strain magnitudes and rate

2) Very compliant surfaces (e.g. sand), which may increase energy expenditure and influence muscle-related risk factors and kinematics

3) Downhill slopes, which may decrease shock attenuation and increase loading magnitude and rates

4) Altered terrain, which may alter kinematics to load less accustomed skeletal sites.

Shoes and Inserts

The role of shoes and inserts on bone loading and BSI risk is a topic of ongoing debate . Located at the foot-ground interface, shoes and inserts act as filters that theoretically attenuate ground impact forces. In addition, they have the potential to influence motion of the foot and ankle and the subsequent mechanics proximally in the kinetic chain. Shoes and inserts may influence bone loading and have an effect of BSI risk via these two mechanisms.

REFERENCES

Brukner, P., 2012. Brukner & Khan's clinical sports medicine. North Ryde: McGraw-Hill