Medial Tibial Stress Syndrome (Shin Splints) – Risk Factors
There are several risk factors are associated with the development of medial tibial stress syndrome, including activity type and intensity, gender, BMI, previous running injury, bone morphology, and foot biomechanics.
There are several risk factors associated with the development of medial tibial stress syndrome, commonly known as «shin splints», including activity type and intensity, gender, BMI, previous running injury, bone morphology, and foot biomechanics.
Training type, volume and intensity
Sudden increases in training volume or intensity and starting a new activity increases the risk of developing MTSS (1). Similar to tibial stress fractures, most cases of MTSS develops during the first 3-4 weeks of increased loading, including the first 3-4 weeks of military training (2).
This is due to the nature of the bone remodeling process, in which bone remineralization lags behind bone demineralization causing the tibia to be at its weakest 3-4 weeks after being subjected to increased loads and to be relatively weaker for the first 8 weeks (2,3).
Women are at a significantly greater risk of developing MTSS than men. Systematic reviews of research show that female athletes are at 1.7-2.4 times greater risk of developing MTSS than male athletes (4,5), and similar risk has been found among female military recruits (2). The reasons for this are; however, several factors can be highlighted:
The Female Athlete Triad refers to the interrelationship between low energy availability (with or without disordered eating), menstrual dysfunction and low bone mineral density in physically active females.
Relative energy deficiency in sports (RED-S) reduces female estrogen levels, which is detrimental to bone health, and are one of the main reasons for why women are at an increased risk of developing bone stress injuries including MTSS and stress fractures, than men.
Read more: The Female Athlete Triad
Women have, on average, narrower tibias and less cortical cross-sectional area (CSA) than men (6). This makes the tibia less able to withstand the bending forces it is subjected to during walking, running and jumping. Compressive strength is proportional to CSA, while bending and torsional strength are exponential to cross-sectional moment of inertia (CSMI). This means that a small difference in either tibial CSA or diameter significantly affects its mechanical resistance to the bending loads it is subjected to (7).
The incidence of MTSS seems to be higher in women who train alongside men and toward the same end result (2). The reason for this is unclear.
A number of studies have investigated gender-related differences in running kinematics, and have fond several distinct differences (2). However, how this relates to the development of MTSS is uncertain.
History of MTSS and other running injuries
A history of MTSS seems to be one of the most robust risk factors for developing MTSS. A recent systematic review found that athletes with a history of MTSS had a 3.7 times greater risk of developing MTSS (4). Two prospective studies have since demonstrated increased risks of 5.0 (8) and 18.3 (9) in individuals with a history of MTSS.
It is intuitive to think that the risk of developing MTSS is likely to be higher than what has been found in these studies, since they do not take into account men and women who have stopped training due to MTSS.
Weight and BMI
Higher body weight and higher BMI are both significant risk factors for developing MTSS (4,5,8). It is believed that this is due to an increased load on the tibia during activity.
Several biomechanical factors have been associated with increased risk of developing MTSS. This includes a clear correlation between a greater degree of foot pronation and the prospective risk of developing MTSS.
In particular, a navicular drop of more than 10 mm on the «navicular drop test» – which is the degree of vertical change in position of the navicular bone between a non-weight-bearing and a weight-bearing position, has repeatedly been shown to increase the risk of developing MTSS (4,5,10).
Several other biomechanical factors have also been linked to increased risk of MTSS, including the angle between the lower leg and calcaneus at heel strike, the standing foot angle (angle between the tibia, navicular bone and first metatarsal bone), early heel lift during running, and increased passive hip external rotation with a the hip flexed (4).