Conquering Medial Tibial Stress Syndrome
What Some Key Risk Factors Reveal About MTSS And TSF
Women are at least twice as likely to develop MTSS as men, particularly if they have a body mass index (BMI) of less than 21 kg/m2.5-7 However, female gender is only one of many factors for increased risk that researchers have proposed. Most of the studies that have looked at risk factors for tibial stress injuries have focused on TSF although MTSS can be linked to many of these as well. Typically, these studies have broken down these risk factors into extrinsic and intrinsic categories. Extrinsic factors include: training errors (with regard to frequency, duration and intensity); surface type and inclination; and shoe type and wear. Intrinsic factors include: endocrine factors (and their relationship to the female athlete triad of amenorrhea, disordered eating and osteoporosis); bone geometry and density; structural and biomechanical abnormalities; nutritional status; and previous running and injury history. Most of these risk factors have been well documented, particularly with regard to TSF. However, I would like to take a closer look at three specific risk factors that have an impact on MTSS. Indeed, some of these risk factors may help shed light on the relationship between MTSS and TSF. Decreased regional bone marrow density. Recent studies have shown that athletes with MTSS demonstrated lower bone marrow density in the affected region of their tibias in comparison to non-athlete and athletic controls.4 However, this finding was truly regional in that the athletes with MTSS and decreased regional bone marrow density in fact had higher than normal bone marrow density in other regions as one would expect in athletes. Additionally, the decreased regional bone marrow density increased following recovery. However, it is uncertain as to whether this is a cause or a result of MTSS. Interestingly, there was decreased bone marrow density in the unaffected leg among those with unilateral MTSS.4 This suggests the decreased regional bone marrow density preceded (and perhaps caused) the MTSS. In either case, there seems to be a clear association between MTSS and locally decreased tibial bone marrow density. Bone geometry. Multiple studies have demonstrated a relationship between smaller tibial cross-sectional areas and tibial stress injuries.8-11 Long bones with narrow diaphyseal widths will bend to a greater extent when loaded than those with wider diaphyses. This supports the tibial bending theory of tibial stress injuries. This theory suggests that chronic repetitive loads that induce tibial bending cause bone stress around the site where maximum bending occurs. This corresponds to the most common location for MTSS. This theory also provides support for the pathophysiologic link between MTSS and TSF. Biomechanical abnormalities and structural malalignments. Despite the common acceptance of biomechanical/ structural contributions to the development of tibial stress injuries and other exercise-induced leg conditions, there continues to be conflicting data in the current peer-reviewed literature in regard to identifying specific biomechanical risk factors. Researchers have paid much attention to biomechanical abnormalities, particularly excessive subtalar joint pronation (in both degree and velocity) and its relationship to tibial stress injuries. However, only two prospective studies have demonstrated a relationship between excessive subtalar joint pronation and MTSS.5,7 Other studies have been inconclusive or conflicting in this regard.