A variety of factors both intrinsic and extrinsic often combine, resulting in the development of a stress fracture. Intrinsic risk factors Intrinsic risk factors are related to an individual’s history, morphology or metabolism. Whilst not always easy (and in some cases impossible) to modify these risk factors, an appreciation of them will highlight ‘at risk’ individuals, marking them as priorities for holistic management.
The key intrinsic risk factors are: Gender Females appear to be at greater risk of bone injury than males for a number of reasons. Their more slender bones, gait differences, and unfavourable biomechanical conditions during running caused by a wide pelvis, coxa vara and genu valgum and smaller femoral neck have been offered as possible explanations. 2 Delayed age of menarche and reduced calf girth have been found to be the best independent predictors of stress fractures in women.
6 Also, an association between stress fractures and the female athlete triad (eating disorder, dysmenorrhea and low bone mineral density), particularly in female distance runners, has been reported. 10 The female athlete triad is discussed in greater detail in chapter 32 . Vitamin D Deficiency/UV index Vitamin D plays an important role in bone health via calcium and phosphorous homeostasis, and its deficiency can lead to increased risk of bone injury.
Athletes at risk of vitamin D deficiency include those who train indoors or in early morning and late afternoon, have dark skin pigmentation , wear clothing that covers most or all of their body, regularly use sunscreen or consciously avoid the sun, are missing limbs, have gastrointestinal malabsorption (e.g. Coeliac disease or fat malabsorption) or have a family history of bone injury, disorders or vitamin D deficiency.
4 The principal source of vitamin D comes from exposure to ultraviolet B (UVB) radiation from sunlight. 4 Small amounts of vitamin D can be found in foods but generally will still result in low vitamin D intake. Therefore it is reasonable to advocate dietary supplementation in athletes with low levels found on testing.