Ground Reaction Forces and Bone Parameters in Females With Tibial Stress Fracture

Kim Bennell; Kay Crossley; Jyotsna Jayarajan; Elizabeth Walton; Stuart Warden; Z. Stephen Kiss; Tim Wrigley

Disclosures

Med Sci Sports Exerc. 2004;36(3) 

In This Article

Abstract and Introduction

Purpose: Tibial stress fracture is a common overuse running injury that results from the interplay of repetitive mechanical loading and bone strength. This research project aimed to determine whether female runners with a history of tibial stress fracture (TSF) differ in ground reaction force (GRF) parameters during running, regional bone density, and tibial bone geometry from those who have never sustained a stress fracture (NSF).
Methods: Thirty-six female running athletes (13 TSF; 23 NSF) ranging in age from 18 to 44 yr were recruited for this cross-sectional study. The groups were well matched for demographic, training, and menstrual parameters. A force platform measured selected GRF parameters (peak and time to peak for vertical impact and active forces, and horizontal braking and propulsive forces) during overground running at 4.0 m·s-1. Lumbar spine, proximal femur, and distal tibial bone mineral density were assessed by dual energy x-ray absorptiometry. Tibial bone geometry (cross-sectional dimensions and areas, and second moments of area) was calculated from a computerized tomography scan at the junction of the middle and distal thirds.
Results: There were no significant differences between the groups for any of the GRF, bone density, or tibial bone geometric parameters (P > 0.05). Both TSF and NSF subjects had bone density levels that were average or above average compared with a young adult reference range. Factor analysis followed by discriminant function analysis did not find any combinations of variables that differentiated between TSF and NSF groups.
Conclusion: These findings do not support a role for GRF, bone density, or tibial bone geometry in the development of tibial stress fractures, suggesting that other risk factors were more important in this cohort of female runners.

Running athletes commonly sustain tibial stress fractures causing considerable interference to training and competition. These skeletal overuse injuries are the result of the failure of bone to successfully adapt to the repetitive loads encountered during running. The number of loading cycles required to initiate stress fracture development is related to the magnitude and rate of loading applied, and to the ability of bone to resist loading (bone strength).[7]

During running, a ground reaction force (GRF) is generated with each foot strike that is equivalent to 2-4 times body weight in the vertical direction.[28] Although this is partly attenuated by joint structures and soft tissues, considerable force is transmitted to the bones of the lower limb. This results in bone deformation (strain) and internal forces acting upon units of area of bone (stress). Bone strain may become excessive as a result of increases in load magnitude, the rate of loading, or the number of loading cycles. In humans, direct measurement of bone strain through the surgical attachment of a bone strain gauge has both ethical and methodological constraints. GRF provides an indirect measure of both the magnitude and rate of external load on the lower extremity during weight-bearing activity.[1]

It is unclear whether differences in GRF are evident in athletes with and without stress fractures. In two cross-sectional studies, Grimston and colleagues[16,17] found significant differences in GRF between those with and without a history of stress fracture at various sites. However, in the initial study, the forces were higher in the stress fracture group whereas in the subsequent study they were lower. Conversely, we were unable to find a link between GRF and tibial stress fractures in male runners.[10] These conflicting results highlight the need for further research investigating the role of GRF in stress fracture-prone individuals.

The ability of bone to resist deformation during running depends on a number of factors including bone mass and bone geometry. Theoretically, low bone mineral density (BMD) could contribute to the development of a stress fracture by decreasing the resistance of bone to repeated loading. However, comparisons of regional BMD in individuals with and without stress fracture have been inconclusive.[7] The discrepancy between results may reflect differences in populations, gender, measurement techniques, and bone regions.

The relationship between bone geometry, bone strength, and stress fractures has been examined in male[2,14,22,25] and female[3,15] military recruits, and in male runners.[10] More stress fractures were sustained by male recruits with a smaller medio-lateral tibial width than by those with a wider tibia as measured using standard radiographs.[13,14,22,25] These findings were confirmed in another prospective study of male recruits where dual energy x-ray absorptiometry (DXA) was used to derive tibial structural geometry[2] and in our cross-sectional study of male runners using computerized tomography (CT).[10] Results in female populations are less consistent and confined to military recruits.[3,15] Thus, although there is some evidence that geometric differences consistent with a weaker bone may increase the risk of stress fracture in individuals undertaking intense physical activity, this has not been verified in female athletic populations.

As no study has examined the role of external loading during running together with bone strength indices in female runners who have previously sustained a stress fracture, we aimed to investigate GRF, bone density, and tibial bone geometry parameters in female runners with and without a history of tibial stress fracture. In a cross-sectional study design, we hypothesized that female runners with a history of tibial stress fracture would have higher GRF, lower regional bone density, and smaller tibial bone geometric parameters than those without a history of stress fracture.

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