THE CORRELATION OF TIBIAL GEOMETRIC DIMENSIONS WITH TIBIAL STRESS REACTIONS

Abstract

Tibial bone stress reactions are a commonly occurring source of exertional lower limb pain amongst the active population, in particular runners and the military. MR imaging has been shown to demonstrate the continuum of bone stress reactions from marrow oedema, periosteal oedema, to stress fracture. Why these reactions occur predominantly along the postero-medial border and mid to distal tibia remain unclear. The purpose of this investigation was to study tibial cross-sectional geometry at 5 sites along the tibial diaphysis and at the sites of stress reaction. Results were analysed to determine any links with-in subjects between legs, site of stress reaction, geometry and then between males and females. Subjects for this prospective observational study were all active with pain of less than 3 months duration, 14 were male (1control) and 11 female (4 controls). Axial T1 weighted images where used to take cortical measurements of antero-posterior (AP), medio-lateral (ML) widths and the anterior (ANT), postero-medial (PM) and posterolateral (PL) corners. FSE-IR images were used to locate bone stress reactions and their geometry was measured. Observations of tibial shape and that of the site of stress reaction was made. RESULTS: The AP and ML diameters are narrowest in the mid to mid-distal tibia (P = 0.0001). Here the tibial axial shape is at its most triangular and the PM and PL corner widths largest. This same mid to mid-distal area of the tibia, where the area moment of inertia is increased, was the site for 73% of stress reactions. The stress reactions involved marrow oedema and periosteal fluid along the medial border extending to the PM corner. Endosteal oedema and signs of endosteal buttressing at the PM corner were also demonstrated. SUMMARY: Cross-sectional geometry and shape influences the site of stress reaction. In response to stress, the tibia compensates by increasing the width of the PM and PL corners through buttressing. A further longitudinal study is required to determine whether measureable tibial geometry is predicted of bone stress injury.