Modification of midfoot bone stress with functional foot orthoses

Studies of foot orthoses suggest that they can improve foot pain and function, although the precise mode of action of foot orthoses is poorly understood. It is proposed that they may act through the modification of abnormal stresses or motions occurring within the foot. The central aim of
this thesis is to explore whether functional foot orthoses can systematically modify bone stress in the midfoot as measured on magnetic resonance imaging.
Bone marrow lesion patterns quantified on magnetic resonance imaging was proposed as a surrogate measure of bone stress in the foot. A reliable method of bone segmentation and BML volume measurement was developed and applied in this thesis. In the interventional study of this
thesis, the effect of functional foot orthoses on mechanical medial midfoot pain, foot impairment, patterns of bone marrow lesions and foot kinematics were investigated. Thirty seven participants with mechanical midfoot pain and medial midfoot bone marrow lesions participated in the study and were allocated to wear either functional foot orthoses (n=21) or a cushioning insole (n=16). The effect of the orthosis intervention on foot pain, impairment and volumes of magnetic resonance bone marrow lesions was compared in each group. In addition, the gait parameters and foot kinematics were assessed in a subset of 20 participants (functional foot orthoses n=10 and cushioning insole n=10). Foot pain and foot impairment outcomes improved more in the functional foot orthoses group than the control group wearing cushioning insoles. The
results suggest that the volumes of bone marrow lesions in the medial foot bones were reduced systematically in the functional foot orthoses group. In comparison, those wearing the cushioning insole showed no change greater
than measurement error. There was no evidence in the small subset of 7 participants, that foot kinematics were systematically altered when wearing either the cushioning insole or functional foot orthoses compared to in-shoe
only analyses. The results reported in this thesis suggest that the biomechanical mechanism of functional foot orthoses in treating foot pain could be the modification of internal forces rather than their systematically influencing
magnitudes of foot motion. This new data indicates that functional foot orthoses appear to have the potential to reduce foot pain and alter patterns of bone marrow lesions (a surrogate measure of bone stress) in the medial
midfoot bones and further work is now required to explore this formally in larger studies.