BIOMECHANICAL STUDY OF STRESS IN THE 5TH METATARSAL

Objective. The stress throughout the fifth metatarsal was determined u nder various loading conditions, in order to better understand the cau ses of fractures to this bone. Design. A mathematical approach was tak en, in which the stresses were analysed using the methods of beam theo ry. Background. Finite element analysis has frequently been used to de termine the stress in bones. Beam theory provides an easier method for determining the force and moment resultant in any cross-section. The distribution of stress throughout the cross-section can then be found by solving certain partial differential equations defined on the cross -sections. Methods. Cross-sections of the bone were obtained by slicin g a mould, into which the bone was placed, at numerous intervals along its length. Analytic expressions describing each cross-section were o btained by fitting a Fourier series to a sequence of points along the boundary. Results. The maximum stress found in the fifth metatarsal re sulted from an oblique load, and had a magnitude less than would occur in a subject during normal walking. Conclusions. Since the magnitude of the stress is submaximal, this study lends theoretical support to t he clinical observation that the diaphyseal fracture is indeed a stres s fracture. Relevance Our analysis adds a biomechanical rationale to t he pathomechanics of diaphyseal stress fractures of the fifth metatars al. It suggests that inversion during repetitive activities may predis pose the foot to fractures at a predictable location. (C) Elsevier Sci ence Ltd.