Mechanical properties of the human metatarsal bones

Despite the incidence of metatarsal fractures and the associated risk of signi ̄cant disability, little is known about the biomechanical properties (strength and sti®ness) of metatarsal bones. In most cases a single metatarsal bone ( ̄rst, second and ̄fth) has been investigated. An extensive investigation of the biomechanical properties of the metatarsal bones is essential in the understanding and prevention of metatarsal injuries. Entire sets of metatarsal bones from four feet were tested. The ̄rst foot was used to ̄ne-tune the testing set-ups. To measure the sti®ness, each metatarsal bone was subjected to non-destructive four-point-bending in the sagittal and transverse planes, axial compression and torsion. Strain was measured at two locations. To measure the strength, each metatarsal bone was tested to failure in torsion. Signi ̄cant di®er- ences ðp < 0:0001Þ existed among the sti®ness of the ̄ve metatarsal bones: (i) in torsion the ̄rst metatarsal bone was 2␣3 times sti®er than the others; (ii) in four-point-bending and axial compression this di®erence was less pronounced than in torsion; (iii) di®erences were smaller among the other metatarsal bones; (iv) the second metatarsal bone was less sti® than the third and fourth in bending. The second, third and fourth metatarsal bones were sti®er in the sagittal than in the transverse plane ðp < 0:0001Þ. Conversely, there was no signi ̄cant di®erence between the two planes of bending for the ̄rst and ̄fth bones. During destructive testing, all metatarsal bones exhibited a linear elastic behavior and brittle failure. The torsional strength at failure ranged between 1.9 Nm and 6.9 Nm. The ̄rst metatarsal bone was stronger than all the others. Sti®ness in di®erent loading conditions and failure were measured and compared for all metatarsal bones. These data corroborate previous biomechanical studies concerning the role and load sharing of the di®erent metatarsal bones.