Mechanical properties of the human metatarsal bones

Despite the incidence of metatarsal fractures and the associated risk of significant disability, little is known about the biomechanical properties (strength and stiffness) of metatarsal bones. In most cases a single metatarsal bone (first, second and fifth) 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 first foot was used to fine-tune the testing set-ups. To measure the stiffness, 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. Significant differences (p <0.0001) existed among the stiffness of the five metatarsal bones: (i) in torsion the first metatarsal bone was 23 times stiffer than the others; (ii) in four-point-bending and axial compression this difference was less pronounced than in torsion; (iii) differences were smaller among the other metatarsal bones; (iv) the second metatarsal bone was less stiff than the third and fourth in bending. The second, third and fourth metatarsal bones were stiffer in the sagittal than in the transverse plane (p <0.0001). Conversely, there was no significant difference between the two planes of bending for the first and fifth 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 first metatarsal bone was stronger than all the others. Stiffness in different 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 different metatarsal bones.