Finite element study of tibial impact orientation and diaphyseal strain

Direct blow tibial shaft fractures are common in contact sports, yet how limb support state and impact orientation modulate cortical loading remains unclear. This study aimed to quantify the effects of boundary conditions representing different limb support states, combined with impact orientation, on mid-diaphyseal cortical stress during transverse impacts.

A cortical finite element model was constructed from a public statistical shape model dataset and validated against cadaveric bending stiffness and fracture thresholds. Three idealized boundary conditions represented different limb support states: fully supported (SCI), proximally supported (SCII), and minimally supported (SCIII). Each received 10 m/s impacts from a rigid impactor to anterior or medial mid-shaft surfaces; SCIII additionally included distal and proximal impacts. Peak maximum principal stress (S1), peak tensile strain, and a stress-based risk ratio were extracted from ten simulations.

The minimally supported limb experienced at least 28% higher peak stress than the proximally supported limb under identical mid-shaft impacts. Peak stresses of 214-267 MPa under SCIII exceeded quasi-static cortical tensile strength thresholds (150-200 MPa), while peak strains (1.27-1.59%) remained below the $\sim$ 2% failure strain. Stress-based risk ratios reached 1.11-1.39 for SCIII mid-shaft impacts. Time-aggregated stress contour maps confirmed distinct spatial stress signatures for each boundary condition.

Collision configuration and impact location are biomechanically important variables for injury mitigation. Mid-shaft-focused shin guard coverage with energy-absorbing materials merits prospective evaluation.