Stress and strain of the radial shaft with marginal notch and compensating elements explored with computer modelling

Introduction The incidence of pathological fracture of the radius at the site of a marginal defect following graft harvesting reaches 31 %. A finite element computer simulation model allows for non-invasive determination and prediction of the stress and strain (SS) of the bone, the strength and susceptibility to fracture under various loads and strengthening methods.
The objective was to present the results of the finite element analysis on the influence of various marginal notch shapes, bone curvature and methods for increasing the strength on the SS of the radial shaft.
Material and methods Based on anatomical preparations of the human radius, solid-state linear-elastic modeling of the entire cortical diaphysis of the radius was performed including the shaft with rectangular and  triangular marginal notches, curvature in two planes using different reinforcing plates and fixation methods under non-destructive tensile, compressive, torsional and bending loads. The longitudinal stability of the bone was determined. ANSYS and NX Siemens software packages were used in the study.
Results A triangular cutout reduced bone stress by 21.4 % in tension and by 51.5 % in torsion as compared to a rectangular cutout increasing the longitudinal stability margin by 1.18 times. Bi-planar bone curvature increased stress and reduced the tensile load-bearing capacity by 2.89 times. A 2 mm thick semi-tubular plate, compared to a flat narrow plate of similar thickness and 10 mm width reduced the level of maximum stresses in the bone model by 1.2–1.5 times in tension and by 3.5–3.9 times in torsion for different cutouts. Measurements of longitudinal stability for a semitubular plate increased critical stresses by 1.3–1.5 times for different osteotomies as compared to a bone without a cutout and plate.
Discussion With all the loads, the strength conditions of the bone model with a cutout were provided when fixed with a plate at least 2 mm thick on four 2.0 mm bicortical screws inserted two distally and two proximally to the cutout.
Conclusion The findings demonstrated practical use of bone plates reducing SS of the radius with any cutout.

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