Evaluation of the Mechanical Strength Properties of a Bioresorbable Osteosynthesis System Bent in a Staircase Pattern

Comparison of PLLA and Titanium Osteosynthesis Systems

Abstract

The aim of this study was to evaluate the mechanical strength properties of a poly-L-lactide (PLLA) bioresorbable osteosynthesis system (Neofix^®) that was bent in a staircase pattern and to compare the mechanical strength of this system with the mechanical strengths of conventional titanium osteosynthesis systems (Modus^® 1.5 and Modus^® 2.0) that were bent in the same way.
A straight 4-hole plate of Neofix^® was bent in a staircase pattern with step height of 5mm using a heated bender and fixed to artificial bones with 8-mmlong screws. Straight 4-hole titanium plates were bent in the same pattern and fixed to artificial bones with 8-mmlong screws. Plate thicknesses of Modus^® 1.5 and Modus^® 2.0 were 0.6mm and 1.0mm, respectively. Artificial bones were mounted in a mechanical testing machine (Autograph, Shimadzu Corporation) and forces were applied at a rate of 2mm/min to determine tensile strengths, bending strengths and shear strengths. Eachtest was repeated three times, and critical forces and patterns of hardware failure were recorded.
Mean tensile strength of Neofix^® was 19.1±2.0 kgf, which was about half the value of Modus^® 1.5 (38.2±0.6 kgf). Mean bending strength of Neofix^®, which was bent more than 45 degrees, was 1.56±0.08kgf, which was slightly higher than that (1.39±0.11kgf) of Modus^® 1.5 and 43% of that (3.63±0.24kgf) of Modus^® 2.0. Mean shear strength of Neofix^® was 19.9±0.8kgf, which was 38% of that (52.8±1.5kgf) of Modus^® 1.5 and 14% of that (142.0±3.8kgf) of Modus^® 2.0.
Neofix^® bent in a staircase pattern showed lower tensile strength and lower shear strength than those of the two types of titanium plates bent in the same way, although the bending strength of Neofix^® was similar to that of the titanium plates.