Abstract
Osteoarthritis is a debilitating disease affecting over 1.7 million people in the UK annually. Total ankle replacements are an increasingly sought option for repairing a late stage arthritic ankle, but result in the removal of significant portions of bone regardless of tissue quality. Hence, the mapping of bone quality would allow the use of targeted treatments at earlier stages of the disease. This study aims to develop characterisation methodologies using porcine tissue to investigate the mechanical properties of subchondral bone in the ankle.
N=11 talar bone plugs (6mm diameter) were extracted from porcine ankles and embedded into Delrin endcaps using a thin layer of PMMA cement. These were scanned under micro-CT (16 microns) and subjected to quasi-static uniaxial compression to determine apparent stiffness for each specimen. Specimen-specific continuum FE models were developed, with material properties derived from the greyscale value of the underlying image. A python-based least squares regression (Opti4Abq, N=6) was used to minimise the difference between experimental and model stiffness values, to determine the coefficient linking greyscale and mechanical properties. Apparent stiffness, elastic modulus and compressive strength were compared to BV/TV, which was derived using BoneJ (a bone image plugin for the NIH ImageJ).
The results show positive correlations between BV/TV and compressive strength, stiffness and Young's modulus. Average BV/TV across all samples was 0.45. Average experimental and computational stiffness were 986N/mm and 891 N/mm respectively. A 21.8% RMS error was found using the validation set (N=5), which was of similar order to the calibration set. Some specimens saw issues with misalignment of the specimen faces and the loading platens, likely causing overestimation of mechanical properties.
This study has developed methods that can be translated for use with human ankle bone and will lead to the development of an accurate means of mapping arthritic bone in the ankle.
