Osteoarthritis (OA) is a multifaceted joint disease which poses significant socioeconomic burdens. Managing the burden of OA demands continual improvements to treatment strategies. Computational modelling, for example finite element modelling, could be a complementary asset here. The predictive accuracy of such models, however, relies on an accurate mechanical description of tissues that comprise the joint. In this thesis, we explore the micromechanical impact of OA on subchondral bone.

Microscale elasticity and strength of subchondral bone was assessed by compression of micropillars fabricated using ultrashort pulsed laser ablation. A numerical model incorporating the laser-tissue interaction, Raman spectroscopy, and energy dispersive X-ray microanalysis all indicated the bone tissue that comprised the micropillars was unaffected after laser ablation.

Micropillars located in none-diseased (ND), and OA subchondral bone were compressed quasi-statically. In silico micropillar compression equipped with an elastoplastic material model was used to back-calculate the elastic modulus and strength of the constituent tissue. Elastic modulus remained unchanged between ND and OA subchondral bone, whereas strength increased in OA subchondral trabecular bone. Pillar matched Raman spectroscopy and quantitative backscattered electron imaging revealed mineralisation is the underlying determinant of elastic modulus and strength at the microscale.

The effect of microdamage on subchondral bone strength was investigated. The equine athlete served as a model, where repetitive exercise induces subchondral bone microdamage accumulation. A multimodal imaging method was developed to identify a surrogate for existing microdamage in vivo. This surrogate variable was incorporated into a nonlinear constitutive model for bone tissue. Whole bone modelling showed a significant reduction in stiffness and strength at both material and whole bone levels due to pre-existing microdamage.

The methods and results presented in this thesis give valuable insights into mechanisms that affect subchondral bone strength at the micro- and macroscale, which could be of value in the development of interventions used to alleviate the socioeconomic burdens associated with this debilitating joint disease.