Nanoindentational technique for the evaluation of articular cartilage mechanical properties in osteoarthritic knee - What the MRI does not tell us

The differences in mechanical properties of articular cartilage (AC) from distinct regions of the knee are of particular interest. Herein, it is investigated the variation of the hardness and reduced modulus in the femoral condyles of osteoarthritic human knees. Four anatomical regions (e.g. distal medial, distal lateral, proximal medial, proximal lateral condyles of femur) were assessed by nanoindentation technique. The obtained values were processed according to the Oliver – Pharr method. Mean values for hardness were 0.8 and 1 MPa. No statistical differences were found between the distal and proximal condyles, neither when correlating the lateral and medial compartment of the knee. The measured reduced modulus was ranging between 6.2 and 10.45 MPa, and there were moderate correlations between the medial and lateral condyles, but no correspondence between the distal and proximal regions was detected. Histological analyses were also performed to support the mechanical measurements. It was possible to observe mild to severe fibrillation of the superficial zones and weak staining of safranin o was indicating the loss of glycosaminoglycans from the tissue. It was found a relation of mechanical quality and histological appearance of the tissue supporting the fact that nanoindentation technique can be a powerful tool in fundamental studies and possibly to build theoretical models and run simulation studies to analyse OA disease progression.