Table 2.

. Definitions for each grade of microdamage in the two regions of interest

Mid-condylar
Mild	Few visible cracks. Little or no disruption of overlying cartilage.
Moderate	Some bone microdamage: either a network of microcracks, showing early signs of lateral fracture formation, or shallow and highly localised subchondral collapse. Little or no disruption of overlying cartilage.
Severe	Extensive subchondral micro-cracking, involving one or more of bone comminution, lateral fracture, and/or subchondral collapse. Typically substantial disruption of overlying cartilage, often accompanied by reparative tissue at the articular surface.
Parasagittal groove
Mild	Occasional cracks in the calcified cartilage, predominately slopping towards the sagittal ridge, sometimes associated with clusters of much smaller subchondral bone cracks.
Moderate	Frequent cracks in both the calcified cartilage and subchondral bone, typically exhibiting an oblique/counter-oblique morphology. Limited disruption of the deep zone hyaline cartilage may be present.
Severe	Extensive cracking of the calcified cartilage and subchondral bone with the formation of large hyaline cartilage lesions in association with the hard tissue microdamage.