Table 3.

Macroscopic OA severity grading system used in this paper for articular cartilage of baboon knees. The corresponding stages in the modified Outerbridge system³³ used for humans are also indicated.

Grade	Severity	Modified Outerbridge system33	Gross observations
1	Unaffected	0	No signs of any cartilage degradation
2	Mild OA	1, 2	Presence of cartilage fibrillation (i.e., obvious macroscopic alterations of at least the superficial layer of the articular cartilage that manifest as surface roughening or striations), but no cartilage lesions
3	Moderate OA	3	Presence of cartilage degradation to the point of lesion development (i.e., clear indication of erosion of articular cartilage, regardless of lesion size) but no eburnation
4	Advanced OA	4	Presence of any amount of eburnation (i.e., devoid of cartilage, polished subchondral bone surface – indicative of bone-on-bone contact)