Table 1.

Summary of five factors retained from Principal Components Analysis, in order of percent variation accounted for by the factor, and relationship to OA severity.

Variation Explained (%)	Factor	Name	Composition	Direction
30.3%	1	Articular Cartilage Integrity	Articular cartilage area and thickness, Articular Cartilage Structure score, Safranin-O staining score	Lower factor score: more severe OA
18.8%	2	Chondrocyte Viability	Chondrocyte cell death area and %, number of viable articular chondrocytes, viable articular cartilage area	Higher factor score: more severe OA
9.9%	3	Subchondral Bone	Subchondral bone area and thickness	Higher factor score: more severe OA
8.5%	4	Meniscus	Weight-bearing meniscus area and chondrocyte cell death within the meniscus	Lower factor score: more severe OA
7.0%	5	Periarticular Bone	Size of axial and abaxial osteophytes, if present	Higher factor score: more severe OA