Microstructure parameters at subchondral bone. (a)Bone area fraction (B.Ar/T.Ar), trabecular thickness (Tb.Th), trabecular number (Tb.N) and trabecular separation (Tb.Sp) were assessed at subchondral bone. (b)Subchondral plate thickness. (c)Biomechanical-related structural parameters, fractal dimension (FD) and polar moment of inertia (Ip), at subchondral bone. HEALTHY (n = 7), OA (n = 7), OP (n = 8) and OPOA (n = 8) knees. OA, osteoarthritis; OP, osteoporosis. Values are expressed as mean ± SEM; *P < 0.05 vs. HEALTHY, #P < 0.05 vs. OA.