SIRT1 and osteoarthritis: flSIRT1: full-length sirtuin-1; BMI: body mass index; KOOS: knee injury and osteoarthritis outcome score; VAS: visual analogue scale; MAC: most affected compartment; ThCtAB: mean cartilage thickness over the total subchondral bone area; dABp: percentage of denuded subchondral bone area; JSW: joint space width; NT/CT: N-terminal/C-terminal; flSIRT1: full-length sirtuin-1; PIIANP: N-propeptide of collagen IIA; CTX-II: C-terminal cross-linked telopeptides of type II collagen