What does the gut microbiome teach us about osteoarthritis development and progression?

Osteoarthritis is a degenerative disorder of the whole joint and the leading cause of chronic disability in older adults, yet no disease-modifying therapy exists. Here we review what the gut microbiome teaches us about how osteoarthritis develops and progresses. We outline a biologically plausible gut-joint axis in which an altered intestinal community, a more permeable gut barrier, translocated microbial products, and low-grade systemic inflammation converge on the joint, together with the recently described bile acid and incretin changes. Animal experiments supply the strongest causal evidence, as removing, perturbing, or transplanting the microbiome alters joint damage. Human studies remain observational and often discordant, reflecting differences in the joint studied, in population, and in method; functional measures such as circulating endotoxin reproduce more reliably than taxonomic ones. We appraise therapeutic opportunities, including dietary fiber, prebiotics, weight loss, and incretin-based agents, and define the research agenda required before microbiome-directed therapy enters practice.