It is noteworthy that hypertrophic‐like chondrocytes appeared in the inner AF during degeneration, the morphologies of which apparently differed from those of normal inner AF, and these cells expressed type X collagen and MMP13,94 suggesting these cells contribute to IDD phenotypes as is the case in osteoarthritis.95 Thus, we speculate that the appearance of these cells in the inner AF may be a key event in the development of IDD. The gene discussed is MMP13; the disease is intervertebral disk degenerative disorder.