Normal and osteoarthritis menisci, stained with alizarin red. Menisci were derived from (a) a 39-year-old female osteosarcoma patient, (b) a 43-year-old male osteosarcoma patient, (c) a 42-year-old male osteoarthritis (OA) patient, and (d) a 49-year-old female OA patient. The normal menisci exhibited a smooth, white and glistening surface, with no signs of degeneration (a and b). OA menisci showed discoloration and a rough surface. Degeneration was apparent (c and d). (e), (f) There were no calcium depositions in the normal menisci; (g) to (j) calcium deposition was present in all OA menisci. Representative images of grade 0 (e and f), grade 1 (g), grade 2 (h), grade 3 (i) and grade 4 (j) of alizarin red staining are shown.