Fig. 1

Changes in the numbers of colony-forming cells in synovial fluid (SF) and their colony areas in a rat osteoarthritis (OA) model. A Scheme of the experiment. Partial medial meniscectomy (pMx) was performed on either the right or left knee, and the contralateral knee received sham surgery (joint capsule incision). After 2, 4, and 6 weeks, SF and the knee joints were collected. Intact knees that received no surgery were also prepared. B Representative images of cell colonies stained with crystal violet. C Colony number per knee (n = 6). D Area per colony. *p < 0.05 by the Mann–Whitney U test between the sham and pMx groups (black asterisks). *p < 0.05 by Kruskal–Wallis/Steel tests between the intact and pMx groups (orange asterisks) and intact and sham groups (blue asterisks)