Intradiscally injected MSCs maintain disc height. (a) X-ray image of normal rabbit spine for measurement of disc height index. (b) Sequential changes of disc height index after transplantation of synovial MSCs. Average percentages of the value are shown with standard deviations. **P < 0.01 between the degeneration group and the normal group or the MSC group (n = 10 at each time point) by two-factor ANOVA and Turkey-Kramer post-hoc test. (c) Disc height index at two weeks after transplantation of bone marrow or synovial MSCs. Average percentages of values with standard deviations. **P < 0.01 between the bone marrow or synovial MSC group and the degeneration group (n = 6 for each group). (d) Representative T2-weighted MR images of intervertebral discs at 2 to 24 weeks after operation.