A kinked or wavy tail and depleted calcium sacs are two surefire symptoms of MBD. You can check the gecko’s calcium sacs by looking at the underside of her throat — if you can see two white ovals there, her calcium sacs are fine. If they are very small or nonexistent, you have a problem.
UVB is strongly recommended for mourning geckos, and it does a very good job of preventing and helping to heal MBD. If you’re not using a UVB bulb, install a 5-7% UVB like the Zoo Med Reptisun Compact 5.0 13w over the terrarium mesh. If you have a bulb, check to make sure it hasn’t expired (they expire and need replacement every 6 months).
Offering a dish of calcium powder with vitamin D3 and dusting feeder insects with the same also helps restore bone density.