There are a number of vitamins & minerals that work synergistically for bone health (magnesium, vitamin D, calcium & vitamin K2 are some of the most common).
Magnesium plays an important role in converting Vitamin D into its active form.
Vitamin D is essential for the absorption of calcium (without sufficient Vitamin D the body cannot effectively absorb calcium, regardless how much calcium is consumed).
Then Vitamin K2 helps ensure that calcium is directed to the bones rather than building up in arteries (helping prevent arterial calcification).
All these vitamins & minerals are really important to ensure optimal absorption & transportation of calcium into the bones.
However, health conditions such as osteoporosis should be consulted with a healthcare professional who can best understand your needs.