Surgical removal of the tailbone at the base of the spine.
Because the only dividing line between 10% and 0% is the presence of painful residuals, evidence that documents ongoing pain after the coccyx removal is what matters most. Medical records showing complaints of tailbone or low back pain at follow-up visits, physician notes confirming tenderness or pain on examination of the coccygeal area, and imaging or procedure notes confirming that a partial or complete removal took place all support a 10% rating. A VA or private examination that specifically addresses whether pain persists after the surgery is particularly useful. Statements from you describing how the pain affects sitting, daily activities, or your ability to work can also help show that painful residuals are present. Records showing no pain complaints or a normal clinical exam after healing would be consistent with a 0% rating.
Conditions that are often caused or made worse by this one. If you have any of these, they may be claimable as secondary service connection.