Question
When I lay on my back and completely relax, my tailbone pops. It is ususally from sitting for a long period of time. When it pops it makes a popping noise and my pelvis lowers just a tad. No one has ever heard of a tailbone popping and I want to know why it is happening and if it's safe.

Answer
Hello Melissa,

   Yes, this is very common.  Every joint in the body has gas that is in the joint fluid.  When the joint releases or moves it may have a "popping" sound from the gas releasing.  Muscles move bones so, when lying on your back and relaxing the muscles your tailbone/sacrum may move.  Sometimes this can be due to ligament laxity (ligaments are stretched or loose) causing the joint to move easily.  Low back strengthening excises for 4-6 months will usually help.

Have a great day,
Dr. Brendon O'Brien D.C.