The rigidity of the pelvis means there is virtually no movement between the bones of the pelvis. There is some motion around the sacro-iliac joint and symphysis pubis but these are often related to either trauma or child birth.
Fractures of the pelvis are very serious due to the potential blood loss and are often hard to see. If present then immediate and fast medical intervention is required in order to apply compression to the region.
Coccyx dislocations caused by landing heavily on your bottom can cause major issues to the function of the pelvic muscles.