dislocate, dissociate

Dislocate or dislocate means to put out of joint or out of proper position, as a limb or an organ--
You could dislocate the child's shoulder if  you lift him by the arms.
How did your grandmother dislocate her hip?

Dissociate or dissociate ( sometimes spelled disassociate ) means to separate; to break off ties--
When he found out what the company was up to, he tried to publicly dissociate himself from it.

Dissociate is also a psychological term, meaning to keep one or more mental processes separate from the conscious mind, as after trauma--
He tends to dissociate because it makes him feel better, at least as a short-term measure.

Now that you know that, you can say--
"He may dissociate, and claim he doesn't remember the accident, unless you ask him "how did you dislocate your shoulder?"