Scar tissue is assorted connective tissue the body produces in an attempt to close up an injury. While sturdy, it tends to lose the original tissue function, including touch and feel. In real life, pain in scars is usually caused by sensitivity in the skin around the scar rather than in it.
In fiction, this tissue has an interesting ability to ache or throb when someone's old nemesis comes by, [...] [tvtropes.org]