LOS ANGELES: TOM Selleck is battling a secret medical conditional! The Blue Bloods actor, 68, suffers from arthritis that becomes so excruciating at times he requires a stunt double just to film ordinary scenes. “Tom’s days as the car-jumping scuba-diving action star are a thing of the past,” a source said. “He hates that his arthritis slows him down. Like most stars, there’s a stunt double for dangerous action shots, but Tom even uses the guy for simple scenes, like getting in and out of his police car.“His arthritis bothers him more some days than others. But Tom’s an old-school, true professional, so he never complains about the pain.–SP