By Joseph Salvador The former Celtics point guard was traded after a significant hip injury in 2017. Celtics center Robert Williams has been playing through constant pain in the NBA Finals because of a knee injury. According to Yahoo Sports’ Chris Haynes, the Celtics’ medical staff ensured Williams that he’s not at risk of worsening his knee while playing through it. It appears one former Boston star has seen this movie before and commented on the report about Williams’s injury. “Heard that before lol,” Isaiah Thomas said on Twitter. The former Celtics star point guard might be alluding to how…