Brandon Roy has only been in the NBA for five short seasons, but already has to call it quits due to on going trouble with his knees. 

Brandon Roy has been one of the best things to happen to the Portland Trail Blazers in recent years.  Unfortunately for Roy, he has had to deal with frequent knee trouble the last few seasons due to a medical condition that leaves him with less cartilage between his knees.  That condition has now forced him into medical retirement.  A shame to see this happen to a young player with such promise.

This is a very difficult and painful day. I love the game, I love the Portland Trail Blazers and I love our fans, but after consulting with my doctors, I will seek a determination that I've suffered a career ending injury, pursuant to the rules of the collective bargaining agreement.

-Brandon Roy official statement

Roy also added that his health and family are his primary concern.  For a player of his caliber to hang it up you know it must be a serious issue.  He did not report to practice with the team on Friday and the Blazers are looking into possible options for him.