Oklahoma City Thunder guard Russell Westbrook will miss the first 4-6 weeks of the NBA season after undergoing arthroscopic surgery on his right knee Tuesday. General manager Sam Presti said Westbrook had knee swelling that would not subside, and the procedure was intended to solve the problem once and for all. He said doctors found that the source of swelling was due to a loose stitch and Westbrook’s meniscus has healed properly. The team said the procedure was successful. Westbrook had surgery in May to repair cartilage in his right knee after he was hurt in Game 2 of Oklahoma City’s first-round playoff series with Houston. He had had never missed a game in his five NBA seasons before the injury.