In the episode where Brad hurts his knee, he hurts his left knee. In this episode, his right knee is bandaged.
Brad injured his left knee mid season 8. At the end of season 8, he returns to the doctor to have his knee checked after over exerting it and his right knee is bandaged.
At the very beginning of the episode, Al is worrying about Tim being late to Tool Time. But just after Al looks out into the audience, Tim can be seen standing behind the large silver Tool Time door, waiting for his entrance.