The Magic Tortoise Taijiquan School, located in the Research Triangle area of North Carolina, USA, offers classes, workshops, private tutoring and teacher training in taijiquan (t'ai-chi ch'üan: a Chinese internal style martial art and exercise for relaxation, energy, and overall well-being), qigong (ch'i-kung: energy work), and related studies. Since 1979.
Dissertation on Taijiquan teaching and teachers in America (UNC-CH 1991) including section on Knee Safety (Chap IV) at https://www.magictortoise.com/100flowersindex.htm