i was also born with that same birth defect. every time my knee dislocates, it slides to the back of my leg and has to be repositioned by an ER doctor. surprisingly, it hasn't happened in over a decade- since i've been riding heavily. my suspicion is that my muscles have developed much more, helping to keep it in place better. all the physical therapy excercises i've learned over the years have been to strengthen the muscles around the knee.