Knee Pain Due to Ankle?

this passed month i have been doing therapy on my knww for PFPS (patellofemoral pain syndrome). my PT tells me that its more of a tightness, mobility, flexibilty issue instead of a strength issue. been getting alot of ultra sounds and MFR to loosen things up. i still train and play basketball. i dont notice much with my training in the gym but a do notice a little bit with my basketball, expecially explosiveness when taking of on that leg.

my main question would be is how does the ankle relate to the knee with regards to knee problems. i have sprained my ankle (same foot) several times nd have noticed that my ankle caves in when i walk. i suspect that this can be the cause of my knee pain. is this possible? are there any tips on how i can fix this? any help would be appreciated. if you guys need more info just let me know thanks!