Best treatment for 90y/o woman w/ displaced ankle fracture w/ history of wound healing/infection issues/high bp/irregular heartbeat/elevated kidney?

Ankle fracture : If it's displaced you need surgery because the bone when formed will not align and your ankle will heal abnormally. If it's a non-displaced fracture you could be ok with a hard cast or boot brace and with time it will heal. But you need to see an orthopedic doctor to make this judgement call.

Orthopedic : evaluation along with optimal medical treatment by her internist or family physician. It all depends on her overall quality of life, her wishes, and the risks of surgery. Age does not solely determine treatment. I know patients her age who are vigorous and live great lives and those 20 years younger who could not tolerate treatment for this.

Complicated: Obviously many issues in this case. Such as - exactly which bone(s) are broken and how badly and was it an open fracture? Also - what was pt's walking status prior to this fracture? If this is an unstable ankle fracture that needs surgery, then the patient and family will have to talk about whether to take the risk of surgery, or decline, and thereby accept that pt may not be able to walk.