If you have a pre-existing medical condition or any doubts about your physical readiness, please consult a physician—ideally one who specializes in movement and critical thinking. While there may be rare instances requiring extra caution, evaluating your specific medical history is beyond my scope of practice and certainly can't be assessed in an FAQ. 

It is helpful to keep in mind that for the vast majority of human history, the deep squat was an unavoidable part of daily life. It is how billions of humans have pooped and rested for millions of years.

You'll need to discuss the limits of your specific joint replacements with your surgeon or physician. A knee or hip replacement may create limits to range of motion that make the deep squat impossible. 

If your medical professional clears you, please remember to ABC: Always Be Calibrating to your body's signals.

Never force through painful positions. Be patient and aim for small, gradual improvements. 

While different body shapes result in different-looking deep squats, there is a configuration your body can achieve safely and comfortably. Your specific skeletal proportions don't change the fact that your body is designed for this movement; it just means your version of the squat will be unique to you.