Once agreed with your physiotherapist, your squat exercise maybe progressed to being performed with a barbell on your back.
Create a shelf for the bar across the top of your back with your trapezius muscles – being careful to avoid placing the bar on the lower part of your neck.
Have an erect spine, with a natural arch in the lower back. Have your feet in a comfortable position, between hip and shoulder width apart. You may find it more comfortable to have your feet slightly turned out. As you squat down try to maintain a parallel alignment between your trunk and your shin bones.
Also try to ensure the alignment of your knees over your feet.