Dear M10001

How are you? I dont have very much to add but I am just going to add a little to what Alophysio has said. I am going to agree fully with alophysio on this advice, however like he said, without a good assessment physically we can only make speculations.

You pointed out that squatting with your heels down makes the hip uncomforable but not when the heel is up. It sounds like you have a few muscle length relationship issues, If I imagine what your posterior limb muscles are doing when you squat ( I mean your hamstrings and calf muscles) I would say your calf muscles are partcularly tight. These muscles (calfs and hamstrings are two joint muscles) , by two joint we mean the cross two joints and can influence movement in those joints, a short calf muscle would mean its superior attachments can pull on the femur when short, this can cause a superior glide as alophysio has described, especially if you have short hip flexors as well (particularly the quads)...think of a synergy of muscles working to try to give effecient movement...

As alophysio described, a joint (or bone ends making a joint ) will only move within the path of least resistance...if you are having a hip that naturally falls into external rotation when you bend then probably the external rotators are tight as well...

Just a brief description, the quads move the pelvis anteriorly, the hamstrings posteriorly...when bending you should have a posterior tilt of the pelvis to give room for the hips to move properly... this may not be happening in your case...

Arthritic changes owing to whatever pathology (osteomyelitis etc ) may have caused some degeneration in a few tendons, plus pain protection as you have walked over the years may have contributed to some shortening as well in a some tendons....

so your hamstrings are probably long, your calves are probably short, your quads are probably short, and your hip external rotators are probably short...this can make your gluteus muscles generally weak

In a addition, because you described a hip that doesnt go down when you squat compared to the other i would think that the posterior structures of the hip may be stiff, as you need the head of the femur to sink down to complete the motion of flexion. If this is not happening, then your spine will compensate by moving too much causing some discomfort.

This brief analysis may explain why you are getting stress in your thigh, hip and back when you squat. Shooting in your leg may also indicate tight rotators of the hip or generally overworked hamstring (my guess is the rotator) as these can compress your sciatic nerve...

I would suggest a good assessment of the length tension relationship of the muscles that control your pelvis as they relate to your hip and knee, and muscles that control the knee and foot, compare them to the other limb...

What you may need are some specific stretching exercises...

cheers