My knee function stopped after THR anterior approach

*TLDR: Had THR anterior entry over one year ago and now my knee isn't functional. *

I had my THR over one year ago. During the first week or so, when the physical therapist came to the house to see me, he was having me do a leg extension. I was surprised to find that I couldn't perform it. (I had a lateral release of the knee done approximately a year or so before the THR and made what I thought had been a pretty successful recovery, returning to athletic activities).

As my physical therapy progressed, I was still unable to maintain a good amount of control over the knee extension. I explained to my surgeon, who must have misunderstood me, and they told me to return to my knee surgeon. I found out that the surgeon had written in the medical notes that I had pain since the knee surgery (not accurate). I returned to the knee surgeon who immediately said nerve damage without feeling my knee movement. I requested an MRI, and they agreed, but also ordered an EMG. The MRI said nothing wrong with the knee and the EMG showed some nerve damage. The knee surgeon referred me back to the hip surgeon. The hip surgeon said no, not nerve damage, but the MRI showed nothing and because the MRI images are only still photos and not showing the movement of the knee, it could have been scar tissue/debris in the canal causing issues/pain. I went to a third doctor - he advised my knee quit functioning due to muscle atrophy. 3 doctors, 3 theories. I had trouble believing atrophy, because my lack of knee function was IMMEDIATE after the hip replacement. I agreed to a scope from the 2nd doctor (hip surgeon), after the neurologist said he doubted that the nerve damage would not be affecting the entire leg and only the knee function, and doubting that the muscle atrophy would have been so profound to have happened that quickly. The scope showed nothing. My surgeon now says it is psychosomatic. The theory is the pain in my knee has made it so my brain is signaling the knee not to function to avoid the pain. That being said, after the THR, why wouldn't the brain shut down my hip instead? I hadn't had knee pain in a long time.
Anyway, over a year later and I can not walk up stairs leading with the bad leg. My brain says I can do it, but my leg seems to fail to function. My knee is highly unstable when I try to walk down the stairs leading with the good leg. So my opposite leg has been doing ALL of the work for over a year. The opposite leg has had enough and now I think I've torn that muscle 6 months ago - it hasn't healed yet and seems to be getting worse. I also pulled my back during physical therapy. The physical therapists said I have sufficient muscle in both the calf and the quad doing isolated exercises, but somehow I fail when doing compound exercises. They said the compensation for the knee is extremely obvious during physical therapy and when I thought I had been progressing, somehow my body managed to find a way to 'cheat' and use a part it wasn't supposed to, just further injuring myself and leading me to feel so frustrated.
My last doctors visit I was told my knee is structurally sound, and riding a stationary bike will fix both of my legs. I am willing to try this, but I used the stationary bike in PT and wasn't making progression with the compound movements.
Anyone with any advice or similar experience? This can't be my new normal.