Hi Frank,
I am so sorry to read about the problems with your boy.
It's still well known with Chows, kneeproblems, most of
the time it's a rupture or partual rupture from the ligamentus
posterior. For instance, when they are eating from the
bowl they stand on 4 legs. With a ligament problem they
pull up the leg, put it down etc, because they cannot
stretch enough in the knee, caused by the instability.
Ligament and meniscus problems are not visible on an
x-ray, only arthrosis or patella luxation.
With the right orthopedic "schublade" examination the
vet can make a diagnose. Look at you tube, knee injury,
And please Frank let the vet be careful with aneasthetics
with Chows. And if he needs surgery you always can make
x-rays from his hips when he already is sleping, but I am
almost

sure that's not his problem.
Unfortunately I have had 4 Chows with the same story,
they all had surgery, but it all went well.
Keep us informed, greetings from Holland and Ted