Liz Buchanan BVSc MRCVS
Hello! You sound from your phrasing as if you're in the States -is that correct? What breed is your dog? I am picturing a Jack Russel, but I think that's all conjecture; possibly your user-name put ideas into my head.
Anyway, you sound to be seeing mild muscle reduction, favouring one side with occasional momentary balance loss, bow-legged stance on one side while descending stairs, occasional paw knuckling. You don't think that there's any sign of pain. At first glance that sounds like neurological change, possibly as a result of spinal disease e.g. disc disease, but the truth is that it could also be well-concealed hip or spinal pain (they do this!) or even, at a pinch, brain-related. A full neurological exam - which is done in the conscious patient - can help your vet to give a fairly precise anatomical location for any abnormalities and may rule some of these in or out.
Your vet might also pin-point whether that out-turned knee is related, or a secondary problem.
Very often, a neurological exam will tell your vet where in the nervous or skeletal system, physically, the problem is - what it is can often be guessed at, from the location and the breed and the exact classification of of the signs (also, from the response to treatment). Sometimes imaging is recommended to say for definite what it is, but it should be okay to say if that is something you have decided against. We would still strongly recommend working it out this way round however, because guessing a diagnosis from the clinical signs is rarely effective and can result in your giving the wrong treatment.
I hope that something here is useful.