Rottweiler right should lameness increased, muscle wastage

7 year old Rottie (my baby) came up lame after catching ball in park 2 months ago, happened before and disappeared, hasn't this time. Much worse to the point the point of him barely wanting to use it, limps so badly at times it seems broken. Osteo X-Rays have come up negative twice, done a month apart after seeing a specialist. Blood work negative, doesn't seem to have a tear of the obvious ligaments that normally would be injured. When I pressed the specialist for an answer after the assessment she believed something more nefarious was going on in the joint/nerves of right front shoulder IE; Cancer. To be fair, I wanted her honest diagnosis. Next step would be CT Scan but it's pricey and might just confirm diagnosis. Increased muscle wastage of Bicep and Tricep is noted, more than what would occur from lack of usage. Currently on medication for pain and anti-inflammatory, his exercise has been reduced down only the shortest of walks (10 minutes and slow) at most twice a day. I don't know what to do. Money is always a consideration, but if someone told me I needed to do ligament surgery too, I'd do it tomorrow. It's hard to commit to paying for something so nebulous at this point when maybe the answer is it's unfixable and paying 4-7k would only confirm that. Any help is appreciated. I love him and am at a loss at this point.

Sorry for lack of paragraphs. I'd written the post with them but for some reason it has condensed into a run on blob of words. Apologies.

Hello and thank you for sharing this difficult case. I feel your frustration.  I was indeed thinking the same as your vet when I read it; it sounds as though something is affecting the nerves to the leg; an MRI scan might tell them more.  It is expensive, but the scan might feel justified if it were to change what you do.  Is it likely to change what you do? - this an important question.  What else could be causing those symptoms?  If your vet can't think of anything else, can the specialist?  Can a pathologist with an advanced knowledge of muscles / nerves?  I would never criticise a client for declining such scans, especially if it is unlikely to change anything and it is important to recognise if such a scan is unlikely to change the outcome.  Financial and practical considerations come into human healthcare too, but in the uk this financial weighing-up happens behind the scenes so we are unaware if it.  I think this contributes to feelings of inadequacy in owners when it comes to making practical decisions regarding animal healthcare.

In short then, 1) Do the specialists think it is likely to change your dogs' quality of life? 2) This nay be obvipus, but Money spent on a case and the odds of success have nothing to do with how much you love the patient.  Although it can feel like it at a time like this, every healthcare system in the world is based on practical financial decisions. 3) You cannot know for sure without a diagnosis, but even a diagnosis is not helpful unless it changes what they would do. 4) Finally, this is a grisley idea, but if it did come to the worst, would a post mortem be helpful to you and prehaps to other dogs in the future? - it may be something worth considering. I realise that my answer is horribly practical, but hope that something there is useful.