Yes I have two little Shetland Sheepdogs. One of them became acutely lame at 9 months old - I really wasn't sure what the cause was but emailed X-rays and spoke to the specialist ortho vet who reckoned it was displacement of the superficial digital flexor tendon - a condition only ever seen in Shelties and very occasionally in greyhounds! Hardly any Shelties about so I had never even heard of it and neither had my colleagues or friends (bad mum feeling!!) or her (in my opinion very good) breeder.
Anyway I visited the ortho vet and he said if it was his wife's wee pup he wouldn't operate and see what happens. About 4-6 weeks later she was back to normal and has been fine since! Now, that injury is totally different to ALD obviously, but I guess what I'm saying is it pays to listen to the specialist. It's easy for me because I have decided who I trust with my clients pets and who has the best surgical outcomes, I can't imagine how difficult it is when you don't have this info :(
So worst outcomes if you don't operate now: little one will develop arthritis at a young age, will need lifelong medication and possibly put to sleep at a young age
Worst outcome if you operate: surgery is unsuccessful and arthritis and pain sets in a lot quicker and you'll have less time with him.
Also, even if surgery was as successful as can be, he will still get arthritis in those joints, albeit at a later date than if you don't operate.
Ahh I don't know. Tbh if someone told me it would be cruel, involve suffering etc I'd just let nature take its course, provide pain relief if/when the time comes and let him enjoy his happy life now.
He's a very lucky chap to have you as his owner!