I'm in the exact same situation as you are peppersmummy.
My old girl is 13 and a half and has arthritis in her back legs as well as one of her front. She had surgery to both the back legs for torn cruciate ligaments nearly ten years ago so arthritis was inevitable.
I'm assuming the injections you are talking about are cartrophen injections?
I just started my girl on them last week and she had her second one today. With the first one she also got a dose of anti-inflammatories and i was told by the vet that this only lasts 24 hours or so in the system so to watch and see if she picked up a bit and then dropped back down. I didn't notice any difference so she just got the cartrophen injection today.
I did however notice that about 4 days after the first injection she picked up a bit and was trying to play games with my other dog.
I'm assuming the cartrophen has had some effect so she will get at least another two injections,possibly four.
It might be worth you giving him anti-inflammatories as well to see if they work on him.Different dogs seem to respond to different things.
I tried all the different glucosamine supplements but none of them seemed to do anything for my girl.
I would recommend either keeping him inside at night when it's cold or at the very least having a bed that is up off the cold ground.
If you think dogs can't count, try putting three dog biscuits in your pocket and then giving Fido only two of them. ~Phil Pastoret