arthritis injections

[hippychickuk]

my dads dog snoopy started having real problems walking last night. hes been to the vet a few times, because his legs have been a bit iffy. and mostly the vets have given him anti inflams. but by today, he wasnt using his back right leg, and was holding it up, and not even putting it on the floor. so my uncle gave my dad and snoopy a lift to the emergency out of hours vets. and they said he had severe arthritis. and gave him a arthritis injection. im unsure what the jab was called. by the time he got to the car to go home, he was walking ok.
i asked dad and my uncle how long the injection will last for and they said 24 hours?!?!? surely they have this wrong and it will last longer than that?? i know it was an out of hours vets, but it cost my dad £76. also, is this much more than what you would pay at the vets during normal times?? its going to work out very expensive for my dad if he has to pay this. would this be covered on pdsa??