Our customer asked if the Metacam given to her lame cat could have caused the blocked bladder which happened 36 hours later.
There will not be a direct link with the Metacam, but possibly an indirect one:
Any male cat prone to any cystitis type problem is at risk of developing urethral obstruction at some point in future. It is not rare. Various factors increase that risk, including illness of some other type, altered eating and drinking habits, reduced mobility for a while (and holding on to the urine for longer than normal) etc. These other things might have triggered the cystitis, but it could have happened just the same, with or without the Metacam.
Personally I would suggest that in future you do not give your cat any dried food. If he eats only moist food, he is very unlikely ever to get these urinary problems, because they are rare in cats producing dilute urine. Cats on dried food can produce very concentrated urine at times, which is a risk factor in itself.