I agree with NG; unless you carry out these much needed xrays you can never be too sure. Perhaps you could reach an agreement with your vet in which you can pay off the costs associated with xrays, etc in due course or by making weekly or monthly repayments. I'm also a big fan of GLUCOSAMINE for both dogs and humans alike. I have been using Glucosamine for 2 years and I couldn't be happier. Life would be so much more difficult for me due to knee problems if not for this wonderful product; I have found the same applies to dogs; I used Glucosamine on my elderly rough collie for the last 2 years of his life and they made a noticeable difference.
What breed is your puppy? some small breeds can be prone to luxating patellas or otherwise known as slipping kneecaps and in this case they tend to lift the lef off the ground when they're running about....
Please be wary of using Rimadyl - it is known to cause liver and kidney failure; I wonder if your vet alerted you to these risks? I have included a link that you will find informative as to the risks of using Rimadyl. Give Glucosamine a shot and you may be pleasantly surprised. All the best of luck.
http://www.srdogs.com/Pages/rimadyl.html