Thank you so much for the advice. I plan on getting him a life vest this weekend. He's even small enough to use the tub as his "pool". He's doing much better, but still not 100%.
He saw an orthopedic surgeon, but only to rule out the need for surgery. His regular vet is the one who has seen him through the fracture.
I think we will also start a walking regiment. A friend of mine has a yorkie and a german shepard and they go on a hike every weekend. Her yorkie's little legs are just so muscular and strong. I think it's a really good idea for us especially since these little babies have a higher chance of having the knee problems.
Thanks again, your input was very helpful!