The one thing I always suggest to people faced with the decision to operate or not on LP is to have the opinion of a board certified orthopedic surgeon. You can find one at:
American College of Veterinary Surgeons
As for crate rest, someone said something about 3 months...I have never heard of that length of time for recovery! Also, the comment about only 48% being successful?? I really don't believe that is accurate. It is my understanding that once repaired the knee is very stable!
Now, IF they tear the cruciate ligament, surgery is a must to avoid arthritis. It not repaired the arthritis develops quickly and is painful.
Puppies, if their growth plates are still open, always need surgery to correct LP if they have it! Adult pups are different. Most surgeons say that if it is not causing issues, then surgery is not needed.
Key in helping to avoid problems is keeping the pup at his ideal body weight. Also, it is best to try to train them not to jump on and off of furniture. Steps and/or ramps are helpful if your pup is getting on furniture.