Hi, I'm Dr. Deb.
Candy asked me to answer your question since you'd prefer to chat with a vet about Max's problem.
In all honesty, her response is very thorough and is exactly what I would have said to you.
Many of the smaller breeds can manage very well with ACL injuries and this is not a reason to euthanize, in my opinion. Many of my clients with older dogs who have been diagnosed with this problem elect not to have surgery done on their dogs...finances being one reason but also because they don't want to put their older dogs through the procedure.
These legs will eventually heal but they just take much longer to do so without surgery. The knees will develop arthritis in them because they are unstable.
I've seen a fair number of dogs with this problem lead excellent quality lives; the smaller dogs appear to do much better than the larger ones, obviously.
In addition to the excellent suggestions that Candy provided, I encourage owners to add supplements to their dog's diet since arthritis can develop in the affected leg.
1. I’m a huge fan of joint supplements such as Dasaquin or Cosequin which are veterinary products specifically formulated for dogs. Quality control is a big problem with these products since what’s on the label is not necessarily what’s in the bottle which is why I mentioned specific brands. These are available on the internet.
2. Also, fish oil supplements can be helpful since they have anti-inflammatory properties. Welactin and 3V Derm Caps are good veterinary products and are also available on the internet. It takes several weeks for these products to build up in the system, so you might not see immediate results. But once started, these supplements should be continued for them to be effective; you wouldn't stop and start them, in other words, like you would drugs...but you may already know this.
3. Another option would be Zeel which is a combination homeopathic that can be used in conjunction with other NSAID medications and has a very low incidence of adverse effects (LINK) Dose would be one tablet two to three times a day....I'd go with three times a day for the first 2 weeks, then drop back to twice a day for maintenance.
4. Alternative therapies such as hydrotherapy, laser therapy, massage therapy and even acupuncture have been shown to be very useful for joint problems.
I would definitely continue pain medication in addition to anti-inflammatory drugs (such as Metacam, Rimadyl, Previcox or Deramaxx). I like Tramadol for pain control and it's also very inexpensive but every vet has their own preference.
The specific answer to your question is that I wouldn't even consider euthanasia at this point. I would try medical management and physical therapy and give him some time to show improvement.
I hope this helps. Deb