Think about ligaments is -- they don't heal. The knee CAN stabilize on its own with very controlled exercise only, by the means of scar tissue forming around the joint and stabilizing it that way. But the ligament will never heal, whether it's a full or partial tear.
Jasmine had acl surgery on both knees, with 3 months apart (the second one went 3 months after the surgery on the left leg). Her left acl was torn, right acl was partially torn or stretched and tore eventually.
If you're sure about the diagnosis, I would say that surgery is the only way, unless you're sure you''ll be able to control your dog completely and at all times. The problem with injured acl is, that the longer it is left unchecked, the more arthritis develops.
So my suggestion would be do a surgery. I've been through this with Jasmine twice. It is heartbreaking, but I do believe it's the best thing to do. Which surgery to chose is a different question all together. There is the popular TPLO. You can find descriptions, pictures and I think even an animation of the procedure on the internet. Another option is TTA. This surgery is quite different. Not all surgeons believe in this one. But I talked to Orthopedic department of University of Colorado back in the day, they do both and believe in both and recommend one over the other on individual basis. The main differences I see between those are these:
TPLO - the bulk of the surgery is on a weight-bearing part of the bone, so it takes longer for the dog to bear weight on the leg. Personally to me it looks like it's potentially safer and more stable.
TTA - the bulk of the surgery is done on the front of the shin bone, non-weight-bearing part of the bone. Looks that the dog should start bearing weight sooner, potentially I'd figure it might be less painful, on the other hand, personally to me it doesn't look as solid.
Both of these involve chopping and repositioning of bone.
Both of these are clearly quite invasive. They work really well if they are done well and nothing goes wrong in the post-op.
Then there is an older, much less invasive extracapsular repair. This one is much less invasive, it involves drilling small holes in the bones and stabilising the joing using surgical lines (kind of like fish lines type of deal). We opted for that one, because we found an amazing vet and he did a custom version of the surgery, where he stabilized the joint at more points than it's usually done. It requires strict post op, but we just liked it for the minimal invasiveness. If something goes wrong, there are always options.
Then there is a newer variation of the extracapsular repair, called TightRope. This one is quite similar with some differences.
Then of course there is always a brace route, from the braces I researched I like OrthoPets the best. The guy who runs it used to make braces for athletes. He's got it quite figured out. He has good report with the Orthopedic department of University of Colorado.
Ok, here are roughly the options. I've been exactly where you are, desperately reaching for non-surgical option. As I said, it is possible for the scar tissue to form without the surgery, but keeping the knee stabilized enough just by controlling motion doesn't really seem feasible to me.
The brace works fairly well, but for a younger dog, I hate to say I think surgery is the best option. The question then remains which one. They each have their pro's and con's.
Yes, thyroid hormone controls cell metabolism -- meaning when its levels are low, it affects the entire body. So it does seem that the ligaments are one of the things that suffer.
There are two types of acl injuries as the cause is concerned. One reason is an accute injury - where some severe trauma to the joint causes the ligament to break. In these cases often only the one ligament is affected and the other one remains fine. Second reason is degeneration of the ligament tissue, where the ligament keeps getting weaker and weaker until eventually lets go. In these cases there is high probability of the other knee going at some point as well.
These are all very crappy facts. But they need to be faced. Because not doing anything prolongs the dog's pain, and the arthritis caused by this will only get worse.
One other note, we did the extracapsular repair in combination with stem cell treatment. Mostly because we hoped that it might 'save' the other knee. Well, it didn't. But it really helped with the recovery and it really works well for the arthritis.
If you want, you can contact me directly, sadly, I know pretty much everything there is to know about acl injuries and treatment options.
Jana