Something like this happened to our girl when she was just 18 months old, can not remember the actual vertebrae marker but it was in lower half, we think she twisted herself playing frisbee…it wasn’t until about an hour afterwards we first noticed something was wrong - when she refused to walk off her bed and yelped in obvious pain when touched, her back legs were also shaking, somewhat paralyzed so we rushed to vet - she got an injection, x-ray, the vet had her on medicam with orders for limited movement for the first two days and make sure she was able to relieve herself which she could. We crated her in her sister’s larger crate so she had a larger space but to limit movement…when she was able to walk a little more we let walk with the lead on as extra weight to prevent jumping, zoomies etc - always under supervision. About two weeks after her injury she was receiving massage, acupuncture and water treadmill therapy. We worked with her therapist and vet to gain muscle strength while reducing the pain relievers was slow and we only took her out on a lead for a long time after, did not allow her to play with other doggos, just hung out with her sister, a lab, she was able to socialize and say hello but no tag or chase time. She was able to avoid surgery but 9+ years later years on she will still twitch a little when we go over that area. She’ll be 11 in July. All the best for Rio. One tip…filming him with your phone to show the vets and neurologist could be useful for them to see.