Hi there Lincoln and family, welcome. We are sorry you had to join our club but glad you found us now. YAY for good healing! That's terrific. 

What you are describing could be phantom pain (see link) or it could be a residual suture is bugging him. Most times, it's phantom pain and it usually resolves itself but Gabapentin can usually speed up the problem. Was he given any Gabapentin before and after surgery? If so, how long? Most dogs are given it as a preventive.

What happens with this condition is that the severed nerves are still communicating to the brain, basically trying to tell it to move the limb and when it's not there, a little short circuit happens. Gabapentin keeps the nerves calm and prevents this communication. Acupuncture can also help. You can tell I'm not a vet right?! Here's a pain expert who can explain it better than me:

If you suspect your dog is experiencing it, get on the phone with your vet asap and let them know, then ask for a prescription. It's a relatively benign drug tolerated by almost all dogs.

Meanwhile if Lincoln hasn't has rehabilitation therapy, you should consider it. Getting a Tripawd into rehab is sooo helpful and can also pinpoint sudden pain onsets like this. The best part is the Tripawds Foundation may pay for your first rehab visit so please check it out OK?

Keep us posted!