I will never understand why an owner has to “surrender” a beloved part of their lives so that it can receive needed care. If a rescue, or donor, wants to be charitable and cover costs then just do it without destroying a dog’s life long bond with its owner. Breaks my heart.
It's not that they need to. Surrendering a pet one can't afford is the alternative to neglecting or killing them. (The latter might happen anyway; shelters have limited capacity and resources too.) Unfortunately, creatures legally considered "property" are entitled to even less than us humans are.
Exception to "don't need to surrender" is if the pet parents have a contract with whoever they got the animal from, stipulating the return of the pet under certain conditions. Dunno if that's the case here though. And adopters/buyers often break those contracts...
Warning: I start rambling here 😅 While veterinarians and their staff have ethical standards (see the AVMA's PVME) and laws to follow—as medical practitioners for humans do—ultimately, a veterinary clinic/hospital is a business first. They're not really required to serve anyone who can't pay them.
I hope most vets wouldn't turn away emergency patients due to lack of payment upfront, rather than inability to provide necessary care, but it's legal. Whereas for humans, ERs specifically are required to treat critical patients (see EMTALA).
However...an ACL repair for a human wouldn't meet that standard, either. It's much more likely to be covered by our someplaces-mandated health insurance, at least? (As long as the ACA is in place and requires coverage for pre-existing conditions...)
I guess the real comparison is: would CPS remove a human child from their parent's custody if they couldn't pay for surgery to fix the kid's knees? Maybe, if it's considered medical neglect! Maybe not, if ACL reconstruction goes against the parent's religion!