No, I would not buy a horse with neck arthritus diagnosis.
We had such a horse, lame when we got her as a 2yr old and we knew it. Only horse I ever got just because she had charisma! Ha ha. She was just “off”, short stride on the right front, but improved a lot as a 3yr old. Took her to my lameness Vet who kept her a couple days trying different blocks. No reason for lameness and no improvement. His suggestion was to work her to the right twice as much h, trying to stretch things she did not use when loose. Seemed to work, she was pretty even moving as a 4yr old starting her driving career.
She was very nice to use, just did not collect well, got dancy with a vertical face. That was OK, still doing Driving at training, moving long, nose out was fine. Got a match so she was driven as a Pair, nose was not so obvious. Took her to a clinic where nose out was an issue with Clinician. He said bring her back to free lunge, see what we could notice. Several horse friends around the arena, not seeing anything. I got in front of her, saw her nose twitch right every time her rt front landed! The AHA moment. Did not happen going left. So she went to the College Vet clinic for neck X-rays. Pictures showed previous broken bones in the neck, healed, a bit of arthritis. Going with face vertical was painful!
The Clinic folks said bring her over here we will put her down for you. Husband said “No Way!!” They said she has a damaged neck, not a performance horse, best to let her go. They figured she had done a somersault going downhill as a yearling, when her being off, limping, appeared. Damaged the neck then. Husband said “She performs just FINE. She rides, drives, jumps without a problem. She is here to see why she could not comfortably bring in her nose, not to kill her!” Docs and students did not believe him so he gave a demonstration out in the parking lot, jumping parking barricades, some rollbacks, spins on the lawn. They were amazed! He packed her up in the trailer and brought her home. She worked hard for us, Leader in the Four doing CDE things over the years, trail riding the Cross State Ride, being the go-to horse for us.
We continued using her until she was about 14 and the arthritus got worse.
She has 4 wonderful foals for us, all as nice minded as she was, good workers AND competitive for us. She was put down at age 28 with a broken leg from a pasture accident.
She was VERY cool, interested in people, the horse everyone went to first. Queen of all she surveyed!. But managing her was enough to keep husband (the Farrier) tearing his hair out! He tried many kinds of shoes on her, which really developed his skills in diagnosing issues on other horses! They would work for awhile, then she would change. Retired, she was not limping lame, just off.
She cost a dollar, her seller knew we would give her a good place and I did love looking at her, should she never get sound! But knowing now what she taught us, I would not own another with neck arthritis.