Hey Katie,
I think it might be better to fly, especially after
both lumbar and cervical surgeries.
Laguardia Airport is about 20 minutes from Lennox Hill Hospital in "normal" traffic.
Newark Airport is about 40 minutes from Lennox Hill Hospital in "normal" traffic.
Personally, I would have a car service to get to/from the airport. There are many car services to choose from in NYC.
Here is an example of a car service that offers a sedan to Laguardia from Manhattan for $40 or an SUV for $80. The car service vehicles are very nice and most are limo quality. Just an idea for a comfortable ride to/from the airport.
Good luck with your arrangements...if you need help with NYC related info, I'm there often so I might be of help.