Visiting Magic Kingdom with a medical condition doesn't mean you have to restrict your visit to shows and other ground based attractions. There is still plenty you can do.
Sure, a back injury or serious heart condition might not allow you to ride something like Tron: Lightcycle Run but that doesn't mean you can enjoy the rest of the park.
Most of the rides at Magic Kingdom won't cause you and problems, even if you have a back injury or other condition that requires you to use a motorized vehicle. In fact, many rides have front of the line access for those in wheelchairs and on carts.
For years my wife and I tried to convince my wife's parents to join us at Disney and by the time they did, they were on one of those little scooter carts and couldn't ride rollercoasters. That didn't stop them from having fun.
At Magic Kingdom there are rides you may not be able to get on but there are plenty you can.
While Tron, Space Mountain, and even the Barnstormer may not be ideal for guests with medical conditions, here are some that you shouldn't miss because you are not able to walk or have a bad back that you can't mess up.
Pirates of the Caribbean - This dark boat ride has one small drop that ends with a quick splash down. There is no huge jolt to your body or even a minor one. The hill isn't big and the entry at the bottom is pretty smooth. The rest of the ride is a simple slow move through the mock pirate villages.
The Little Mermaid - In this constantly moving ride, you enter a shell and slowly move through the attraction. There are no jolts and no surprise bumps or jarring movements. For some, getting in and out of the shell seating can be a problem since the entry point is on a moving pad but cast members are there to assist those who may need it.
Dumbo and Aladdin Magic Carpet ride - These are great rides to take with your kids or grandkids and if you are worried about riding them, don't. The entry to the cars are both step-in entry making it easy to get in and out without having to take big steps over a ledge to get there. The ride itself is as smooth as you want to make it. If you want to go high, push the lever and then leave it alone. There are slight bumps on decent but nothing that will put you out for the rest of the day.
The Carousel - It's a carousel and if you can't get on a horse, you can sit on one of the benches and relax.
Seven Dwarfs Mine Ride - If you absolutely have to ride a rollercoaster, this is perfect for those with back issues. There is a steep hill but no other coaster at Disney is this smooth as the coal cars swing back and forth thus taking pressure off the body like a normal coaster does when it slams you up against the side of the cars. It might be a little much for some but if you can ride some rides and coasters, this is one of the easier on the body.
People Mover - The biggest part of this attraction is riding the moving escalator map to the top and then back to the bottom when you exit. Otherwise, it's a relaxing smooth ride around Tomorrowland.
Haunted Mansion - Like Little Mermaid, you will enter on a moving platform but entry to the caretaker cart is easy and there are no jump scares on this slow moving attraction.