I've started doing lat pull-down, planning to achieve a weight of 100 kg/10 repetitions. A thought hit me: while lat pull-down seems similar to pull-ups, the amount of tension (pull) on the core body is actually a lot more. During pull-ups, only the lower body essentially pulls on the core body, but during lat pull-down the entire weight you are working with pulls on the core body. I'm mostly worried if the spine can handle this load, since, as far as I understand, it's mostly built to handle compression, not tension.
It's literary the same movement. If your spine doesn't dismember when you do a weighted pull up, it won't break when you do a lat pulldown.
Your muscles are keeping your vertebrae close together, if you try hanging from a bar and relaxing your back and hips completely as if you were dead, you will feel an immense pain in your spine.
But this will never happen in a lat pull down. So if you are really scarred, technically the machine is "safer" that the bar version.
Even though, the only way to injure your spine when doing pull ups is when you are deliberately trying to do so on purpose, like in the example I described above.
The lat pull down is a safe alternative for people too weak to do normal pull ups.