@Garn - I think the safety of crossfit depends completely on the trainer at your local crossfit box. I've been to some that are great, they won't let you get away with crappy form and help you know your limits when you are working with an injury. I've seen others that just want to see you lift as much weight as fast as you can regardless of form and that is not the answer. I would check out several gyms close to you and see which one fits you the best. That being said as a Chiropractor I think Squats and Deadlifts, when done properly, are very beneficial for the low back and can help you not only recover from a low back problem but can prevent future low back problems. (If I could get all my patients to squat and deadlift some moderate weight they would be a lot healthier.)