My Dr said its Genitic. I've had it over 30 years. It cause infusion all disks by growing excessive bone tissue. Mysacroliac joints are frozen, which means I can't do the cha cha mambo but I still have the rhythm! In my life of AKS, it is a constant battle of good over bad body feelings. The best that I can do is to move on as though the problem doesn't exist. I know it sounds crazy, but true. Be active in every thing you do or say, AKS will try to slow you down. Don't slow, but rest too, knowing you will keep active. AKS will hammer on you, but you have to stay tough and keep the smile. The human body is a very powerful, don't underestimate what you can do. Only you can teach it to adapt to this weird Genitic gene that all humans carry, it can activate anytime. You may be lucky to deactivate or slow the bone growth your body thinks it needs by making yourself do what you want to, if it doesn't then work on something else you appreciate. You will adjust. Life is a challenge

Ankylosing is stiffening or fusing.  AS/Ankylosing Spondylitis is in the spine and sacroiliac joints.  It is an auto-immune disease.