Usually ossification occurs in damaged or injured muscles. The thigh (quadriceps muscle) and arm (triceps or biceps muscle) are affected most often. For some people, this process can happen without trauma or injury. In such cases, there may be a hereditary link.
A recent study at the Scoliosis and Spine Center of Maryland compared patients with and without ossification after a total disc replacement (TDR). They were unable to find any differences between the two groups even after two years. Range of motion was equally good and definitely improved over the pre-operative motion.
Further study is needed to investigate any long-term changes that may occur two or three decades from now. TDRs are too new to have this kind of data yet.