ั่ั้่ัุ้่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่่ั่ั่Heterotopic ossification (HO) following spinal cord injury (SCI) was first described by Dejerine and Ceillier in 1918 as paraosteoarthropathy. The ossification process involves the formation of mature lamellar bone, which is indistinguishable from normal bone, in soft tissues surrounding paralyzed joints (see the following image). The bone is not connected to periosteum and becomes encapsulated as it matures.