Gkiatas I, Xiang W, Nocon AA, et al. - This research was sought to distinguish the incidence of heterotopic ossification (HO) in patients undergoing revision total knee arthroplasty (TKA) for either stiffness or aseptic loosening/instability and determine if the presence of HO is associated with an inferior absolute range of motion (ROM) and ROM gains. Researchers prospectively enrolled a total of 87 individuals and separated them into two cohorts to evaluate ROM after revision TKA (2017-2019). The data illustrated that in patients undergoing revision TKA, the presence of HO is greater for stiffness. The study indicated that HO severity seems to have a major effect on preoperative and postoperative ROM trajectory. This information should help assist patient expectations and indicates the requirement for a comprehensive, standardized classification system for HO.