Heterotopic ossification (HO) is a condition defined by the formation of mature lamellar bone with bone marrow in soft tissues, mainly occurring around major joints. HO may be caused by either neurogenic or traumatic processes, including operative procedures, and often both may be involved simultaneously. Postoperative development of HO is a common and sometimes disabling problem in patients who receive prosthesis-based treatment in the extremities, such as total hip arthroplasty (THA). In general, HO becomes apparent on radiographs 3 or 4 weeks after THA, with progression to mature lamellar bone in 3-6 months [1]. The incidence of HO after THA varies, ranging from 0.6 to 90%, although an average incidence of approximately 53% after THA has been reported [2-4]. Often, the HO that develops after THA is minor and not clinically significant. We report a rare case of a patient who developed massive HO around the prosthesis after limb-salvage treatment for osteosarcoma, which should be distinguished from local recurrence of osteosarcoma and might be a reason for prosthesis stability.
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