Clarifying the Structure and Bone Mineral Content of Heterotopic Ossification

Abstract

Heterotopic ossification (HO) has been reported as a pathologic process characterized by ectopic bone growth in muscle and/or periarticular regions. Previous reports have speculated that HO manifests as cancellous bone, cortical bone, or woven bone. Confusion regarding HO bone morphology has resulted from radiographic assessments and light microscopy, which lack the resolution required for accurately determining advanced bone architecture. Therefore, a more thorough histologic assessment using scanning electron microscopy (SEM) and backscatter electron (BSE) imaging was needed to improve HO characterization. HO samples were collected from five adult trauma patients after surgical resection and examined with radiography, BSE, and histologic stains. BSE data demonstrated that HO was composed of a heterogeneous mixture of cortical and cancellous bone with distinct regions of fibrocartilage. Bone mineralization levels varied on a patient-specific basis, with the highest percentage of hypermineralization occurring in the oldest patient. BSE and histologic stains also indicated HO remodeling continued even after 3 y from injury to resection, as evident by osteoclastic resorption and osteoid deposition. BSE provided a more accurate understanding of HO bone mineralization and structure which may lead to improved surgical planning and treatment strategies for prevention of HO recurrence after resection.