Heterotopic ossification (HO) is a diverse pathologic process, defined as the formation of extraskeletal bone in muscle and soft tissues. HO can be conceptualized as a tissue repair process gone awry and is a common complication of trauma and surgery. This comprehensive review seeks to synthesize the clinical, pathoetiologic, and basic biologic features of HO, including nongenetic and genetic forms. First, the clinical features, radiographic appearance, histopathologic diagnosis, and current methods of treatment are discussed. Next, current concepts regarding the mechanistic bases for HO are discussed, including the putative cell types responsible for HO formation, the inflammatory milieu and other prerequisite “niche” factors for HO initiation and propagation, and currently available animal models for the study of HO of this common and potentially devastating condition. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

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Pierre Robin sequence and Treacher Collins syndrome are both associated with mandibular hypoplasia. It has been hypothesized, however, that the mandible may be differentially affected. The purpose of this study was to therefore compare mandibular morphology in children with Pierre Robin sequence to children with Treacher Collins syndrome using three-dimensional analysis of computed tomography (CT) scans. A retrospective analysis was performed identifying children with Pierre Robin sequence and Treacher Collins syndrome receiving CT scans. Three-dimensional reconstruction was performed and ramus height, mandibular body length, and gonial angle were measured. These were then compared to control children with normal mandibles and to clinical norms corrected for age and sex based on previously published measurements. Mandibular body length was found to be significantly shorter for children with Pierre Robin sequence while ramus height was significantly shorter for children with Treacher Collins syndrome. This resulted in distinctly different ramus height/mandibular body length ratios. In addition, the gonial angle was more obtuse in both the Pierre Robin sequence and Treacher Collins syndrome groups compared with the controls. Three-dimensional mandibular morphometric analysis in patients with Pierre Robin sequence and Treacher Collins syndrome thus revealed distinctly different patterns of mandibular hypoplasia relative to normal controls. These findings underscore distinct considerations which must be made in surgical planning for reconstruction.

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