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Link Between Clinical Predictors of Heterotopic Ossification and Histological Analysis in Combat-Injured Service Members

BACKGROUND

Heterotopic ossification (HO) is a debilitating condition that occurs following traumatic injury and may restrict range of motion and delay rehabilitation. The timing and efficacy of surgical resection have varied widely, and there is a gap in knowledge between clinical predictors of HO recurrence and histological analysis.

METHODS

Thirty-three service members seen at Walter Reed National Military Medical Center for symptomatic HO were enrolled in an institutional review board-approved study. Participants took oxytetracycline on four scheduled days prior to HO resection to determine the mineral apposition rate (bone growth rate).

RESULTS

Detailed histological analyses included scanning electron microscopy with backscattered electron imaging and light microscopy. Data indicated that the mineral apposition rate of trauma-induced HO was approximately 1.7 μm/day at the time of operative intervention, which was 1.7 times higher than the rate in non-pathological human bone. The mineral apposition rate and postoperative alkaline phosphatase values were demonstrated to be positively and significantly related (ρ = 0.509, p = 0.026, n = 19). When the analysis was limited to patients with no more than a two-year period from injury to excision (thereby removing outliers who had a longer time period than their counterparts) and traumatic brain injury and nonsteroidal anti-inflammatory drugs (known correlates with HO development) were controlled for in the statistical analysis, the mineral apposition rate and recurrence severity were significantly related (ρ = -0.572, p = 0.041, n = 11).

CONCLUSIONS

Data demonstrated a link between benchtop research and bedside care, with the mineral apposition rate elevated in patients with HO and correlated with recurrence severity; however, a larger sample size and more clinical factors are needed to refine this model.

LEVEL OF EVIDENCE

Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Sequential imaging demonstrating os odontoideum formation after a fracture through the apical odontoid epiphysis: case report and review of the literature

INTRODUCTION

The mechanism of formation of an os odontoideum is controversial and likely multifactorial. One theory states that the apex of the odontoid separates from the body because of a fracture. The intact alar and apical ligaments pull the fractured segment superiorly. The independent vascular supply of the apex allows the fractured bone to remain viable and remodel into the smooth, corticated bone characteristic of an os odontoideum. However, there are no publications with direct radiographic evidence supporting the theory.

CASE REPORT

In this paper, the authors present a 7-year-old child with a fracture through the apical odontoid epiphysis, extending into the body of the dens. Serial imaging studies demonstrate progressive separation of the apex from the body of the odontoid. The fractured segment begins to remodel and assume the classic form of an os.

CONCLUSION

The authors consider this case to be radiographic evidence supporting an acquired/traumatic origin of os odontoideum. Further, the mechanism of fracture through a cartilaginous epiphysis may explain the formation of an os after "normal" x-ray images or following seemingly minor trauma.