The Impact of Cigarette Smoking on the Formation of Heterotopic Ossification Among Service Members With a Traumatic Amputation.

BACKGROUND

Heterotopic ossification (HO), the abnormal formation of lamellar bone in soft nonosseous tissue, has been identified as a potential complication following a traumatic amputation or traumatic brain injury (TBI). HO occurs at a dramatically higher rate among military casualties than among civilian casualties. Most investigators agree that in order for HO to form three conditions must be present: (1) osteogenic precursor cells, (2) an inducing agent or event, and 3) an environment conducive to ostoegenesis. Therefore impacting on any of these three conditions should impact on the formation of HO. Anecdotal clinical reports seem to show a decreased incidence of HO among cigarette smokers. The negative effect of smoking on bone growth as well as poor healing overall is well established in the literature. It makes intuitive sense that tobacco smoking would negatively impact on an environment conducive for HO. A review of the literature found no published work that evaluated a possible link between HO and tobacco use. This study sought to determine if a relationship exists between tobacco use and the formation of HO.

METHODS

A retrospective data review was conducted of military medical records for service members (SMs) who have experienced a traumatic amputation. Cases were matched to controls on the basis of factors known to be associated with the development of HO including age, gender, comorbid TBI, and deployment status. Bivariate logistic regression models were used to test for associations between age, gender, TBI, and deployment status with tobacco use.

RESULTS

A total of 3,132 records of SMs with an amputation were included for analysis with 18% overall developing HO. Those that developed HO were more likely to be younger, have sustained a TBI and to use tobacco compared to those that did not develop HO. An odds ratio analysis found that SMs who experienced a deployment-related traumatic amputation were 7.34 times more likely, SMs with a TBI were 6.45 times more likely, and smokers were 1.27 times more likely to develop HO when compared to nondeployment-related amputations. Older age and female gender were found to be protective against developing HO. In the final model after matching on potential confounders, tobacco use was not related to HO among this sample.

DISCUSSION

The incidence of HO among SMs with a traumatic amputation or TBI was similar to that found in other research. Also found in this study and supported in the literature is age as a confounder for HO and the prevalence of tobacco use among SMs who have deployed. However, female gender as protective against the development of HO was an unexpected finding mainly because there are so few studies of SMs with traumatic amputations including women in the analysis. In the final analysis, given all the literature on the negative impact of smoking on bone healing, it seems counterintuitive that HO formation is unrelated to smoking status. The methodology used in this study has inherent limitations and a prospective study should be conducted to validate results.