Development of an experimental method for well-controlled blast induced traumatic limb fracture in rats

Abstract

Heterotopic ossification (HO) is a consequence of traumatic bone and tissue damage, which occurs in 65% of military casualties with blast-associated amputations. However, the mechanisms behind blast-induced HO remain unclear. Animal models are used to study blast-induced HO, but developing such models is challenging, particularly in how to use a pure blast wave (primary blast) to induce limb fracture that then requires an amputation. Several studies, including our recent study, have developed platforms to induce limb fractures in rats with blast loading or a mixture of blast and impact loading. However, these models are limited by the survivability of the animal and repeatability of the model. In this study, we developed an improved platform, aiming to improve the animal’s survivability and injury repeatability as well as focusing on primary blast only. The platform exposed only one limb of the rat to a blast wave while providing proper protection to the rest of the rat’s body. We obtained very consistent fracture outcome in the tibia (location and pattern) in cadaveric rats with a large range of size and weight. Importantly, the rats did not obviously move during the test, where movement is a potential cause of uncontrolled injury. We further conducted parametric studies by varying the features of the design of the platform. These factors, such as how the limb is fixed and how the cavity through which the limb is placed is sealed, significantly affect the resulting injury. This platform and test setups enable well-controlled limb fracture induced directly by pure blast wave, which is the fundamental step towards a complete in vivo animal model for blast-induced HO induced by primary blast alone, excluding secondary and tertiary blast injury. In addition, the platform design and the findings presented here, particularly regarding the proper protection of the animal, have implications for future studies investigating localized blast injuries, such as blast induced brain and lung injuries.