Heterotopic Ossification Following Extremity Blast Amputation: An Animal Model in the Sprague Dawley Rat

Abstract

Abstract : The purpose of phase (II) of the study was to investigate the effects of local wound management, specifically pulsatile lavage and closure through the zone of blast injury versus debridement above the zone of injury, on the prevalence and severity of ectopic bone formation following extremity blast amputation in a rat model. Thirty-six Sprague-Dawley rats underwent hindlimb blast amputation via a column of propelled water following detonation of a submerged explosive. There were three treatment groups (each n=12): Group 1 was irrigated with 1L of diluted chlorhexidine solution using pulsatile lavage and closed through the zone of blast injury; Group 2 underwent syringe irrigation and debridement above the zone of injury (ZOI) with through-knee amputation; and Group 3 underwent both pulsatile lavage and through-knee amputation. The control group (n=12) was irrigated with 250ml of chlorhexidine solution using a bulb syringe and minimal debridement of skin edges. The animals were followed with serial AP and lateral radiographs until euthanasia at 24 weeks, at which time HO severity was quantified as (0) absent, (1) mild, (2) moderate, or (3) severe, and HO type was qualified as contiguous with the residual limb or as distinct ectopic bony islands. No HO contiguous with the amputated residual limb occurred in any animal that underwent through-knee amputation above the zone of injury compared with a high prevalence of HO in the residual limbs closed through the zone of injury, suggesting that the local inflammatory milieu plays a critical and essential role in HO induction. Animals treated with pulsatile lavage developed more HO than animals amputated at a comparable level and irrigated with a bulb syringe; high-pressure irrigation appeared to potentiate the HO response and deserves further study.