• Oliver Tannous, Cullen Griffith, Robert V O'Toole, and Vincent D Pellegrini.
• Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
• J Orthop Trauma. 2011 Aug 1;25(8):506-10.

ObjectiveTo create an animal survival model for heterotopic ossification (HO) in the residual limb of the rat after extremity blast amputation. The hypothesis was that extremity blast amputation spontaneously stimulates development of HO in the residual limb.MethodsTwelve Sprague-Dawley rats underwent localized exposure to a controlled, high-energy blast. Seven rats were designated for hind limb amputation and five for forelimb amputation. Our protocol produced extremity amputation through detonation of an explosive while protecting the animal proximal to the specified amputation level. Immediately after injury, the rat underwent wound management and primary surgical closure. Radiographs of the amputated limbs were obtained every 2 weeks. Heterotopic bone was radiographically classified as periosteal growth (Type A) or noncontiguous growth (Type B). A kappa statistic was calculated for interobserver strength of agreement on the presence of HO. Fisher exact test was conducted to assess the significance of the difference in hind limb and forelimb HO rates.ResultsNine of 12 animals survived the procedure. The three nonsurvivors were all hind limb amputees, and each died of various related causes. All four surviving hind limb amputees exhibited Type A HO, and three of four also exhibited Type B HO within the injured stump. One of five forelimb amputees exhibited Types A and B HO.ConclusionsWe have developed a reproducible model for HO in the residual limbs of blast-amputated rats without addition of exogenous osteogenic stimulus. Hind limb amputation demonstrated a predilection for HO formation in comparison with forelimb amputation (P < 0.05).

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