There is only one observational retrospective study which noted an association between Warfarin use and HO post SCI. Buschbacher et al. (1992) studied 227 patients with SCI. None of the 33 patients treated with Warfarin post SCI were diagnosed with HO; among the remaining 193 patients, 34 were diagnosed with HO but not one of these individuals had been treated with Warfarin. The authors speculated that Warfarin provided a protective or inhibitory effect against HO.
There is Level 5 evidence (from one observational study: Buschbacher et al. 1992) that Warfarin inhibits the development of heterotopic ossification post spinal cord injury.