Neurological heterotopic ossification (NHO) is the abnormal formation of ectopic bones in soft tissues, which occurs in 10-53% of patients with spinal cord injuries (SCI). NHO leads to reduction of joint movement and compression of blood vessels and nerves. The aetiology of NHO is poorly understood, consequently there is no effective treatments other than surgical resection. To identify the factors contributing to NHO, we utilize an animal model¹, in which NHO is induced following a combination of SCI and muscular injury (induced by intramuscular injection of cardiotoxin (CDTX)). To identify the genes upregulated specifically in muscle from mice with NHO, muscular mRNA isolated from mice receiving SCI or Sham surgery plus intramuscular injection of CDTX or PBS was analysed using expression microarrays. A significant increase of tumour necrosis factors α (TNFα) was observed in muscle in SCI + CDTX compared to SHAM + CDTX four days post-surgery. TNFα expression in injured muscle was confirmed by quantitative PCR and immunohistochemistry analysis. To examine if TNF affects osteogenesis in muscle progenitors, murine muscle satellite cells and interstitial cells were sorted from the muscle of naïve mice and cultured in osteogenic medium with/without recombinant mouse TNFα. The osteogenic capacity quantified by alizarin red and Von Kossa stain showed that recombinant TNFα significantly increased the osteogenic potential. Finally, to test if TNFα can be a therapeutic target, NHO mice were treated with clinically available TNF antagonist, etanercept, from the time of surgery to ten days post-surgery. We demonstrated that etanercept significantly reduced HO volume quantified via micro-computational tomography. In conclusion, the up-regulation of TNF in muscle is involved in NHO formation, possibly through enhancing osteogenic capacity of muscle progenitor cells. Moreover, blocking TNF might be a potential therapeutic approach.