Abstract: Objective To investigate the MRI findings of perihip heterotopic ossification (HO) in the early, mid and late stages. Methods The MRI of 44 inpatients with HO from February, 2011 to September, 2013 were reviewed, in which 20 cases (28 joints) were in early stage, 18 cases (24 joints) in mid stage and 6 cases (8 joints) in late stage. For the enhanced T1WI, 9 cases (11 joints) were in early stage, 6 cases (7 joints) in mid stage, and 3 cases (4 joints) in late stage. The χ2 trend test was used to evaluate the MRI signal change with the HO maturity. Results With the maturity of hip HO, the signal intensity of T2WI reduced (χ2=16.773, P<0.001), fat signal on T1WI increased, the enhancement reduced (χ2=16.048, P=0.007). Conclusion The MRI findings of perihip HO are characteristic in MRI in all the stages. MRI is useful for the diagnosis of perihip HO, especially for the early HO.

Key words: heterotopic ossification, hip, magnetic resonance imaging