X-ray observation of heterotopic ossification after total hip arthroplasty

Purpose: To study the incidence and X-ray findings of heterotopic ossification (HO) after total hip arthroplasty (THA). Methods: 333 cases (352 hip) after THA were followed by X-ray examination for 1-12 years. Evaluation of HO from X-ray films using broker's classification was made and X-ray findings were correlated with sex, age and operative causes. Results: In the study, HO after THA was noted in 69 cases on X-ray films. The incidence was 20.7%. Higher in the male than in female by 7.2%, but no significant correlation with the age (P>0.05). Most (85.5%) of HO happened within one year after operation but in one case as long as eight years after operation. In this group, 85.0% of the HO belonged to Grade I-III, the remaining was grade IV. Severe HO was most frequently noted in the patients operated for Ankylosing Spondylitis. On X-ray film, the calcifications were located on external side of hip joint in early stage, and later also seen on internal side, the former being the dominant side. Calcification usually took the form of stripe or patch. Conclusion: HO is a common post-operative complication. X-ray plain film is a simple tool on diagnosing this disease and planning clinical therapy