Patients who had total hip arthroplasty were categorized according to
the risk of development of ectopic bone. Radiation therapy was administered
after operation to those considered to be at high risk of formation of
ectopic bone. The dosage used was 2,000 rads given in ten fractions (875
rets). Forty-eight hips in forty-two patients were treated from 1970 to
1977. Massive formation of ectopic bone did not occur in any hip when the
radiation was given relatively early after operation. Thus, we believe that
radiation aids in the prevention of formation of ectopic bone. Radiation
was found to be of doubtful value, however, hence the ectopic bone was
visible on radiography.