The severity of heterotopic ossification was determined from the
radiographs of eighty-three men in whom osteoarthrosis had been treated
with a primary total hip arthroplasty with cement. The medical records of
these patients were then reviewed, with the reviewer having no knowledge of
the radiographic findings. A similar operative approach and technique had
been used in all patients. There was no association between the amount of
intraoperative loss of blood or the duration of the operation and the
severity of formation of heterotopic bone. The over-all rate of occurrence
of heterotopic ossification was 72 per cent. Of the fifty-eight patients
who had received aspirin throughout their course in the hospital, two (3
per cent) had severe ectopic ossification (grade III or IV8). In contrast,
twelve (48 per cent) of the twenty-five patients who had received no
aspirin or in whom aspirin had been discontinued so that anticoagulation
could be begun had severe heterotopic ossification. The difference in the
severity of the ossification between the two groups is significant (p less
than 0.0001).