To the Editor.—In their fine article entitled "Heterotopic Ossification in Abdominal Operation Scars" in the July issue of the Archives (107:87-88, 1973), Drs. Eidelman and Waron alluded to the unknown cause of the condition.
In two patients I have treated (one a woman) again with vertical midline scars, it was thought that trauma to the xiphoid during the incision with possible seeding of the wound accounted for the subsequent ossification. At reoperation, care was taken to avoid this, and no further ossification occurred.
For those infraumbilical, midline incisions one would tend to implicate urothelial tissue of the urachus, since the ossifying potential of urothelium is well known.