A biomechanical study of healing rat skin incisions after delayed primary closure.

The biomechanical strength of delayed primary closure wounds was assessed by in vitro determination of their relative failure energy. This is the most accurate measure of the wound's ability to resist rupturing forces. Primary closure wounds were used as controls, and measurements were always made at equal intervals after wounding--ten, 20 and 60 days. There was no differences in energy values for three, four and five day delayed wounds tested ten days postoperatively. For six day delayed wounds, however, the energy values were lower than for control wounds after ten days. Twenty days postoperatively, this difference had disappeared. The three day delayed primary closure wounds had now developed significantly higher energy values than the control wounds. When tested 60 days postoperatively, the energy values for both three and six day delayed primary closure wounds were almost double those of the control wounds. It was concluded that, in short term healing--ten days, delayed primary closure with moderate delay intervals of three to five days had no biomechanically adverse effects. In long term healing--60 days, delayed primary closure wounds showed a pronounced increase of wound strength compared with primary closure wounds. Extrapolated to the clinical situation, there would, thus, be no reason from a biomechanical point of view to hesitate to use the delayed primary closure procedure whenever primary closure is not clearly indicated.