Goodsall's flaw.

The commentary begins with, "I firmly believe that hardly any contemporary surgeon proceeds to operate on an anal fistula merely after predicting the course of the fistula with Goodsall's Rule". However, the reality is that most anal fistula operations in the United States are performed by non-specialist surgeons (e.g. general surgeons). No, to the contrary, Goodsall's rule must be scrapped and replaced with something that's not only more accurate in predicting the course of anal fistulas, but easier to remember for the student, resident and practicing surgeon alike - the Midline rule. [Extracted from the article]