Further context would be useful here; the meaning could be that the in the digital examination, it was easy to push the finger through the sphincter and the coloanal junction (following a resection, presumably?), because the sphincter tone was decreased, however, to me it could just as easily mean that there is a break in the sutureline of the coloanal anastomosis, which a finger can pass through. Presumably the sentences around would demonstrate what is meant.