Damage to anal sphincter/levator ani muscles caused by operative procedure in anal sphincter-preserving operation for rectal cancer

BackgroundDetails of postoperative damage to anal sphincter tonus following sphincter-preserving operation for rectal cancer remain unclear.MethodsPostoperative anal tonus was measured using 3-dimensional (3D) vector manometry in 56 patients. Anal length with pressure from any direction was defined as total length (TL). Length with circular pressure (LCP), which is only measurable using 3D manometry, was also evaluated.ResultsIn operations associated with low anastomosis, both TL and LCP at rest were significantly shortened when compared with control (high interior resection [HAR]). In particular, degraded LCP at rest was obvious. Anal lengths in squeezing state were preserved except in cases with intersphincteric resection (ISR). Postoperative incontinence score inversely correlated with functional anal length at rest.ConclusionsAlthough the sphincter muscles are mechanically preserved, function of the internal sphincter and subsequent defecatory function can be degraded in cases with operative procedures including surgical maneuvers at the pelvic floor.