What affects continence after anterior resection of the rectum?

Functional results after anterior rectal resections are commonly considered satisfactory but variable percentages of postoperative incontinence are often reported. Continence was evaluated after 20 low anterior resections (LAR) and 13 high anterior resections (HAR) by means of clinical assessment, anorectal manometry, and evacuation proctography. Whereas all HAR patients had perfect continence, 10 patients (50 percent of the LAR group had occasional episodes of soiling from liquid feces, 5 patients (25 percent had frequent soiling or occasional incontinence for solid feces, and 1 patient (5 percent had frequent solid stool loss requiring surgical treatment. Anal canal resting pressure at 3 and 4 cm from the anal verge was significantly lower in the LAR group (P less than 0.02 and P less than 0.05, respectively) than in the HAR group. However, the maximum voluntary contraction did not differ between the two groups. Rectoanal inhibitory reflex was found to be present in 17 of the 20 patients with LAR and in all patients with HAR. The volume at which the anal sphincter is continuously inhibited was significantly reduced in the LAR group (P less than 0.001). Also, the conscious rectal sensibility volumes were found to be significantly reduced for threshold, constant, and maximum tolerated volume. Threshold volume for internal sphincter relaxation was lower than the threshold volume for rectal sensation in some patients with LAR. This could allow postoperative fecal soiling. Rectal compliance was decreased (P less than 0.001) in the LAR group. Evacuation proctography, performed in six LAR patients affected by major soiling or solid stool loss, revealed an abnormal obtuse anorectal angle and pathologic lowering of the perineum at rest and during defecation. The concomitance of internal and sphincter impairment, reduction in rectal compliance, and previous pelvis floor muscle damage are postulated as cause affecting continence in patients who underwent LAR.