Electrophysiologic and manometric assessment of failed postanal repair for anorectal incontinence.

The reason for failure to improve fecal incontinence after postanal repair in idiopathic (neurogenic) anorectal incontinence is unknown. The authors have studied 20 patients whose anorectal continence was not improved after Parks' postanal repair. Anorectal manometry, single fiber EMG of the external anal sphincter muscle, and measurements of the pudendal nerve terminal motor latency were studied before and nine months after postanal repair. All 20 patients had evidence of reinnervation within the external anal sphincter muscle before operation; 17 had a raised pudendal nerve terminal motor latency and all 20 had low resting voluntary contraction anal canal pressures. No significant differences were found between the resting, voluntary contraction anal canal pressures and single fiber EMG fiber density values before or after postanal repair. However, a significant increase in the pudendal nerve terminal motor latency was found after postanal repair (P less than 0.001) using a student's paired t test. These results suggest that, in patients who are not rendered continent by postanal repair, a continuing neuropathic process takes place.