Faecal incontinence happens when a person passes faeces (stools) without the usual control, whereas someone with constipation passes stools less often than normal and with difficulty. Both conditions can severely affect people's quality of life. Sacral nerve stimulation (SNS) involves inserting electrodes in the lower back and connecting them to a pulse generator. This produces pulses of electricity that affect the nerves controlling the lower part of the bowel and the anal sphincters (the rings of muscle that keep the opening of the anus closed). Initially, a temporary lead is connected to a pulse generator outside the body. If symptoms are improved enough, this is replaced by a permanent lead connecting the electrodes to a pulse generator implanted in the abdomen or buttock.
This review included two studies of SNS for faecal incontinence involving 36 people and one study of SNS for constipation involving two people. The studies had a crossover design, so that the participants experienced equal periods with stimulation 'off' then 'on', or vice versa. The level of stimulation was such that participants could not tell whether the system was 'on' or 'off'.
In one study, following the crossover period, participants chose the period of stimulation they had preferred, while still unaware whether this was 'on' or 'off'. Outcomes were reported separately for 19 participants who preferred the 'on' period and five who preferred the 'off' period. The group of 19 experienced 59% less episodes of faecal incontinence per week during the 'on' period than during the 'off' period. However, the group of five experienced 118% more episodes of faecal incontinence per week during the same periods. Four of 27 participants with an implanted system experienced a problem that led to the device being removed. In the second study, participants experienced 83% less episodes of faecal incontinence during the 'on' compared with the 'off' period. This study did not report whether any problems occurred. The study assessing SNS for constipation reported an increase of 150% in the frequency of passing stools per week, and 46% less time with abdominal pain and swelling, during the 'on' compared with the 'off' period. No problems occurred.
The very limited evidence suggests that SNS can improve continence in some people with faecal incontinence, and reduce symptoms in some people with constipation. However larger, good quality studies are needed to provide more reliable evidence on the effectiveness of SNS for these conditions.