Objectives: To describe the development of screening tests and to identify re-operation rates after the permanent implant phase, and its characteristics, of the Interstim (Medtronic, Inc., Minneapolis, MI, USA) device for sacral nerve stimulation (SNS).
Patients and methods: We retrospectively reviewed the charts of women who had SNS between January 1998 and December 2005; their demographic, clinical and surgical information was abstracted. Descriptive statistics, chi-square and analysis of variance were used to compare the results.
Results: In all, 95 patients had 105 test procedures; 30 peripheral nerve evaluation (PNE) and 75 staged tined leads. Response rates were lower in the PNE than in the tined lead (40% vs 67%, P = 0.01). The indication for SNS was associated with the response rate, with urinary retention having the highest response (71%, P = 0.01). For the 55 implanted devices, there were 18 revisions (33%) and eight explants (15%). The main reasons for revision or explants were loss of efficacy (16/26) and pain at the implant site (six of 26). The median (range) time to intervention after implantation was 17 (1.2-75.0) months, and this was significantly associated with the indication. Revisions due to pain at the implant site were within the first year, and re-operations due to loss of efficacy after 1-2 years, whereas battery replacement was required on average 4 years after initial implantation.
Conclusions: This study confirms the higher response rates of the tined-lead staged technique over PNE. Unobstructive urinary retention had the highest response rates. The reason for revision appeared to be largely predicted by the length of time since implantation.