Pattern of mechanical failure of inflatable penile prosthesis

The inflatable penile prosthesis (IPP) is a well-established and effective treatment for patients suffering end-stage erectile dysfunction who have failed treatment with pharmacotherapies including oral medications, intracavernosal injections, and intraurethral vasoactive agents.1,2 It provides an excellent treatment choice with long term reliability, as well as high patient satisfaction rates around prosthesis appearance, restoration of function, and quality of life. While modifications to the IPP have advanced since its initial introduction, the hydraulic nature of the IPP devices remains an inherent risk of mechanical failure,3 which necessitates revision surgeries or replacement of these devices. A population-based database in the United States showed that 11% and 16% of IPP patients required reoperation at 5- and 10-year follow-up, respectively, after their initial implant.4 Currently, there are limited studies in the literature regarding IPP revision surgeries due to mechanical failure. Our study aims to describe the IPP failure patterns including site and mechanism of failure in our patient cohort. We conducted a single center retrospective analysis of all patients who had undergone initial and revision penile implant surgery between 1 April 2018 to 1 April 2023, using a search of the operative item numbers 37 432 and 37 426 of the Australian Medicare Benefits Schedule (MBS). All eligible patient files were reviewed and data including patient demographics, operation details, implant details, and mechanical failure finding details were collected using an encrypted Microsoft Excel worksheet (Microsoft Corp., WA, USA). Data analysis was performed using Microsoft Excel and Stata (StataCorp., TX, USA) with the assistance of a statistician. We considered mechanical failure related revision surgeries as surgeries that involve presumed or obvious fluid leak because of one or more defects in devices such as fracture/tear in cylinder/tubing, cylinder aneurism, or pump failure. “Sticky pump” is a phenomenon whereby there is difficulty cycling the pump in situ, however, intraoperatively, once the pump is externalized, it seems to cycle normally. Data on sticky pumps have been included, although these may result from static friction or scarring within the pump capsule rather than mechanical failure. We identified and captured a cross-sectional snapshot of 115 patients who underwent penile implant revision during the 5-year period. Figure S1 shows a flowchart of patient inclusions and exclusions. 40.9% (n = 47) of the patients required more than one revision surgeries. Seventy-six cases of IPP revision surgeries due to mechanical failure were identified. 64.5% (n = 49) of the failed implants were Coloplast (Coloplast Corp., Minneapolis, MN, USA) and 35.5% (n = 27) were Boston Scientific (Boston Scientific, Marlborough, MA, USA). The median months of implant in situ were 48.5 months (IQR 10.9–88.2). Table S1 shows the details of IPP mechanical failure revision cases. IPP mechanical failure patterns and characteristics are summarized in Table S2, Figures S2A–C and S3. Of the 76 failed IPP implants, 16 failed at two identifiable sites, most commonly leaks in both cylinders. Ten cases did not have failure site details available. As a result, we identified 82 occurrences of IPP mechanical failure. Of all types of failure, device leak or tear in general was the commonest, accounting for 73.2% (n = 60) of all the failure cases. Pump failure was the second commonest type of failure, accounting for 7.3% (n = 6). Of the failed Boston Scientific implants, 63.2% (n = 24) failed due to device leak or tear, whereas 81.8% (n = 36) of failed Coloplast implants were due to device leak or tear. Of all sites of failure, the cylinder (n = 31) was the commonest, accounting for 37.8% of all failed implants. Overall tubing failure accounted for 29.3% of the failure (n = 24), most commonly being failure of pump-cylinder tubing within 3 cm of pump (n = 11), followed by pump-cylinder tubing within 3 cm of cylinder (n = 8). Of the two cases of reservoir leaks, one case had obvious tear in the reservoir resulting in fluid leak. The other case was assumed reservoir leak as IPP was not explanted and the rest of the system was intact. In the context of failed IPP implants, the cylinders accounted for 61.8% and 20.8% of the failures for Boston Scientific and Coloplast, respectively. Conversely, the tubing accounted for 8.8% and 43.8% of the failures for Boston Scientific and Coloplast, respectively. According to our data, cylinder leak or tear resulting in fluid loss is the prevailing combination of the site and type of mechanical failure. While Boston Scientific introduced a parylene coating to the AMS series in the early 21st century to increase IPP durability and reliability, the hydraulic nature of IPP still remains an inherent risk to cylinder tear/rupture. 29.3% of all observed IPP mechanical failures occurred in the tubing, with tubing close to the pump and the cylinder respectively the more frequent sites of failure. Tubing failure was identified as the main cause of early failure in three-piece IPPs particularly the connection site between cylinders and pump. Sharp bends may occur at the tubing insertion into the pump or the connection junction, and this may increase the likelihood of tubing fractures. To our knowledge, this is one of the only Australian based studies on mechanical failure of IPP in the literature, with a large sample size of 115 patients. The results and outcome from this study offers valuable insights into the use of IPP in Australian urological practice and opportunities to compare the survival rates with data from other countries. There were several limitations to our study. Single center studies may underestimate the incidence of mechanical failure and presentations for prosthesis follow-up and management. The short 5-year target period of review limited the opportunity to investigate the long-term survival rates of these prostheses. Data on some of the original implantation surgery were not captured because they were inserted at other institutions. Consequently, it restricted the study’s capacity to determine whether there was a difference in mechanical failure rates across device manufacturers. Additionally, given its retrospective design, a proportion of the operation reports or product model information sheets were incomplete. Older patients tend to under-report or opt to not undergo revision surgery.3 This further led to selection bias and a skewed sample population. To conclude, our study summarized the pattern of mechanical failures of IPP. These findings may inform clinicians and patients during IPP surgery decision-making process, as well as providing important feedback to prosthesis manufacturers regarding the focus of future research and development directions. Further prospective studies with longer follow-up duration will help calculate more accurate long-term IPP failure rates and identify more potential factors associated with mechanical failure. Eldho Paul for assistance with statistical analysis. None declared. Dr Christopher Love is a member of the Speaker’s Bureau for Coloplast and a member of the Medical Board for Rigicon.