Abstract
OBJECTIVES
To perform a population based comparison of inflatable versus semi-rigid penile prostheses to determine contemporary rates of re-operation and identify factors impacting the type of prosthetic implanted.
METHODS
Patient level discharge data and revisit files from the Agency for Healthcare Research and Quality for semi-rigid and inflatable prosthesis procedures performed for erectile dysfunction from 2006-2009 in the state of California were examined. Regression analysis was performed to determine differences between the procedures in terms of infectious and non-infectious failure. Regression analysis was performed to identify factors associated with revision and to identify associations between potential risk factors and the type of implant performed.
RESULTS
A total of 2263 cases were included in the study (1824 inflatable, 439 semi-rigid). The overall re-operation rate was 7.42%. There was no difference in the overall revision rate between the 2 groups (7.52% semi-rigid, 7.40% inflatable, p=0.94). The re-operation rate secondary to infectious complications was 3.6% (4.5% semi-rigid vs 3.23% inflatable, p= 0.18). The revision rate secondary to non-infectious failure was 2.96% in the semi-rigid versus 4.17% in the inflatable group (p=0.25). Medicaid insurance (OR 2.25, CI 1.41, 3.61), African American (OR 1.7, CI 1.20, 2.49) race, age over 80 (p=0.046), and diabetes (OR 1.67, CI 1.07, 2.59) were associated with receiving a semi-rigid implant.
CONCLUSIONS
Re-operation rates for infectious and non-infectious failure are equivalent between the semi-rigid and inflatable penile prostheses. Socio-demographic factors appear to significantly influence the type of prosthesis a patient receives.
Keywords: Penile prosthesis, Prosthesis-related infections, device removal, Erectile dysfunction, prosthesis failure
Introduction
With an estimated 20,000 procedures per year, multi-component, inflatable penile prosthesis placement is the most common treatment for erectile dysfunction refractory to medical therapy1. Device infection remains the most dreaded complication of penile prosthesis implantation as this inevitably results in additional operations with an increased risk of infection, tissues loss, urethral injury and penile shortening2. Historically, infection rates have been cited as 3-5%3, however, rates of less than 1% are often quoted in contemporary single surgeon series 4. Non-infectious failure rates increase over time, with non-infectious survival rates of 97.6 and 93.2% at 3 and 5 years in a contemporary cohort5. However, both infectious and non-infectious survival rates are largely based on single institution, retrospective series and it is unclear if they can be generalized to a larger population of patients.
While the multi-component penile prosthesis represents the most common surgical therapy for ED, the semi-rigid prosthesis is considered an acceptable alternative. The malleable prosthesis has traditionally been offered to patients with impaired strength or coordination and is considered to have a lower infectious/ non-infectious failure rate. However, there is currently no data in the literature comparing outcomes of malleable versus inflatable prosthesis placement. In addition, the indications for type of prosthesis performed remain poorly defined.
Our study is novel, as it aimed to evaluate the rate of re-operation for penile prostheses for both infectious and non-infectious indications in a population based cohort. We further sought to compare the complication rates of inflatable versus malleable prostheses and identify factors associated with the type of implant performed.
Materials and Methods
Data Source and Cohort
We examined patient level discharge data and revisit files from the California Inpatient, Emergency, and Ambulatory surgery databases from the Healthcare Cost and Utilization Project (HCUP) sponsored by the Agency for Healthcare Research and Quality (AHRQ). CPT and ICD-9 codes were used to identify patients undergoing semi-rigid or inflatable penile prosthesis placement (in both inpatient and ambulatory settings) from 2006 to 2009. Patients with ICD-9 codes indicative of replacement or whom had undergone previous surgery for erectile dysfunction (data starting in 2005) were excluded from the cohort. Table 1 lists the relevant CPT and ICD-9 codes used in our analysis.
Table 1.
ICD-9 and CPT Codes
| ICD-9 Code | Description |
|---|---|
| ED Diagnosis Codes | |
| 607.84 | Impotence of organic origin |
| 302.72 | Psychosexual dysfunction with inhibited sexual excitement |
| 607.85 | Peyronie's disease |
| 607.89 | Other specified disorders of penis |
| 607.9 | Unspecified disorder of penis |
| Revision Codes | |
| 996.30 | Mechanical complication of unspecified genitourinary device implant and graft |
| 996.39 | Other mechanical complication of genitourinary device implant and graft |
| 996.59 | Mechanical complication of other implant and internal device not elsewhere classified |
| 996.65 | Infection and inflammatory reaction due to other genitourinary device implant and graft |
| 996.76 | Other complication due to genitourinary device implant and graft |
| 996.79 | Other complications due to other internal prosthetic device implant and graft |
| CPT Codes | Description |
|---|---|
| Initial Placement | |
| 54400 | Insert semi-rigid prosthesis |
| 54401/54405 | Insert self contained (inflatable) prosthesis |
| Removal/Revision | |
| 54402 | Removal or replacement of semi-rigid or inflatable penile prosthesis |
| 54406 | Removal multicomponent penile prosthesis |
| 54407 | Removal, replacement or repair of multicomponent penile prosthesis |
| 54409 | Revision of penile prosthesis |
| 54411 | Removal/replacement of all components of a multi-component penile prosthesis through an infected field |
| 54415 | Removal of semi-rigid or inflatable penile prosthesis without replacement |
| 54416 | Removal/replacement semi-rigid or inflatable penile prosthesis at the same operative session |
| 54417 | Removal/replacement of semi-rigid or multi-component penile prosthesis through and infected field |
HCUP provides all payor discharge level data collection of hospitalizations, outpatient surgeries, and emergency room visits from participating states6. The California database was used as it provides data from all three of these locations7 . Patients are linked amongst the various settings by revisit files. Patients with follow up care in another state would not be captured in this data set; however, the patient travel across state lines is presumably lower in California compared to smaller, less geographically isolated states.
Outcome Variable
The primary outcome was device removal or revision. Follow up data was available through 2010. The results were stratified into revisions/removals performed for infectious vs. non-infectious indications based on ICD-9 codes.
Statistical Analysis
Multi-component and semi-rigid prostheses were initially compared by survival analysis using the Kaplan-Meier approach. To account for possible confounding due to differences in patients receiving the two types of prostheses, Cox proportional hazards modeling was applied. We examine age, race, insurance status, hospital volume (categorized as < 1 case every other month, < 1 case per month, or at least one case per month), and comorbidity (methods of Elixhauser, et al.)8 as possible confounding factors for removal or revision of the prosthesis. Race was categorized as white, black, Hispanic, or other. Insurance status was classified as commercial, Medicare, or Medicaid/self-pay.
Using logistic regression, we then used these same variables to explore reasons why patients received multi-component and semi-rigid prostheses.
All data was analyzed using SAS, version 9.2. The study was approved by the institutional review board of Washington University in St. Louis. Statistical significance was defined as p < 0.05.
Results
A total of 2263 cases were included in the cohort (1824 inflatable vs. 439 semi-rigid). Table 2 lists baseline demographics and co-morbidities of the two groups. 2 patients were excluded due to incomplete records. The overall reoperation rate was 7.42% (7.40%% inflatable, 7.51% semi-rigid, p=0.94). The mean time to reoperation was 176.67 days.
Table 2.
Baseline Patient Demographics
| Semi-Rigid | Inflatable | p-value | |
|---|---|---|---|
| Number of Patients | 439 | 1824 | |
| Age | |||
| 50-54 | 21.0% | 79.0% | 0.1210 |
| 55-59 | 18.8% | 81.2% | |
| 60-64 | 14.6% | 85.4% | |
| 65-69 | 19.2% | 80.8% | |
| 70-74 | 19.6% | 80.4% | |
| 75-79 | 23.1% | 76.9% | |
| 80+ | 28.4% | 71.6% | |
| Hospital Volume | |||
| Low | 22.8% | 77.2% | <0.0001 |
| Middle | 14.9% | 85.1% | |
| High | 16.0% | 84.0% | |
| Race | |||
| White | 16.4% | 83.6% | 0.0004 |
| Black | 25.6% | 74.4% | |
| Hispanic | 20.5% | 79.5% | |
| Other/Unknown | 24.3% | 75.7% | |
| Insurance | |||
| Medicare | 19.5% | 80.5% | 0.0027 |
| Medicaid / Self Pay | 31.8% | 68.2% | |
| Commercial | 17.9% | 82.1% | |
| Comorbidity | |||
| 0 | 15.5% | 84.5% | 0.0197 |
| 1 | 20.9% | 79.1% | |
| 2 | 21.8% | 78.2% | |
| 3+ | 20.5% | 79.5% |
A total 79 (3.49%) patients underwent re-operation for infectious indications (3.23% inflatable vs. 4.56% semi-rigid, p=0.18). The mean time to failure for infectious complications was 94.6 days. Additionally, 89 patients (3.93%) underwent re-operation for non-infectious failure (4.17% inflatable vs. 2.96% semi rigid, p=0.25). The mean time to failure for non-infectious complications was 225.7 days. There was no significant difference in re-operation rate for overall, infectious, or non-infectious indications between the cohorts (see Figures 1 and 2).
Figure 1.
Survival analysis comparing failure due to non-infectious indications
Figure 2.
Survival analysis comparing failure due to infectious indications
Results of the proportional hazards modeling revealed no significant differences in infection related failures by age group, race, insurance status, comorbidity, or hospital volume. Non-infectious failures were less common in low volume hospitals compared to high volume hospitals (HR 0.62; 95% CI 0.39 , 0.99).
In our exploration of reasons why patients received multi-component versus semi-rigid implants, we found age over 80 (OR 2.18; 95% CI 1.18 , 4.02), African American race(OR 1.72, CI: 1.20, 2.49), any comorbidity (OR 1.55, 1.66, 1.64 and 95% CI 1.17-2.07, 1.22-2.25, and 1.15-2.35 for one, two and three or more comorbidity), and Medicaid/Self pay insurance status (OR 2.25, CI: 1.41, 3.61) were associated with receiving a semi-rigid instead of a multi-component implant.
Comment
Penile prosthesis implantation represents the primary surgical therapy for erectile dysfunction refractory to medical therapy. Our data represents the first study, to our knowledge, to examine outcomes of penile prosthesis surgery on a population level.
A true knowledge of the re-operation rates of penile prostheses is critical for the prosthetic surgeon as this represents the most dreaded complication of these procedures, particularly in the setting of infection. The current antibiotic impregnated models from the 2 primary manufacturers of penile prostheses became widely available in 2001 (Inhibizone, AMS, Minneapolis, MN, USA) and 2003 (Mentor Corporation, Santa Barbara, CA, USA). Long term revision rates of 1.19 to 1.4%10 due to device related infections have been reported using data collected from the device manufacturers at the time of implantation/revision. Using the “No Touch” technique, rates of less than 1% have been reported by Eid et al11. However, in a prospective study comparing surgical site skin preparations, our high volume center observed 1 year revision rate of 6%12. Our current study suggests that the revision rate secondary to infection is at least 3.23% in a population based series of implants, performed in the antibiotic coated era. Possible explanations for this finding include more accurate ascertainment of surgical revisions. The non-infectious complication rate of 3.93% in our series is similar to that reported in the literature, and would be expected to increase with longer follow-up of patients. It is important to note that the early non-infectious failures may not represent mechanical failure of the device, but rather reflect complications related to implanation technique. As longer term follow up becomes available, a more accurate assessment of true device malfunction would be expected to become apparent. Interestingly, patient comorbidity was not associated with infectious or non-infectious failure. The higher rate of comorbidity in the malleable group at baseline was adjusted for in our analysis, and we found no difference after adjusting for these differences. Although diabetes was very common in our cohort (n = 617), this finding is in contrast to those of Wilson et al, in which diabetes mellitus was found to be a clear risk factor for infection2. Interestingly, we found no difference in revisions among low or high volume hospitals. Our results provide valuable information for counseling patients regarding the real world rate of revision prior to inflatable penile prosthesis placement.
Currently, there are no accepted guidelines regarding the indications for placement of a semi-rigid versus inflatable penile prosthesis. Traditionally, urologists have recommended semi-rigid prosthesis placement in cases of impaired hand coordination or strength which would limit a patient's ability to operate the pump of an inflatable, multi-component device. An additional purported benefit of the semi-rigid prosthesis is a lower infectious and non-infectious complication rate when compared to the inflatable devices. However, our data contradicts this notion, demonstrating a similar rate of re-operation for both infectious and non-infectious indications in our population based cohort.
Lastly, our study suggests that racial and socio-economic disparities exist with regards to the type of prosthesis a patient receives. The finding that patients with higher comorbidity burdens are more likely to receive a semi-rigid prosthesis seems appropriate, as these patients are more likely to have impaired hand strength/coordination or may be advised to undergo semi-rigid prosthesis placement based on the perceived lower infectious risk. However, our multivariate model also identified age, black race, and Medicaid/self pay insurance status as significant predictors for receiving a semi-rigid prosthesis. This may reflect the lower cost of this implant, however, it remains concerning since the muti-component implant is considered the “gold-standard” surgical treatment for erectile dysfunction by many surgeons. Since lower socioeconomic status is associated with the highest risk of having erectile dysfunction13, the improved access to care with healthcare reform provides an opportunity for the urologic community to identify and eliminate these disparities.
Limitations of our study include the retrospective nature, as a review of administrative data. Our study showed no difference in failure rates between malleable and inflatable penile prostheses. Two factors could affect these results. First, the maxiumum follow up of 4 years in our cohort may not have been long enough to allow the development of mechanical complications in patients treated with inflatable prostheses. Second, our study may have been underpowered to show a true significant difference between the two types of implants. Although the study population was large, the rate of revisions was low, and the absolute difference in complications between malleable and inflatable prosthesis small. Performance of power calculations show that a study population of our size has 90% power to show an absolute difference of 2% in either mechanical or infectious complications. As the absolute difference in complications did not reach this level, we can say with certainty that absolute differences in mechanical or infectious complications would not be as high as 2% between the types of prostheses. However, the observed difference of about 1% between the types of prostheses may in fact be statistically significant in a larger study population.
Furthermore, the use of diagnosis codes to define reasons for failure is dependent upon proper coding at the time of surgery, which may not always be accurate. Our data set is also limited to the state of California, and may not reflect the overall population in the United States or elsewhere. Lastly, some patients may have had follow up outside of the state of California, which would not be captured in this database. However, this would result in an increase in the actual failure rate as compared to our current results.
Conclusions
With similar overall revision rates at approximately 7.5%, we found no difference in the rate of failure for infectious and non-infectious indications between semi-rigid and inflatable penile prostheses. However, racial and socio-economic disparities appear to exist with respect to the type of implant a patient receives. Our results assist urologists in providing appropriate counseling for patients and provide the background for further explorations into disparities in penile implants.
Acknowledgments
Disclosures:
• This publication was supported by the Washington University Institute of Clinical and Translational Sciences grants UL1 TR000448 and KL2 TR000450 from the National Center for Advancing Translational Sciences. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.
• The Center for Administrative Data Research is supported in part by the Washington University Institute of Clinical and Translational Sciences grant UL1 TR000448 from the National Center for Advancing Translational Sciences (NCATS) of the National Institutes of Health (NIH), Grant Number R24 HS19455 through the Agency for Healthcare Research and Quality (AHRQ), and Grant Number KM1CA156708 through the National Cancer Institute (NCI) at the National Institutes of Health (NIH).
Footnotes
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