This is the first clinical study to describe the incorporation of local antibiotics into an SIS biologic hernia graft. The study demonstrates that the addition of gentamicin into a biologic device is safe, with low measured systemic gentamicin levels at 24 hours, and has a rate of graft infection that is not consistent with reported rates in the literature. This study may encourage further study into graft construction utilizing high levels of local antibiotics in contaminated settings.
Deep surgical site infection directly involving the AHRD is not consistent with what has been previously described for non-antibiotic impregnated biologic grafts when placed in patients at high risk of infection. However, this finding closely mirrors the findings of a single arm study using a rifampin/minocycline-coated, non-crosslinked porcine acellular dermis, in which implant of the device in complex abdominal wall reconstruction patients was associated with a low 30-day rate of postoperative surgical site occurrences/postoperative complications [21].
Table 4 summarizes studies utilizing biologic grafts in single-stage repair in contaminated fields and describes infection rates 2 to 3 times higher than what was observed in the current study. A recent systematic analysis reported that the pooled infection rate for biologic graft materials placed in contaminated fields was 35.5% [1].. Using data from Kanter’s series of ventral hernia repair [22], an infection rate of approximately 55% would be predicted in this study’s patient mix of clean-contaminated, contaminated and dirty patients. Three previous case series have described the use of SIS in contaminated fields. Madani et al [19] placed SIS in 46 patients with clean-contaminated (35%), contaminated (24%) and dirty (41%) fields and reported a 30% rate of graft infection. They also reported that all infected grafts required re-operation and explantation. Ueno et al [23] utilized SIS in 18 ventral hernia repairs with potentially contaminated (50%) and grossly contaminated fields (50%). In their series, they reported a 40% infection rate and one patient in which the graft was completely degraded by the infection. Helton et al [11] described SIS hernia graft use in 31 patients with dirty and clean-contaminated fields, with 13 (42%) patients experiencing infections involving the graft.[28] It is clear that biologic grafts are not more resistant to infection over other materials. However, direct comparison of this antibiotic impregnated graft with these retrospective studies is not possible and this study only serves to generate future hypothesis.
Many of the studies outlined in Table 4 describe the requirement for graft explanation or partial debridement [11,18,23]. No graft debridement or surgical explantation was required in our study.
The rate of hernia recurrence was 25% in this study and was similar to other reports that used SIS in contaminated fields with reported recurrence rates of 26% at 1 year [11], 30% at 15.7 months [23] and 43% at 47 months [19]. We hypothesized that a lower rate of graft infection would be associated with a lower hernia recurrence rate, but this was not demonstrated. Bacterial degradation of the biologic graft in the setting of infection has been postulated to be a major factor contributing factor to hernia recurrence. However, our study suggests that there may be other, more dominant factors than infection that affect hernia recurrence. Other studies have also failed to demonstrate an association between infection and hernia recurrence [23]. Although the reduction of graft infection is desirable in terms of requirements for repeat surgical procedures, wound care and systemic antibiotics, it does not appear to be the panacea for hernia recurrence. Further research is required to explore the mechanisms behind hernia recurrence in order to direct innovations to mitigate them.
The observed gentamicin level at 24 hours in this study was well below levels associated with toxicity (trough level < 2 mg/L), and no patient experienced a complication directly attributable to gentamicin. One patient had renal impairment that was felt to be secondary to hypovolemia. There was a high rate of overall complications, with almost all patients having at least one complication. This is similar to other studies of single-staged repair in contaminated settings and speaks to the complex and challenging nature of these cases.
This study is one of the few prospective, multi-center studies examining the repair of incisional hernias in contaminated settings. The majority of reports on this patient population are retrospective and are limited to a single institution or single-surgeon experience. To our knowledge, the only other prospective study in this patient population, the RICH study, examined the performance of a non–cross-linked, porcine, acellular dermal matrix [18].
There are multiple limitations of this study including lack of comparative group, lack of blinding, randomization and relatively short follow-up of 12 months. Long term follow-up of repairs using porcine acellular dermis demonstrate recurrence rates increasing out to three years, with a median time to recurrence of over 2 years [14]. Our sample size of 24 is small, although is of average size for studies examining this patient population. There is the potential for selection bias, as this study does not describe what patients declined to be involved in the study or how the surgeons selected patients for surgery. Additionally, 25% of the patients were current smokers, which is known to have a negative effect on outcomes, and one patient of CDC Class I was included against the inclusion criteria. This study was also industry sponsored with its inherent potential for bias, however there are no plans to move forward with this prototype device to market.
We acknowledge that comparative clinical studies need to be completed before any recommendations can be made regarding what type of graft should be utilized in contaminated settings. Furthermore, the use of light-weight permanent mesh in the retrorectus space is being described more frequently in the literature as an option for single-staged repairs[1,17]. Future studies should examine the incorporation of local antibiotics into this setting.