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 is associated with a less than expected rate of graft infection. This study may pioneer a new direction in graft construction utilizing high levels of local antibiotics in contaminated settings.
Deep surgical site infection directly involving the AHRD was located was less frequent than what has been previously described for non-antibiotic impregnated biologic grafts when placed in patients at high risk of infection. 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 5 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], whereas the current study had a 8.3% rate of graft infection. Making direct comparisons with these retrospective studies may be difficult because of variations in mesh position and the use of bridging techniques. 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. Direct comparison to our study population is difficult as about one third of patients had a bridged repair. 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. In their conclusions, Helton et al [11] recommended that because of the high rate of infection observed in contaminated fields, the fascia should not be closed primarily over SIS to avoid a closed space infection. Because bridged repairs are associated with an increased risk of recurrence, the current study protocol required the graft to be covered primarily with fascia; despite this, a lower rate of graft infection was observed as compared to rates reported previously [11,19,21].
Many of the studies outlined in Table 5 describe the requirement for graft explanation or partial debridement [11,18,23]. No graft debridement or surgical explantation was required in our study. The incorporation of gentamicin into the SIS graft may account for the dramatically lower rate of graft infection and obviate the need for graft explantation.
The rate of hernia recurrence was 25% in this study and was similar to other studies that have utilized biologic grafts for repair in contaminated fields, as demonstrated by Table 5. The three separate reports that used SIS in contaminated fields reported 26% [11], 30% [23] and 43% [19] recurrence rates for patients in which the fascia was re-approximated over the graft, and even higher rates in situations in which the SIS was used to bridge the defect. 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].
One limitation of this study is the 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. This study also lacks a comparison arm owing to the difficulty of identifying an appropriate control. Because of the differing inherent risks of materials (synthetic, autologous, and reconstructive tissue matrix), it was considered more important to establish outcomes using a single novel antibiotic impregnated biologic matrix in this difficult hernia population rather than to randomize patients to different types of bioprosthetic repair.
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.
In conclusion, the incorporation of gentamicin into a porcine derived submucosa biologic graft is associated with a lower-than-expected rate of graft infection for patients undergoing single-stage repair of ventral hernia in contaminated settings. This study of a novel device provides important insight into future biologic hernia graft development.