Porcine mesh hernia grafts do not promote remodeling and collagen deposition

By James E. Barone MD

NEW YORK (Reuters Health) - A study of patients whose porcine mesh hernia grafts were removed for various reasons found minimal to no neovascularization, remodeling, or new collagen deposition in the excised tissue.

In a telephone interview, senior author Dr. Yuri W. Novitsky told Reuters Health, "In this study, we found that the grafts-particularly cross-linked ones-were essentially unchanged even when they were removed several years after they were placed."

Dr. Michael G. Sarr, a professor of surgery at the Mayo Clinic in Rochester, Minnesota has published on porcine grafts. He said, "The paper shows us that the premise put forth by the biologic industries for the incorporation and vascularization of extracellular dermal matrix is probably not true."

As reported online in Surgery, the investigators, from University Hospitals Case Medical Center in Cleveland, Ohio, analyzed porcine tissue removed from 14 patients, including seven with cross-linked grafts and with non-cross-linked grafts. All of the grafts had been inserted as underlays in the intra-peritoneal area.

"None of the cases in this series were patients who we had originally operated on," said Dr. Novitsky. Although in the past one of the co-authors had used porcine mesh as an underlay, they currently do not use that method.

Demographic and hernia baseline characteristics were similar for cross-linked and non-cross-linked cases, except that the mean number of previous abdominal operations was higher in cross-linked patients (7.4 vs. 3.99; p=0.008).

In the cross-linked mesh cohort, grafts were removed for recurrence in five patients, wound infection in one, and enterocutaneous fistula in one. Mesh removal was required in the non-cross-linked group for recurrence in five and wound infection in two.

At the interface between the mesh and the host tissue, cross-linked grafts showed no acute inflammation and minimal-to-mild chronic inflammation with mild foreign body reaction and moderate fibrous capsule formation. Cross-linked graft matrices did not demonstrate any cellular penetration, neovascularization, biodegradation, or remodeling.

The non-cross-linked grafts behaved in a similar way except that they exhibited mild-to-moderate foreign body reaction and neovascularization and minimal cellular penetration and remodeling of the matrices.

"This is the first paper in humans that shows that there is no in-growth and virtually no vascularization in any of the grafts that were excised," said Dr. Sarr, who was not involved with the study.

The authors speculated that the intra-peritoneal placement of the underlay graft may not be ideal and suggested that positioning the mesh in the sublay position under the rectus muscles might allow for better graft vascularization.

Because the grafts were placed against the peritoneal surface which is made up of only mesothelial cells, the underlay position may not provide an adequate fibroblast or neovascularization supply for remodeling. Dr. Novitsky said, "Our study may not be a reflection of how biologics work but rather just how they appear when placed as an underlay."

They are using non-cross-linked porcine mesh placed in the retro-rectus position as part of a prospective randomized trial comparing it to synthetic mesh in clean-contaminated and contaminated cases. Dr. Novitsky said, "If we have a patient who is outside the study, we generally place synthetic mesh in the sublay position."

"We don't use the cross-linked porcine bioprosthesis intraperitoneally anymore and don't use a porcine bioprosthesis as a patch for a definitive hernia repair, said Dr. Sarr. His group uses non-cross linked porcine grafts as a means of achieving short term abdominal wall stability-for six to nine months-when the abdomen cannot otherwise be closed.

Dr. Charles E. Butler, Chairman of the Department of Plastic Surgery at the M.D. Anderson Cancer Center, who has authored numerous papers on porcine mesh, agreed. He told Reuters Health that the intraperitoneal plane "is one of the least favorable locations for porcine acellular dermal matrix remodeling, cellular infiltration, host incorporation, and revascularization."

"One likely explanation for the results of this small study is precisely what the authors point out; these patients are 'failures'" said Dr. Butler. He feels it would have been more relevant to obtain explants of porcine mesh abdominal wall reconstructions from patients undergoing laparotomy for reasons other than failure.

The authors say they considered the possibility that because the grafts that were removed were all in patients whose surgery had failed, the findings may not represent what happens in patients whose surgery was successful. However, since four of the 14 patients did not have hernia recurrences, they thought remodeling should have been identifiable.

Dr. Butler, who did not participate in this research, was concerned that it involved a "highly-selected group of patients who had numerous unfavorable characteristics including hernia recurrences, infections, multiple previous abdominal surgeries and previous hernia repairs, massive recurrences and high BMIs."

Dr. Butler added, "The low amount of remodeling observed may certainly be the effect rather than the cause of the failure." In his group's practice, the vast majority of non-cross-linked porcine mesh repairs are successful over the long-term and do not require reoperation or explantation of mesh.

"If you intend to use a porcine graft as an underlay, you are unlikely to get any biologic behavior and/or remodeling," said Dr. Novitsky.

Dr. Sarr agreed and said, "If you are using either type of porcine mesh as your definitive repair, expect a high recurrence rate. I would never put it intraperitoneally because it is hard to dissect bowel off the undersurface."

"Unfortunately, this study of failure-only patients may not represent the appropriate group to be evaluating important biologically-relevant interactions between host and implanted bioprosthetic mesh materials," said Dr. Butler. "Nonetheless, it does raise interest and certainly will stimulate the desire to obtain more information on this important subject."

SOURCE: http://bit.ly/1hNAHq9

Surgery 2014.

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