Evaluation of the Gross and Histologic Reactions in the Skin of the African-Clawed Frog (Xenopus laevis) to Five Commonly Used Suture Materials
Amphibian medicine and surgery is becoming commonplace in aquariums and zoos, research settings, and in exotic animal practice. One problem following amphibian surgical procedures is dehiscence of sutures following a severe tissue reaction, which can result in a loss of tissue integrity, inflammation, and infection. Since no published information exists on the preferable suture material(s) for use in the skin of aquatic amphibians, the tissue reactions to five commonly used suture materials--3-0 silk, monofilament nylon, polyglyconate, polyglactin 910, and chromic gut--were investigated using the African clawed frog, Xenopus laevis, as a model in order to generate a scientifically-based recommendation. Since polyglyconate sutures have been reported to cause the least reaction in fish skin, it was hypothesized that the same would be true for aquatic amphibians.
Twelve adult Xenopus laevis were subjects. On day 1 each frog was anesthetized and six stab incisions were made on the ventrum. A single simple interrupted suture was placed in five of the six stab incisions with each suture type such that one suture material was used at each site and all five suture materials were used in each frog. One stab incision was not closed with any suture material and served as the control. Sutures were visually graded daily for gross signs of dehiscence and inflammation on a scale of zero to five where 0 indicated no gross reaction and 5 indicated severe changes. A biopsy of each suture site was taken in six subjects on day 7 and in the other six subjects on day 14. Biopsies were coded and histologic changes were evaluated blindly by a single pathologist on a six-point scale where grade zero indicated no deviation from control tissue and grade five indicated severe changes.
Three main categories of tissue changes occurred with suture placement- edema, epidermal changes, and inflammation. The edema seen in response to suture placement was predominantly dermal but extended to the subcutis and epidermis in more severe reactions. Epidermal changes noted included epidermal hyperplasia, increased apoptosis and remodeling, and necrosis at the base of epidermal pegs. The inflammation seen in response to the suture materials was predominantly mixed (heterophilic/lymphocytic) perivascular dermatitis in the deep dermis, though heterophils were the most numerous cell type seen in severe reactions. Suture granulomas were seen in many of the day 14 biopsies and occurred more frequently in cases where suture materials dehisced than when sutures remained intact.
All suture materials elicited significantly stronger tissue reactions, both grossly and histologically, than the control stab incision alone. The suture to statistically elicit the least histologic suture reaction was the monofilament nylon, followed in order by polyglyconate and polyglactin 910, chromic gut, and silk. No significant differences were noted in reaction scores between day 7 and day 14. The histologic grade of severity by suture type correlated well with mean gross scores where the lowest gross reaction scores were assigned to nylon, polyglactin 910, and polyglyconate. Silk and chromic gut caused more severe gross reactions. Polyglactin 910 had the lowest incidence of dehiscence (8%) followed by polyglyconate and nylon (17%), silk (25%), and chromic gut (67%); however, no dehiscence was noted prior to day 7. No significant differences were noted in reaction scores between day 7 and day 14 or between male and female frogs.
While the gross skin reactions to polyglactin 910 and polyglyconate were clinically indistinguishable from the monofilament nylon, the data show that the monofilament nylon caused the least histologic tissue reaction with a low incidence of dehiscence. Therefore, it can be concluded that, of the five suture types investigated in this study, monofilament nylon is the preferred suture for use in amphibian skin.