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Comparison of polyglactin-910 and polydioxanone for closure of the linea alba following caudal ventral midline laparotomy in sheep
Abstract
This study compared incisional complications after ventral midline laparotomy using 2 absorbable suture materials for apposition of the linea alba in sheep. The linea alba of 93 yearling sheep was sutured by 3 veterinarians in a simple continuous pattern using either polyglactin 910 (PG910; group PG) or polydioxanone (PDS; group PD). A blinded observer assessed surgical sites at the time of suture removal. Multivariate logistic regression was used to assess the association between incisional complications and variables (suture material used, veterinarian, skin suture removal time). The odds of incisional complications did not vary significantly with the type of suture material used (P = 0.11), veterinarian (P = 0.61) or skin suture removal time (P = 0.36). Most incisional complications were cutaneous suture sinus formation. Either PG910 or PDS may be used for linea alba closure in sheep.
Résumé
Comparison de l’utilisation du polyglactin 910 et du polydioxanone pour suturer la ligne blanche lors de laparotomies ventrales médianes caudales chez la brebis. Cette étude compare les complications incisionnelles suite à une laparotomie ventrale médiane en utilisant 2 fils de sutures pour l’apposition de la ligne blanche chez la brebis. La ligne blanche de 93 brebis a été suturée par 3 vétérinaires en points simples continus avec du polyglactin 910 (PG910; groupe PG) ou du polydioxanone (PDS; groupe PD). Une observation à l’aveugle des sites chirurgicaux a été effectuée lors du retrait des points de suture. Une régression logistique multivariée a été utilisée pour déterminer l’association entre les complications incisionnelles et les variables (matériel de suture utilisé, vétérinaire et temps de retrait des sutures cutanées). Les chances de complications ne variaient pas selon le type de matériel de suture utilisé (P = 0,11), le vétérinaire (P = 0,61) ou la période de retrait des points cutanés (P = 0,36). La majorité des complications étaient des fistules associées aux sutures cutanées. Le PG910 ou le PDS peut être utilisé pour l’apposition de la ligne blanche chez la brebis.
(Traduit par les auteurs)
Introduction
Laparotomies are currently performed in the ewe for embryo transfer (1–3), and for various therapeutic (4–8), exploratory (9), and research (10–12) purposes. Standard approaches to the ovine abdomen include right or left mid-paralumbar, ventral midline, and ventral paramedian laparotomies. The ventral midline approach is commonly used to gain access to the reproductive tract such as for elective and emergency cesarean sections (5,7), ovariectomy (13), embryo transfer (3), and research procedures (11,12). This approach can be performed under general anesthesia or sedation and local or regional anesthesia with the sheep in dorsal recumbency. The incision is generally started at the level of the umbilicus and progresses caudally for the appropriate length for the required surgical procedure.
Recommendations for suture patterns and suture selections to reconstruct the ventral midline abdominal wall in sheep undergoing laparotomy are often based on clinical experience and knowledge from other livestock species. An in vitro study showed that the llama linea alba is similarly strong after closure using either a simple continuous pattern or an inverted cruciate pattern (14). A simple continuous pattern was recommended for linea alba closure in llamas because of its easy and rapid application (14). Research on linea alba closure in horses showed that a simple continuous pattern is stronger than interrupted patterns (15–17). Few articles report details about the type of closure (number of layers, suture patterns, suture material type and size) performed on ventral midline laparotomies in sheep. One study reported using absorbable suture material in a continuous pattern for re-apposition of the linea alba (7), whereas another described using USP size No. 3 surgical chromic gut in a simple interrupted pattern (10). In one retrospective study describing the rate and types of surgical site complications in sheep, ventral midline laparotomy was compared to left mid-paralumbar approach for cesarean sections in ewes. Eighteen percent of the ewes undergoing a ventral midline approach developed complications including mild to moderate degrees of incisional pain and/or the presence of some discharge (7). The authors could find no study comparing suture type for closure of ventral midline laparotomies in sheep.
We chose to compare 2 synthetic absorbable suture materials (PDS and PG910), because these 2 suture materials are commonly recommended for closure of the linea alba in other large animals (18–21). Polydioxanone is a monofilament suture material that loses 50% of its tensile strength by 45 d after implantation and is completely absorbed by 180 d. Polyglactin 910 is a braided multifilament suture material that loses 50% of its tensile strength by 21 d after implantation and is completely absorbed by 56 to 70 d. Both suture materials have similarly low tissue reactivity and similar relative knot security (22).
The objective of this study was to perform a prospective, randomized, and blinded study to determine the rate of incisional complications for a clean surgical procedure (ovarian follicular aspiration) through a caudal ventral midline laparotomy in ewes using either PG910 or PDS to close the linea alba incision. Use of PG910 for closure of the linea alba was a risk factor for postoperative surgical incision infection in a population of horses having ventral midline laparotomies (23). The authors’ clinical impression is that the use of either PG910 or PDS for closure of the linea alba in ruminants does not effect the rate of incisional complication. Therefore, we hypothesized that re-apposition of the linea alba with PG910 or PDS after caudal ventral midline laparotomy in ewes undergoing follicular aspiration would result in similar incisional complication rates.
Materials and methods
Animals
The study protocol was approved by the Institutional Animal Care and Use Committee at Kansas State University. Ninety-three clinically healthy yearling Rambouillet ewes (Ovis aries) weighing a mean of 116 kg (range: 98 to 140 kg) were used. All ewes were part of a reproductive physiology study requiring laparotomy harvest of follicles (24). That study protocol included randomly assigning ewes to treatment diets. Ewes were randomly assigned to the suture type using a block structure to ensure that suture types were equally distributed across diets to control for nutritional variations. Ewes were fed free choice prairie hay or alfalfa hay with minimal grain supplement at various levels based on group assignment. All ewes were fed daily with free choice water available throughout the study period except when food and water were withheld for 12 h prior to surgery. The day of surgery was designated as day 0. After surgery all ewes were fed a maintenance diet of ground alfalfa, corn silage, and distiller’s grain.
The ewes were allowed an acclimatization period of 14 to 23 d before surgery and were housed in groups of 15 to 16 ewes in 6 dry lots during this period. One day before surgery, the animals were transferred to 3 × 10 m pens bedded with pine wood shavings until 5 d after surgery. Then ewes were housed in groups of 15 to 16 in 6 dry lots with a large turn out area (approximately 5 × 20 m).
Preoperative protocol
Immediately before surgery, the wool was shorn. A dose of procaine penicillin G (Norocillin Injection, 300 000 units/mL; Norbrook, Lenexa, Kansas, USA), 22 000 IU/kg body weight (BW), IM, and flunixin meglumine (Banamine Injectable Solution, 50 mg/mL; Intervet/Schering-Plough Animal Health, Summit, USA), 1.1 mg/kg BW, IV, were given to all ewes 15 min before surgery. All ewes were sedated with a combination of butorphanol tartrate (Butorphic Injection, 10 mg/mL; LLOYD Laboratories, Shenandoah, Iowa, USA), 0.025 mg/kg BW, IV, xylazine hydrochloride (AnaSed Injection, 20 mg/mL; LLOYD Laboratories), 0.05 mg/kg BW, IV, and ketamine hydrochloride (KetaVed, 100 mg/mL; Vedco, St. Joseph, Missouri, USA), 1 mg/kg BW, IV (25) to induce recumbency. Ewes were placed in dorsal recumbency and limbs were attached to the surgery table in abduction and partial extension to facilitate access to the caudal ventral region of the abdomen. The ventral abdomen was clipped from the xyphoid to the cranial aspect of the udder and cleansed using iodine surgical scrub. A line block was performed with 2% lidocaine hydrochloride (Lidocaine Hydrochloride Injection, 20 mg/mL; Hospira, Lake Forest, Illinois, USA) infused subcutaneously along the linea alba beginning immediately cranial to the udder and extending cranially for 10 cm. The skin was aseptically prepared using alternating scrub cycles with iodine surgical solution and 70% isopropyl alcohol.
Surgical procedures
All laparotomies were performed during a total of 5 d over a period of 10 d. Sheep were randomly assigned to a day of surgery (surgical day 1, 2, 3, 4 or 5) blocked by their assignment to treatment diets. A longitudinal skin incision was performed over the linea alba using a No. 21 scalpel blade starting at the brim of the pelvis immediately cranial to the base of the udder and extending for 10-cm cranially towards the umbilicus. A plane of dissection was established through the subcutaneous tissue adjacent to a subcutaneous vein usually located parallel and immediately ventral to the linea alba until the linea alba was exposed. The abdominal wall was grasped with thumb tissue forceps and tented, and a stab incision was made through the linea alba using a No. 10 scalpel blade. Using Metzenbaum scissors, the incision was continued through the linea alba and peritoneum. Following opening of the abdominal cavity, the animal was placed in a 30° Trendelenburg position to facilitate exposure to the caudal abdomen. The uterine horns and ovaries were localized by digital palpation and exteriorized through the incision. Follicular aspiration was performed by a surgery assistant using a sterile tuberculin syringe and needle. Following follicular aspiration, the animal was replaced in the initial level position. The linea alba was apposed in a simple continuous pattern using either USP No. 1 polydioxanone (PDS II, Ethicon Endo-Surgery, Somerville, New Jersey, USA; group PD) or USP No. 1 polyglactin 910 (Coated VICRYL, Ethicon Endo-Surgery; group PG). Following closure of the linea alba, the skin was apposed in a simple continuous pattern using USP No. 1 polypropylene (PROLENE, Ethicon Endo-Surgery). Ewes were confined to a pen for 5 d after surgery in order to limit exercise.
Surgical approach and exteriorization of the reproductive tract were performed by the same veterinary surgeon for all ewes. Follicular aspiration was performed by the same surgery assistant for all ewes. Following follicular aspirations, 3 veterinarians performed laparotomy closure. Ewes, suture selection, and surgeon were randomized to study day. Veterinarian 1 performed linea alba closures on surgical day 1 using PG910 (n = 18). Veterinarian 2 performed all linea alba closures on day 2 using PG910 (n = 18) and on day 4 using PDS (n = 19). The third veterinarian performed all linea alba closures on day 3 using PDS (n = 18) and on day 5 using PG910 (n = 10) or PDS (n = 10). Veterinarians were trained to perform suture closure using moderate tension over the length of the continuous suture placed into linea alba and skin. When performing a knot, the first throw consisted of a surgeon’s knot (26) with a total of 6 throws at the beginning of a continuous pattern and 7 throws at the end of the continuous pattern. Veterinarians and surgeon wore scrub suit, surgical head covers, facemasks, sterile gowns, and gloves. Surgeries were performed in a clean, dedicated livestock operating room.
Postoperative monitoring
Ewes were visually monitored twice daily for appetite, drinking behavior, activity level, defecation, and urination. Ewes were confined to a small pen for 5 d followed by restriction to a large pen for 30 d. During this time, ewes had uncontrolled exercise. Perioperative pain management involved the administration of daily flunixin meglumine, 1.1 mg/kg BW, IV, for 3 d. Suture removal was performed 14 to 23 d (average: 18.5 d) after surgery, at which time the incisions were closely examined visually and by palpation by a graduate student blind to the treatment allocation in order to assess healing and determine presence of surgical site infection (SSI) or incisional herniation. Surgical site infection was defined as presence of purulent drainage from the incision and was categorized as suture sinus formation and incisional abscess formation. Visual and manual assessment of the surgical sites was repeated 5 or 6 d after suture removal (average: 5.2 d). All assessments of the surgical sites and suture removal were performed with ewes restrained on their dock. Surgical site infection was considered a minor complication, whereas incisional herniation was considered a major complication. If an incisional complication was observed both at the time of suture removal and again 5 to 6 d later, this finding was only used once for statistical analysis. Incisional complications were treated according to the attending veterinarian’s recommendation.
Statistical analysis
Data were entered into a spreadsheet (Microsoft Excel 2010; Microsoft Corp., Redmond, Washington, USA) for statistical analysis and generation of descriptive statistics. For statistical analysis, outcome was classified as “absence” or “presence” of incisional complications. Univariate analysis was first performed with an exact Chi-Square test (SAS v.9.3; SAS Institute, Cary, North Carolina, USA). A multivariate logistic regression model (SAS v.9.3) was used to examine the effect of veterinarian, type of suture material and time of skin suture removal on the outcome. A value of P < 0.05 was considered significant. None of the interactions could be evaluated because the study design was not factorial.
Results
Surgical procedures
The 93 ewes underwent surgery on 5 different days (between 18 and 20 ewes/day). The average surgical time was 20 min per ewe on surgical day 1, 13 min on days 2 and 3, and 12 min on days 4 and 5. Polydioxanone and PG910 were used to close the linea alba of 47 and 46 ewes, respectively. Closure of the linea alba was easily performed by all 3 veterinarians. In a small number of ewes, moderately distended loops of small intestine obstructed the field of view during closure of the linea alba and increased difficulty placing sutures. All ewes recovered uneventfully from the procedure.
Animal monitoring
All ewes had normal appetite, drinking behavior, activity level, defecation, and urination after surgery and throughout the 30-day study period. While housed in dry lots, ewes were soiled by mud during the first month after surgery due to heavy rainfall. Total precipitation for the month was 8.8 cm (27).
Incisional complications
Incisional complications occurred in 29 ewes (31.2%). Most were minor complications (28 ewes; 30.1%); 1 ewe had a small (3-cm) incisional hernia. Of the minor complications, suture sinus formation was found in 26 ewes and superficial incisional abscessation in 2 ewes. Within group PG, 22 ewes developed suture sinus formation associated with the skin sutures, 1 developed superficial incisional abscess, and 1 developed incisional herniation. Within group PD, only 4 ewes developed suture sinus formation and 1 developed superficial incisional abscess. Univariate analysis showed that suture material and skin suture removal time influenced the prevalence of incisional complications as detailed in Table 1. The multivariate linear regression model revealed that the odds of complication did not vary significantly with veterinarian (χ2 = 1.0, P = 0.61), suture material used to suture the linea alba (χ2 = 2.6, P = 0.11), and skin suture removal time (χ2 = 0.82, P = 0.36).
Table 1
Univariate analysis results
| Variables | Group | Description | Incisional complications | P-value |
|---|---|---|---|---|
| Suture material | PG | PG910 | 52.2% | < 0.0001 |
| PD | PDS | 10.6% | — | |
| Veterinarian | PG | Vet 1 | 66.7% | 0.06 |
| PG | Vet 2 | 55.6% | — | |
| PG | Vet 3 | 20.0% | — | |
| PD | Vet 2 | 15.8% | 0.64 | |
| PD | Vet 3 | 7.1% | — | |
| Skin suture removala | PG | 14–18 d | 20.0% | 0.03 |
| PG | 22–23 d | 61.1% | — |
All ewes with SSI had the surgical site cleansed with diluted povidone iodine after suture removal. Abscesses were drained as needed. At the time of suture removal 7 ewes from group PG and 1 ewe from group PD received procaine penicillin G, 22 000 IU/kg BW, IM, q24h for 5 days to treat SSI. All SSIs were completely or nearly resolved at the time of reevaluation of the surgical sites 5 to 6 d after suture removal.
Discussion
From our findings, the odds of incisional complications appear to be similar for PG910 and PDS for closure of the linea alba in sheep when variables (veterinarian and suture removal time) affecting the outcome are controlled. The prevalence of incisional complications (31.2%) in our study is lower than that previously reported following ventral approaches to the abdomen of cattle (35.7%) (28), but greater than that for ventral midline laparotomies in horses (15% to 25.4%) (23,29,30) and ewes (18.2%) (7). It is possible that the increased prevalence of incisional complications in our study reflected the prolonged period before skin sutures were removed. Most of the incisional complications encountered in our study were minor and represented suture sinus formation associated with the skin sutures.
Bacterial contamination of the skin around the area of the healing surgical site was increased due to mud in the environment of the ewes and the ventral location of the surgical sites. Presence of dirt could have more easily favored the formation of biofilm and sinuses around the skin sutures in sheep having late suture removal (22 to 23 d), as was the case in ewes of group PG. These findings stress the importance of management of the postoperative environment in prevention of SSI.
Incidence of incisional herniation was not different between PG and PD groups in our study despite the presence of incisional infection (31). Sample size and low frequency of incisional herniation may have limited detection of a small difference between study groups.
We chose to re-appose the laparotomy incisions in 2 continuous layers to increase efficiency. Two-layer closure of ventral midline approach has been validated in the horse for closure of ventral midline celiotomy (32). A continuous pattern for closure of the linea alba, as performed in our study, is expected to be stronger than an interrupted suture pattern and leaves less suture material as a foreign body in the incision (15). Skin may be re-apposed in simple interrupted, simple continuous, or Ford-interlocking suture pattern using a synthetic monofilament suture material, such as polypropylene. We chose to use a simple continuous suture pattern for its speed and simplicity.
The main limitation in the interpretation of our data is that the study design did not allow for control of all confounding factors. Skin sutures were removed at various times after surgery. Incisional complications are expected to occur more commonly when non-absorbable skin sutures are left in place for periods longer than that required for skin healing. Sutures may act as foreign body around which a biofilm may form. The variable periods before suture removal acted as a confounding factor for which the effect could only be determined in group PG. Therefore, it is possible that the greater prevalence of incisional complications only reflect the longer period before skin suture removal. Three veterinarians, with practice experience ranging from 1 to 5 y, closed the laparotomy incisions. Risk of incisional complication may be increased when less-experienced surgeons are responsible for closing surgical sites (30). With 3 veterinarians closing the incision, factors such as tissue bite size, tension on the continuous patterns, and ratio of length of suture inserted to the wound length may have varied between ewes. However, an effect of the veterinarian was not found. Differences in average surgical time could have played a role in the prevalence of incisional complications. Operative time is an extrinsic risk factor for development of incisional complications after laparotomy in horses. Risk of postoperative incisional complications is twice as likely when duration of laparotomy is longer than 2 h (33). In the authors’ opinion, it is unlikely that the variable, but short average surgical duration played a role in the development of SSI in the present study. Furthermore, it was impossible to determine the effect of surgery duration because all incisions closed with the longest surgical times were closed with the same suture material (PG910). Suboptimal environmental conditions are more likely to have played a role in SSI in this study.
The results of this study indicate that delays in suture removal from patients in contaminated environments may increase the risk of development of complication, particularly skin suture sinus formation. This complication is expected to be self-limiting after skin suture removal. Either PG910 or PDS may be used for closure of the linea alba in a ventral abdominal incision in sheep.
Acknowledgments
This research was funded by New Generations Feeds, Belle Fourche, South Dakota, and the Kansas Agricultural Experiment Station (Contribution No. 14-365-J). The authors thank Harold Mellieon, Stephanie Pulley, Michael Macek, Mikki Nienhueser, Stephanie Bailey, Hannah Leventhal, and Theresa Rathbun from the Department of Animal Science and Industry, and Drs. José J. Bras and Brandon D. McBride from the Department of Clinical Sciences, Kansas State University for help with surgeries and sheep handling during the project. The authors also thank Dr. Guy Beauchamp from the Faculté de médecine vétérinaire, Université de Montréal for assistance with statistical analysis. CVJ
Footnotes
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References
Articles from The Canadian Veterinary Journal are provided here courtesy of Canadian Veterinary Medical Association
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