Comparison of incisional bursting strength of a bidirectional absorbable knotless suture material versus a standard continuous absorbable suture material for closure of the equine linea alba

Objective: To evaluate the use of bidirectional knotless barbed suture material for closure of the equine linea alba. Study design: Laboratory study. Animal or sample population: Adult light horse cadavers ( n = 24). Methods: A 25 cm incision was made through the linea alba, and a 200 L poly-urethane bladder was positioned within the abdomen. The linea alba was closed either using USP2/EP5 bidirectional polydioxanone barbed suture or USP2/EP5 standard polydioxanone suture in a simple continuous pattern. Closure time was recorded for each suture type. The bladder was air-insufflated at 40 L/min, and the pressure at body wall failure recorded. The length of suture used for wound closure and wound failure modes were recorded. Suture length, closure time, bursting pressure, and failure modes were compared using Welch-Aspin t -tests. Results: The incisional bursting pressure was comparable between the two groups ( p > .05). Less suture material ( p < .01) was required with the barbed


| Horses
A total of 24 mature horses, weighing over 350 kg, that were euthanized for reasons unrelated to the study were randomly assigned to either a barbed suture or a standard suture group.Experimental work was carried out on animals within 2 h of euthanasia in common with previous studies investigating suture efficacy.Information regarding breed, sex, age, and use was recorded for each cadaver.
The inclusion criteria for cadavers were as follows: No previous history of abdominal surgery or obvious abdominal wall abnormalities.Post-experimental histopathological examination of cadaver material was also performed to exclude any cases with underlying pathology which could have affected the results.
Ethical approval was sought and obtained from the School of Veterinary Medicine ethics and welfare committee.Owners were provided with an information sheet, following which they were asked to sign a consent form allowing the cadavers of their horses to be used for the study.

| Surgical procedure and instrumentation
Following euthanasia, cadaver horses were placed in dorsal recumbency, and a 4 cm-wide nylon strap was placed around the abdomen just cranial to the pelvis to prevent failure and herniation through the inguinal fascia and/or rectum during abdominal inflation, as previously reported by Magee and Galuppo. 29 40 cm ventral midline skin incision was made over the linea alba that was identified by palpation, and the subcutaneous tissue was then dissected to allow observation of the suture/linea alba construct during testing.A plastic template and tissue pen were used to standardize the length of the linea alba incision and position and to standardize suture placement.The fascia of the abdomen was marked for 25 cm using the pen beginning at the umbilicus and extending cranially.Using a No. 10 scalpel blade, the linea alba was incised starting at the umbilicus.Any deviation from the linea alba, which resulted in exposed muscle fibers, was recorded.The peritoneum was entered bluntly using the index finger, and the defect was enlarged.
Incisional testing was performed using an experimental model described by Magee and Galuppo. 29A custom 0.9 Â 1.2 m rectangular, 200 L capacity polyurethane bladder (New World Mfg, Cloverdale, California) was positioned flat in the abdomen along the ventral body wall. 29Onecentimeter incisions were made between the 14th and 15th rib, in the middle one-third of the left and right intercostal space, to provide access for the ingress and egress tubing (0.8 cm outer diameter). 29The ingress tubing was exteriorized through a right lateral stab incision while the egress tubing was exteriorized through a left lateral stab incision. 29he ingress tubing was connected to an air compressor (MaxxAir Premium Compressor, Heyner, Brandenburg, Germany) and a flow meter (MMA-26 flow meter; Dwyer Instruments, Michigan City, Indiana) for bladder insufflation. 29The egress tubing was connected to a transducer (PX 212 series pressure transducer; Omega Engineering, Stamford, Connecticut) and digital display (DP 25B-S strain gauge meter; Omega Engineering) for pressure recording. 29ll incisions were closed using a simple continuous pattern with tissue bites standardized at 15 mm from the edge of the incision and 15 mm apart by using the previously placed marks.
Cadavers were randomly assigned by selecting a number one or two from a bag for closure of the line alba to two different groups: 1. Barbed suture: Closure of the incision using one pack of polydioxanone USP2/EP5 bidirectional knotless barbed suture on a swaged 1/2 curve 48 mm taper needle with a 90 cm working length (Quill; Quill PDO; Surgical Specialities Corporation, Wyomissing, Pennsylvania).Closure of the linea alba was started at the center of the incision.The suture line was ended outside the incision (10 mm cranial or caudal) before being reversed by taking two retrograde passes for 2 cm to lock the suture in position as described by the manufacturer. 3. Standard suture: Closure of the incision using one pack of polydioxanone USP2/EP5 on a swaged 1/2 curve 48 mm taper needle with a 150 cm working length (PDS, Ethicon, Johnson and Johnson, Markham, Ontario, Canada).Closure of the linea alba using the standard suture was started at the caudal aspect of the incision in one section with a knot at each end.The cranial and caudal knots were placed outside the incision (10 mm cranial or caudal) and tied with a surgeon's knot followed by four square throws (six throws total), leaving the suture ends 10 mm long.The knots were tied using Mayo-Hegar needle holders.
Celiotomies were created by an ECVS diploma holder and closed by a surgery resident under supervision of the ECVS diploma holder.The skin and subcutis were left unopposed to allow observation of the suture and linea alba construction during insufflation of the polyurethane bladder.Closure time for each incision was recorded using a stopwatch.The length of the suture material used for incisional closure was recorded, in centimeters, by measuring the suture that was left after closure and comparing this with the original suture length.

| Testing
After closure of the incision, the polyurethane bladder was inflated at 40 L/min, and the bursting pressure (mmHg) of the abdomen was recorded.Each failure was recorded using a digital video recorder (iPhone 7, Apple, California), allowing failure method, time to failure and any other complications to be recorded.Digital images of all failed incisions were taken using a digital camera (iPhone 7, Apple, California).For each incision, the mode of failure (suture or fascia) was recorded after evaluation of slow-motion video with direct visualization of the incision site.
Failure mode (suture or abdominal wall) was determined for each incision.Suture failure for the standard suture was defined as suture breakage in close proximity to the knot, knot slippage, knot breakage, or breakage more than 1 cm away from the knot before abdominal wall failure.Suture failure for the barbed suture was defined as the breakage of the suture at any point.Failure of the abdominal wall was defined as a "local failure," when intact suture tore through the linea alba, or as "remote failure," when the body wall failed adjacent to the incision.Type of failure modes were expressed as percentages for each suture type.Failure of the abdominal wall was defined as a "local failure," when intact suture tore through the linea alba, or as "remote failure," when the body wall failed adjacent to the incision.Type of failure modes were expressed as percentages for each suture type.

| Statistical analysis
Welch-Aspin t-tests were used to compare centimeter deviation from the linea, closure time, amount of suture used for closure of the incision, bursting pressure, and failure mode between the barbed and standard suture material.

| RESULTS
A total of 24 equine cadavers were used, and breeds included Thoroughbreds, Warmbloods, Native breed ponies and crossbreeds.Ages ranged from 4 to 17 years.All horses weighed over 350 kg (range 364-598 kg).Histopathological examination of tissue adjacent to the incision sites did not identify any pre-existing abnormalities that could have influenced the results in any of the cadavers.
Suture failure was the main failure mode for both the barbed and standard sutures (83% of cases), occurring in close proximity to all the knots for the standard suture group and at various locations along the suture for the barbed suture group (Table 2).Suture failure of the barbed suture resulted only in a partial breakage of the incision with most of the residual portion of the suture line remaining unaltered (both edges closed) in all cases; suture failure of the standard suture resulted in a complete breakdown of the suture line in all cases.The remaining two cases of the barbed suture group failed laterally from the linea alba (remote failure; 17%) while one case of the standard suture group failed immediately adjacent to the line alba (local failure; 8.5%) and the other case failed laterally from the linea alba (remote failure; 8.5%) (Table 2).There were no effects of age, breed, or sex.

| DISCUSSION
The use of a bidirectional barbed suture material represents a novel and attractive approach to the closure of the equine linea alba.Despite the self-locking system, bidirectional barbed sutures were found to be easy to use. 1,3t was determined that the bidirectional barbed knotless suture did not have a higher bursting strength than the standard suture with similar mean bursting strengths values being recorded in both groups.Closure of the equine line alba using the barbed suture took less time and resulted in less suture material within the wound than the standard suture.
The suture size selected was USP2, currently the largest commercially available size for barbed sutures.Many ex vivo studies have suggested that larger sutures would be preferable for the closure of the equine linea alba. 27,36Despite this, USP2/EP5 suture materials, including polydioxanone, are commonly used in clinical practice following colic surgery with no reported increase in incisional complications. 22,28,30,31,35,397,38 Acute abdominal dehiscence following ventral midline celiotomy in horses has been reported to occur at the body wall, along the suture line or at the knot with suture breakage or knot slippage. 24,40In this study, suture failure was the principle mode of failure (83% of cases), occurring in close proximity to all the knots for the standard suture and at various locations along the suture line for the barbed suture.The results for the standard suture are comparable with the failure mode described in other studies. 27Anderson et al. 27 reported that the main mode of failure when using USP2/EP5 polyglactin 910 in a simple continuous pattern was at the suture line at the level of the knot (80% of cases).While studies using larger polydioxanone suture material (USP7/EP9) in a simple continuous pattern have reported that abdominal wall failure was the only mode of failure. 26,27,37The findings reported in this study suggest that modifying the structure of a monofilament suture thread such as in the barbed suture material does not affect the mechanical response of the suture. 17,18he characteristics of the barbed suture and its specific mode of failure may play a crucial role in preventing acute abdominal dehiscence in live horses.In this study, suture failure of the barbed suture resulted only in a T A B L E 1 Mean ± SD for measured variables for closure of the equine linea alba using the barbed suture and standard suture material.partial breakage of the incision, the length was not recorded, while most of the residual linea alba remained closed.Previous studies have suggested that in cases where the barbed suture should fail or the tissue tear at one point of the incision the rest of the incision could remain closed preventing dehiscence due the suture failing only as far as the nearest barb. 20This is supported by a recent clinical trial which found that barbed sutures, when used for abdominal fascial closure, reduced the incidence of acute abdominal dehiscence in people. 20nly the adoption of the use of barbed sutures in clinical cases will determine how the specific mode of failure of barbed suture may affect the incidence of postoperative dehiscence.

Barbed
In this study, it was noted that the mean value for the amount of suture left in the abdominal wall was less for the barbed suture compared to the standard suture.This finding is likely related to the absence of knots when using the barbed suture and has been reported by others. 1,3,41ne of the purported advantages of reducing the amount of suture material in the incision is that this should result in less inflammatory reaction and reduce the effect of the presence of the suture on infection risk. 2,3However, studies using animal models and evaluating histological sections of the line alba following closure have not reported any significant reduction in tissue inflammation between a polydioxanone barbed suture material over a standard polydioxanone suture material. 17,18A recent clinical trial on the closure of the abdominal wall in human surgery did not find any significant difference in the incidence of surgical site infection between cases in which a barbed suture or a standard suture was used. 20Further studies are required to determine how barbed sutures have an impact on the healing of the equine linea alba.
During this study, only one pack of barbed suture was utilized for each cadaver horse; however, if a clinical case with a longer incision required a second length of suture, this could simply begin in the center of the open section of the wound extending in both directions as described.There is no reason to believe this would affect the strength of the closure.
41][42][43] Multiple studies support the assumption that an extended duration of surgery and anesthesia are associated with higher surgical site infection rates. 28,31,44In human arthroplasty the reduced wound closure time obtained when using barbed sutures has been reported to reduce overall costs by saving operative time. 4,5he ex vivo model used in our study has been utilized widely and has been reported to closely reproduce the three-dimensional forces placed on a ventral midline incision following laparotomy in a horse. 27,29Alternative ex vivo models, that place the suture and body wall construct in a universal material testing machine and then perform a single cycle to failure test, have also been used to test suture materials and closure techniques for the equine linea alba. 36,45However, testing the bursting strength would seem to be a more appropriate method, allowing the forces to be more evenly distributed along the sutured linea alba and the abdominal body wall and therefore, more closely simulating the conditions that could be encountered postoperatively during recovery from general anesthesia or during an episode of violent colic that may result in acute abdominal dehiscence. 24,27he main limitation of this study was that the sudden increase in abdominal pressure used in this ex vivo model does not necessarily represent a good model for delayed suture failures that are more likely due to repeated cycling fatigue of the suture material and incision. 27,32Furthermore, bursting strength values representative of the changes in intra-abdominal pressures that can occur in live horses during the postoperative period are unavailable. 27Because of these limitations, studies using this ex vivo model should not be considered a complete replacement for studies involving clinical cases and should instead be considered auxiliary and informative for the development of clinical trials in the future.
In conclusion, closure of equine linea alba using a bidirectional knotless barbed suture material reduced the amount of foreign material in the incision and decreased closure time without compromising incisional strength.All these features could make the bidirectional barbed suture material an attractive alternative to conventional standard sutures.Due to the results of this study, it is anticipated that these findings will inform a study involving clinical cases which will allow further investigation into the use of barbed sutures for closure of the line alba in live horses.

AUTHOR CONTRIBUTIONS
Bellitto NA, DVM (Hons), MRCVS: The primary author made a substantial contribution to the interpretation of data of the work and manuscript preparation.Barcel o Oliver F, DVM, MRCVS: Contributed to data collection, data analysis, and critical revision of the manuscript.Pollock PJ, BVMS, PhD, CertES (Soft Tissue), FHEA, DipECVS, FRCVS: Contributed to the study design and critical revision of the manuscript.All authors approved the final version of the manuscript.
Lenka Veselovska, and the owners who so kindly donated the cadavers used in this study.Finally, we acknowledge the generous funding of the PetPlan Charitable Trust.
Failure mode for closure of the equine linea alba using the barbed suture and standard suture material.
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