Traditionally, closure of body wall incisions in companion animals has been accomplished by use of either a simple interrupted or simple continuous suture pattern. Closure with a simple interrupted suture pattern has the theoretical advantage in that the integrity of the entire incision is not compromised if a single suture breaks or cuts through the tissue. For that reason, a simple interrupted pattern may be advantageous for patients in which wound healing might be compromised or that are at an abnormally increased risk for wound dehiscence.1 However, the knot volume for simple interrupted patterns is greater than that for continuous suture patterns and may increase the risk of patient discomfort and tissue disruption, which in turn can increase the risk of foreign body reaction or infection.2,3 A simple interrupted pattern also takes longer to perform than continuous suture patterns and thereby increases the anesthesia duration for patients. Use of self-locking knots is an alternative to conventional surgical knots. Results of a previous study2 indicate that when polydioxanone or nylon suture material is used, the efficiency ranges from 0.88 to 0.96 for self-locking knots, compared with a mean efficiency of 0.7 for conventional knots. Furthermore, self-locking knots have zero slippage and a significantly smaller volume than conventional knots.2
The Aberdeen knot, a type of self-locking knot, was described by Sir James Learmonth in the 1930s.4 In human medicine, the Aberdeen knot is used as a starting and ending knot for continuous suture patterns during abdominal, visceral, vascular, and dermal closures.4,5 Various in vitro studies3,5–7 have evaluated the biomechanical properties of self-locking knots in relation to standard knots. In 1 study,6 the median tensile strength for an Aberdeen knot was slightly greater than that for both surgeon and square knots when single suture strands were tested. In another study5 that involved the use of plasma- and fat-coated polydioxanone suture material, starting and ending Aberdeen knots had greater tensile strength and a lower knot volume than starting and ending square knots. In a study7 in which closure of intradermal incisions in canine cadavers was terminated with either an Aberdeen or square knot, Aberdeen knots had greater stiffness and sustained comparable maximum loads and displacements relative to square knots. In a study3 that involved porcine skin, Aberdeen knots had less slippage (0%) than conventional square knots (10%); however, strength was comparable, and the peak load to failure did not differ between the 2 types of knots. Despite those findings, Aberdeen knots are not commonly used for surgical closures in veterinary medicine.
Aberdeen knots have been used in an intermittent fashion for closure of laparotomy incisions in human patients.1 This technique involves closure of the incision by use of a simple continuous suture pattern with Aberdeen knots tied every 4 to 6 bites. Theoretically, this method should be faster to perform than a simple interrupted suture pattern and have the same advantage of maintaining overall incisional integrity should 1 point within the suture line fail. Results of a retrospective study1 of laparotomy fascial wound closure in human patients indicate that patients with incisions closed with a simple continuous pattern with intermittent Aberdeen knots had a lower rate of chronic wound pain, infection, and stitch granuloma development and a similar rate of wound dehiscence, compared with patients with incisions closed with a simple interrupted pattern. To our knowledge, a study to evaluate the tensile strength of the body wall when closed with a simple continuous suture pattern, compared with that when closed with a simple continuous suture pattern with intermittent Aberdeen knots, has not been performed in human or veterinary medicine.
The purpose of the study reported here was to compare the tensile strength and time to completion between a simple continuous suture pattern with intermittent Aberdeen knots and conventional methods used for closure of the body wall of dogs. We hypothesized that the tensile strength of a continuous closure with intermittent Aberdeen knots would be greater than that of a simple continuous closure, but less than that of a simple interrupted closure, and that the time to completion for the continuous closure with intermittent Aberdeen knots would be significantly less (ie, faster) than that for a simple interrupted pattern.
Materials and Methods
Experiment 1
The study consisted of 2 experiments. In experiment 1, five 8.25 × 23.5-cm strips of leather were obtained from a commercial supplier.a The leather strips were cut into 18 equivalent 5 × 5-cm blocks (sample size, n = 18). A line was drawn with a marker along the midline (ie, 2.5 cm from the edge) of each block as a guide for future transection. Ten pinpoint markings were then made on both sides of the line to indicate where suture bites would be placed; the markings were placed 0.5 cm from the midline. The initial dot was placed 0.25 cm from an edge of the leather block, and subsequent dots were placed 0.5 cm from the previous dot such that the tenth and final dot on each side of midline was 0.25 cm from the opposite edge of the block (Figure 1). After all markings were completed, each block was transected along the midline. Each block was then sutured back together by use of 2–0 polydioxanone in 1 of 3 suture patterns by 1 board-certified veterinary surgeon (DAU) such that each suture pattern was replicated 6 times (ie, on 6 blocks). Pattern 1 consisted of 10 simple interrupted sutures tied with square knots with 5 throws/knot. Pattern 2 consisted of a simple continuous pattern with a total of 20 bites that was begun with a square knot with 5 throws and ended with an Aberdeen knot. Pattern 3 consisted of a simple continuous pattern with intermittent Aberdeen knots (intermittent Aberdeen pattern); this pattern was begun with a square knot with 5 throws and had an Aberdeen knot tied between the 7th and 8th bites, 13th and 14th bites, and 19th and 20th bites. All Aberdeen knots were tied in a 3 + 1 configuration with 3 throws and 1 turn (Figure 2) because that configuration has reportedly good holding strength.8 All suture tags were cut to 3 mm in length.
Photographs depicting a strip of leather that was delineated with a marker into 3 equivalent 5 × 5-cm blocks before (A) and after each block was sutured with 1 of 3 suture patterns (B; experiment 1). A—A line indicating the location of the subsequent midline incision and pinpoint dots indicating the locations for placement of suture bites were made on the leather strip before it was cut into individual blocks. For each block, 10 dots were placed on each side of the marked incision. Each dot was approximately 0.5 cm from the marked incision, and the initial dot was placed 0.25 cm from an edge of the block with subsequent dots placed 0.5 cm from the previous dot such that the 10th and final dot on each side of the incision was 0.25 from the opposite edge of the block. After all markings were completed, each block was transected along the midline, then sutured with 2–0 polydioxanone in 1 of 3 suture patterns by 1 board-certified veterinary surgeon. B—Suture pattern 1 consisted of 10 simple interrupted sutures tied with square knots with 5 throws/knot. Suture pattern 2 consisted of a simple continuous pattern with a total of 20 bites that was begun with a square knot with 5 throws and ended with an Aberdeen knot. Suture pattern 3 consisted of a simple continuous pattern with intermittent Aberdeen knots (intermittent Aberdeen pattern); this pattern was begun with a square knot with 5 throws and had an Aberdeen knot tied between the 7th and 8th bites, 13th and 14th bites, and 19th and 20th bites. All Aberdeen knots were tied in a 3 + 1 configuration with 3 throws and 1 turn. All suture tags were cut to 3 mm in length. Each suture pattern was replicated on 6 leather blocks.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Photographs depicting a strip of leather that was delineated with a marker into 3 equivalent 5 × 5-cm blocks before (A) and after each block was sutured with 1 of 3 suture patterns (B; experiment 1). A—A line indicating the location of the subsequent midline incision and pinpoint dots indicating the locations for placement of suture bites were made on the leather strip before it was cut into individual blocks. For each block, 10 dots were placed on each side of the marked incision. Each dot was approximately 0.5 cm from the marked incision, and the initial dot was placed 0.25 cm from an edge of the block with subsequent dots placed 0.5 cm from the previous dot such that the 10th and final dot on each side of the incision was 0.25 from the opposite edge of the block. After all markings were completed, each block was transected along the midline, then sutured with 2–0 polydioxanone in 1 of 3 suture patterns by 1 board-certified veterinary surgeon. B—Suture pattern 1 consisted of 10 simple interrupted sutures tied with square knots with 5 throws/knot. Suture pattern 2 consisted of a simple continuous pattern with a total of 20 bites that was begun with a square knot with 5 throws and ended with an Aberdeen knot. Suture pattern 3 consisted of a simple continuous pattern with intermittent Aberdeen knots (intermittent Aberdeen pattern); this pattern was begun with a square knot with 5 throws and had an Aberdeen knot tied between the 7th and 8th bites, 13th and 14th bites, and 19th and 20th bites. All Aberdeen knots were tied in a 3 + 1 configuration with 3 throws and 1 turn. All suture tags were cut to 3 mm in length. Each suture pattern was replicated on 6 leather blocks.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Photographs depicting a strip of leather that was delineated with a marker into 3 equivalent 5 × 5-cm blocks before (A) and after each block was sutured with 1 of 3 suture patterns (B; experiment 1). A—A line indicating the location of the subsequent midline incision and pinpoint dots indicating the locations for placement of suture bites were made on the leather strip before it was cut into individual blocks. For each block, 10 dots were placed on each side of the marked incision. Each dot was approximately 0.5 cm from the marked incision, and the initial dot was placed 0.25 cm from an edge of the block with subsequent dots placed 0.5 cm from the previous dot such that the 10th and final dot on each side of the incision was 0.25 from the opposite edge of the block. After all markings were completed, each block was transected along the midline, then sutured with 2–0 polydioxanone in 1 of 3 suture patterns by 1 board-certified veterinary surgeon. B—Suture pattern 1 consisted of 10 simple interrupted sutures tied with square knots with 5 throws/knot. Suture pattern 2 consisted of a simple continuous pattern with a total of 20 bites that was begun with a square knot with 5 throws and ended with an Aberdeen knot. Suture pattern 3 consisted of a simple continuous pattern with intermittent Aberdeen knots (intermittent Aberdeen pattern); this pattern was begun with a square knot with 5 throws and had an Aberdeen knot tied between the 7th and 8th bites, 13th and 14th bites, and 19th and 20th bites. All Aberdeen knots were tied in a 3 + 1 configuration with 3 throws and 1 turn. All suture tags were cut to 3 mm in length. Each suture pattern was replicated on 6 leather blocks.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Photograph of an Aberdeen knot with a 3 + 1 configuration (ie, 3 throws and 1 turn), which was used for all such knots in both experiments 1 and 2.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Photograph of an Aberdeen knot with a 3 + 1 configuration (ie, 3 throws and 1 turn), which was used for all such knots in both experiments 1 and 2.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Photograph of an Aberdeen knot with a 3 + 1 configuration (ie, 3 throws and 1 turn), which was used for all such knots in both experiments 1 and 2.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Experiment 2
Seventeen cadavers of dogs that were euthanized for reasons unrelated to the study were used for experiment 2. Four samples were obtained from each cadaver, resulting in a sample size of 68. The cadavers had been stored at −40°C since euthanasia and were defrosted in a cooler at a temperature of 4°C within 9 days prior to initiation of the experiment (defrosting time). The sex, body weight, and reproductive status were recorded for each cadaver. Additionally, the duration between defrosting and experimental implementation and between experimental implementation and freezing of samples was recorded.
After each cadaver was defrosted, the ventral portion of the abdomen was shaved and cleaned of hair and debris. A No. 10 scalpel blade was used to incise the skin and subcutaneous tissue to the level of the body wall. Metzenbaum scissors were used to dissect the subcutaneous tissue from the external rectus sheath. Then, a water-based paint pen was used to highlight the linea alba from the xiphoid process to the pubis. The marker was then used to delineate 4 blocks along the midline. Each block was 5 cm in length from the cranial to caudal edge and extended 2.5 cm laterally on either side of the linea alba. Pinpoint markings were made with the paint pen to indicate where suture bites would be placed in the same manner as that used for the leather blocks of experiment 1. Each block was classified into 1 of 4 sites on the basis of its craniocaudal location along the linea alba (Figure 3).
Representative photograph of the ventral portion of the abdomen of a canine cadaver after the skin has been incised and deflected, the subcutaneous tissue has been dissected to the level of the body wall, and four 5 × 5-cm tissue blocks along with the linea alba and locations for suture placement have been delineated with a water-based paint pen (experiment 2). Each tissue block was categorized into 1 of 4 categories on the basis of its location within the cadaver. Location A was the most cranial and was located just caudal to the xiphoid; locations B, C, and D followed sequentially in a caudal direction, with location D being the most caudal and located just cranial to the pubis. Seventeen cadavers were used in experiment 2. Within each cadaver, each of the 4 tissue blocks was assigned to 1 of 4 treatments (ie, 17 replications/treatment). For 3 of the 4 blocks, the linea alba was incised then closed with 2–0 polydioxanone in 1 of the 3 suture patterns (simple interrupted, simple continuous, or intermittent Abderdeen) described in Figure 1 by 1 of 2 surgeons (a board-certified veterinary surgeon [experienced surgeon] and a fourth-year veterinary student with 1 year of clinical experience [novice surgeon]). The linea alba was left intact for the remaining block (control). A block randomization method was used to assign a treatment to each block, with suture pattern considered the primary outcome factor and dog, site, and surgeon included as additional factors in the randomization. See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Representative photograph of the ventral portion of the abdomen of a canine cadaver after the skin has been incised and deflected, the subcutaneous tissue has been dissected to the level of the body wall, and four 5 × 5-cm tissue blocks along with the linea alba and locations for suture placement have been delineated with a water-based paint pen (experiment 2). Each tissue block was categorized into 1 of 4 categories on the basis of its location within the cadaver. Location A was the most cranial and was located just caudal to the xiphoid; locations B, C, and D followed sequentially in a caudal direction, with location D being the most caudal and located just cranial to the pubis. Seventeen cadavers were used in experiment 2. Within each cadaver, each of the 4 tissue blocks was assigned to 1 of 4 treatments (ie, 17 replications/treatment). For 3 of the 4 blocks, the linea alba was incised then closed with 2–0 polydioxanone in 1 of the 3 suture patterns (simple interrupted, simple continuous, or intermittent Abderdeen) described in Figure 1 by 1 of 2 surgeons (a board-certified veterinary surgeon [experienced surgeon] and a fourth-year veterinary student with 1 year of clinical experience [novice surgeon]). The linea alba was left intact for the remaining block (control). A block randomization method was used to assign a treatment to each block, with suture pattern considered the primary outcome factor and dog, site, and surgeon included as additional factors in the randomization. See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Representative photograph of the ventral portion of the abdomen of a canine cadaver after the skin has been incised and deflected, the subcutaneous tissue has been dissected to the level of the body wall, and four 5 × 5-cm tissue blocks along with the linea alba and locations for suture placement have been delineated with a water-based paint pen (experiment 2). Each tissue block was categorized into 1 of 4 categories on the basis of its location within the cadaver. Location A was the most cranial and was located just caudal to the xiphoid; locations B, C, and D followed sequentially in a caudal direction, with location D being the most caudal and located just cranial to the pubis. Seventeen cadavers were used in experiment 2. Within each cadaver, each of the 4 tissue blocks was assigned to 1 of 4 treatments (ie, 17 replications/treatment). For 3 of the 4 blocks, the linea alba was incised then closed with 2–0 polydioxanone in 1 of the 3 suture patterns (simple interrupted, simple continuous, or intermittent Abderdeen) described in Figure 1 by 1 of 2 surgeons (a board-certified veterinary surgeon [experienced surgeon] and a fourth-year veterinary student with 1 year of clinical experience [novice surgeon]). The linea alba was left intact for the remaining block (control). A block randomization method was used to assign a treatment to each block, with suture pattern considered the primary outcome factor and dog, site, and surgeon included as additional factors in the randomization. See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Within each cadaver, each of the 4 blocks was assigned to 1 of 4 treatments. For 3 of the 4 blocks, the linea alba was incised and then closed with 1 of the 3 suture patterns (simple interrupted [pattern 1], simple continuous [pattern 2] or intermittent Aberdeen [pattern 3]) described for experiment 1, whereas the linea alba was left intact for the remaining block (control). A block randomization method was used to assign a treatment to each block, with suture pattern considered the primary outcome factor and dog, site, and surgeon included as additional factors in the randomization. Closure of the linea alba was performed by either a board-certified veterinary surgeon (experienced surgeon; DAU) or a fourth-year veterinary student with 1 year of clinical experience (novice surgeon; EB). All suture patterns were completed with 2–0 polydioxanone, and the sutures were placed through only the external rectus sheath to mimic in vivo abdominal closure. Suture tags were trimmed by the surgeon during closure to simulate in vivo surgery and cut precisely to 3 mm after the assigned suture pattern was completed to maintain consistency. The time to completion was defined as the time that elapsed between the surgeon placing the first suture bite and cutting of the last suture tag for the assigned pattern. It was measured in seconds and recorded for each block.
After all 4 treatments had been completed on a cadaver, the tissue blocks were excised from the abdomen along the marked lines (Figure 4), individually wrapped in a moist paper towel, and placed in a sealed freezer bag.b The tissue blocks were immediately placed in a cooler and maintained at 4°C until they could be frozen. All samples were frozen within 48 hours after completion of suturing.
Representative photographs of tissue block specimens assigned to the simple interrupted (A), control (B), intermittent Aberdeen (C), and simple continuous (D) treatments described in Figure 3 after completion of the assigned treatment and excision of the blocks from a canine cadaver. See Figure 3 for remainder of key.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Representative photographs of tissue block specimens assigned to the simple interrupted (A), control (B), intermittent Aberdeen (C), and simple continuous (D) treatments described in Figure 3 after completion of the assigned treatment and excision of the blocks from a canine cadaver. See Figure 3 for remainder of key.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Representative photographs of tissue block specimens assigned to the simple interrupted (A), control (B), intermittent Aberdeen (C), and simple continuous (D) treatments described in Figure 3 after completion of the assigned treatment and excision of the blocks from a canine cadaver. See Figure 3 for remainder of key.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
A flash-freezing method was used to freeze the tissue blocks and prevent deterioration of the specimens prior to mechanical testing. Briefly, 100 mL of 99% isopentane was placed in a beaker that was surrounded with dry ice and cooled for 10 minutes. Then, 100 mL of dry ice was added to the isopentane and allowed to intersperse for 10 minutes, during which time the tissue blocks were soaked in a 30% sucrose-PBS solution for 2 minutes and then individually wrapped in aluminum foil. The foil-wrapped specimens were then placed in the prepared isopentane–dry ice mixture for 1 to 2 minutes, after which the specimen was considered frozen. The flash-frozen tissue blocks were then stored at −80°C until mechanical testing.
Mechanical apparatus and testing
Tissue block specimens were defrosted for 24 hours at 4°C prior to mechanical testing. The maximum tensile force was measured for each leather block of experiment 1 and tissue block of experiment 2 by use of a custom-built uniaxial testing apparatus.c Two motors applied displacement in the direction perpendicular to the suture line, during which force was measured by an attached load cell. Custom-built clamps were used to hold each specimen such that the plane of the tissue was parallel to the ground. The addition of steel material with a corrugated surfaced on the opposing surfaces of the clamps provided a gripping surface to prevent slippage of the specimens. The dimensions of each specimen were measured in millimeters with a digital fractional calipere before and after mounting. Measurements included the length of the specimen parallel to the suture line (block width), length of the specimen perpendicular to the suture line between the clamps (block length), and maximum thickness of the specimen along the suture line. The load cell was set to the zero position prior to mounting and the nondeformed position after mounting. The nondeformed position was defined as the distance for which the load cell provided a reading of 0 g without the specimen becoming compressed.
Each tissue specimen of experiment 2 was preconditioned for 10 cycles at 40% strain, measured with reference to the unloaded dimensions after mounting. This preconditioning protocol ensured repeatable results throughout the mechanical test. Preconditioning was performed on several pilot leather block specimens similar to those created for experiment 1. The block dimensions and Fmax did not differ significantly between preconditioned and unpreconditioned specimens; therefore, experiment 1 specimens were not preconditioned before mechanical testing.
Each specimen was distracted at a rate of 100 mm/min until failure was achieved. During each test, data were captured with a video cameraf at 54 frames/s. A computer software programg was used to capture and analyze tensile strength as described.3,6 For each specimen, the Fmax was recorded, and the video recording was reviewed frame by frame to determine mode of failure. Modes of failure included knot breakage, knot unraveling, tearing of tissue not adjacent to the suture line, and tearing at the suture-tissue interface (suture cut through).
During testing of experiment 2 specimens, the 4 initial specimens tested slipped from the custom-built grips at first distraction. Those specimens were retested a second time with the custom-built grips engaging the tissue closer to the suture line (mean distance from suture line, 9 mm). None of the 4 specimens slipped from the grips during the second test. The remainder of the tissue block specimens of experiment 2 underwent mechanical testing with the tissue engaged by the custom-built grip at approximately the same location as that used for the second test for the 4 initial samples. The Fmax recorded during the second test for each of the initial 4 specimens (range, 80.9 to 133.6 N) was within the Fmax range (42.7 to 238.2 N) for the remainder of the experiment 2 specimens that underwent only 1 test; therefore, the mode of failure for each of the 4 initial specimens was included in the analysis.
Statistical methods
All statistical analyses were performed with a commercially available software package.h Mode of failure and Fmax were the outcomes of interest, or dependent variables, for both experiments 1 and 2. For experiment 1, the only independent variable assessed was suture pattern. For experiment 2, time to completion was also assessed as a dependent variable, and independent variables assessed included suture pattern, block site, sex of cadaver, and surgeon. The correlation between sex (a between-dog factor) and each outcome variable was assessed by means of a 1-way ANOVA. The respective correlations between the other independent variables and each outcome variable were evaluated by means of a repeated-measures 1-way ANOVA with compound symmetry used to model covariance.
For all models, error terms were assessed for normality with a Shapiro-Wilk test and visual evaluation of a probability plot, and normality was confirmed in all cases. Values of P ≤ 0.05 were considered significant for all main effects. When multiple pairwise comparisons among block sites or suture patterns were necessary, a Bonferroni adjustment (0.05/number of pairwise comparisons) was used to prevent type I error inflation and establish significance. Adjustment for multiplicity was not performed. Results were presented as the mean ± SE. Additionally for tissue specimens of experiment 2, linear regression was used to evaluate the respective effects of the duration from the cadaver being placed in the cooler for defrosting to initiation of suturing (ie, time from defrosting to suturing) and duration from completion of suturing to flash-freezing on Fmax.
A pre hoc power analysis was not performed because similar experiments had not been performed; thus, the SD for the results could not be predicted. However, the number of specimens used in experiment 2 was comparable to that used in another study9 in which biomechanical variables of stainless steel facial stables and polypropylene suture material for closure of the linea alba of dogs were evaluated.
Results
Experiment 1
For the sutured leather block specimens of experiment 1, the mean tensile strength for specimens sutured with a continuous pattern (simple continuous and interrupted Aberdeen patterns) was significantly greater than that for specimens sutured with the simple interrupted pattern. The mode of failure was suture rupture for all specimens. For all 6 of the specimens sutured with the simple interrupted pattern, a single knot failed initially and then knot failure was propagated through the remaining knots; the fourth knot from an edge was the first knot to fail for 4 of the 6 specimens. The videos for 2 of the 12 specimens closed with a continuous suture pattern were unsuitable for data analyses; therefore, there were only 10 specimens evaluated for the simple continuous and interrupted Aberdeen patterns combined. Among those 10 samples, there was not a common location for initial suture failure or propagation of suture line failure. Some specimens failed at an edge initially with subsequent suture rupture in the center, whereas other specimens had suture failure near or at the middle of the suture line initially. The mode of failure was knot failure for 1 specimen, suture failure at the middle of the suture line for 5 specimens, and simultaneous failure of a knot and suture at the middle of the suture line for the remaining 4 specimens.
The mean ± SE Fmax for specimens sutured with the simple interrupted pattern (201.58 ± 6.69 N; range, 195.17 to 212.90 N) was significantly lower than that for specimens sutured with the simple continuous pattern (255.65 ± 48.92 N; range, 198.67 to 322.16 N; P = 0.012) and specimens sutured with the intermittent Aberdeen pattern (261.62 ± 24.98 N; range, 221.57 to 291.54 N; P = 0.007). However, the mean Fmax did not differ significantly (P = 0.744) between specimens sutured with the simple continuous pattern and those sutured with the intermittent Aberdeen pattern.
Experiment 2
For the tissue specimens of experiment 2, there was a small negative correlation (R2 = 0.292) between time from defrosting to suturing and Fmax, which was not significant (P = 0.589). To remove any effect of incising and suturing of the tissue specimens, that analysis was repeated for the control samples only, and similar results were obtained (Figure 5). The time from completion of suturing to flash-freezing of the specimens was not significantly (P = 0.051) correlated with Fmax. The Fmax was not significantly associated with surgeon (P = 0.213), suture pattern (P = 0.515), or sex of the cadaver (P = 0.353) but was significantly (P = 0.015) associated with block site. The mean ± SE Fmax for blocks located at site B (137.25 ± 9.49 N) was significantly (P = 0.002) greater than that for blocks located at site D (109.93 ± 9.49 N) but did not differ significantly for any of the other 5 pairwise comparisons. When data were combined into 2 block-site strata for analysis (ie, data for block sites A and B [cranialmost sites] were compared with data for block sites C and D [caudalmost sites]), the mean ± SE Fmax for the cranialmost sites (155.14 ± 12.8 N) was significantly (P = 0.038) greater than that for the caudalmost sites (104.88 ± 12.1 N).
Scatterplot of cadaver defrosting time by subsequent Fmax for control tissue block specimens obtained from each of 17 canine cadavers that were used in experiment 2. Each dot represents the results for 1 cadaver, and the line represents the linear regression line, which had an equation of y = −7.1881x + 166.15, R2 = 0.292, and P = 0.589.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Scatterplot of cadaver defrosting time by subsequent Fmax for control tissue block specimens obtained from each of 17 canine cadavers that were used in experiment 2. Each dot represents the results for 1 cadaver, and the line represents the linear regression line, which had an equation of y = −7.1881x + 166.15, R2 = 0.292, and P = 0.589.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Scatterplot of cadaver defrosting time by subsequent Fmax for control tissue block specimens obtained from each of 17 canine cadavers that were used in experiment 2. Each dot represents the results for 1 cadaver, and the line represents the linear regression line, which had an equation of y = −7.1881x + 166.15, R2 = 0.292, and P = 0.589.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.115
Among the 51 tissue blocks that were sutured with 1 of the 3 suture patterns, the most common mode of failure was suture cut through at the suture-tissue interface (n = 34) followed by tearing of tissue not adjacent to the suture line (19), knot breakage (4), and knot unraveling (2); some tissue blocks had multiple modes of failure. The mode of failure was tearing of tissue not adjacent to a suture line for all 17 control tissue blocks. For the 2 tissue blocks that failed because of knot unraveling, it was a square knot that unraveled. Mode of failure was not significantly associated with surgeon (P = 0.738), suture pattern (P = 0.255), or block site (P = 0.231).
The mean time to completion for the simple interrupted pattern (352.47 seconds) was significantly (P < 0.001) greater than that for both the simple continuous pattern (132.06 seconds) and intermittent Aberdeen pattern (158.12 seconds), but did not differ significantly (P = 0.039 [P < 0.017 required for significance after Bonferroni adjustment for multiple pairwise comparisons]) between the simple continuous and intermittent Aberdeen patterns. The mean time to completion did not differ significantly (P = 0.156) between the experienced surgeon and novice surgeon for any of the 3 suture patterns (Table 1).
Mean time to completion for each of 3 suture patterns (simple interrupted, simple continuous, and intermittent Aberdeen) used to close incisions in the linea alba of 5 × 5-cm tissue block specimens obtained from the ventral portion of the abdomen of 17 canine cadavers for each of 2 surgeons (a board-certified veterinary surgeon [experienced surgeon] and a fourth-year veterinary student with 1 year of clinical experience [novice surgeon]).
| Both surgeons | Experienced surgeon | Novice surgeon | ||||
|---|---|---|---|---|---|---|
| Suture pattern | No. performed | Mean time to completion (s) | No. performed | Mean time to completion (s) | No. performed | Mean time to completion (s) |
| Simple interrupted | 17 | 352.47 | 9 | 325.11 | 8 | 383.25 |
| Simple continuous | 17 | 132.06 | 9 | 110.00 | 8 | 156.88 |
| Intermittent Aberdeen | 17 | 158.12 | 8 | 136.00 | 9 | 177.78 |
| Total | 51 | 214.21 | 26 | 192.46 | 25 | 236.84 |
The simple interrupted pattern consisted of 10 simple interrupted sutures tied with square knots with 5 throws/knot. The simple continuous pattern consisted of 20 bites and was begun with a square knot with 5 throws and ended with an Aberdeen knot. The intermittent Aberdeen pattern consisted of a simple continuous pattern with Aberdeen knots placed intermittently; this pattern was begun with a square knot with 5 throws and had an Aberdeen knot tied between the 7th and 8th bites, 13th and 14th bites, and 19th and 20th bites. All Aberdeen knots were tied in a 3 + 1 configuration with 3 throws and 1 turn. All suture tags were cut to 3 mm in length. The mean time to completion did not differ significantly (P = 0.156) between the experienced and novice surgeons.
Discussion
In the present in vitro study, use of the Aberdeen knot as the ending knot in a simple continuous suture pattern as well as in an intermittent fashion during a continuous suture pattern was assessed for body wall closure in dogs. Results of studies involving horses10 and human patients11 indicate that the thickness of the linea alba, orientation of collagen fibrils, sex of the patient, and width of tissue bites affect the tensile strength of sutured or intact linea alba. Those factors were eliminated during experiment 1 of the present study because the suture patterns assessed were applied to uniform leather specimens, and the width of the suture bites were precise and consistent. We hypothesized that a simple interrupted pattern would have greater tensile strength than the 2 continuous suture patterns assessed because, if 1 suture in a simple interrupted pattern fails, the remainder of the suture line maintains its integrity. However, results of the present study indicated that multiple knots in a simple interrupted suture pattern failed almost simultaneously when the suture line reached its Fmax. Furthermore, the mean Fmax for both of the continuous suture patterns evaluated was significantly greater than that for the simple interrupted pattern, which led us to reject our hypothesis. In fact, results of this in vitro study indicated that a simple continuous suture pattern and intermittent Aberdeen suture pattern had comparable biomechanical properties when used to close the body wall of canine cadavers.
In experiment 1 of the present study, the mean Fmax did not differ significantly between leather specimens that were closed with the simple continuous pattern and those closed with the intermittent Aberdeen pattern. Results of a post hoc power analysis indicated that a sample size of 240 would be necessary to detect a 10-N difference between those 2 suture patterns. Although the magnitude of change in tensile strength that would be clinically relevant is currently unknown, investigators of another study9 reported that a tensile strength difference of 7 N was significant between 2 methods of body wall closure in dogs. It is possible that use of a larger sample size than that used in experiment 1 would have yielded significant differences between the simple continuous and interrupted Aberdeen patterns.
In experiment 2, tissue block site was the only independent variable assessed that was significantly associated with Fmax. In human patients, gender affects the biomechanical properties of the body wall,11 and age is presumed to have similar effects on those properties. Among the 17 canine cadavers used for experiment 2, 4 were female and 13 were male, and statistical analysis indicated that sex was not significantly associated with Fmax. However, a significant association between sex and the Fmax of the body wall may have been identified had a larger sample size with a more equal distribution of males versus females been evaluated. The age of the dogs at the time of euthanasia was not recorded for any of the cadavers used in the present study; therefore, we could not assess the effect of age on Fmax. Body weight was excluded from statistical analyses because medium-sized and large cadavers were specifically selected for experiment 2 to ensure that four 5 × 5-cm tissue blocks could be obtained from the ventral midline of each cadaver. The mean Fmax for the 2 cranialmost block sites (A and B) was significantly greater than that for the 2 caudalmost block sites (C and D), and the mean Fmax for block site B was significantly greater than that for block site D. Those differences may indicate that the holding strength of the linea alba decreases as it courses from the xiphoid to the pubis. Differences in the anatomic arrangement of the external and internal abdominal oblique and transverse abdominal muscles in the cranial to caudad direction are theorized as the basis for observed changes in the holding strength of the linea alba of human patients11 and may be responsible for differences in the holding strength of the linea alba of dogs as well. Within the linea alba of humans, the holding strength of transversely oriented collagen fibers is significantly less than that of longitudinally or obliquely oriented collagen fibers, and the majority (> 50%) of the infraumbilical (area caudal to the umbilicus) portion of the linea alba consists of transversely oriented collagen fibers, particularly in females (60.4%).11 In pigs, the holding strength of transverse collagen fibers associated with the infraumbilical linea alba is significantly less than that for the supraumbilical (area cranial to the umbilicus) linea alba, presumably because the presence of the external and internal abdominal oblique muscles increases the thickness and contributes to the holding strength of the supraumbilical linea alba relative to the infraumbilical linea alba.12 It is unclear whether the same holds true for dogs, although the results of the present study suggested that the holding strength of the supraumbilical linea alba was greater than that of the infraumbilical linea alba. Therefore, it may be beneficial to use a suture pattern with a high holding strength and Fmax when closing the infraumbilical portion of the linea alba in dogs.
In the present study, the intermittent Aberdeen pattern was completed more rapidly than the simple interrupted pattern, regardless of surgeon experience. In fact, the failure frequency and time to completion did not differ significantly between the experienced and novice surgeons for any of the 3 suture patterns evaluated. A possible explanation for that finding was that the 3 suture patterns evaluated were easy for the novice surgeon to master. However, time to completion and ease of closure improved over time for both surgeons, likely because surgeon familiarity with the suture patterns and tissue characteristics increased with repetition. This may have introduced bias in measurement of the time to completion for each suture pattern.
Use of an intermittent Aberdeen suture pattern for closure of body wall incisions in veterinary patients has several potential benefits. It can be performed more rapidly than a simple interrupted suture pattern, which will decrease the surgical and anesthesia times for patients. Additionally, it may decrease the risk for incisional dehiscence relative to use of a simple continuous suture pattern and decrease the risk for surgical site infections owing to a decrease in the volume of suture used, compared with that for simple interrupted suture patterns. However, further research is necessary to confirm or refute those suppositions.
A limitation of the present study was the lack of available information regarding the interaction between cadaver tissue and the custom-built tensiometer used for mechanical testing of the study specimens. Adjustments, such as increasing the grip strength by modification of the custom-built tissue clamps, had to be made to the apparatus during the initial stages of testing so that specimens could be appropriately tested without a high rate of slippage.
Another limitation of the present study was the lack of data regarding the effect of freezing and re-freezing on tissue specimen integrity. Of the 51 tissue specimens that underwent suturing, the majority (34 [67%]) failed because of suture cut through at the suture-tissue interface. It was impossible to determine whether those failures were representative of failures that would have occurred in vivo or were artifacts caused by weakening of the tissue microfibers induced by freezing and thawing of the specimens. The tissue block specimens were frozen and thawed a minimum of 2 times prior to mechanical testing: once in situ when the cadaver was frozen after euthanasia and again following completion of suturing and excision from the cadaver. Also, a small proportion of the cadavers had been stored frozen for an extended period (approx 1 year) before being thawed for experiment 2. Additionally, suturing of the external rectal sheath only might have adversely affected the holding strength of the suture line if tissue degradation in the cadaveric specimens was significantly different than that in in vivo tissue. However, the purpose of the present study was to compare the tensile strength among the 3 suture patterns. Therefore, although the Fmax for suture lines in cadaveric tissue might be lower than that expected in in vivo tissue, the overall relationship of tensile strength among the suture patterns should be representative of that in live dogs. Finally, the fact that the majority (34/51 [67%]) of sutured tissue specimens failed because of suture cut through indicated that, in this study, the tissue specimens tended to fail before the suture material. It is unknown whether the same would be true for in vivo tissues, but if it is, then the suture pattern used would have no effect on the tensile strength, and it may be more important to use the suture pattern that can be completed the quickest. However, this study needs to be repeated in live or recently deceased animals to determine that. Results of experiment 1 indicated that the mean tensile strength for both the simple continuous and intermittent Aberdeen patterns was significantly greater than that for the simple interrupted pattern, which may or may not be clinically relevant.
Results of a study10 involving horses indicated that the optimal distance from an incision through the linea alba for placement of sutures was 15 mm. In 2 studies9,13 involving dogs, sutures were placed 5 and 7 mm from the edge of a linea alba incision, and a decrease in the tensile strength of the closures was not detected. In a study14 involving body wall closure in rats, the strength of the suture line when sutures were placed 5 mm from the edge of the incision did not differ significantly from that when sutures were placed 10 mm from the edge of the incision. It is possible that suture bites placed 5 mm from the edge of an incision, as they were in this study, might contribute to failure at the suture-tissue interface. Regardless of the reason, suture cut through at the suture-tissue interface was the most common mode of failure for all 3 suture patterns evaluated in the present study. Thus, it appeared that none of the patterns evaluated was obviously superior in preventing tissue failure at the suture-tissue interface. Further investigation of the efficacy of the intermittent Aberdeen pattern for body wall closure should include comparing the tensile strength of that pattern in in vivo tissues with that measured for the cadaveric tissues of this study. Additionally, because of the in vitro nature of this study, we were unable to evaluate complication rates associated with suture reactions and wound dehiscence among the 3 types of body wall closure assessed, and an in vivo study similar to that performed in human patients1 is warranted to assess the efficacy of the intermittent Aberdeen pattern beyond its tensile strength.
Results of the present in vitro study suggested that a continuous suture pattern with intermittent placement of Aberdeen knots (intermittent Aberdeen pattern) may be a feasible method for body wall closure in dogs. The tensile strength of the intermittent Aberdeen pattern was significantly greater than that for a simple interrupted suture pattern and comparable to that for a simple continuous pattern, 2 methods traditionally used for body wall closure in veterinary medicine. Although not evaluated in the present study, the use of intermittent Aberdeen knots may provide additional closure security, compared with that provided by a simple continuous suture pattern with only 2 knots. An intermittent Aberdeen pattern is simple to learn and perform and minimizes the time required to close extensive abdominal incisions, compared with that required by use of a simple interrupted suture pattern. Although in vivo studies are necessary to further elucidate the advantages and disadvantages associated with the use of an intermittent Aberdeen pattern for body wall closure in dogs, we propose that its strength is comparable to conventional methods of closure and consider it an acceptable alternative for body wall closure in veterinary patients.
Acknowledgments
The authors thank Chase Gunderud for technical assistance.
ABBREVIATIONS
| Fmax | Maximum force at failure |
Footnotes
Realeather Crafts, New Albany, Ind.
Ziploc freezer bags, SC Johnson & Son Inc, Racine, Wis.
Uniaxial testing apparatus built at the College of Engineering, Michigan State University, East Lansing, Mich, in partnership with Telphase Technologies LLC, South San Francisco, Calif.
Mr. Grip strips, Woodmate Corp, Grimes, Iowa.
6-in/150-mm Electronic Caliper, Fowler High Precision, Newton, Mass.
PiA1000-60gm GigE camera, Basler AG, Ahrensburg, Germany.
LabVIEW 2013 SP1, National Instruments, Austin, Tex.
SAS, version 9.3, SAS Institute Inc, Cary, NC.
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