In veterinary medicine, cystotomy is a frequently performed procedure, and is most commonly indicated in patients with bladder calculi, traumatic bladder rupture, bladder neoplasia, and congenital anomalies such as ectopic ureter (5,18). Failure of cystotomy closure can lead to adhesions, fibrosis, prolonged hospitalization, uroabdomen or peritonitis, which can lead to death in severe case (1,25). Therefore, an ideal suture in cystotomy closure should be completely fluid-tight, easy to apply, cause minimal tension on the incision surface, cause no adhesion formation, maintain the diameter of the bladder lumen, and provide anatomical reapposition between the layers of tissue (23).

When closing the cystotomy, methods for single-layer or double-layer suture patterns using apposition or inverting suture patterns are conventionally suggested (16-18,24). Several studies have argued that single-layer suture patterns are more suitable because they are not significantly different from double-layer suture patterns in terms of the degree of urine leakage and wound strength, but rather provide a shorter running time and healing period and a lower possibility of side effects and tissue damage (12,13,23,25). In addition, in studies comparing the appositional and inverting suturing patterns in the cystotomy closure, no significant difference was found in pressure at the time of leakage between the two suture patterns (2,9,13,23). In previous studies, the single-layer appositional suture pattern did not differ from the double-layer inverting suture pattern in the short-term complication rate and hospitalization period for cystotomy closure in clinical situations (12,25).

The simple continuous suture pattern (SC), running suture pattern (RN), and Ford interlocking suture pattern (FI) are included the continuous appositional suture pattern (15,17). The SC is composed of knots only at both ends of the incision. After making a knot at the starting point, it passes through the tissues perpendicular to the incision from one side to the other. RN is achieved by diagonally advancing along the incision line. In FI, sutures penetrating the tissues are interlocked. In general, it is known that simple continuous suture pattern has better fluid-tight ability than simple interrupted suture pattern, and studies applied to cystotomy closure showed better results (7,17).

To date, no study has compared the continuous appositional suture patterns during cystotomy closure. Therefore, the purpose of this study was to compare continuous appositional suture patterns such as SC, RN and FI.

Specimen collection and experiment preparation

Thirty urinary bladders of slaughtered pigs, weighing 100-110 kg and 6 months of age, were removed en bloc from the slaughterhouse. The remaining urine was carefully drained to avoid damaging the mucous membrane of the lumen. The bladders were washed with saline, leaving 3 cm of the urethra and 2 cm of the ureter. After that, the weight of each specimen was measured, ranging between 55-60 g. Each ureter was ligated near the ureter-bladder junction. After inserting the tube through the urethra until the tip was located at the urethra-bladder junction, the urethra was tightened using a cable tie. The tube was connected through a three-way valve to a pressure transducer connected to a pressure monitor (BM7 VET PRO, Bionet, Korea) and an infusion pump (KL-602, Beijing KellyMed Co, China) to inject the solution into the bladder (Fig. 1). A 1% povidone-iodine-saline solution was prepared to check for leakage.

Figure 1. Apparatuses used to infuse urinary bladders to measure bursting pressure and bursting volume for circular bursting wall tension (CBWT) determinations.

Categorization of the basis of suture pattern

The 30 bladders were randomly categorized into three groups (SC, RN, and FI), with 10 bladders in each group. All bladders were soaked in a heated water bath at 35-36°C for at least 20 min before incision. An incision was made on the ventral surface of the bladder according to the pre-drawn 35 mm lines, and sutures were performed in the manner assigned to each group. The beginning and end of each continuous suture method were completed by making six square knots. For sutures, 3/0 polyglyconate (Maxon^TM, Covidien^TM, USA) swaged on a tapered needle was used.

In the SC group, after the first knot, the suture was passed through the bladder serosal surface 5 mm from the edge of the incision line, and then passed through the bladder mucosal surface opposite the incision line on the same vertical level. The interval between sutures was 5 mm. The SC consisted of 14 needle passes through the bladder wall (Fig. 2A).

Figure 2. Each suture pattern used in the experiment. (A) Simple continuous suture pattern. (B) Running suture pattern. (C) Ford interlocking suture pattern.

In the RN group, after the first knot, the route of the first suture passed the wall in the same way as in the SC group, and closure was advanced by 5 mm above the incision. In this way, the suture was placed at the end of the incision, and the suturing was finished with a knot. The RN consisted of 8 needle passes through the bladder wall (Fig. 2B).

In the FI group, the same interval length as that of the SC group was applied, but the incision was closed by applying the Ford interlocking suture patterns in which the sutures were interlocked on the serosal surface. The FI consisted of 14 needle passes through the bladder wall and six interlockings of the suture (Fig. 2C).

The suture time was defined as the time taken from the first pass after the completion of the first knot to the completion of the last knot, and it was measured for all tests. For consistency in each suture trial, one operator performed all sutures.

Evaluation of bladder leakage

After suturing was completed 1% povidone-iodine-saline solution was injected at a rate of 1300 mL/hr using an infusion pump. Then, the bladder lumen pressure and accumulated infusion volume of the solution were measured when leakage of the 1% povidone-iodine-saline solution was observed. The pressure and volume at the time of leakage were called the bursting pressure (BP) and bursting volume (BV), respectively. The leakage site and the suture length used for cystotomy closure by removing the suture were recorded.

Derivation of the circular bursting wall tension

The circular bursting wall tension (CBWT) expressing the bursting strength was derived from the BP and BV measured for all tests. Assuming that the bladder was a sphere, the radius at the time of rupture could be calculated from the BV using the following formula:

$$BV=\frac{4}{3}\pi r^3$$

$$r=\sqrt[3]{\frac{3BV}{4\pi }}$$

BV = bursting volume (mL), r = radius of the sphere when rupture occurs (cm).

CBWT was calculated by applying Laplace’s law, which defines the relationship between pressure and wall tension in hollow organs (11,20,23). The formula for deriving the CBWT is as follows:

$$CBWT=\frac{BP\times r\times 1.33\times {10}^3}{2}$$

CBWT = circular bursting wall tension (dyne/cm), BP = bursting pressure (mmHg), r = radius of the sphere (cm), 1 mmHg = 1.33 dyne/cm.

Statistical analysis

To statistically analyze of the results, the mean values and the standard deviations (SD) were calculated. All experimental results were expressed as mean ± SD and were presented in tables and figures. The three groups were compared statistically with a one-way analysis of variance (ANOVA) using GraphPad Prism software (GraphPad Software, USA). For all tests, p < 0.05 was considered to be statistically significant.

Bladder weight, suture time and suture length

The weight of the bladder did not differ significantly (p > 0.05) between the three groups (mean ± SD, 59.0 ± 1.48 g, 58.2 ± 1.54 g, 59.0 ± 1.48 g for SC, RN and FI, respectively). The mean ± SD of suture times were 349.9 ± 74.00 sec, 215.9 ± 28.29 sec, and 465.6 ± 84.47 sec in SC, RN and FI groups, respectively. The length of the suture for RN was the shortest, followed by SC and FI in that order (mean ± SD , 60.8 ± 7.47 mm, 40.5 ± 2.73 mm, 91.2 ± 13.12 mm for SC, RN and FI, respectively). The length of suture and the suture time were significantly different (p < 0.05) between the groups (Table 1).

Table 1 . The weight of the bladder, the suture time, and the suture length for SC, RN, and FI group (Mean ± SD).

Parameters	Group SC (n = 10)	Group RN (n = 10)	Group FI (n = 10)	p value
Bladder weight (g)	59.0 ± 1.48	58.2 ± 1.54	59.0 ± 1.48	> 0.05
Suture time (sec)	349.9 ± 74.00	215.9 ± 28.29	465 ± 84.47	< 0.05
Suture length (mm)	60.8 ± 7.47	40.5 ± 2.73	91.2 ± 13.12	< 0.05

SC, simple continuous suture pattern; RN, running suture pattern; FI, Ford interlocking suture pattern..

Sites of leakage

No suture breakage or untying occurred in the bladder. In this study, leakage of the bladder was observed at two sites: leakage through the incision line directly and the suture hole made by penetration of the suture. In the SC, no leakage occurred at the incision line. In FI, 2 of the 10 bladders showed leakage in the incision line, and in RN, 4 of the 10 bladders showed leakage (Table 2). The remaining bladders in the RN and FI groups showed leakage through the suture hole. The leakage at the incision line in the FI group occurred in the wrinkled areas between the incision edges.

Table 2 . The leakage site in SC, RN, and FI groups.

Leakage site	Group SC (n = 10)	Group RN (n = 10)	Group FI (n = 10)
Incision line	0	4	2
Suture hole	10	6	8

SC, simple continuous suture pattern; RN, running suture pattern; FI, Ford interlocking suture pattern..

Bursting pressure (BP) and bursting volume (BV)

The mean ± SD of BP were 3.9 ± 0.83, 2.9 ± 0.83, and 5.1 ± 1.22 mmHg in SC, RN and FI groups, respectively. A statistically significant difference was observed between SC and FI groups and between RN and FI groups. However, there was no significant difference between the SC and RN groups (Fig. 3).

Figure 3. BV, BP, and CBWT measurement in SC, RN and FI groups. SC, simple continuous suture pattern; RN, running suture pattern; FI, Ford interlocking suture pattern; BP, bursting pressure; BV, bursting volume; CBWT, circular bursting wall tension; ns, not significant. *p<0.05, ***p<0.001, ****p<0.0001.

The mean ± SD of BV were 349.9 ± 68.58 mL, 234.9 ± 61.73 mL, and 402.7 ± 119.09 mL in SC, RN, and FI groups, respectively. A statistically significant difference was observed between the SC and RN groups and between RN and FI groups. However, there was no significant difference between the SC and FI groups (Fig. 3). From the result, we observed that as BP increased, BV showed a proportional increase too.

Circular bursting wall tension (CBWT)

The mean ± SD of CBWT in the SC, RN, and FI groups were 11206 ± 2229.6, 7284 ± 2041.3, and 15489 ± 4399.0 dyne/cm, respectively (Fig. 3). Statistically significant differences were observed in CBWT among all groups. RN showed the weakest tension, while FI showed the strongest tension among the groups.

In many studies, delayed operating and anesthesia times were associated with adverse effects, such as infection (3,4,6). Therefore, several studies comparing cystotomy closure methods have suggested that shorter operation time is a positive factor (7,12,13,20). As the result of this study, it is expected to further contribute to shortening the operation time in the following order: RN, SC, and FI. Thus, the risk associated with adverse effects such as infection was also thought to be lower in the order of RN, SC and FI.

The suture material at the incision line can act as a foreign body, which can delay healing and contribute to infection (26). In addition, the presence of a foreign body in the abdominal cavity is one of the most common reasons for adhesions (8,22). The larger the suture volume exposed to the abdominal cavity, the more severe the adhesion (8,14,22). Adhesion of the bladder to the body wall or organs in the abdominal cavity after cystotomy can interfere with normal bladder filling or emptying (22). Therefore, a smaller amount of suture material used is thought to have better results with respect to recovery. From the results of this study, it can be inferred that the most severe foreign body reaction in the closure occurs when FI is applied in clinical practice because the longest length of the suture is used in FI. In addition, because of the largest amount of suture made by the interlocked sutures on the serosal surface of the bladder in FI, intraperitoneal adhesion is thought to be the most severe.

In the RN, leakage occurred at the incision line in 40% of the bladders. It can be suggested that this result was due to the instability of the incision line caused by the long gap between the sutures and the tension acting on the suture while pulling to tighten the suture, causing the bladder surface to move parallel to the incision line. In FI, leakage occurred at the incision line in 20% of bladders. The reason for this result, even with the same distance between sutures as the SC, was probably the wrinkles at the edges of the incisions. These wrinkles were formed because, the interlocking part applied a force to the serosa in the vertical (seroso-mucosal) direction as the suture progressed. As a result, the edge of the incision where interlocking existed was relatively deep compared to the opposite edge. When tension is applied, the RN and FI are thought to have a relatively smaller degree of apposition compared to the SC that is thought to have a relatively better apposition at the suture sites. According to previous studies, the most common leakage site for appositional sutures in the cadaveric bladder was the suture hole (20,23). However, in clinical situations, cystotomy leakage at the suture hole is rare (20). In this experiment, all bladder leakages occurred through the suture hole in SC. The suture hole was also the most common leakage site in RN and FI. Therefore, it is thought that the possibility of urinary leakage in the bladder is further reduced if appropriate apposition is achieved in which leakage does not occur at the incision line during bladder occlusion in vivo.

Bursting strength refers to the resistance to an increase in intraluminal pressure, and it can be expressed as either BP or CBWT (11,23). CBWT is considered to represent the bursting strength more accurately because it takes into consideration the size and shape of the lumen (11,19,23). Therefore, the CBWT results obtained in this study were considered more accurate than the results of simply measuring only BP and BV.

In this study, by comparing the values of CBWT, it was found that FI had better fluid-tight ability than the other suture patterns in terms of mechanical aspects. In the FI suture, the connection between the sutures was made once more on the serosal surface, and the greater tension caused by the use of longer sutures on the incision line caused the strongest CBWT. However, in the RN, the lowest tension on the incision line due to the wide interval between sutures and the use of fewer sutures was thought to be the cause of the lowest CBWT.

The epithelium and connective tissues in the in vivo bladder stretch to accommodate urine and maintain low pressure, as the bladder tension increases, and histological reorganization of smooth muscle cells occurs (10,21). In this experiment, such changes were not observed in the ex vivo bladder, even though the fluid injection rate was much faster than the in vivo urine output. Thus, BP and BV values are thought to become larger in clinical situations than in cadaveric situations. Accordingly, it is thought that CBWT values also increase.

Because this experiment was conducted ex vivo, evaluation of the differences in postoperative healing was not possible according to the suture patterns. In addition, evaluating the effect of physiological responses, such as inflammation, on fluid-tight ability after surgery was not possible. These points are considered limitations of experiments performed ex vivo, and additional studies in vivo may help to evaluate aspects that could not be evaluated in this study.

The fluid-tight ability of the FI was superior to that of the SC in the mechanical aspect. However, FI does not seem suitable for cystotomy closure because of the high possibility of side effects due to foreign body reactions in vivo, the low efficiency of suturing and the difficulty of suturing. Although RN sutures are relatively efficient and easy to suture, their apposition and fluid-tight abilities were poor. Thus, if RN is to be used for cystotomy closure, it should be performed with a suture interval smaller than 5 mm, or a urinary catheter should be used after cystotomy to reduce the inner pressure of the bladder during the initial recovery phase. Therefore, SC is considered preferable to RN and FI for cystotomy closure because of its adequate fluid-tight ability, good apposition, and appropriate efficiency.

This work was supported by the 2022 education, research and student guidance grant funded by Jeju National University.

The authors have no conflicting interests.