Cyclic pulse loads generate the new concept in abdominal wall reconstruction: suture closure

INTRODUCTION

In daily life, the abdominal wall gets stressed by repetitive peaks of intraabdominal pressure while moving, defecating, or coughing. Therefore, an existing abdominal wall reconstruction needs to withstand these repetitive loads^[1]. However, currently, up to 20% of the sutured incisions reopen results in hernias^[2]. A reconstructed abdominal wall behaves as a coherent compound and must, therefore, be assessed as such^[3,4]. To improve clinical care, abdominal wall closure should be examined closely and need to be tested under lifelike conditions to obtain a realistic estimation of their behavior and durability.

For this purpose, we built a bench test that delivers repetitive cyclic pressure impacts, simulating coughs^[5,6]. Increasing the amount of the pressure impacts and their height leads to the development and enlargement of a hernia. This process of reconstruction failure starts early after closure^[7,8].

The formation of an incisional hernia reveals an insufficiency of the compound, specifically the sutured abdominal wall. The long-term success of a repair is determined by the creation of a successful synergy among the individual components. The suture technique determines the load distribution of the intraabdominal pressure on the abdominal wall. Additionally, the combination of the chosen material, the individual tissue qualities, the type of defect, and the load determines the durability of the reconstruction^[3,9].

In a randomized controlled study (ESTOIH study), the best results to date were achieved by means of the short stitch technique compared to the long stitch technique (4.23% vs. 8.24%) in the 1-year follow-up, with both groups using Monomax®^[10]. The current EHS guidelines recommend a continuous small-stitch-small-bite technique with a suture to wound length (SWL) of at least 4:1. It is recommended to use a slowly resorbable suture. No specific recommendation is suggested regarding the suture material and size^[11,12]. Previous studies showed that the careful execution and standardization of surgical sutures enhance the outcome significantly^[13,14].

Despite active research to continually improve hernia reconstruction, recurrence rates remain high^[2]. The performed experiments contribute to the active discussion about the optimal suturing techniques for median abdominal wall closure.

MATERIAL AND METHODS

The bench test for generating cyclic pulse loads

We used stiff porcine and elastic bovine tissues as models for the abdominal wall. German pigs and cattle were butchered at one to two years of age and delivered to the lab cooled on the same day. The porcine tissues consist of the entire abdominal wall with similar properties to the human abdominal wall^[15]. The bovine tissues include the oblique abdominal muscles, simulating thin and soft abdominal walls. The two tissue types differ in their distinct median elasticity^[16]. The model tissues were repeatedly loaded with cyclic impacts on our validated bench test, as previously described^[13,16]. The test bench simulates high pressure impacts on the sutured tissue with a customizable pressure plateau phase and maximum pressure, as it can occur during heavy coughing. One out of three of our patients coughs over 400 times in the first 24 hours postoperatively^[17]. Accordingly, we loaded the reconstructed tissues 425 times with cyclic pressure impacts. The bench test is shown in Figure 1.

Figure 1. (A) Photo of the bench test and its elements (1: water cylinder with cover plate, 2: tank opening where pressure impacts are applied to the mounted tissue, 3: base frame with pipe system including inlet and outlet valves and pressure tank); (B) Mounted sutured tissue on the bench test during maximum pressure impact, suture tension is measured.

We investigated the performance and stability of various suture techniques for midline abdominal incisions. We chose two different types of defects. For defect type one, we cut a 15 cm long medial incision into the tissues. For defect type two, we punched an additional 5 cm large circular defect in the center of the incision. The incisions were solely sutured in large-bite (0.8-1.2 cm bites) or small-bite (0.5-0.8 cm bites) technique with Monomax^® or PDS^® sutures USP 2-0 or USP 1. ^® Monomax® suture material is manufactured of poly-4-hydroxybutyrate. It differs from PDS^® in its ultra-long resorption time of 18 months and elasticity of 90%. The SWL ratio had to exceed 4:1^[10,18]. The incisions with defects were closed in a standardized technique^[13] by two surgeons experienced in suture technique research. The nomination terminology is given in Table 1. The exact test setup for each test is shown in Table 2.

Table 1

Nomination system

	Abbreviation	Meaning
Tissue	B:	Bovine tissue
	P:	Porcine tissue
Test bench settings	120 /150 /180 /210 /240	Maximum pressure in mmHg
Cover plate	sO	Square opening, A = 256 cm2
	cO	Circular opening, A = 490 cm2
Defect	IN	Incision 15 cm
	DC5	Defect circular 5 cm
	INDC5	Incision + defect circular
Materials	MM 20 /1	Monomax® USP 2-0 or 1
	PDS 20	PDS® USP 2-0
Technical details	SBu SBs	Small-stitch-small-bite unstandardized suturing Small-stitch-small-bite standardized suturing
	LBu LBs	Large-stitch-large-bite unstandardized suturing Large-stitch-large-bite standardized suturing

Table 2

List of the 15 test series performed with a total of 150 tests with each setup and the likelihood of secure closure (LOSC)

Series	Title	Tissue	Defect shape	Defect size (cm)	Suture USP	SSSB / LSLB suture	Standardization	Amount of stitches (n)	S:W-L-Ratio	LOSC until ST (%)
ES 1	P-210-0.2sP-sO-IN-MM20-SBu	porcine	incision	15	2-0	SSSB	no	23.7	4.4	100
ES 2	P-210-0.2sP-sO-IN-MM20-LBu	porcine	incision	15	2-0	LSLB	no	13.8	4.4	100
ES 3	B-210-0.2sP-sO-IN-MM20-SBu	bovine	incision	15	2-0	SSSB	no	23	4.3	100
ES 4	B-210-0.2sP-sO-IN-MM20-LBu	bovine	incision	15	2-0	LSLB	no	13.8	4.4	100
ES 5	P-210-0.2sP-sO-IN-MM1-SBu	porcine	incision	15	1	SSSB	no	22.4	4.4	100
ES 6	P-210-0.2sP-sO-IN-MM1-LBu	porcine	incision	15	1	LSLB	no	13.9	4.4	100
ES 7	B-210-0.2sP-sO-IN-MM1-SBu	bovine	incision	15	1	SSSB	no	22	4.3	100
ES 8	B-210-0.2sP-sO-IN-MM1-LBu	bovine	incision	15	1	LSLB	no	13.9	4.3	100
ES 9	P-210-0.1sP-sO-INDC5-PDS20-SBs	porcine	incision+circular	15 + 5	2-0	SSSB	yes	21	4.1	100
ES 10	P-210-0.1sP-cO-INDC5-MM20-SBs	porcine	incision+circular	15 + 5	2-0	SSSB	yes	27	4.5	90
ES 11	P-210-0.1sP-cO-INDC5-PDS20-SBs	porcine	incision+circular	15 + 5	2-0	SSSB	yes	23.5	4.3	40
ES 12	P-210-0.1sP-cO-INDC5-PDS20-SBs 1	porcine	incision+circular	15 + 5	2-0	SSSB	yes	24	4.2	30
ES 13	P-210-0.1sP-cO-INDC5-PDS20-SBs 2	porcine	incision+circular	15 + 5	2-0	SSSB	yes	22	4.1	30
ES 14	P-180-0.1sP-cO-INDC5-PDS20-SBs-1	porcine	incision+circular	15 + 5	2-0	SSSB	yes	22	4.1	50
ES 15	P-180-0.1sP-cO-INDC5-PDS20-SBs-2	porcine	incision+circular	15 + 5	2-0	SSSB	yes	22	4.1	40

The test was terminated if the reconstruction failed or if 425 DIS impacts were delivered. Failure was defined as slackening of the suture, tearing of the suture through the tissue, or tearing of the tissue itself. The occurrence and onset of the failure pattern were observed in the experiments. The study comprises a total of 15 experimental series (ES), each involving ten experiments [Table 2].

RESULTS

In eight ES (1-8), we performed a structured investigation of four influencing factors on the suture durability. We varied the stitch spacing (Large-Bite vs. Small-Bite), the suture material (Monomax^®vs. PDS^®) and the suture thickness (USP 1 vs. 2/0), and the tissue type (bovine and porcine). The WSL showed no significant variation with values between 4.3 to 4.4 throughout ES 1-8 [Table 2]. In series 9-15, we investigated further influencing circumstances such as the standardization of the suture, a different suture material, an additional defect, a larger impact area, or a lower peak pressure.

Figure 1 illustrates the comparison of unstandardized Small-Bite stitches vs. Large Bite stitches performed with a USP 2/0 or USP 1 Monomax^® suture, closing midline incisions (ES 1 + 2, 5 + 6). 100% durability was obtained in all series, regardless of the stitch spacing, thread thickness, and tissue type.

The durability drops by 10%-50% when adding a circular defect into the incision and using the cover plate with the larger opening. We used a standardized small-stitch-small-bite technique with USP 2/0 Monomax^® or PDS^® sutures.

The standardized small-bite Monomax^® suture (triangles) provided secure closure in 9 out of 10 experiments [Figure 2]. It showed a 50% higher likelihood of secure closure (LOSC) (P = 0.064) than the PDS^® suture (dots).

Figure 2. Likelihood of secure closure (LOSC) until suture failure of USP 2/0 or UPS 1 Monomax^® sutures in Small-Bite (SB) or Large-Bite (LB) technique closing a 15 cm long midline incision in porcine and bovine tissue depending on the amount of DIS impacts with 210 mmHg.

Series 11-13 and series 14 + 15 had the same experimental setup, with a peak pressure of 210 mmHg or 180 mmHg. 30%-40% of the sutures held securely when exposed to 210 mmHg [Figure 3]. When the peak pressure lowers by 30 mmHg, the LOSC rises by 20%-30%. Figure 4 the upper and lower graph show differences in the durability between 200 and 400 DIS impacts due to the stochastic nature of the process. The graphs converge at 425 impacts. This demonstrates the reproducibility of the process with 425 impacts^[15].

Figure 3. Likelihood of secure closure (LOSC) until suture failure of USP 2/0 PDS^® sutures in standardized Small-Bite (SSSBs) technique closing a 15 cm long midline incision with a 5 cm large circular defect (INDC5) in porcine tissue depending on the amount of DIS impacts with 180 mmHg (B) or 210 mmHg (A).

Figure 4. Likelihood of secure closure (LOSC) until suture failure of USP 2/0 Monomax^® (MM) or PDS^® sutures in standardized Small-Bite (SSSBs) technique closing a 15 cm long midline incision with a 5 cm large circular defect (INDC5) in porcine tissue depending on the amount of DIS impacts with 210 mmHg.

DISCUSSION

The bench test we used allows the simulation of everyday loads on the abdominal wall. According to modern biomechanics, the tissue and reconstruction need to be considered and assessed as a compound.

The durability of a suture closure does not solely depend on the accurate execution of one specific factor. The interplay of the individual influencing factors determines the outcome of the suture closure of the abdominal wall. This applies to any experimental and clinical setting. It is the base of the existing GRIP/CRIP concept^[19,20]. The standardized suture, used in ES 9 - 15, provides an instruction for secure suture closure by combining the influencing factors^[13]. However, the success of a suture is limited by external influences, e.g., defect size, retention force of the tissue, applied strain, and impact area.

Previous experiments have shown that the addition of a circular defect to the incision reduces the durability of unstandardized wound closure with MonoMax^® to 0%. Standardization of the suture technique can increase the durability to 100%^[13]. Increasing the impact area and using PDS^® instead of Monomax^® sutures again lowered the durability. Our experiments revealed clear differences in the durability of sutures with Monomax^® or PDS^® sutures. This is in contrast to the literature, which indicates only minor differences between various sutures^[12,21].

In low-risk cases, an unstandardized suture closure seems to be stable, regardless of the chosen technique and material. In high-risk cases, such as larger defects or unstable tissue, Monomax^® small-stitch-small-bite sutures in standardized protocol appear to be a safer choice^[13].

CONCLUSION

Secure closure of median abdominal wall incisions is achievable with sutures regardless of small or large bite technique and material thickness. But as can be seen from the GRIP/CRIP concept, larger defects require more complex reconstruction. For larger defects, suture closure alone may not be sufficient, depending on the circumstances. A larger impact area, for example, lowers the durability. This experimental study revealed that Monomax® sutures provide a higher level of closure security than PDS® sutures. The thickness of the suture showed no difference. It is advisable to choose the safest suture technique and mesh reinforcement in larger abdominal wall defects.