Kidney resection rightfully occupies a priority position in the treatment of localized renal cell carcinoma. It not only provides high oncological results but also allows preserving the renal parenchyma, thereby reducing the risk of chronic kidney disease and cardiovascular catastrophes, which is especially important in young patients [1][2]. This is also confirmed by the fact that, according to the European Urological Society recommendation base, open kidney resection is considered the surgery of choice compared to minimally invasive (laparoscopic or robotic) nephrectomy [3]. The main technical problem, especially in patients with large endophytic formations, is the closure of a renal wound with reliable hemostasis and a low risk of urine leakage [4–6]. The need to remove the kidney from the bloodstream at this stage of the operation also introduces a time factor that determines the risk of ischemic and reperfusion damage to the kidney [3][4]. Despite the abundance of proposed physical and chemical methods to ensure hemostasis, mechanical suturing of a renal wound with a surgical suture remains the most widely used method [7][8]. In this matter, there is no unambiguous opinion on the method of execution and the seam row, the threads used, and the additional materials that strengthen the seam line [8]. Thus, according to experimental studies, to achieve a hemostatic effect in the abundantly blood-supplied renal parenchyma, it is necessary to create tissue tension 5.0 – 15.0% less than its strength limit [9][10]. This does not consider the rise in perfusion pressure in hypertensive patients or edema, as well as a decrease in the strength limit of the parenchyma because of reperfusion.

Therefore, the operating surgeon is faced with a narrow window of permissible loads when suturing a kidney wound. On the one hand, a decrease in tension in the seam area threatens bleeding, and on the other – exceeding the strength limit by thread eruption and, accordingly, the same hemorrhagic complications.

The study aims to evaluate the mechanical properties of the renal parenchyma under experimental conditions and to justify ways to prevent suture eruption.

Mechanical tests of the strength characteristics of the layers of the renal parenchyma were performed on a sectional material of 60 cadaveric kidneys. The tensile strength of kidney tissues was studied on a bursting machine. In three series of experiments, the mechanical strength of the layers of the renal parenchyma, the options for applying a through seam and the effectiveness of using gaskets to prevent thread eruption were also studied.

In the first series of experiments, the following options for applying a nodal seam were compared: 1) on the medulla and tissues of the renal sinus; 2) decapsulated organ; 3) through all layers, including the capsule (Fig. 1). In the second series, comparative tests of vertical and horizontal nodular sutures were performed through all layers of the kidney (Fig. 1). In the third series of experiments, similar parameters were studied for variants of a horizontal nodular seam reinforced with 1 cm wide synthetic material pads that prevent thread eruption: hemostatic mesh (Surgicel, «Ethicon Inc.», «Johnson & Johnson Company», Cincinnati, OH, USA), tapes made of prolene mesh («Lintex», St. Petersburg, Russia) and polytetrafluoroethylene vascular prosthesis.

The research was carried out using the equipment of the Center for Collective Use “Technologies and Materials of the Belgorod State National Research University” on the universal rupture testing machine Instron 5882 (Instron, «Illinois Tool Works Inc.», Glenview, IL, USA) (Fig. 2).

The prepared kidney with a nodular suture was placed on a slide table, the ends of the threads were fixed in vertically positioned clamping mechanisms of the bursting machine. The tensile speed in all tests was standard – 10 mm per second, the elongation of the threads (mm) and the load (L) were recorded. The maximum load was taken as the ultimate strength; when exceeded, the sample was destroyed (thread eruption). For standardization, the kidney was stitched with a straight piercing needle, which was 5 mm away from its transverse incision. The step between the adjacent seams was 10 mm. In total, 40 mechanical tests were performed with each suturing option. The kidney tissue is characterized by pronounced anisotropy and heterogeneity, which does not allow it to be considered either from the position of an elastic or from the position of a viscous body. The attempts made to allow and study linear and shear deformations are accompanied by a large error, which did not allow considering such a characteristic as the modulus of elasticity of the kidney tissue (Young's modulus).

Ethical statement. During the development and implementation of the experiment, the authors of this study focused on recommendations to conduct qualitative medical research “Standards for reporting qualitative research: a synthesis of recommendations” developed by Enhancing the Quality and Transparency of Health Research [11]. The study was approved by the Ethics Committee of the Belgorod State National Research University based on familiarization with the provided design materials and the implementation plan of the experiment (Protocol No. 7 dated September 19, 2018).

Statistical analysis. For statistical processing, all data were formalized and automatically entered a database created since Microsoft Office Excel spreadsheets («Microsoft Corp.», Redmond, WA, USA) using the research equipment software. Statistical analysis of the results obtained was carried out using the IBMÒ SPSS Statistics 19.0 software («SPSS: An IBM Company», «IBM SPSS Corp.», Armonk, NY, USA). The samples obtained had a normal distribution, quantitative values are represented by the arithmetic mean, and the confidence interval is the standard deviation. The confidence level is p < 0.05.

During mechanical tests, it was found that the medulla and tissues of the renal sinus had the highest strength among the layers of the renal parenchyma. The average tensile strength in this series of experiments was 23.58 ± 9.17 N. According to the results of the first series of experiments, the mechanical strength of the cortical substance in the absence of the capsule was minimal, amounting to 8.4 ± 2.89 N (p < 0.01). The presence of a renal capsule significantly increased the tensile strength to 14.89 ± 1.77 N compared with a decapsulated kidney (p < 0.05) (Figs. 3, 4).

Replacement of the vertical seam through all layers with tying a knot along the resection line with a similar horizontal mattress seam statistically significantly increased the tensile strength to levels comparable to the tensile strength of the medulla, which was 27.35 ± 12.04 N (p < 0.01) (Fig. 5).

In the third series of experiments, to increase the strength of the horizontal mattress seam and exclude its eruption, the authors used a 1 cm wide hemostatic mesh (SurgicelÒ), tapes made of a prolene mesh (LintexÒ) and a vascular polytetrafluoroethylene prosthesis of a similar width as pads. The use of hemostatic mesh (SurgicelÒ) does not significantly affect the tensile strength of the horizontal mattress seam 23.58 ± 9.17 N (p > 0.05). The use of a prolene mesh as a gasket prevents the seam from erupting at a load of 31.48 ± 9.98 N, which is significantly higher than the native seam and protection with a hemostatic SurgicelÒ mesh (p < 0.05). The maximum strength of the horizontal mattress seam was obtained for a polytetrafluoroethylene vascular prosthesis tape, in some cases it exceeds the strength of a polyglycolide thread with a diameter of 1 USP or 0.4 mm and averages 45.61 ± 6.1 N (p < 0.01) (Fig. 6).

Currently, the scientific literature devoted to the problems of hemostasis during kidney resection discusses the issue of so-called seamless resection using various options of electrosurgical or laser hemostasis, adhesive composites, as well as superselective embolization [3][5][10]. The ideology of this approach is to preserve a larger volume of functioning parenchyma [10][12]. However, even a combination of these hemostasis methods does not provide a complete guarantee of its effectiveness according to most studies on kidney resection with extrarenal formations of up to 2 cm [1][2][13]. On the other hand, the depth of thermal damage to the parenchyma can reach 8–13 mm, which does not fit into the optimal approach for nephron-sparing and increases the risks of urinary fistula formation [2][4][8]. Thus, nephrorrhaphy remains the main method of final hemostasis during kidney resection in patients with large and intrarenal tumors [4][8].

The main critical point when suturing the kidney parenchyma during its resection is the time of its execution, since the latter is associated with both the duration of organ ischemia and the volume of blood loss and the risk of thread eruption [2][8]. Proponents of multi-row sutures in the kidney wound report better adaptation of the edge of the wound, while opponents of this approach in the form of an argument put forward an argument about the loss of 13.0 to 20.0% of the functioning kidney parenchyma due to its inclusion in the suture line [9][10][12][13].

This study shows that isolated suturing of the cortical layer, especially in the unsatisfactory condition of the kidney capsule, the use of vertical nodular or continuous winding sutures, is associated with the risk of thread eruption. Thus, the data obtained by the authors call into question the recommendations for applying a cortical suture, especially on a decapsulated kidney, as this will not increase the strength of the suture and may cause hemorrhagic complications due to the eruption of sutures. That is, without increasing the strength of the seam, this increases the time of its execution and the frequency of hemorrhagic complications.

The horizontal mattress suture has been shown to be positive when closing the wound not only of the kidney but also of the liver and spleen [14]. Data from this study correlate with experimental results of studying the mechanical strength of the kidney parenchyma obtained in pigs and rats. Thus, these models can be used as homologous when conducting a chronic experiment. When compared with the results of a few studies, the stress created in the tissues at such a strength limit of the horizontal mattress seam exceeds the pressure of blood leakage by 20% [9][10]. The authors believe that the restrictive reasons for performing Kuznetsov-Pensky and Oppel sutures are the complexity of their application, the presence of many ligatures in the wound, and the high consumption of suture material. Consequently, the optimization of the method of applying a horizontal mattress seam will not only increase the strength and, accordingly, reduce the risk of hemorrhagic complications (which follows from the second series of comparative mechanical tests), but will also contribute to its more frequent use.

The use of pads to increase the strength of a surgical suture when suturing a kidney wound has a long history [15][16]. Auto fabrics (paranephrium, Gerot fascia and peritoneum), and synthetic materials are most often used for these purposes [16]. The disadvantages of the first are their variable physical and mechanical properties and a possible insufficient amount in a particular patient. Several researchers recommend the use of hemostatic sponges and meshes to strengthen the renal suture line [16–18]. The authors of this study have obtained negative results of applying such an approach using a hemostatic SurgicelÒ mesh, which did not increase the strength of the horizontal mattress seam. The authors can explain the data obtained by the fact that the authors of the above-mentioned publications used hemostatic materials to strengthen less durable vertical seams, which could be accompanied by a statistically significant increase in tensile strength. Mesh woven prolene prostheses can be a definite alternative, and the authors’ data indicate a statistically significant increase in the tensile strength of the joints under study when using a tape made of a prolene mesh LintexÒ (p < 0.05). However, one should note the manual difficulties in positioning this material when suturing the kidney and the risks of violating the integrity of the mesh structure when modeling it to the appropriate clinical situation. This is probably why a few reports suggest the manufacture of special implants for suturing a kidney wound [17][19]. Polytetrafluoroethylene, used for the manufacture of vascular prostheses, is the most convenient in manual positioning and modeling, as well as priority from the side of mechanical characteristics. Thus, the aortic part of the prosthesis is sufficient for any options for closing a renal wound and provides the maximum strength of a single-row suture with virtually no risk of thread eruption (p < 0.01).

An analysis of the advantages and disadvantages of the above methods of final hemostasis during kidney resection indicates the expediency of suturing the renal parenchyma. The study of the mechanical strength of the layers of the renal parenchyma showed the inexpediency of performing a cortical suture; the use of a horizontal mattress suture significantly increases the tensile strength compared to the vertical; maximum mechanical strength characteristics were obtained while using polytetrafluoroethylene gaskets.