String theory: placement of locking ligation clips in sliding renorrhaphy for partial nephrectomy

Since its first description in 1887 by Czerny, partial nephrectomy has undergone significant technical developments and has become 'gold standard' treatment of localised RCC [1]. Partial nephrectomy is performed with an open, laparoscopic, or robotic approach depending on patient anatomy, complexity, and surgical experience. Minimally invasive approaches have now been demonstrated to have similar oncological outcomes [2] compared to open surgery; however, they can be limited by the difficulty of haemostasis. The laparoscopic approach confers longer operating time [3], principally due to the difficulty in closure of the renal defect, or renorrhaphy. In traditional renorrhaphy, sutures were placed and tied across the renal defect, a more challenging and time-consuming process in laparoscopic surgery. A technique of sliding-clip renorrhaphy was described by Agarwal et al. [4] and Singh et al. [5] with the aim to reduce warm ischaemia time and reduce tearing of renal parenchyma. This technique involves securing sutures with haemostatic clips rather than knot tying. This technique has now been widely adopted and has been shown to provide superior closing tension [6], and significant improvements in operating time, warm ischaemia time, blood loss and complication rate [7]. The advantages of speed, tension control after securement and clips acting as a pledget need to be balanced against the risk of the suture sliding in the clip, causing tension loss and potentially bleeding. It has been previously asserted that certain positions within the clip can better secure the suture from sliding, including the hinge mechanism and centre of the clip [8]. However, this has not been tested in any published literature to date. The aim of this study was to determine if the placement location of polymer locking ligation clips has an effect on its securement and resistance to sliding on a suture. Sutures of differing material and make were attached to a digital electronic force gauge (HF-500 Graigar; Shenzhen Graigar Technology Co., Ltd. Guangdong, China) in a stabilising apparatus as shown in Fig. 1a–c. Large (Purple-10 mm) Weck Hem-o-lok® polymer locking ligation clips (Weck Closure Systems, Research Triangle Park, NC, USA) were applied with a standard laparoscopic applicator 10 mm from the end of the suture. Manual gradually increasing force was applied until the clips were displaced off the sutures and the peak force was recorded, measured in Newtons (N). To ensure validity with in vivo conditions the experiment was repeated with clips initially applied 5 mm from the end of a water-soaked suture and slid back a further 5 mm in a opposite direction to the force application (imitating sliding clips down towards the renal tissue) to test if an initial counter-directional slide or a wet surface would affect surface properties and resistance. A range of sutures were tested including braided, monofilament and barbed (in-line, with or against barbs). Clips were placed at five positions along the clip: hinge end, centre, within hook, one-third and two-thirds distance from the hook (Fig. 1c). Clips and sutures were not reused. A one-way ANOVA was used to compare the peak forces of each clip placement location across all suture types. A P < 0.05 was considered statistically significant. Mean displacement forces across all suture types and locations are summarised in Fig. 1d. Sutures were best secured within the hooking mechanism of the polymer locking ligation clips, irrespective of suture type, requiring a mean peak force of 19.50 N (95% CI 17.5–21.5 N) to displace the clip 10 mm along an 0-polydioxanone (PDS) suture. Similarly, placement of clips under the hook and two thirds to the hook provided reasonable resistance of 14.68 N (95% CI 12.91–16.46 N) and 4.98 N (95% CI 3.40–6.55 N), respectively. Placement of the clips towards the hinge end (centre, one third to hook or hinge) were the least secure locations, each requiring a <2 N. There was variability in the peak force across different sutures, ranging between 0.5 N (95% CI 0.34–0.66 N) for 3-0 poliglecaprone 25 (Monocryl®; Ethicon Inc., Somerville, NJ, USA) to a maximum 2.76 N (95% CI 2.45–3.07 N) for 3-0 V-Loc sutures when clips were placed in the centre position. Larger, braided sutures required greater peak forces to displace clips placed at the hooking mechanism. 0-polyglactin 910 (Vicryl®; Ethicon Inc.) and 0-PDS sutures required 25.26 N (95% CI 23.68–26.84 N) and 25.04 N (95% CI 23.55–26.52 N) respectively, compared to a mean peak of 16.62 N (95% CI 15.81–17.42 N) for 3-0 poliglecaprone 25 (Monocryl) sutures. There were no significant differences noted with initial counter-directional sliding or water-soaking, with a mean peak force of 1.5 N (95% CI 1.32–1.98 N) required at the centre of 0-PDS suture compared to 1.34 N (95% CI 1.14–1.54 N) without (P = 0.26). Significant differences in the mean peak force required for displacement for both clip positions and suture types were demonstrated (P < 0.001). The benefits of the sliding clip renorrhaphy technique—speed and buttressing of the renal tissue—are of little use if the closure of the renal defect is not secure. Contrary to previous assertations, our experiments demonstrate that within the hooking mechanism is the most secure location for clip placement over any suture. However, this may not be the ideal in all situations – the resistance to displacement provided by the hooking mechanism is high enough that it may be difficult to tighten the suture. As a result, despite providing the most security, it is not necessarily the most practical position in initial clip application. Positioning the clips near the hook appears to provide improved resistance to displacement whilst still being relatively easily pushed up the thread for initial placement. This result quantifies and confirms the common practice of placing an initial clip in a location able to slide, allowing adjustment and utilising the pledget function, followed by further clips to secure tension. Demonstrating the higher security of the thread within hook mechanism may obviate the need for the common practice of triple-clipping sutures allowing fewer clips to be left in the surgical bed. Knowing the differing resistances to displacement gives options to surgeons in situations where more or less resistance is desirable. The significance of the forces needed to displace clips is unclear; it is unknown if pressures of such magnitude are encountered following a renorrhaphy; however, previous reports of suture tension of at least 3.42 N for effective closure suggest this additional strength is required [9]. The main limitations of this study are that it remains an ex vivo experiment. Peak force was chosen as postoperative coughing or straining is likely to place the highest force on the renorrhaphy; however, is it unclear if constant pressure the renal parenchyma would place on the clip and suture interface would be a larger concern. Similarly, displacement by 1 cm is an arbitrary threshold. However, both are unlikely to change the direction and magnitude of the differences between locations and sutures. Similarly, sutures were wetted to simulate the operative field; however, may not necessarily represent the 'slipperiness' of sutures that pass through renal tissue. Small changes to the placement of polymer locking ligation clips in the sliding renorrhaphy technique can result in significant changes to the displacement forces and suture security in partial nephrectomy. Application of clips at or near the hooking mechanism, rather than at the hinge or centre will provide the greatest resistance to clip displacement along a suture thread. The authors would like to thank Teleflex for providing the Hem-o-Lok clips used to perform this experiment. The authors declare that they have no conflicts of interest.