Comparison of ligation security between monofilament polydioxanone and pseudomonofilament polyamide sutures in a standardized vascular model

Abstract

The objective of this study was to determine whether ligation security in a standardized in-vitro vascular model is primarily influenced by tying force or filament configuration when comparing 2 commonly used suture materials: monofilament polydioxanone and pseudomonofilament polyamide. A standardized latex vascular model subjected to controlled intraluminal pressure (150 mmHg) was used. USP 2-0 sutures were applied using a 4-throw surgeon’s knot at 5 predefined tying-force levels (6, 8, 10, 12, and 14 N). Three time intervals between the first and second throw (0, 10, and 20 s) were evaluated. A total of 300 ligations were tested. Leakage was defined as a detectable increase in distal pressure during a 30-second observation period. The effects of tying force, time interval, and suture material were analyzed using multivariate logistic regression. Tying force was significantly associated with leakage (P < 0.001). Leakage was eliminated only at 14 N for both materials, whereas high leakage rates occurred at lower force levels regardless of suture material. Time interval and suture material were not independently associated with leakage. These findings indicate that ligation security in this model is determined primarily by tying force rather than by filament configuration.

Introduction

Hemorrhage remains a clinically relevant complication in routine small animal surgery, particularly during procedures involving vascular pedicles. Although the overall incidence of severe bleeding during ovariohysterectomy is low, intraoperative hemorrhage remains a recognized surgical risk (1,2). The likelihood of bleeding may be influenced by the surgeon’s level of experience and by the ligation technique used (3).

Hand-tied suture ligation continues to be widely used in small animal practice because of its simplicity, availability, and familiarity. Surveys of commonly used procedures demonstrate substantial variation in selection of suture material that reflects differences in the level of surgical experience and postgraduate training, as well as perceived knot security, rather than consistent evidence-based standards (4).

Multifilament sutures have historically been favored for vascular ligation based on the assumption that increased surface friction enhances knot security. Multifilament materials are associated with greater capillarity, however, which may facilitate bacterial transport along the suture (5). Pseudomonofilament sutures, which contain a multifilament core, may also exhibit increased capillarity compared with true monofilament materials, although this has not been specifically quantified. As a result, surgeons often balance perceived knot reliability against concerns about infection risk and tissue reaction.

Experimental studies evaluating knot mechanics have demonstrated that suture configuration can influence slippage and tensile holding strength under controlled testing conditions (6). Nevertheless, these effects are not uniform across materials. In a comparative in-vitro study, coated multifilament polyglactin 910 exhibited greater slippage than certain monofilament materials, suggesting that filament architecture and surface characteristics may influence performance in ways that are not solely predictable based on braid structure (7). These findings indicate that filament configuration alone does not consistently determine knot security.

Monofilament polydioxanone has become increasingly adopted for vascular ligation because of its predictable absorption profile and low capillarity. In contrast, pseudomonofilament polyamide consists of a multifilament core surrounded by an external sheath and has been used in some settings with the aim of combining the frictional properties of multifilament sutures with a smoother external surface, although these characteristics have not been consistently quantified in the literature. In clinical practice, such configurations may represent an intermediate approach to balance handling characteristics, knot security, and capillarity, although the mechanical implications of this compromise remain unclear.

Whether the presumed frictional advantages of pseudomonofilament configuration translate into improved ligation security under physiologic intraluminal pressure conditions remains unclear. Much of the available literature evaluates knot performance under isolated tensile-loading rather than pressure-based vessel occlusion models. Therefore, the objective of this study was to evaluate the relative contributions of tying force and filament configuration to the ligation security of 2 commonly used suture materials in a standardized vascular model subjected to controlled intraluminal pressure.

We hypothesized that if filament configuration was the dominant determinant of ligation security, pseudomonofilament polyamide would demonstrate better resistance to leakage than monofilament polydioxanone. Alternatively, if execution-related factors had more impact, differences between materials would decrease when adequate tying force was applied.

Materials and methods

Study design

This was a controlled in-vitro experimental study designed to evaluate ligation security under standardized intraluminal pressure conditions.

Suture materials

Two commercially available USP 2-0 (metric 3) suture materials were evaluated. The first was monofilament polydioxanone (MonoPlus; B. Braun, Rubí, Spain) and the second was pseudomonofilament polyamide (Supramid; B. Braun), which consists of a multifilament core surrounded by an external sheath. All ligations were done using new 15-cm suture segments. A pseudomonofilament suture was selected to represent an intermediate configuration between multifilament and monofilament materials, allowing evaluation of how differences in filament configuration may influence ligation security under controlled conditions.

Vascular model and pressure system

A standardized latex tube was used to simulate a blood vessel (internal diameter 3 mm; wall thickness 0.75 mm; length 30 mm). The dimensions were selected to provide a consistent and reproducible model for evaluating ligation under controlled intraluminal pressure, rather than to replicate a specific anatomical vessel.

The tube was incorporated into a closed hydraulic system consisting of a syringe pump (NE-1000; New Era Pump Systems, Farmingdale, New York, USA), a proximal pressure transducer (PX409 Series; OMEGA Engineering, Norwalk, Connecticut, USA), and a distal pressure sensor (Honeywell 26PC Series; Honeywell International, Charlotte, North Carolina, USA) (Figure 1 A, B).

Figure 1.

Experimental vascular model and pressure system. A — Photograph of the experimental vascular model. B — Schematic representation of the system. Fluid was delivered by a syringe pump through a proximal pressure transducer (PT₀₁), across the latex vessel segment (orange), and past a distal pressure transducer (PT₀₂). A ligature knot (N) was applied at the midpoint of the vessel segment to assess occlusion under controlled intraluminal pressure.

Normal saline was infused at a constant rate of 10 mL/h. After ligation at the midpoint of the tube, intraluminal pressure was increased to 150 mmHg (± 3 mmHg) and maintained for 30 s, representing a high physiological arterial pressure and providing a stringent condition for evaluating ligation security. Leakage was defined as any distal pressure elevation greater than 0 mmHg during the 30-second observation period, indicating incomplete occlusion of the simulated vessel lumen, including both complete and partial failures of occlusion.

Ligation technique and experimental conditions

All ligations were done using a standardized 4-throw surgeon’s knot consisting of 2 initial throws followed by 2 square throws. This knot type was selected because it is widely used in clinical practice and provides a consistent and reproducible configuration, allowing standardization across all experimental conditions. One strand of the suture was connected to a digital tensiometer (Mark-10 Series 3; Mark-10 Corporation, Copiague, New York, USA) to standardize and record the applied tying force.

Five predefined tying-force levels (6, 8, 10, 12, and 14 N) were tested. Three time intervals between the first and second throw (0, 10, and 20 s) were evaluated. It was required that the designated force must be achieved during each throw, but was not maintained after knot seating.

Each combination of suture material, tying force, and time interval was repeated 10 times, resulting in a total of 300 ligations. The number of repetitions per subgroup (n = 10) was selected to allow stable estimation of leakage proportions while maintaining feasibility of the experimental protocol. All ligations were done by the same operator to minimize inter-operator variability. The operator was a senior surgical resident with prior experience in routine soft tissue surgical procedures.

Statistical analysis

Leakage (binary outcome: leakage versus no leakage) was analyzed using multivariate logistic regression. The model included tying force, time interval, and suture material as fixed effects. Odds ratios (OR) with 95% confidence intervals (CI) were calculated. Statistical significance was set at P < 0.05. Statistical analyses were conducted using SAS version 9.4 (SAS Institute, Cary, North Carolina, USA).

Results

A total of 300 ligations were evaluated, and all experiments were successfully completed and included in the analysis.

Tying force was significantly associated with leakage (P < 0.001). At 6 N and 8 N, leakage occurred in all ligations for both suture materials. At 10 N and 12 N, leakage rates decreased but remained substantial. Complete elimination of leakage occurred only at 14 N for both monofilament polydioxanone and pseudomonofilament polyamide. Leakage proportions for each experimental condition are illustrated in Figure 2.

Figure 2.

Leakage frequency according to applied tying force for monofilament polydioxanone (solid line) and pseudomonofilament polyamide (dashed line). Values represent the percentage of ligations demonstrating leakage at each force level (n = 30 per suture material per force level).

Multivariate logistic regression analysis confirmed that tying force was the only variable independently associated with leakage. Increasing tying force was associated with a significant reduction in the probability of leakage. Suture material was not significantly associated with leakage after adjustment for tying force (P = 0.94).

The time interval between the first and second throw was not independently associated with leakage in the multivariate model. However, longer delay intervals were associated with numerically higher leakage rates at intermediate force levels (10 N and 12 N). Detailed interval-specific leakage data are presented in Table I.

Table I.

Leakage frequency according to tying force, interval between first and second throws, and suture material.

Tying force (N)	Interval (s)	Pseudomonofilament polyamide	Monofilament polydioxanone
6	0	10/10 (100%)	10/10 (100%)
6	10	10/10 (100%)	10/10 (100%)
6	20	10/10 (100%)	10/10 (100%)
8	0	10/10 (100%)	10/10 (100%)
8	10	10/10 (100%)	10/10 (100%)
8	20	10/10 (100%)	10/10 (100%)
10	0	8/10 (80%)	7/10 (70%)
10	10	8/10 (80%)	7/10 (70%)
10	20	7/10 (70%)	8/10 (80%)
12	0	2/10 (20%)	4/10 (40%)
12	10	3/10 (30%)	4/10 (40%)
12	20	4/10 (40%)	4/10 (40%)
14	0	0/10 (0%)	0/10 (0%)
14	10	0/10 (0%)	0/10 (0%)
14	20	0/10 (0%)	0/10 (0%)

Detailed interval-specific leakage frequencies observed under controlled intraluminal pressure (150 mmHg). Values represent n/N (%), where n is the number of ligations demonstrating leakage and N is the total number of ligations done within each tying force and interval subgroup (n = 10).

No significant interaction between suture material and tying force was identified, indicating that the effect of tying force on leakage did not differ between the 2 suture materials.

Discussion

The primary finding of this study was that ligation security in this standardized in-vitro vascular model was determined primarily by tying force rather than by filament configuration. Complete elimination of leakage occurred only at 14 N for both monofilament polydioxanone and pseudomonofilament polyamide. This value was not predefined as a clinical threshold but was informed by preliminary pilot observations and emerged as the force at which complete occlusion was consistently achieved in this model. At lower force levels, high leakage rates were observed regardless of filament configuration, which suggests that insufficient force during knot seating is a major determinant of ligation failure in this model.

Multifilament sutures have historically been favored for vessel ligation based on the assumption that increased surface friction enhances knot security. Experimental studies have demonstrated that filament configuration can influence slippage and tensile-holding strength under controlled loading conditions (6,7,8). However, variability between materials, coatings, and testing conditions indicates that filament architecture alone does not consistently predict knot performance.

Importantly, most published studies evaluate knot security using linear tensile testing rather than pressure-based occlusion models. Leitch et al (9) reported that ligation behavior under simulated pedicle conditions may differ from pure tensile testing outcomes. In the present study, ligation security was assessed under controlled intraluminal pressure, a condition that more closely approximates the mechanical requirements of clinical hemostasis.

In this model, pseudomonofilament polyamide, which is historically selected for its presumed frictional advantages, did not demonstrate superior resistance to leakage compared with monofilament polydioxanone. These findings suggest that theoretical increases in inter-filament friction may not necessarily translate into improved ligation security once adequate circumferential compression of the vessel wall has been achieved.

From a biomechanical perspective, knot performance reflects the interaction between material properties, knot configuration, and applied load magnitude (10,11). Effective vascular ligation requires sufficient circumferential compression to occlude the lumen and maintain occlusion under pressure. Within the range tested, the magnitude of applied tying force appeared to exert a greater influence on leakage prevention than differences in filament configuration.

Although the time interval between the first and second throw was not an independent predictor in multivariate analysis, longer delay intervals were associated with numerically higher leakage rates at intermediate force levels. This pattern may reflect partial relaxation of applied tension before knot consolidation, a phenomenon described in experimental knot studies (11). However, these differences were not statistically significant after adjustment for tying force, which may be related in part to the sample size and limited statistical power to detect small effects, including potential interaction effects between variables.

From a clinical perspective, these findings suggest that material selection alone may not compensate for inadequate tying force. Surveys of small animal surgical practice reveal variation in suture selection based largely on differences in surgical experience and level of training rather than on consistent mechanical evidence (4). When sufficient tying force was consistently applied, monofilament polydioxanone provided ligation security comparable to pseudomonofilament polyamide in this experimental setting. Given its absorbable nature and low capillarity (5), monofilament polydioxanone may therefore be selected without evidence of inferior mechanical performance under the conditions tested.

This study has limitations. The latex tube model does not replicate the compliance, structural heterogeneity, or biological behavior of living vessels, including coagulation and physiological vasoreactivity, and its dimensions were not intended to correspond to specific canine vascular anatomy or account for variability across vessel sizes, species, and physiological or pathological states, e.g., hypotension or hypertension. Therefore, direct extrapolation to clinical conditions should be made with caution.

In addition, only 1 knot configuration and suture size were evaluated. All procedures were done by a single operator, and therefore the potential influence of operator experience on ligation security was not evaluated. Nevertheless, the standardized design permitted isolation of mechanical variables that are difficult to control in vivo and provided controlled experimental evidence regarding the relative contributions of tying force and filament configuration to ligation security.

Within the limitations of this model, these findings suggest that adequate tying force may be more important than the selection of suture material, and that monofilament polydioxanone can be used without evidence of inferior ligation security under the conditions tested.

In conclusion, in this standardized in-vitro vascular model, ligation security was determined primarily by the magnitude of applied tying force rather than by suture filament configuration. When sufficient tying force was applied, monofilament polydioxanone and pseudomonofilament polyamide demonstrated comparable resistance to leakage under controlled intraluminal pressure.