Effect of fluid media on the mechanical properties of continuous pattern-ending surgeon's, square, and Aberdeen knots in vitro*

Knot Security 101: A Comprehensive Practical Review to Optimal Knot Configuration, Pulling Direction, Throw Count, and Tail Length

Background

Knots are the weakest structural point in a suture line and inevitably weaken almost all suture materials. This practical review critically evaluates the factors, such as suture material properties, gauge, configuration, throw count, and tail length, that affect knot security.

Methods

A PubMed search between the years 1934 and 2023 identified relevant studies that addressed factors relating to knot security. Studies that investigated knots and sutures solely used in laparoscopic and arthroscopic surgery were excluded. Knot configurations assessed were the Aberdeen, sliding, square, and surgeon's.

Results

Eighty-six articles were included in this review article and demonstrated that knot security varies greatly between suture materials and gauge. Knot security also varies by configuration, throw count, conditions, tail length, and stitch type. Throw count differs by knot configuration, with the Aberdeen knot being most secure with three throws and one to two turns compared with three to five throws for surgeon's and square knots. The optimal tail length was 3 mm.

Conclusions

This practical review demonstrates that there are significant differences in knot security based on a variety of factors. It is challenging to propose an ideal knot because most studies did not evaluate knot security using a broad variety of suture materials, gauges, and throws for each of the most common knots. Although this review article demonstrated several applicable findings, additional robust studies are needed to simplify proposals.

In vitro evaluation of the effect of tris-EDTA and 0.0005% chlorhexidine solution on the strength of two absorbable sutures

OBJECTIVE

To determine the effect of 0.0005% chlorhexidine and tris-EDTA solution on the strength of three commonly used suture types for closure of equine ventral midline celiotomy.

STUDY DESIGN

Controlled laboratory study.

SAMPLE POPULATION

Knotted loops (n = 10/group, 150 knot constructs total).

METHODS

Strands of 2 polyglactin 910, 3 polyglactin 910, and 2 polydioxanone were tied to form knotted loops. All knotted loops were mounted on a tabletop force measurement machine system and loaded at 100 mm/min until the breaking force (N) was determined. The breaking force (N) of knotted loops using dry suture was recorded at study start, then of knotted loops soaked in either 0.0005% chlorhexidine and tris-EDTA for 20 min followed by incubation in equine serum (treatment) or serum alone (control) for 14 and 21 days. Analysis of variance (ANOVA) compared the breaking force between the treatment and control groups at each time point.

RESULTS

There was no significant difference in the breaking force of 2 USP polyglactin 910 (p = .35, confidence interval [CI] = -0.21-0.59), 3 USP polyglactin 910 (p = .61, CI = -0.41-0.24), or 2 USP polydioxanone (p = .76, CI = -0.63-0.46) soaked in 0.0005% chlorhexidine and tris-EDTA solution followed by equine serum when compared to each respective suture soaked in equine serum only.

CONCLUSION/CLINICAL SIGNIFICANCE

Since 0.0005% chlorhexidine and tris-EDTA solution did not exhibit a significant effect on the breaking force of the absorbable sutures studied, the solution may be used for incisional lavage in the clinical setting.

Knot holding capacity of two different high-strength sutures-a biomechanical analysis

PURPOSE

The number of seven required throws per knot was previously reported as providing sufficient security against slippage. A novel high-strength suture featuring dynamic tightening may allow for throw number reduction without compromising stability. The aims of this study were to (1) investigate the influence of the throw number and the effect of different ambient conditions on the knot security of two different high-strength sutures, and (2) compare their biomechanical competence.

METHODS

Two sutures (FiberWire (FW) and DynaCord (DC)) were considered for preparing alternating surgical knots. The specimens were stratified for exposure to different media during biomechanical testing-namely air (dry), saline solution (wet), and fat (fatty-wet). A monotonic tensile ramp loading to failure was applied in each test run. For each suture and ambient condition, seven specimens with three to seven throws each were tested (n = 7), evaluating their slippage and ultimate force to failure. The minimum number of throws preventing suture unraveling was determined for each suture type and condition.

RESULTS

For each suture type and condition, failure occurred via rupture in all specimens for the following minimum number of throws: FW-dry-7, wet-7, fatty-wet-7; DC-dry-6, wet-4, fatty-wet-5. When applying seven throws, FW demonstrated significantly larger slippage (6.5 ± 2.2 mm) versus DC (3.5 ± 0.4 mm) in wet (p = 0.004) but not in dry and fatty-wet conditions (p ≥ 0.313).

CONCLUSIONS

The lower number of throws providing knot security of DC versus FW in the more realistic wet and fatty-wet conditions indicates that the novel DC suture may allow to decrease the foreign body volume and save surgical time without compromising the biomechanical competence.

Evaluation of the in vitro performance of the double forwarder knot, compared to square and surgeon's knots using large gauge suture

OBJECTIVE

The aim of the study was to evaluate the strength and size of the double forwarder (DF) knot in 2 and 3 USP polyglactin 910 when used to form a ligature and to compare the knot holding capacity (KHC), size and weight of the DF knot to surgeon's (SU) and square (SQ) knots with varying numbers of throws.

STUDY DESIGN

Laboratory study.

STUDY POPULATION

Knotted suture.

METHODS

Knots were tied using 2 and 3 USP polyglactin 910 and tested on a universal testing machine under linear tension. Mode of failure and (KHC) were recorded. Knot volume and weight were determined by digital micrometer and balance. KHC, size, and weight between knot type, number of throws, and suture type and size were compared using ANOVA testing, with p < .05 as significant.

RESULTS

In both suture types, DF knots had a higher KHC than SQ/SU knots (p < .004), with the exception of SU knots with 6-8 throws in 3 USP polyglactin 910 (p > .42). All DF knots failed by suture breakage at the knot, as did all SQ/SU knots with >6 throws. DF knots in 2 and 3 USP polyglactin 910 were larger and heavier than SQ and SU knots when the same number of throws was applied (p < .003).

CONCLUSION

Self-locking DF knots provided increased strength compared to SU/SQ in large gauge suture but only when fewer than six throws are applied to SU/SQ knots.

CLINICAL RELEVANCE

The new DF knot could be an alternative for a secure ligature.

The effect of medical grade honey on tensile strength, strain, and Young's modulus of synthetic absorbable suture material used in equine surgery

BACKGROUND

Medical grade honey (MGH) has been introduced as a protective measure against surgical site infections in equine surgery, but the effect on suture material has not been investigated.

OBJECTIVE

To evaluate the effect of MGH on the tensile properties of three synthetic absorbable suture materials.

STUDY DESIGN

In vitro experiments.

METHODS

Ten strands of Polydioxanone USP 2 (PD2), Polyglactin 910 USP 2 (PG2) and Polyglecaprone USP 2-0 (PC2-0) were incubated 1, 7, 14, 21 and 28 days in MGH, phosphate-buffered saline (PBS), equine plasma (EP) and MGH mixed with equine plasma (HP). Mechanical testing was performed recording maximum load at failure (N), strain at failure and Young's modulus (N/mm2 ). The results were reported from a Welch or regular ANOVA.

RESULTS

PD2 in MGH had a significantly higher tensile strength compared to PD2 in EP (p < 0.05, mean difference (md) = 16.95 N, CI95% (9.19-24.70 N)) and PBS (p < 0.05, md = 14.48 N CI95% (6.73-22.23 N)) on day 7 and the remaining time points. PG2 incubated in MGH had a significantly higher tensile strength compared to EP (p < 0.05, md = 69.28 N CI95% (64.16-74.40 N)) and PBS (p < 0.05, md = 56.90 N CI95% (51.78-62.02 N)) until day 28. PC2-0 incubated in MGH had a significantly higher tensile strength compared to EP (p < 0.05 md = 12.40 N CI95% (4.59 N-20.20 N)) and PBS (p < 0.05 md = 11.23 CI95% (3.42-19.03 N)) on day 7 and the remaining time points.

MAIN LIMITATIONS

The sutures were unloaded during incubation and a single cycle to failure test was only performed, which does not reflect the in vivo environment where shear forces are present.

CONCLUSIONS

MGH did not negatively affect the tensile strength of the suture material and can safely be applied in contact with suture materials commonly used in equine surgery.

Laparoscopic Surgery: A Systematic Review of Loop and Knot Security, Varying with the Suture and Sequences, Throws, Rotation and Destabilization of Half-Knots or Half-Hitches

Surgical knots are sequences of half-knots (H) or half-hitches (S), defined by their number of throws, by an opposite or similar rotation compared with the previous one, and for half-hitches whether they are sliding (s) or blocking (b). Opposite rotation results in (more secure) symmetric (s) knots, similar rotation in asymmetric (a) knots, and changing the active and passive ends has the same effect as changing the rotation. Loop security is the force to keep tissue together after a first half-knot or sliding half-hitches. With polyfilament sutures, H2, H3, SSs, and SSsSsSs have a loop security of 10, 18, 28, and 48 Newton (N), respectively. With monofilament sutures, they are only 7, 16, 18, and 25 N. Since many knots can reorganize, the definition of knot security as the force at which the knot opens or the suture breaks should be replaced by the clinically more relevant percentage of clinically dangerous and insecure knots. Secure knots with polyfilament sutures require a minimum of four or five throws, but the risk of destabilization is high. With monofilament sutures, only two symmetric+4 asymmetric blocking half-hitches are secure. In conclusion, in gynecology and in open and laparoscopic surgery, half-hitch sequences are recommended because they are mandatory for monofilament sutures, adding flexibility for loop security with less risk of destabilization.

Cadaveric Evaluation of Load to Failure in Canine Gingiva Apposed With Varied Suture Patterns Using Poliglecaprone 25

The purpose of the study was to determine the effect of suture pattern and repair length on the load to failure in an ex vivo canine gingival model. Healthy mandibular gingiva and mucosa were harvested from fresh cadavers euthanized for purposes unrelated to the study. Samples were randomly assigned by length and pattern. Lingual and buccal free gingival margins were apposed using a simple interrupted (SI), cruciate (XT), simple continuous (SC), or unidirectional knotless continuous barbed suture (SF) closure technique with USP 4-0 poliglecaprone 25^{i, ii} applied over 2 lengths (3 cm and 6 cm). A custom template was used to ensure uniform suture bite application. Surgical time was recorded. Using a soft tissue mechanical testing frame, samples were tensioned to failure. Testing was video recorded and reviewed in conjunction with the tension trace data for tension at initial failure (T_fail) and maximum tension sustained (T_max). Two factor ANOVA by length and pattern was performed followed by individual one way T-tests. Statistically significant findings were XT-SC-SF patterns were quicker to perform than SI. SF was more likely to fail by suture breakage than tissue tearing, and SF withstood less tension at the 3 cm length than SI-XT-SC. No significant difference was detected in T_max or T_fail between SI and SC or XT. The study demonstrates that SC and XT are comparable to SI in tension resistance and faster to perform suggesting that SC and XT could replace SI for extraction site closure although further in vivo testing is required.

Equine Standing Surgical Extraction Techniques

Dental repulsion techniques reported in the past decades have a high incidence of complications. Although the practice of surgical extractions in horses is limited because of the training, instrumentation, and experience required to perform these techniques, veterinarians should be aware these procedures are available, general anesthesia is not required, and when performed by skilled veterinary dentists they have low complication rates. Surgical techniques are often used after failure of other extraction techniques to remove retained tooth root and fragments or to debride chronically contaminated orofacial lesions. However, surgical extractions should be considered during initial treatment planning of all complicated cases.

In vitro evaluation of the modified forwarder knot used to end a continuous suture pattern in large-gauge suture

OBJECTIVE

To evaluate the strength and size of forwarder end (FE) knots modified to end continuous suture lines compared with Aberdeen (AB), square (SQ), and surgeon's (SU) knots.

STUDY DESIGN

In vitro mechanical study.

STUDY POPULATION

Knotted suture.

METHODS

Knots were tied with 2 USP (United States Pharmacopeia) polydioxanone, 2 USP, and 3 USP polyglactin 910 and tested on a universal testing machine under linear tension. Mode of failure and knot holding capacity (KHC) were recorded, and relative knot security (RKS) was calculated. Knot volume and weight were determined by digital micrometer and balance. Knot holding capacity, RKS, size, and weight between knot type, number of throws, and suture type and size were compared by using analysis of variance testing, with P < .05 considered significant.

RESULTS

In all suture types and number of throws, FE knot KHC/RKS was 28% to 66.99% (1.2-1.6 fold) stronger compared with SQ/SU knots (P < .001). For 2 USP polydioxanone, FE knots had 10% (1.1 fold) higher KHC/RKS compared with AB knots (P < .042). However, in 2 and 3 USP polyglactin 910, FE knot KHC/RKS values were not different from those of AB knots (P > .080). Forwarder end/AB knots failed by suture breakage at the knot, whereas some SQ/SU knots unraveled. Forwarder end knots in 2 and 3 USP polyglactin 910 were 21.1% to 44.4% (1.2-1.4 fold) smaller compared with SQ/SU knots (P < .028). Forwarder end knots in 2 and 3 USP polyglactin 910 were 40% to 99% (1.4-2.0 fold) larger compared with AB knots (P < .001).

CONCLUSION

Forwarder end knots provided increased KHC/RKS compared with SQ/SU knots.

CLINICAL RELEVANCE

Forwarder end knots should be considered for closures when suture is placed under tension.

Tensile strength and early healing of self-locking and surgeon's knots

OBJECTIVE

To compare the biomechanical properties and healing of ventral midline celiotomies (VMC) closed with a self-locking knot combination and forwarder start and Aberdeen end (F-A) vs a traditional knot combination and surgeon's start and end (S-S).

STUDY DESIGN

In vivo, experimental.

ANIMALS

Twenty-one horses.

METHODS

Fourteen horses underwent VMC, which was closed with either an F-A (n = 7) or an S-S (n = 7) knot combination. Incisions were subjectively graded by masked evaluators for dehiscence, edema, and drainage. Biomechanical testing was performed on three abdominal segments, and histology was performed on one segment from each animal after humane euthanasia 10 days post-VMC. The abdominal wall of control horses (n = 7, no celiotomy) was collected for biomechanical testing.

RESULTS

Forwarder start and Aberdeen end and S-S horses had less tensile strength compared with control horses (P ≤ .001). No differences were detected between treatment groups for any variable evaluated, including tensile strength (P = .975), location of failure (P = .240), and histologic healing at the knot (P = .600).

CONCLUSION

Closure of VMC with self-locking knots resulted in biomechanical and healing features similar to those with a traditional closure technique, with neither restoring the tensile strength of the linea alba.

CLINICAL SIGNIFICANCE

Results of this study provide evidence to support a clinical trial to evaluate long-term performance of the F-A self-locking knot closure in horses.

Assessment of time to completion, number of errors, and knot-holding capacity of square knots and Aberdeen knots tied by veterinary students and student perceptions of knot security and knot-tying difficulty

OBJECTIVE

To assess the time to completion, number of errors, and knot-holding capacity (KHC) for starting and ending square knots (SSKs and ESKs) of a continuous pattern and Aberdeen knots tied by veterinary students and to investigate student perceptions of knot security and knot-tying difficulty for the 3 knot types.

SAMPLE

16 second-year veterinary students.

PROCEDURES

Students created 3 (4-throw) SSKs, 3 (5-throw) ESKs, and 3 (3 + 1 configuration) Aberdeen knots with 2-0 polydioxanone on a custom test apparatus. Time to complete each knot, the number of errors in each knot, and student ratings of knot-tying difficulty and confidence in knot security were recorded. Each knot was tested to failure on a uniaxial tensiometer to determine KHC and mode of failure. Variables of interest were compared by repeated-measures ANOVA or the Friedman test with post hoc pairwise comparisons.

RESULTS

Mean knot completion time for Aberdeen knots was significantly less than mean completion time for SSKs or ESKs. Mean KHC was significantly lower for ESKs than for SSKs; KHC for Aberdeen knots was not compared with these values because of methodological differences. Median error rate was higher for ESKs than for other knot types. Mean difficulty rating for Aberdeen knots was lower than that for ESKs. Most tested knots failed by breakage at the knot.

CONCLUSIONS AND CLINICAL RELEVANCE

Aberdeen knots appeared to be easy for veterinary students to learn and were completed more rapidly and with fewer errors than ESKs. Including this type of knot in surgical skills curriculum for novices may be beneficial.

In vitro evaluation of the knot-holding capacity and security, weight, and volume of forwarder knots tied with size-3 polyglactin 910 suture exposed to air, balanced electrolyte solution, or equine abdominal fat

OBJECTIVE

To evaluate the effect of exposure to a balanced electrolyte solution (BES), or equine abdominal fat on the knot-holding capacity (KHC), relative knot security (RKS), weight, and volume of forwarder knots versus surgeon's knots.

SAMPLE

315 knots tied and tested in vitro.

PROCEDURES

United States Pharmacopeia size-3 polyglactin 910 suture exposed to air (dry [control]), equine abdominal fat (fat-exposed), or BES (BES-exposed) was used to tie forwarder knots with 2, 3, and 4 throws and surgeon's knots with 5, 6, 7, and 8 throws. A universal materials testing machine was used to test the tensile strength of suture and knots to failure, and the KHC, RKS, weight, and volume of knots were determined.

RESULTS

Forwarder knots had significantly higher KHC and RKS and lower volume, compared with surgeons' knots. Forwarder knots tied with fat-exposed suture had greater weight, but not volume, than did forwarder knots tied with dry or BES-exposed suture with the same number of throws.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that forwarder knots were superior to surgeon's knots when configured as start knots intended for continuous lines of suture. Exposure to media did not negatively affect mechanical or physical properties of forwarder knots and may improve specific biomechanical functions, including KHC and RKS.

Bursting strength of surgeon's and self-locking knots for closure of ventral midline celiotomy in horses

OBJECTIVE

To compare the bursting strength and failure mode of ventral midline celiotomy closed with a simple continuous suture pattern with 1 of 2 knot combinations, a novel self-locking knot combination of a forwarder start with an Aberdeen end knot (F-A) and a traditional combination of a surgeon's start with a surgeon's end knot (S-S).

STUDY DESIGN

Ex vivo experimental.

SAMPLE POPULATION

Equine cadavers (n = 14).

METHODS

A 20-cm ventral midline celiotomy was created in 14 equine cadavers. Horses were assigned to celiotomy closure with an F-A or S-S knot combination. Prior to closure, a 200-L inflatable bladder was placed in the abdomen and then insufflated until failure of the celiotomy closure. The horses' signalment, weight, breed, and age, as well as knot combination type, mode of failure, closure time, and bursting strength (mm Hg) were recorded.

RESULTS

The median bursting strength was significantly greater when incisions were closed with the F-A knot combination (388 mm Hg) compared with the S-S knot combination (290 mm Hg) (P = .035). Most incisions failed along the fascia when closed with F-A combinations and at the knot when closed with S-S combinations.

CONCLUSION

The bursting strength of ventral midline incisions in equine cadavers was increased by an average of 25% when closed with the self-locking F-A knot combination.

CLINICAL SIGNIFICANCE

Closing ventral midline celiotomies with an F-A knot combination may provide a more secure closure than the traditional S-S knot combination. Additional in vivo investigation is required prior to recommending this closure in clinical cases.