Influence of emergency physician's tying technique on knot security

Comparison of mechanical properties between Nice knot, Modified Nice knot, and surgeon's knot

BACKGROUND

The success of surgical repairs rely on the effectiveness and integrity of the surgical knots used to secure the repair. The purpose of this study is to examine and compare the performance of the Nice knot, the modified Nice knot, and a commonly used combination of surgeons' and square knots with respect to cyclic loading and load-to-failure usiflueng a high-strength suture composed of ultra-high molecular weight polyethylene in the hands of experienced surgeons.

METHODS

Two experienced surgeons threw 3 different knot types 9 times, consisting of the Nice knot, modified Nice knot, and a surgeon's knot utilizing Ultrabraid #2 sutures. Each knot was subject to cyclic loading and load to failure testing.

FINDINGS

Both surgeons had similar displacement data for the surgeon's knot, while the identity of the surgeon impacted displacement for the Nice knot (p = 0.03) and the modified Nice knot (p = 0.0002). The load to failure for the modified Nice knot (p < 0.001) and the Nice knot (p = 0.001) were significantly impacted by the surgeon tying the knot, while the surgeon's knot was not. Specimens failed where the sutures passed through the loop at the "base" of the knot.

INTERPRETATIONS

The strength and integrity of complex surgical knots are variable between surgeons. While the proposed Modified Nice Knot has a theoretical advantage because the half hitches reinforce the primary knot, in load to failure testing both the Modified Nice Knot and the Nice Knot failed where the suture passed through the loop in the primary knot.

The effect of pulsed lavage irrigation on suture knot security

PURPOSE

The purpose of this study was to determine the effect of low-pressure and pulsed lavage irrigation on suture knot security.

METHODS

Ninety-tied suture loops were measured for baseline circumference and then subjected to no irrigation, bulb syringe irrigation, or pulsed lavage irrigation. The sutures were placed under a load and then measured for final circumference. A larger circumference difference indicated poorer knot security.

RESULTS

There was a statistically significant difference in the knot security between all three groups (p < 0.001). Pulsed lavage resulted in the greatest circumference increase (0.52 ± 0.19 mm), followed by bulb syringe (0.24 ± 0.18 mm), and lastly no irrigation (0.08 ± 0.00 mm). None of the groups had any catastrophic failures. No knots met the predetermined criteria for knot failure.

CONCLUSION

Pulsed lavage irrigation resulted in a statistically significant decrease in suture knot security as compared to bulb syringe irrigation and no irrigation. None of the groups met the currently accepted criteria for clinical suture failure, which has a relatively arbitrary value. While the available literature does not discuss increases in loop circumference for specific orthopedic applications, this small difference suggests that pulse lavage is unlikely to have a clinically significant impact on the suture integrity for most orthopedic procedures.

Evaluation of a Tensiometer to Provide Objective Feedback in Knot-Tying Performance

Training and assessment methods for knot tying by medical students or residents have traditionally been subjective. Objective methods for evaluating creation of a tied knot should include assessing the strength and quality of the knotted suture. The purpose of this study was to evaluate the use of a tensiometer as a feedback device for improving knot-tying performance. Twelve medical students with no knot-tying experience were selected to perform three-throw instrument ties with 00 silk suture. Students were randomly assigned to perform between 10 and 20 baseline knots and then received one of four feedback training conditions followed by 10 completion knots. Subjects were timed, and all knots were pulled in the tensiometer to assess for strength and slippage. Differences between baseline and completed knots for each subject were analyzed with an unpaired t test. Subjects receiving both subjective and tensiometer feedback demonstrated the greatest improvements in knot quality score (KQS) and slip percentage (Subject 1: 0.15 ± 0.9 vs 0.21 ± 0.05, P < 0.04, 75% vs 60%, P = NS; Subject 2: 0.22 ± 0.10 vs 0.29 ± 0.05, P < 0.02, 33% vs 0%, P < 0.05; Subject 3: 0.10 ± 0.07 vs 0.25 ± 0.07, P < 0.0001, 60% vs 10%, P < 0.01). Objective assessment of knot-tying performance is possible using the tensiometer device. Introduction of the tensiometer during the learning phase produced improved KQS and slip percentage in most students regardless of the number of baseline knots tied. Greatest improvements in performance were seen when the tensiometer was used in combination with subjective instruction.

Retention of basic suturing skills with brief or extended practice in veterinary students

OBJECTIVE

To evaluate the effect of practice duration on accuracy, retention, and confidence when learning how to tie basic surgical knots.

STUDY DESIGN

Prospective study.

SAMPLE POPULATION

Fifteen first-year veterinary students.

METHODS

Students were randomly assigned to a 2-week practice (TWP) or an 8-week practice (EWP) to learn how to tie surgeon's, strangle, and miller's knots. Students' knot-tying accuracy and confidence were evaluated immediately after training, at an intermediate time point (2-6 weeks postpractice), and at 12 weeks postpractice.

RESULTS

Students who had been trained during an extended period tied the strangle knot correctly more often at all assessments (P = .025). The ability of students trained for 2 weeks to tie the strangle knot correctly decreased over time (P = .028). These students lost some confidence (P = .03) and repositioned suture more frequently (P = .03) while constructing the strangle knot at the final time point compared with students trained for 8 weeks. Students who completed TWP felt more confident at placing surgeon's knots than friction knots at the final assessment period (P = .0164 miller's knot, P = .0056 strangle knot), whereas confidence did not differ between knot types for students who completed EWP. All students felt less confident with their knot-tying skills at 12 weeks postpractice.

CONCLUSION

Training for 8 weeks rather than for 2 weeks resulted in superior knot tying skills. Students' confidence decreased 12 weeks after training.

CLINICAL SIGNIFICANCE

Prolonged distributed practice is recommended to train students for more complex tasks such as placement of a strangle knot.

Validation of Improvement of Basic Competency in Arthroscopic Knot Tying Using a Bench Top Simulator in Orthopaedic Residency Education

PURPOSE

To validate basic competency in arthroscopic knot tying using a unique simulator device to compare the level of training needed for learning and tying the arthroscopic knot by evaluating the tensile properties of the arthroscopic knots.

METHODS

Three groups of surgeons of various experience levels (postgraduate year [PGY] 1, PGY 3, and experienced surgeons) tied 2 different arthroscopic knots (Tennessee Slider, considered easier, and Weston, considered more difficult) over a 10-week period. Each group went through 3 separate stages of knot tying: stage 1, tying 8 knots without cannula or knot pusher; stage 2, tying 12 knots with knot pusher; and stage 3, tying 20 knots with knot pusher through a cannula that simulates knot tying during surgery. A single load-to-failure test was performed and ultimate clinical failure loads were recorded. Time needed to tie each knot was also recorded.

RESULTS

At stages 1 and 2, the PGY 1 group had a significantly weak knot tensile strength (Tennessee Slider stage 1: 60 v 129 N, P = .001; Tennessee Slider stage 2: 69 v 132 N, P = .0029; Weston stage 1: 73 v 184 N, P = .0000; Weston stage 2: 125 v 173 N, P = .0045) and were slower (Weston: 56 v 30 seconds, P = .0010) than the experienced surgeon group for both knots. At stage 3, only the initial 2 weeks of Tennessee Slider showed a significant difference between groups 1 and 3 (week 6: 87 v 118 N, P = .0492; week 7: 89 v 126, P = .01485). Even though the Tennessee Slider knot is one of the easier arthroscopic knots to learn to tie, the results showed a slow trend of improvement in this knot-tying skill for group 1 after each stage.

CONCLUSIONS

The data validated an important learning effect in all trainees in arthroscopic knot tying over a 10-week period and showed that inexperienced trainees will be able to improve their knot-tying skill with training in 3 stages with a simulator environment.

CLINICAL RELEVANCE

The findings of this study indicated the importance of hands-on experience in performing arthroscopic knot tying, as determined by both knot performance and ultimate suture loop strength. In addition, each orthopaedic resident learned and developed his or her arthroscopic knot-tying skills and provided a foundation for his or her future practice in orthopaedic medicine.

The Nice knot as an improvement on current knot options: A mechanical analysis

PURPOSE

There is currently a wide range of suture knots used in rotator cuff repair. The purpose of this study was to compare a new type of self-locking sliding knot called the Nice knot to the self-locking and sliding Nicky's knot.

METHODS

Nice knots and Nicky's knots were tied and subjected to mechanical testing including a pure traction stress and a series of dynamic stresses. Both knots were tied using standard braided suture and reinforced braided suture. The responses to these stresses were measured in the amount of elongation of the knot, maximum effort needed for failure, stiffness of construct and dynamic stiffness.

RESULTS

With both knots the standard suture had a lower amount of elongation during the dynamic tests than the reinforced braided suture. The reinforced braided suture showed superior results during maximal effort in the pure traction tests. An increased failure rate occurred due to elongation when a dynamic stress was applied to the reinforced suture in both knot types. During dynamic testing the Nice knot showed a decrease in the amount of elongation (P<0.001).

CONCLUSIONS

The Nice knot provides a sliding locking knot option which can decrease the risk of elongation during dynamic stress.

LEVEL OF EVIDENCE

Basic Science Study, Biomechanical Study.

Surgical knot integrity: effect of suture type and caliber, and level of residency training

OBJECTIVE

To evaluate if suture type and caliber or level of residency training affects strength and mode of failure of surgical knots.

DESIGN

All residents in an obstetrics and gynecology training program were invited to tie knots on a bench model using 2 calibers (0 and 3-0) of 2 types of surgical suture (polyglactin 910 and polydioxanone). The failure load, mode of failure, and loop lengths of the knots were determined.

SETTING

University of Texas Southwestern Medical Center, Dallas, Texas.

PARTICIPANTS

Physicians enrolled in the University of Texas Southwestern Medical Center Obstetrics and Gynecology residency training program.

RESULTS

Seventy-one of 73 residents participated. Knots tied with 0-caliber sutures had a higher mean failure load than those tied with 3-0 caliber sutures. For each type and caliber of suture, there were no differences in failure load between each level of residency training. However, senior residents tied knots with shorter loop lengths and had a lower proportion of knots that unraveled or slipped.

CONCLUSIONS

Even though there were no differences in failure loads, senior residents tied tighter and more secure knots than their junior counterparts.

Effects of using a surgical clamp to hold tension while tying knots with commonly used orthopedic sutures

PURPOSE

Tendon repairs are often performed under some degree of tension, and in these instances the use of a clamp to temporarily secure a knot following the first throw can lessen gap formation while subsequent suture throws are made. The effect of clamping on the ultimate tensile load, stiffness, elongation, and mechanism of failure of suture loops has not been investigated for several commonly used orthopedic sutures, and it was the purpose of this study to investigate this issue.

METHODS

Seven different types/sizes of braided nylon or polyblend (PB) suture were uniformly tied around an isolated 35-mm glass cylinder in a laboratory setting using no clamp, a smooth needle holder, or a serrated clamp to hold a surgeon's knot following the first throw. Knots were secured with four alternating half-hitches with reversed posts, and the suture loops were then loaded on custom hooks in an MTS axial loading frame, preloaded, cycled, and loaded to failure. Elongation, ultimate tensile load (UTL), stiffness, and mechanism of failure were recorded.

RESULTS

Six of seven suture loops tied with either clamp showed statistically significant but clinically minimal (<1 mm) increased elongation following cycling. The UTL of No. 2 ForceFiber suture loops tied with serrated clamps were reduced approximately 21% compared to those tied with no clamp (227 N vs. 289 N, P = 0.003) and approximately 18% compared to those tied with a smooth clamp (227 N vs. 278 N, P = 0.016). The use of clamps did not affect the UTL for the other six sutures. Clamp use also had no effect on suture loop stiffness for four suture types/sizes, but decreased stiffness for three. Suture loops tied with a serrated clamp were more likely to fail by untying compared to those tied without a clamp, but showed no difference in mechanism of failure from those tied with a smooth clamp.

CONCLUSIONS

Biomechanical parameters of suture loops were not significantly affected when clamped during tying. Surgeons wishing to temporarily clamp a knot to keep it from slipping during the tying process may do this without concern for weakening the suture.

Arthroscopic suture material and knot type: an updated biomechanical analysis

BACKGROUND

Several new arthroscopic suture materials are available. It is important for surgeons to know which suture-knot combination provides the strongest construct.

HYPOTHESIS

The newer, polyblend sutures have dissimilar load-to-failure characteristics.

STUDY DESIGN

Controlled laboratory study.

METHODS

The load to failure of 4 knots was evaluated (surgeon's, Duncan loop, Samsung Medical Center [SMC], and Roeder) using 5 No. 2 suture materials (Ethibond, Ticron, FiberWire, ForceFiber, MaxBraid). One surgeon tied all knots. Fifteen samples were tested for each suture-knot configuration. Knots were pretensioned to 10 N, then loaded to failure at a rate of 1.0 mm/s. Failure load recorded was the maximum load applied between 0 and 3 mm of displacement. Cyclic loading of suture-knot samples was performed on 3 knots (surgeon's, Duncan loop, and SMC) using 4 suture materials (Ethibond, FiberWire, ForceFiber, MaxBraid). Six samples were tested for each suture-knot configuration. Knots were cyclically loaded from 5 to 40 N at 0.5 Hz for 1000 cycles, then loaded to failure. Data were compared with analysis of variance and the Tukey multiple range test and considered significant at P < .05.

RESULTS

The surgeon's and SMC knots were strongest, particularly if tied using MaxBraid or ForceFiber. With single load-to-failure testing, MaxBraid was significantly stronger than Ethibond, Ticron, or FiberWire, regardless of knot type used. ForceFiber was stronger than Ethibond and Ticron with any knot type, and stronger than FiberWire when tied with a surgeon's knot or Roeder knot. The MaxBraid surgeon's knot (246 N) and MaxBraid SMC knot (239 N) were more than twice as strong as the Ethibond surgeon's knot (111 N) and Ethibond SMC (118 N). With cyclic loading, MaxBraid and ForceFiber were stronger than FiberWire and Ethibond, regardless of knot type tied. The SMC knot using MaxBraid withstood the highest load, and was stronger than the Duncan loop tied with MaxBraid. When stricter criteria (1-mm and 2-mm displacement) for failure were used, MaxBraid and ForceFiber remained superior to other sutures, including FiberWire, but knot type became less significant.

CONCLUSION

Nonabsorbable polyblend sutures are stronger than traditional sutures, but not all polyblend sutures are alike. MaxBraid and ForceFiber provide a stronger knot than FiberWire, Ethibond, and Ticron, particularly if tied using a surgeon's or SMC knot.

CLINICAL RELEVANCE

The SMC knot using MaxBraid provides the strongest knot/suture combination of knots and sutures tested.

Security of knots tied with ethibond, fiberwire, orthocord, or ultrabraid

BACKGROUND

The security of several popular arthroscopic knots to prolonged, incremental, cyclic loads is unknown, as is the security of knots tied with newer, superstrong sutures.

HYPOTHESIS

Some arthroscopic knots are as secure as openly tied square knots, and knots tied with superstrong sutures are more secure than those tied with braided polyester. Some arthroscopic knots are significantly bulkier than openly tied square knots.

STUDY DESIGN

Controlled laboratory study.

METHODS

Five types of openly tied knots (3-throw square, 4-throw square, 5-throw square, 5-throw slip, open SAK [simple arthroscopic knot]), 6 complex arthroscopic knots backed with 3 reversed half-hitches with alternating posts (RHAPs) (SMC, Weston, taut-line hitch, Tennessee slider, Roeder, Duncan loop), and 2 stacked half-hitch (SHH) arthroscopic knots (surgeon's [S=S=S//xS//xS//xS], SAK [S=S//xSxS//xS]) were tied using No. 2 Ethibond around 2 aluminum rods, which were pulled apart with stepwise, incremental, cyclic loads to a maximum force of 120 N (2250 total cycles). Then, 5-throw square knots openly tied with No. 2 Fiberwire, Orthocord, or Ultrabraid were subjected to the stepwise, incremental, cyclic loading protocol extended to a 260-N load level. Before mechanical testing, the height (maximum diameter) of each knot was measured with digital calipers.

RESULTS

For Ethibond, the openly tied 3-throw square knots (56.2 +/- 21.4 N) and 5-throw slip knots (49.9 +/- 26.9 N) reached clinical failure (3 mm of laxity) at significantly lower loads (P < .05) than openly tied 5-throw square knots (90.8 +/- 6.5 N), whereas the openly tied SAK (82.3 +/- 9.4 N) and 4-throw square (84.3 +/- 11.6 N) and all arthroscopically tied knots reached 3 mm of laxity at statistically similar loads. Five-throw square knots openly tied with Fiberwire or Orthocord reached 3 mm of laxity at much higher loads (194.9 +/- 28.4 N and 168.4 +/- 8.6 N, respectively) than those tied using Ethibond (P < .001 for each comparison), but there was no significant difference in performance between Fiberwire knots and Orthocord knots. Although Ultrabraid square knots also were stronger than those tied with Ethibond (137.9 +/- 15.9 N, P < .005), they were not as secure as those tied with Orthocord or Fiberwire (P < .05). Compared with the 5-throw square knots, all arthroscopic knots were significantly bulkier. Especially bulky knots were the Duncan loop and the taut-line hitch. Orthocord square knots demonstrated bulkiness similar to Ethibond square knots, whereas Fiberwire and Ultrabraid square knots were significantly bulkier.

CONCLUSIONS

For braided suture, 5-throw knots optimize square knot security. Open or arthroscopic slip knots can achieve similar security with post switching and loop reversal. Fiberwire, Orthocord, or Ultrabraid openly tied square knots offer greater security than those tied with Ethibond. Arthroscopic knots vary in their bulkiness, but all are significantly bulkier than 5-throw openly tied square knots. Square knots openly tied with Fiberwire or Ultrabraid tend to be bulkier than if tied with Ethibond or Orthocord, which are similar to each other.

CLINICAL RELEVANCE

The 5-throw openly tied square knot remains the gold standard, although the openly tied SAK offers similar security when tying in a hole. Arthroscopic knots, whether complex knots backed up by 3 RHAPs, the 6-throw surgeon's knot, or the 5-throw SAK, give security similar to the standard. Square knots tied with the newer sutures in open fashion are more secure than if tied with braided polyester. Using lower profile knots may be especially important when employing Fiberwire or Ultrabraid, as these sutures tend to result in bulkier knots than those tied with Ethibond or Orthocord.

Comparison of suture welding and hand-tied knots in mini-open rotator cuff repair

PURPOSE

This study was undertaken to compare the results of mini-open rotator cuff repair with outcomes attained with hand-tied knots and suture welds.

METHODS

A total of 50 consecutive patients treated by a single surgeon with mini-open cuff repair and suture welding were retrospectively evaluated and compared with 55 consecutive patients treated with mini-open cuff repair and hand-tied knots. The groups were similar in terms of age, sex, hand dominance, and preoperative duration of symptoms. All procedures were performed in a hospital outpatient surgery center with patients in a lateral decubitus position under general anesthetic. Glenohumeral arthroscopy and arthroscopic acromioplasty were performed in all cases. Rotator cuff tears were repaired through enlargement of the lateral portal. All patients were evaluated before and after surgery with the University of California Los Angeles (UCLA) Shoulder Scale.

RESULTS

In all, 47 of 50 patients treated with suture weld were available for evaluation, with an average follow-up of 26 months. Preoperative UCLA scores averaged 12.5, and postoperative scores averaged 29.6. Of 55 patients treated with hand-tied knots, 40 were available, with an average follow-up of 28 months. Preoperative UCLA scores averaged 13.2, and postoperative scores averaged 31.5.

CONCLUSIONS

No statistical difference in postoperative UCLA scores was noted between the 2 groups (P = .297).

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Arthroscopic sliding knot: how many additional half-hitches are really needed?

PURPOSE

To evaluate the optimal number of additional half-hitches needed to achieve optimal knot-holding capacity (KHC) of lockable sliding knots.

TYPE OF STUDY

Mechanical testing study.

METHODS

Four configurations of arthroscopic knots (Duncan loop, Field knot, Giant knot, and SMC knot) were tested for their knot-holding capacity. For each knot configuration, 6 sequential knots were made including the initial sliding knot and an additional 5 knots by increasing the half-hitches 1 at a time. Each additional half-hitch was made as a reverse half-hitch with alternate posts. For each sequential knot configuration, 12 knots were made using No. 2 braided sutures. On the Servo-hydraulic materials testing system (Instron 8511; MTS, Minneapolis, MN), cyclic loading, load to clinical failure (3-mm displacement), load to ultimate failure, and mode of failure were measured.

RESULTS

Most of the initial loops without additional half-hitches showed dynamic failure with cyclic loading. However, after 1 additional half-hitch, all 3 (SMC, Field, and Giant) knots showed resistance to dynamic cyclic load. After 2 additional half-hitches, the Duncan loop was secured without slippage from the cyclic loading test. The mean displacement after the end of cyclic loading decreased with each additional half-hitch. In particular, the SMC and Giant knot reached plateau at 0.1-mm or less displacement after 1 additional half-hitch. The Field knot and Duncan loop needed 3 additional half-hitches. The SMC knot and Duncan loop needed 1 additional half-hitch to reach greater than 80 N at clinical failure, whereas the other 2 knots needed 2 additional half-hitches. For the load exceeding 100 N for clinical failure, the SMC knot required 3 additional half-hitches and the other 3 knots needed 4 additional half-hitches. Addition of more than 3 half-hitches did not increase the load to clinical failure in the SMC knot. However, load to clinical failure increased up to 4 additional half-hitches in the other 3 knots (P < .05). The load to ultimate failure reached plateau when 3 or more additional half-hitches were made for all knot configurations. As the number of additional half-hitches increased, the mode of failure switched from pure loop failure (slippage) to material failure (breakage). The Duncan loop showed poor loop security--even with 5 additional half-hitches, some failed by slippage (17%). On the other hand, after 3 additional half-hitches, the 3 other knots showed greater than 75% of failure by material breakage mode (SMC and Field 92%, Giant 75%).

CONCLUSIONS

Even with its own locking mechanism, a lockable sliding knot alone does not withstand the initial dynamic cyclic load. For all tested variables, the SMC knot required a minimum of 2 additional half-hitches. All knots showed a near plateau in knot security with 3 or more additional half-hitches. The Duncan loop may need more than 3 additional half-hitches for optimal security.

CLINICAL RELEVANCE

The study shows that the knots tested needed at least 2 additional half-hitches, so this should become standard clinical practice.

A biomechanical comparison of arthroscopic sliding and sliding-locking knots

PURPOSE

To evaluate biomechanical characteristics of 3 arthroscopic sliding and sliding-locking knots and the square knot, the gold standard used in open surgery.

TYPE OF STUDY

Biomechanical investigation.

METHODS

Four different knot types (Weston, square, Duncan loop, and Nicky's) were tested in 5 configurations in a closed-loop system on a materials testing device. Three of the 5 knots were backed up with 3 reverse half-hitches and alternating posts and all sliding and sliding-locking knots were tied using an arthroscopic technique. Twelve knots of each configuration were tested for loop security with a 7-N preload, and for knot security with load to failure at a strain rate of 1.25 mm/second and cyclic loading of a 30-N force for 50 cycles.

RESULTS

No knots subjected to the 7-N preload failed or slipped and all had similar elongation (0.1 +/- 0.1 mm) except Nicky's knot (0.3 +/- 0.2 mm). There was no significant difference in load at failure for the square knot (178 +/- 14 N), the Weston knot backed with 3 half-hitches (168 +/- 14 N), the Duncan loop (160 +/- 20 N), or Nicky's knot (148 +/- 13 N). Most knots with 3 half-hitches failed with rupture at the knot. Under cyclic loading, no knots failed and none elongated greater than an average of 0.3 mm.

CONCLUSIONS

All knot configurations maintained high loop security. All sliding and sliding-locking knots backed with 3 half-hitches had load at failure comparable to the square knot. With cyclic load testing, all knots tested elongated minimally. Additionally, this study confirms that all knots, even the sliding-locking Weston knot, are best backed up with 3 half-hitches alternating posts and directions of the throws.

CLINICAL RELEVANCE

Sliding and sliding-locking knots are becoming increasingly popular among arthroscopic shoulder surgeons. This study provides a biomechanical basis for the clinical use of these arthroscopic knots and compares them with the gold standard, the open square knot.

Comparative study of knot performance and ease of manipulation of monofilament and braided sutures for arthroscopic applications

Our aim was to identify alternative suture materials that might provide superior knot performance and equivalent ease of manipulation by means of an in vitro experimental study. Although used widely for arthroscopic shoulder stabilisation, absorbable poly( p-dioxanone) (PDS) monofilament sutures can lead to dehiscence and clinical failure due to knot slippage and/or loop elongation at low applied loads. With the objective of identifying alternative suture materials that might provide superior knot performance and equivalent ease of manipulation, an in vitro experiment was undertaken in which both Duncan and Snyder knotted loops were tied from four different suture materials using an arthroscopic knot pusher (Surgeon's 6th Finger) and a wooden practice box (Arthrex). Three monofilament sutures, made from polypropylene (PROLENE), poly(glycolidetrimethylenecarbonate-co-dioxanone) (Biosyn) and PDS, and one braided polyester suture (SURGIDAC) were tested. Ease of manipulation was evaluated by measuring the time required to tie the knots, and the knot performance was assessed in terms of loop elongation and loop holding capacity by performing cyclic fatigue testing of the loops while they were immersed in saline on an INSTRON mechanical tester. The PROLENE and SURGIDAC sutures showed improvements in loop elongation and loop holding capacity over PDS, with the Snyder knots being consistently superior to Duncan knots. BIOSYN gave no improvement over PDS. Difficulties were encountered in advancing half-hitch throws of the braided SURGIDAC suture down the cannula, which resulted in longer knotting times. In conclusion, both the polypropylene and polyester sutures gave superior knot performance to PDS, but only the polypropylene gave equivalent ease of manipulation. As a result there may be clinical advantages in replacing PDS with monofilament polypropylene or braided polyester sutures for certain arthroscopic procedures.

Failure characteristics of various arthroscopically tied knots

The current study evaluated multiple arthroscopic knot configurations and compared their properties with open, hand-tied square knots. This is an experimental study done on a material testing system. Number 2 Ethibond Extra and Number 1 Polydioxanone sutures were used. Four types of sliding knot configurations were tested: the Duncan loop, the Tennessee Slider, the Savoie-Modified Roeder, and the Lieurance-Modified Roeder. Two types of nonsliding knots were tested: the Revo knot and a knot consisting of alternating half-hitches tied with the Sixth Finger Knot Pusher. Ten knots were tied of each configuration, using strict arthroscopic technique. Each knot was backed-up with four half-hitches using post switching technique. Knots were tied around two rings and then transferred wet to a materials testing machine. The knots were tested until ultimate failure, with note of clinical failure at 3 mm. Ethibond suture using the Revo knot, the Lieurance-Modified Roeder knot, and the Savoie-Modified Roeder knot were similar in strength to the square knot with comparable failure modes. Polydioxanone suture was more variable; the Revo knot, the Savoie-Modified Roeder, the Tennessee Slider, and the Duncan loop were comparable with hand-tied square knots. All of the open and arthroscopic suture loops tested in this study failed by the suture loops expanding to greater than 3 mm before ultimate failure occurred. The surgeon choosing arthroscopic repair techniques should be aware of the differences in suture material and the variation in knot strength afforded by different knot configurations.

Validity of surgical simulation for the assessment of operative skill

BACKGROUND

Surgical simulators are being promoted as a means of assessing a surgeon's technical skills. Little evidence exists that simulator performance correlates with actual technical ability. This study was undertaken to determine the criterion and construct validity of currently available surgical simulations in the evaluation of technical skill.

METHODS

Simulator assessment was carried out on 36 basic surgical trainees, 37 surgically naïve first-year medical students and 16 experienced general surgical consultants. Some 26 trainees and 36 students underwent repeat assessment after 6 months. A previously validated, 19-point technical skill assessment form, based on direct observation of trainee performance in the operating theatre, was also completed by each trainee's supervising consultant.

RESULTS

An insignificant or weak correlation was found between simulator performance and both duration of basic surgical experience and consultant assessment of technical skill. Six months of basic surgical training led to an improvement in performance, not seen in an untrained control group, in only one of the six simulations tested. Discrimination between surgically naïve and experienced subjects was only demonstrated, in part, for four of the six tasks.

CONCLUSION

The assessment of technical skill needs to be improved. Work is needed to establish the reliability and validity of currently available simulation models before they are formally introduced for high-stakes assessment.

Optimization of stacked half-hitch knots for arthroscopic surgery

PURPOSE

This study was conducted to determine the optimal configuration of stacked half-hitch knots that would give the maximum knot-holding capacity (KHC).

TYPE OF STUDY

Mechanical testing study.

METHODS

The 2 types of suture materials tested were No. 1 PDS II monofilament and No. 2 Ethibond braided (Ethicon, Somerville, NJ) because these are the 2 most commonly used sutures in arthroscopic surgery. Twelve configurations of stacked half-hitch knots including 2 versions of the Revo knot were tested. Knots were tied between 2 steel hooks 7 mm apart on a manual knot-testing machine. The steel hooks were spread apart to break the knot and the KHC was determined by the peak load recorded on the digital force transducer. Maximum KHC was achieved for No. 1 PDS II sutures by locking the knot with 2 RHAPs (reversing half-hitch on alternate post) and, for No. 2 Ethibond sutures, by locking the knot with 3 RHAPs. Because of the possibility of PDS II sutures unraveling, it is recommended for both No. 1 PDS II and No. 2 Ethibond sutures, that all stacked half-hitches be locked with 3 RHAPs. By adding 1 RHAP to the Revo knot, failure by slippage can be eliminated.

RESULTS

The recommended knots tied with braided No. 2 Ethibond sutures were 1.5 times stronger than knots tied with No. 1 PDS II sutures. Although there was variability in the KHC of the recommended knots tied by different surgeons using different knot tiers, the greatest difference in the mean KHC was less than 10%.

CONCLUSIONS

Stacked half-hitch knots locked with 3 RHAPs are unlikely to fail by slippage.

A comparison of ultrasonic suture welding and traditional knot tying

The slippage of knots and the technical challenge of tying them securely are potential impediments to certain arthroscopic procedures. Ultrasonic energy delivered at 70 kHz can be used to weld No. 2 polypropylene suture. This method was compared with a traditional knot (surgeon's knot with four alternating half hitches) tied with an open technique to determine whether welding of sutures is comparable, in mechanical properties, to hand-tied knots. Both loops were fashioned around a 0.25-inch mandrel and then tested. The load to reach 3-mm elongation (point of likely biologic failure of a repair) was significantly greater for welded sutures than for knots. The elongation at ultimate failure was significantly less for welded sutures than for knots. The number of cycles to failure and the creep after initial displacement were similar for both welded and knotted suture loops. The ultimate load to failure was significantly greater for the knotted than for the welded suture. The welding of suture for the repair of musculoskeletal soft tissue presents an attractive alternative to traditional knot tying, particularly for arthroscopic applications.

5th Annual David R. Boyd, MD Lecture: Revolutionary advances in wound repair in emergency medicine during the last three decades. A view toward the new millennium

This lecture provides an overview of advances in wound repair devised by our multidisciplinary team of physicians, scientists, and students. Our collective efforts have devised products, drugs, and concepts that are facilitating wound repair without infection and with the least possible scar. Some of the beneficial products and drugs developed or identified by our laboratory include nitrile examination and surgical gloves, magnification loupes, high pressure syringe irrigation, Shur Clens, as well as a wide variety of different wound closure techniques. In addition, our studies of the mechanism of wound injury, soil infection-potentiating fractions, dynamic and static skin tensions, and microflora of the skin have become important predictors of the outcomes of wound repair. During the new millennium, the computerized clinical information system as well as studies of tissue regeneration should dramatically change our approaches to wound repair.

"Scientific basis of wound closure techniques." Evaluation of a new training program

A formal training program in wound repair entitled "Scientific Basis of Wound Closure Techniques" has been developed and is accredited by the Dannemiller Memorial Educational Foundation. This course is now available at no cost to medical schools, residencies, and continuing education programs for graduate physicians. A manual with its complementing videotape allow the course participant to gain the necessary psychomotor skills to repair wounds. Evaluation of the course taken by third-year medical students and first-year residents demonstrates a high level of satisfaction. After instituting the course, there was a noticeable change in the types of barriers, instruments, and wound closure techniques practiced in our emergency department.

Elongation of arthroscopically tied knots

It has been postulated that some arthroscopic shoulder stabilization failures may be due to knot slippage. In an effort to improve arthroscopic technique, we performed tensile testing on four arthroscopically tied knots with two commonly used suture materials. Handtied square knots served as controls. Sutures of No. 1 Maxon and No. 1 Ticron were used. Four types of sliding knot configurations were tested: the overhand loop, the Duncan loop, the Roeder knot, and the Snyder knot. Knots were tied via a knot pusher, and testing was performed in a normal saline-filled thermoplastic chamber. Knots were tied around two rings connected to a Bionix 858 materials testing apparatus. The knots were tested under conditions of cyclic loading and loading to failure. Results of the testing revealed that the most important factor in knot security was the type of suture material, although there were differences with the type of knot. With the Maxon suture, there was significantly decreased ultimate failure load of all of the arthroscopically tied knots compared with handtied square knots. Knots tied with Ticron were similar in strength for both arthroscopically and handtied groups. The surgeon who chooses a monofilament absorbable suture should be aware that a high percentage of knots fail under low load cyclic testing, and that all of these knots were inferior to handtied square knot controls in testing to failure.

Optimizing arthroscopic knots

Arthroscopic repairs, such as those for shoulder instability, are commonly performed. However, the failure rate after arthroscopic repair appears to be higher than with open surgery. These failures may relate to the challenge of tying secure knots arthroscopically. Many knots tied arthroscopically commonly consist of an initial slip knot to remove slack, and a series of half-hitches. Half-hitches, instead of square throws, are difficult to avoid and result when asymmetrical tension is applied to the strands. For this reason, the security of knots tied arthroscopically may not be equivalent to square knots and a greater rate of failure may occur. The purpose of this study was to determine (1) the security of various arthroscopic knots under cyclic and peak loading conditions, (2) how the surgeon can modify the method or sequence of half-hitch throws to minimize knot slippage or breakage, and (3) whether using an arthroscopic knot pusher affects the security of the same knot tied by hand. The most secure knot configurations were achieved by reversing the half-hitch throws and alternating the posts. These knots performed significantly better than all other knots tested (P < .002). Thus the surgeon can control the holding capacity and minimize suture loop displacement by proper alternation of the tying strands and reversal of the loop when placing the hitches.(ABSTRACT TRUNCATED AT 250 WORDS)

Technical considerations in manual and instrument tying techniques

The purpose of this study was to relate the two-hand (manual) and instrument tie techniques with the ultimate security of granny and square knots constructed in multifilament and monofilament nylon sutures. Instrument-tie technique constructed secure granny and square knots, which failed by breakage rather than slippage. Similarly, two-hand (manual) tie techniques constructed square knots, which achieved knot security, failing only by breakage. In contrast, knot security was not reliably achieved with granny knots constructed by the two-hand (manual) tie techniques, with the knots frequently failing by slippage.