Do Needleless Knots have Similar Strength as the Krackow Suture? An In Vitro Porcine Tendon Study

Assessment of formalin preserved and fresh frozen quadriceps tendon graft-suture constructs for load to failure testing: a biomechanical cadaveric study

PURPOSE

Fresh-frozen specimen availability and cost may be a barrier for initiation of biomechanical studies where soft tissue is used in a construct with other medical devices. The impact of soft tissue preservation method on the outcomes of biomechanical studies in the specific case of graft-suture constructs is relatively unexplored. This study aimed to observe peak loads and failure modes in biomechanical testing of fresh-frozen (FF) versus formalin embalmed (FE) quadriceps tendon (QT) graft-suture constructs for soft tissue fixation in ACLR and assess suitability of FE QT graft constructs for load-to-fail testing.

METHODS

Twenty QT grafts were harvested from human cadaver specimens. Ten grafts came from fresh-frozen donors and 10 from embalmed donors. All grafts were prepared with the modified Prusik knot using a braided composite suture and subjected to tensile loading. Comparisons between the biomechanical properties of the graft-suture constructs were made with unpaired t tests with α = 0.05.

RESULTS

FE and FF constructs displayed similar peak loads and failure modes. FF constructs had greater elongation after pre-tensioning than FE (7.3 vs. 5.5 mm, p = 0.02) and greater elongation after cyclic loading than FE constructs (17.5 vs. 10.5 mm, p = 0.01). Hysteresis was greater for FF constructs at the 50th, 100th, 150th, and 200th cycle (p = 0.02, p = 0.07, p < 0.001, p = 0.004, respectively). FE constructs were stiffer than fresh-frozen (103 vs. 84 N/mm, p < 0.001).

CONCLUSION

FE constructs were significantly stiffer but displayed similar peak load and failure mode to FF which was reflective of the strength of the suture material. FE grafts can offer an alternative to FF grafts in graft-suture constructs for biomechanical studies where load at failure and knot security and strength is of main interest.

Biomechanical and histological comparison of two suture configurations for soft tissue grafts: speedtrap™ versus krackow stitch

To compare 2 different graft preparation techniques to determine biomechanical strength and resultant tissue trauma evaluated by histology. Twelve common flexors of the finger's tendons were prepared with either tubulization (SpeedTrap™) or transtendon stiches (Orthocord™). The stiffness, resistance and energy at maximum load were tested for biomechanical assessment in both groups. After load testing, Samples were stained with hematoxylin and eosin (HE) to evaluate histological damage. We observe that the time to prepare tendons with SpeedTrap™ was 8.3 times faster (1:25 min) than traditional ones (15:02 min). In all cases, the mean values for SpeedTrap™ were higher in terms of strength, stiffness and energy at maximum load than for traditional suture but without significant difference (p > 0.05). The Krackow stitch produces greater structural damage to the collagen fibers while SpeedTrap™ maintains better organized arrangement of the fibers after tubulization preparation. With the results obtained, we can conclude that the tubulization technique allows faster graft preparation with less structural damage to the manipulated tissue without altering the biomechanical resistance provided by the transtendon suture technique.

Krackow Stitch and Whipstitch Use in Distal Biceps Tendon Rupture Repair: A Porcine Composite Bone Biomechanical Study

The suture combination of a Krackow stitch plus a whipstitch can be used to strengthen a tendon rupture repair. We compared biomechanical outcomes of suture repair techniques for distal biceps tendon ruptures using a single Krackow stitch with and without a whipstitch and a whip-stitch alone. Data were obtained from 36 thawed porcine flexor profundus tendons. A cortical button was secured to fourth-generation composite bone using No. 2 FiberWire (Arthrex) and No. 2 FiberLoop (Arthrex). The primary outcome was maximum load to failure. Secondary outcomes were displacement at the bone-tendon interface, total construct elongation, and stiffness. The Krackow plus whipstitch group (mean, 493.82 N; SD, 209.44 N) had a greater maximum load to failure as compared with the single Krackow group (mean, 333.71 N; SD, 172.32 N) (P=.01) and single whipstitch group (mean, 207.27 N; SD, 66.42 N) (P<.001). The single Krackow group (mean, 1.67 mm; SD, 0.89 mm) had a greater bone-tendon interface displacement (P=.01) after preloading and before cyclic loading than the single whipstitch group (mean, 0.83 mm; SD, 0.58 mm). There were no other secondary outcome differences between groups. A repair using Krackow plus whipstitch is biomechanically stronger with no difference in bone-tendon interface displacement, total construct elongation, or stiffness when compared with a single Krackow or single whipstitch. We recommend this repair technique for distal biceps tendon rupture repair, which may accelerate rehabilitation and decrease re-rupture rate. [Orthopedics. 2023;46(4):224-229.].

Biomechanical Characterization of a New Locking Loop Stitch for Graft Fixation versus Krackow Stitch

Background

The purpose of this study was to quantify and compare the biomechanical characteristics of a new locking loop stitch (LLS), developed utilizing the concepts of both running locking stitch and needleless stitch, to the traditional Krackow stitch.

Methods

The Krackow stitch with No.2 braided suture and the LLS with 1.3-mm augmented polyblend suture tape were compared biomechanically. The LLS was performed with single strand locking loops and wrapping suture around the tendon, resulting in half the needle penetrations through the graft compared to the Krackow stitch. Twenty bovine extensor tendons were divided randomly into two groups. The tendons were prepared to match equal thickness and cross-sectional area. Each suture-tendon was stitched and preloaded to 5 N for 60 seconds, cyclically loaded to 20 N, 40 N, and 60 N for 10 cycles each, and then loaded to failure. The deformation of the suture-tendon construct, stiffness, yield load, and ultimate load were measured.

Results

The LLS had significantly less deformation of the suture-tendon construct at 100 N, 200 N, 300 N, and at ultimate load compared to the Krackow stitch (Krackow stitch and LLS at 100 N: 1.3 ± 0.1 mm and 1.0 ± 0.2 mm, p < 0.001; 200 N: 3.0 ± 0.3 mm and 1.9 ± 0.2 mm, p < 0.001; 300 N: 5.1 ± 0.6 mm and 2.9 ± 0.4 mm, p < 0.001; ultimate load: 12.8 ± 2.8 mm and 5.0 ± 1.2 mm, p < 0.001). The LLS had significantly greater stiffness (Krackow stitch and LLS: 97.5 ± 6.9 N/mm and 117.2 ± 13.9 N/mm, p < 0.001) and yield load (Krackow stitch and LLS: 66.2 ± 15.9 N and 237.9 ± 93.6 N, p < 0.001) compared to the Krackow stitch. There was no significant difference in ultimate load (Krackow stitch: 450.2 ± 49.4 N; LLS: 472.6 ± 59.8 N; p = 0.290).

Conclusions

The LLS had significantly smaller deformation of the suture-tendon construct compared to the Krackow stitch. The LLS may be a viable surgical alternative to the Krackow stitch for graft fixation when secure fixation is necessary.

Does the Nice Knot Offer Less Elongation Than the Modified Prusik Knot? An In Vitro Study in Cadaver Quadriceps Tendons

BACKGROUND

ACL graft-suture fixation can be constructed with needle or needleless techniques. Needleless techniques have the advantage of decreased injury, preparation time, and cost. The Nice knot is common among upper extremity procedures, and has been shown to have higher load to failure and less elongation compared with other double loop knots; however, there are no studies that have looked at its use for ACL graft-suture construct to determine whether it offers less elongation relative to other needleless techniques.

QUESTIONS/PURPOSES

In a cadaver quadriceps tendon model, we asked: (1) Does the Nice knot have less elongation than the Prusik knot? (2) Does the Nice knot have increased peak load and stiffness compared with the Prusik knot? (3) What were the modes of failure of each knot?

METHODS

Sixteen quadriceps tendon grafts were harvested from 16 cadaver knee specimens. The median (range) age of the donors was 80 years (70 to 96) and included three male and five female donors. Eight grafts were prepared with the Prusik knot and eight with the Nice knot using a braided polyblend suture. The graft-suture constructs were mounted in a materials testing machine and subjected to a tensile loading protocol beginning with pretensioning of three cycles from 0 to 100 N at 1 Hz followed by a constant load of 50 N for 1 minute then cyclic loading of 200 cycles from 50 to 200 N at 1 Hz. The constructs were loaded to failure as the final step of the loading protocol. Elongations of the construct after each loading step, peak load, stiffness, and graft cross-sectional area were compared.

RESULTS

Construct elongations (median [IQR]) for the Nice knot were lower than that of the Prusik knot after pretensioning (4.4 mm [0.8] versus 5.7 mm [1.4]; p = 0.02), preloading (0.6 mm [0.3] versus 1.0 mm [0.3]; p = 0.005), and cyclic loading (7.4 mm [1.4] versus 10.9 mm [2.1]; p = 0.005). Peak load was not different for the Prusik knot construct compared with the Nice knot (334 N [43] versus 312 N [13]; p = 0.08). Stiffness of the Prusik knot construct (103 N/mm [17]) was no different than the Nice knot construct (110 N/mm [13]; p = 0.13). Graft cross-sectional area of the Prusik knot constructs (85 mm2 [35]) were similar to the grafts of the Nice knot constructs (97 mm2 [31]; p = 0.28). Failure mode of the constructs did not differ between groups; it was caused by suture rupture near the knots that secured the free suture ends to the machine and was seen in all 16 tests.

CONCLUSIONS

The results of this biomechanical study show that the Nice knot construct has similar or greater biomechanical properties compared with the Prusik knot in the graft suture construct, although the magnitude of the differences are not likely to the level of clinical importance.

CLINICAL RELEVANCE

The Nice knot offers an attractive alternative option for needleless ACL graft preparation technique. Future studies should consider comparison to established needle techniques such as Krackow or whipstitch and testing in an intraarticular component in an in vivo model.

Does using high-tensile strength tape improve the fixation strength in tendon graft fixation with needleless suture wrapping techniques compared to a suture?

PURPOSE

To compare the biomechanical properties of a high-tensile strength suture and high-tensile strength tape in tendon graft fixation using two needleless suture wrapping techniques, the modified Prusik knot and modified rolling hitch.

METHODS

Two needleless suture wrapping techniques, the modified rolling hitch (MR) and modified Prusik knot (MP), were utilized. Meanwhile, two kinds of suture materials, a No. 2 braided nonabsorbable high-strength suture (S) and a 1.3 mm high-tensile strength tape (T), were used. A total of 40 porcine tendons were used, which were randomly divided into four groups. Each group was assigned to one of the following groups: MRS, MRT, MPS, and MPT. Each specimen was pretensioned to 100 N for three cycles, cyclically loaded from 50 to 200 N for 200 cycles, and finally loaded to failure.

RESULTS

The MRT group (34.1 ± 3.5%) had a significantly higher value compared with the MRS (29.7 ± 2.3%), MPS (27.1 ± 3.6%) and MPT (29.5 ± 4.0%) groups in term of elongation after cyclic loadings (p = 0.002). In terms of ultimate failure load, there were no significant differences in the MRS (401 ± 27 N), MRT (380 ± 27 N), MPS (398 ± 44 N) and MPT (406 ± 49 N) values (p = 0.539). All specimens failed due to suture breakage at the knots.

CONCLUSION

Compared with the high-tensile strength suture, using the high-tensile strength tape lead to greater elongation after cyclic loading when the modified rolling hitch was used. No differences in terms of elongation after cyclic loading and load to failure were found between the high-tensile strength suture and tape using the modified Prusik knot.

Influence of the integrity of tendinous membrane and fascicle on biomechanical characteristics of tendon-derived scaffolds

The biomechanical characteristics of tendon grafts is essential for tendon reconstructive surgery due to its great role in providing a good mechanical environment for tendon healing and regeneration. In our previous studies, the decellularized tendon slices (DTSs) and decellularized bovine tendon sheets (DBTSs) scaffolds were successfully developed. However, the influence of the integrity of tendinous membrane (endotenon and epitenon) and fascicle on biomechanical characteristics of these two scaffolds was not investigated. In this study, we assessed the integrity of tendinous membrane and fascicle of the tendon derived scaffolds and its effect on the biomechanical characteristics. The results of histological staining indicated that the DBTSs had complete endotenon and epitenon, while DTSs had no epitenon at all, only part of endotenon was remained. Furthermore, the DBTSs, and DTSs with thickness of 900 μm had complete fascicles, while DTSs with thickness less than 600 μm had almost no complete fascicles. The fibrous configuration of epitenon was well-preserved in the surface of the DBTSs but the surface ultrastructure of the DTSs was aligned collagen fibers based on scanning electron microscopy examination. The results of transmission electron microscopy showed that there was no significant difference between the DBTSs and DTSs. Mechanically, the DBTSs and DTSs with thickness of 900 μm showed similar ultimate tensile strength and stiffness to native tendon segments (NTSs). The strain at break and suture retention strength of the DBTSs showed much higher than that of the DTSs (p < 0.05). Additionally, the DBTSs showed higher ultimate load than the DTSs when these scaffolds were sutured with NTSs (p < 0.05) through the modified Kessler technique based on a uniaxial tensile test. This study demonstrated that DTSs may be used as a patch for reinforcing tendon repair, while DBTSs may be used as a bridge for reconstructing tendon defects.

The Biomechanical Properties of a High-Tensile Strength Tape for Tendon Graft Fixation Using the Krackow Configuration

Purpose

To compare the biomechanical properties of a high-tensile strength suture with the high-tensile strength tape for tendon graft fixation.

Methods

A total of 24 porcine tendons were used and were randomly divided into 2 groups. Two kinds of suture materials, a braided nonabsorbable high-strength suture (group S) and a high-tensile strength tape (group T), were used to complete 3 pairs of Krackow stitches on the tendons. Each specimen was pretensioned to 100 N for 3 cycles, cyclically loaded from 50 to 200 N for 200 cycles, and finally loaded to failure. Elongation after cyclic loading, ultimate failure load, and the mode of failure were recorded.

Results

The elongation after cyclic loading between group S (26% ± 5%) and group T (24% ± 5%) were not significantly different (P = .378). The ultimate failure loads in group T (400 ± 38 N) were significantly greater than those in group S (358 ± 21 N) (P = .010). All specimens failed because of suture material breakage.

Conclusions

Compared with the braided nonabsorbable high-strength suture, the high-tensile strength tape had similar elongation values after cyclic loading, but significantly greater ultimate failure load in this porcine in vitro biomechanical model.

Clinical Relevance

A secure suture-tendon construct is especially important when a post-tie fixation technique is used because the mitigating construct may potentially lead to graft loosening and affect graft healing.

Longer stitch interval in the Krackow stitch for tendon graft fixation leads to poorer biomechanical property

PURPOSE

The purpose of this study was to analyze the effects of different intervals between stitch throws on tendon graft fixation with the Krackow stitch.

METHODS

Forty-four porcine flexor profundus tendons were randomly divided into four groups of 11 specimens each. The Krackow stitch with various stitch intervals (2.5, 5.0, 7.5, and 10.0 mm) were evaluated, and named the K-2.5, K-5.0, K-7.5, and K-10.0 groups, respectively. A braided nonabsorbable suture was used to complete each suture-tendon construct. All specimens were pretensioned to 100 N for three cycles, cyclically loaded from 50 to 200 N for 200 cycles, and then finally loaded to failure. Elongation after cyclic loading, ultimate load to failure, and the mode of failure were recorded.

RESULTS

There were significant differences in elongation after cyclic loading among the K-2.5 (31% ± 5%), K-5.0 (32% ± 4%), K-7.5 (34% ± 5%), and K-10.0 (41% ± 8%) groups ( p = 0.004); the post hoc analysis showed significantly smaller values in the K-2.5 and K-5.0 groups than in the K-10.0 group ( p = 0.002 and 0.003, respectively). The stitch interval was correlated with elongation after cyclic loading ( r = 0.52, p < 0.001). Ultimate loads to failure and cross-sectional area were not significantly different across the four groups.

CONCLUSION

The Krackow stitch with stitch intervals of 2.5 and 5.0 mm had significantly smaller elongation after cyclic loading than with an interval of 10.0 mm in this porcine biomechanical study. The stitch interval was moderately correlated with elongation after cyclic loading.

A Biomechanical Comparison of Six Suture Configurations for Soft Tissue-Based Graft Traction and Fixation

PURPOSE

The purpose of this study was to compare 6 different graft fixation techniques to determine the preparation speed, fixation security, biomechanical strength, and resultant tissue trauma.

METHODS

Six different techniques (10 samples each): #2 OrthoCord Krackow stitch, #2 FiberWire Krackow stitch, SpeedTrap, WhipKnot, Loop-in-loop stitch were created in the distal 3 cm of 9 cm bovine flexor tendons. The proximal 3 cm tendon segment was clamped in a testing machine and the distal suture ends secured by pneumatic grips. 3 preload cycles (10N-100N) and 50N static load was followed by 500 cycles (50N-200N) and then loaded to failure. Graft preparation times, 100 and 500 cycle displacement, maximum failure load, stiffness, and failure mode were recorded.

RESULTS

Representative graft preparation times were: OrthoCord Krackow (247s), FiberWire Krackow (401s), FiberLoop (177s), SpeedTrap (42s), WhipKnot (39s), Loop-in-loop (45s). No WhipKnots survived cyclic loading. 100 cycle displacements were: OrthoCord Krackow (11.5 ± 3.9 mm), FiberWire Krackow (8.9 ± 1.2 mm), FiberLoop (14.2 ± 6.1 mm), SpeedTrap (8.8 ± 2.5 mm), Loop-in-loop (10.4 ± 2.9 mm). FiberLoop displaced significantly more than all others (P = .016). Maximum failure loads were: OrthoCord Krackow (364 ± 24N), FiberWire Krackow (375 ± 45N), FiberLoop (413 ± 95N), SpeedTrap (437 ± 65N), WhipKnot (153 ± 42N), Loop-in-loop (329 ± 112N). The most common failure mode was suture breaking. FiberWire containing constructs (Krackow and FiberLoop) shredded or cut through ("cheese wiring") prior to failure in a majority.

CONCLUSIONS

SpeedTrap, WhipKnot and Loop-in-loop were quickest to create (under 1 minute). The Krackow, SpeedTrap, WhipKnot, and Loop-in-Loop did not damage the tendon during cyclic loading. SpeedTrap and Krackow had the least displacement. FiberLoop displaced more than all other groups (P = .016). No WhipKnot completed cyclic loading. The SpeedTrap (437N) and FiberLoop (413N) had the highest ultimate strength.

CLINICAL RELEVANCE

While the SpeedTrap and FiberLoop are the strongest techniques, the FiberLoop shreds the tendon, displaced the most, and took longer to create. Based on these results, the SpeedTrap demonstrates the best overall performance.

A Biomechanical Evaluation of Various Double Krackow Suture Techniques for Soft-Tissue Graft Fixation

PURPOSE

The purpose of this study was to compare the biomechanical properties among the different double Krackow suture techniques for tendon graft fixation.

METHODS

Thirty porcine flexor profundus tendons were randomly divided into 3 groups of 10 specimens each. Three different double Krackow suture techniques were evaluated, namely, the McKeon's double Krackow (MDK) suture, Wilson's double Krackow (WDK) suture, and Ostrander's modified Krackow (OMK) suture. All suture configurations were completed with a braided nonabsorbable suture. Each suture-tendon construct was pretensioned to 100 N for 3 cycles, cyclically loaded from 50 to 200 N for 200 cycles, and then finally loaded to failure. Elongation after cyclic loading, ultimate load to failure, and the mode of failure were recorded for each specimen.

RESULTS

There were significant differences in elongation after cyclic loading among the MDK suture (7.9 ± 3.6 mm, 14% ± 6%), WDK suture (11.6 ± 2.2 mm, 22% ± 3%), and OMK suture (9.6 ± 3.3 mm, 17% ± 6%; P = .018). In addition, although the post hoc analysis showed that elongation after cyclic loading in the MDK suture was significantly less than the WDK suture (P = .004), ultimate failure load and cross-sectional area were not significantly different across the 3 groups.

CONCLUSIONS

In this porcine in vitro biomechanical study, the MDK suture had significantly smaller elongation after cyclic loading than the WDK suture; however, high elongation values may have a potential for risk of clinical laxity. The ultimate failure load was not different across the MDK, WDK, and OMK sutures.

CLINICAL RELEVANCE

Smaller elongation during cyclic loading in a suture-tendon construct represents a lower possibility of tendon graft loosening after ligament reconstruction surgery. The double Krackow suture techniques are attractive options for tendon graft fixation in ligament reconstruction, and the MDK suture could possibly be the optimal choice among the double Krackow suture techniques.

Editorial Commentary: The Krackow Stitch: More Than 30 Years of Tendon Repair and Still Holding Strong

Security at the suture-tendon interface is a critical component of soft tissue fixation. For more than 3 decades, the Krackow stitch has been considered the gold standard for soft tissue fixation. Modifications of the original configuration have withstood the test of time. Many have been evaluated in preclinical and clinical studies for multiple musculoskeletal applications. Most recently, double Krackow suture configurations have been shown to increase the ultimate failure load of the suture-tendon construct. I have learned this stitch and will add it to my soft tissue fixation arsenal.

Superior biomechanical properties and tying time with the modified Prusik knot and Wittstein suture loop to the Krackow stitch

INTRODUCTION

The purposes of the study were to compare (1) the biomechanical properties of the modified Prusik knot, Wittstein suture loop, and Krackow stitch fixation, and (2) the knot tying times for tendon graft fixation among the Krackow stitch, modified rolling hitch, modified Prusik knot, and Wittstein suture loop.

MATERIALS AND METHODS

First, 33 fresh-frozen porcine flexor profundus tendons were randomly divided into three groups of 11 specimens. The experimental procedure was designed to assess elongation of the suture-tendon construct across the modified Prusik knot, Wittstein suture loop, and the Krackow stitch. Multistranded nonabsorbable sutures were used. Each specimen was pre-tensioned to 100 N for three cycles, cyclically loaded to 200 N for 200 cycles, and finally loaded to failure. Elongation, load to failure, and failure mode of each specimen were recorded. Second, the knot tying times for modified rolling hitch, modified Prusik knot, Wittstein suture loop, and Krackow stitch were investigated. The measurements were taken on three different occasions to account for intraobserver repeatability and interobserver reproducibility.

RESULTS

The elongation after cyclic loading of the modified Prusik knot (22 ± 6%), Wittstein suture loop (25 ± 2%) were significantly smaller than the Krackow stitch (31 ± 5%) (p = 0.001 and 0.003, respectively). The failure loads of three groups were not significantly from one another. Meanwhile, the Krackow stitch group (80.9 ± 16.7 s) had significantly longer average procedure time than the modified rolling hitch group (9.2. ± 1.9 s) (p < 0.001), modified Prusik knot group (9.1 ± 1.8 s) (p < 0.001), and Wittstein suture loop group (9.0 ± 2.2 s) (p < 0.001).

CONCLUSIONS

Compared to the Krackow stitch, the modified Prusik knot and Wittstein suture loop had less elongation after cyclic loading and similar ultimate load to failure in this porcine in vitro biomechanical study. Shorter knot tying times were required to complete the modified rolling hitch, modified Prusik knot, and Wittstein suture loop than the Krackow stitch.

Technique using the modified rolling hitch for split peroneus brevis tendon transfer in lateral ankle stabilization

We report our technique for split peroneus brevis lateral ankle stabilization using the modified rolling hitch for tendon graft fixation. Applying the modified rolling hitch for tendon grasping in this procedure was useful, and it could decrease the surgical time and avoid the tendon injury caused by the needle.