Evaluation of biomechanical properties: are porcine flexor tendons and bovine extensor tendons eligible surrogates for human tendons in in vitro studies?

Significant Loss of ACL Graft Force With Tibial-Sided Soft Tissue Interference Screw Fixation Over 24 Hours: A Biomechanical Study

Background

Tibial-sided graft fixation is thought to be critical for the success of anterior cruciate ligament (ACL) reconstruction. Nevertheless, little is known about the graft force after fixation during the first 24 hours after surgery or the influence of screw diameter and length during this time.

Purpose

To investigate the force, over the course of 24 hours, in soft tissue grafts secured with a tibial interference screw and to evaluate the effect of different screw diameters (7, 8, and 9 mm) and lengths (25 and 30 mm) on the force in these grafts.

Study Design

Controlled laboratory study.

Methods

Quadruple-strand flexor tendon grafts were fixed with bioabsorbable interference screws in 60 porcine tibiae. Grafts were pretensioned at 80 N over 10 minutes, and screws were inserted outside-in while a preload force of 80 N was applied. Different screw lengths (25 and 30 mm) and diameters (7, 8, and 9 mm), resulting in 6 groups with 10 specimens each, were tested. After release of the preload, graft force was recorded over 24 hours.

Results

A significant decrease in graft force progressed in all groups over the 24-hour period. In total, a median loss of 75 N (IQR, 68-79 N) compared with the initial loading force was observed. Compared with the loading force of 80 N, this corresponded to a median loss of 91%. No significant differences in the remaining graft force could be found among the 6 different screw length and diameter groups after 10 minutes, 100 minutes, or 24 hours.

Conclusion

Graft force in soft tissue grafts secured with a tibial interference screw decreased substantially over the first 24 hours after fixation. Neither the screw diameter nor the screw length affected the decrease in graft force. This raises substantial questions regarding the remaining fixation strength in vivo.

Clinical Relevance

It should not be expected that ACL reconstruction can mechanically restabilize an injured knee as would an intact ACL. Reconstructed knees should be protected from mechanical overload in the early postoperative period.

The Double Krackow Suture Technique Does Not Offer a Significant Benefit Compared to the Krackow Suture Technique in Subpectoral Biceps Tenodesis Using a Double-Loaded Suture Anchor

PURPOSE

To compare the biomechanical properties of the double simple suture (DSS) technique, Krackow suture (KS) technique, and double Krackow suture (DKS) technique in subpectoral biceps tenodesis using a double-loaded suture anchor in a porcine tendon model.

METHODS

A total of 30 artificial composite (polymer and glass fiber) humeri and porcine flexor profundus tendons with diameter of 4.5 mm were used. The sample size was determined based on the results of the pilot study. Metallic suture anchors with double-loaded No. 2 braided sutures were inserted at the subpectoral tenodesis site, 5 cm from the superomedial corner of the greater tuberosity. Three suture techniques were used to fix the tendons: a DSS used as the control, a KS, and a DKS, which is an alternative tendon graft fixation technique. A preload of 5 N was applied for 2 minutes, followed by cyclic loading for 500 cycles ranging from 5 to 70 N; next, a load-to-failure test at 1 mm/s was performed.

RESULTS

The KS (283.5 ± 57 N) and DKS (270.4 ± 50 N) groups had significantly greater ultimate failure loads as compared with the DSS group (84.1 ± 6.4 N) (P < .001). Meanwhile, the peak displacement at failure loads in the KS group (9.3 ± 2.2 mm) and DKS group (7.8 ± 1.7 mm) were significantly smaller than that of the DSS group (11.3 ± 2.9 mm) (P = .015). Stiffness in the DSS group (36.4 ± 3.0 N/mm), KS group (39.6 ± 2.5 N/mm), and DKS group (36.9 ± 4.6 N/mm) was not significantly different (P = .125). All DSS constructs and 6 KS constructs failed with tendons being cut through by the sutures, whereas the other 4 KS constructs and all DKS constructs failed resulting from suture breakage.

CONCLUSIONS

In this subpectoral biceps tenodesis model, both the KS technique and the DKS technique had similar time 0 biomechanical properties that were better than those of the double simple suture technique.

CLINICAL RELEVANCE

A sturdy suture-tendon structure could prevent clinical failure of a subpectoral biceps tenodesis using a suture anchor.

Independent Suture Tape Reinforcement of Tripled Smaller-Diameter and Quadrupled Grafts for Anterior Cruciate Ligament Reconstruction With Tibial Screw Fixation: A Biomechanical Full Construct Model

PURPOSE

To compare the effect of independent suture tape reinforcement on the dynamic elongation and stiffness behavior as well as ultimate strength of tripled smaller-diameter and quadrupled soft-tissue grafts for anterior cruciate ligament reconstruction (ACLR) with tibial screw fixation in a biomechanical in vitro study.

METHODS

Tripled smaller-diameter (8 mm) and quadrupled (9 mm) bovine tendon grafts with and without suture tape reinforcement (n = 8 in each group) were tested using femoral suspensory and tibial interference screw fixation. The suture tape was femoral sided and fixed independent from the graft by passing it through the suspensory button and securing the 2 open tibial strands with a secondary interference screw. Dynamic testing was performed in position and force control at 250 N and 400 N, followed by pull to failure with the mode of failure noted. Dynamic elongation, stiffness, and ultimate strength were analyzed.

RESULTS

Tripled constructs showed a significantly worse structural performance than quadrupled constructs at higher loads. Reinforcement of tripled and quadrupled grafts substantially decreased total elongation by 56% (4.54 ± 0.75 mm vs 2.01 ± 0.50 mm, P < .001) and 39% (3.25 ± 0.49 mm vs 1.98 ± 0.51 mm, P < .001), respectively, by significantly increasing dynamic stiffness. No statistical significance was found between the reinforced groups. Failure loads of reinforced tripled (1,074 ± 148 N vs 829 ± 100 N, P = .003) and quadrupled (1,125 ± 157 N vs 939 ± 76 N, P = .023) grafts were also significantly improved.

CONCLUSIONS

Independent reinforcement of soft-tissue grafts with suture tape strengthened the performance especially of tripled smaller-diameter grafts for ACLR with tibial screw fixation by significantly improving dynamic elongation at increased stiffness and ultimate strength. Quadrupled reinforced grafts showed no over-constraining and structurally behaved similarly to tripled grafts with reinforcement.

CLINICAL RELEVANCE

Independent reinforcement for ACLR may provide an option for protecting autografts or allografts against irreversible lengthening during the maturation and remodeling phases of healing.

The single-suture technique for anterior cruciate ligament graft preparation provides similar stability as a three-suture technique: a biomechanical in vitro study in a porcine model

PURPOSE

Numerous techniques have been described for the tibial-sided graft preparation in anterior cruciate ligament (ACL) reconstruction. The use of less suture material for graft preparation is thought to improve ingrowth and to reduce the risk for infection. At the same time, the suture construct should be strong enough to resist the surgeon's pull during tensioning of the transplant.

METHODS

In total, 39 fresh-frozen procine deep flexor tendons were used and prepared as four-strand grafts. In the three-suture group (n = 19), graft preparation was performed using three tibial-sided sutures, with each tendon end sutured separately. In the one-suture group (n = 20), a modified graft preparation using only one tibial-sided suture was applied. Each sample underwent load-to-failure testing (N_max) after cyclic pre-loading. To estimate intraoperative tension forces acting on the tibial-sided suture constructs, the maximal tension force of 26 volunteers on such a construct was measured using a load cell.

RESULTS

The biomechanical testing of the two different suture constructs showed a significantly higher load-to-failure for the three-suture group (711 N ± 91 N) compared to the one-suture group (347 N ± 24 N) (p = 0.0001). In both groups, the mode of failure was a tear of the suture in all samples. A failure of the suture-tendon interface was not observed in any case. The median maximal tension force on the construct applied by the 26 volunteers was 134 N (range 73-182 N).

CONCLUSION

The presented single-suture tendon graft preparation resisted to smaller failure loads than the conventional three-suture technique. However, no failures in the suture-tendon interface were seen and the failure loads observed were far beyond the tension forces that can be expected intraoperatively. Hence, the single-suture graft preparation technique may be a valuable alternative to the conventional technique.

The new LassoLoop360° technique for biomechanically superior tissue grip

PURPOSE

Suprapectoral tenodesis is a frequently used technique for treating pathologies of the long head of the biceps brachii (LHBB) tendon. However, so far, no Gold Standard treatment exist. Hence, the arthroscopic LassoLoop360 (LL360) technique is introduced aiming to provide secure fixation and improved biomechanical properties. It was hypothesized, that the LL360 technique would show superior biomechanical response to cyclic loading and ultimate load-to-failure testing compared to the commonly used simple Lasso Loop (SLL).

METHODS

Twenty-two porcine superficial flexor digitorum tendons were prepared using a No. 2 suture according to either the SLL or the LL360 technique. Displacement after cyclic loading (1.000 cycles) between 5 and 30 N, ultimate load-to-failure (ULTF), mode of failure as well as the construct stiffness were tested.

RESULTS

Significantly less displacement was found in the LL360 group (SLL 2.25 ± 0.51 mm; LL360 1.67 ± 0.37 mm; p = 0.01). Ultimate Load to Failure was significantly higher in the LL360 (168.6 ± 29.6 N) as compared to the SLL (124.1 ± 25.8 N, p = 0.02). The LL360 also revealed a significant higher stiffness compared to the SLL (SLL 13.1 ± 0.9 N/mm vs. LL360 19.1 ± 1.0 N/mm, p < 0.001). The most common mode of failure was the suture cutting through the tendon, with a significantly less suture cutting through for the LL360 compared with the SLL (p < 0.05).

CONCLUSION

The LassoLoop360-technique offers superior biomechanical characteristics regarding the tendon-suture-interface compared to the SLL. In the initial healing phase, the suture-tendon-interface is the most vulnerable part of the tendon-suture-anchor construct, the aim of this new technique is to reduce this weakest part of the chain (Ponce et al., Am J Sports Med 39:188-194, 2011). This technique may therefore be beneficial for arthroscopic suprapectoral biceps tenodesis at the entrance of the bicipital groove.

Soft Tissue Fixation Strategies of Human Quadriceps Tendon Grafts: A Biomechanical Study

PURPOSE

To evaluate the effects of different stitching methods and suture diameters on the graft fixation of soft tissue human quadriceps tendon grafts for anterior cruciate ligament (ACL) reconstruction.

METHODS

The Krackow locking stitch (K), whipstitch (W), and baseball stitch (B) were combined with either a 2× no. 2 (#2) or a 1× no. 5 (#5) braided composite suture for graft fixation of 36 human quadriceps tendons in 6 groups. Biomechanical testing was performed using a cyclic protocol with loads between 0 and 100 N. The maximum load until failure, cyclic elongation, and failure mode were recorded.

RESULTS

The highest mean maximum load to failure was observed in the 2 Krackow stitch groups. The K#2 group had significantly higher load to failure values compared with those of the W#2 and B#2 groups (K#2, 553 ± 82 N vs W#2, 392 ± 107 N, P = .0349; K#2 vs B#2 366 ± 118 N, P = .0129). The mean cyclic elongation was lowest in the Krackow groups (K#2, 10.59 ± 2.63 mm; K#5, 13.66 ± 2.3 mm). The regular failure mode was the rupture of the suture for the Krackow stitch (8 of 12) and suture pullout for the whipstitch (11 of 12) and baseball stitch groups (12 of 12).

CONCLUSIONS

The double Krackow stitch with no. 2 braided composite suture exhibits a high maximum load to failure combined with a low amount of elongation in a biomechanical study for human quadriceps tendon soft tissue graft fixation. Unlike the whipstitch and the baseball stitch, it can solidly prevent suture pullout.

CLINICAL RELEVANCE

A safe soft tissue graft fixation technique is especially important for quadriceps tendon grafts with their laminar anatomical structure and physiologically varying diameter. Unlike other grafts for ACL replacement, it fully relies on the soft tissue suture fixation to resist the pullout force.

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.

Adjustable buttons for ACL graft cortical fixation partially fail with cyclic loading and unloading

PURPOSE

Despite good initial pullout strength, it is unclear whether adjustable button (AB) devices for anterior cruciate ligament (ACL) soft-tissue graft fixation, which are based on the Chinese finger trap technique, resist cyclic loading. Furthermore, they have never been tested in a cyclic protocol including complete unloading. It was hypothesized, that the displacement of AB devices with the Chinese finger trap technique would be greater than that of continuous suture loop devices and other available AB mechanisms in a cyclic loading with complete unloading protocol.

METHODS

ACL reconstruction was performed in a porcine knee model using three different types of cortical fixation devices: two different AB devices that use the Chinese finger trap design, one AB device that uses a locked suture loop mechanism and two different continuous loop devices as control groups (n = 40). Specimens were mounted in a material-testing machine (Instron Inc.) that permitted 2500 loading and complete unloading cycles to a maximum of 250 N, as well as continuous elongation recording. A one-way ANOVA was performed for statistical analysis.

RESULTS

The displacement of ABs with a Chinese finger trap loop (mean 8.1; SD 1.5 mm and mean 6.1; SD 1.4 mm) was significantly greater than that of AB with a locked suture loop (mean 4.7; SD 1.0 mm; p < 0.05) and devices with a continuous loop (mean 4.1; SD 0.5 mm and mean 4.4, SD 0.3 mm; p < 0.01). No significant differences were detected between the ABs with a locked suture loop and the continuous loops.

CONCLUSION

Cyclic loading and unloading of AB using the Chinese finger trap technique leads to significantly greater construct lengthening compared with other devices. Complete unloading of the ACL is very likely to occur during rehabilitation after ACL reconstruction. Lengthening of the AB device due to cyclic loading might be a potential mode of failure of the ACL graft fixation. Therefore, when using an AB femoral fixation technique, a locked suture loop design or a careful rehabilitation protocol should be considered.

A Biomechanical Comparison of Alternative Graft Preparations for All-Inside Anterior Cruciate Ligament Reconstruction

PURPOSE

To biomechanically compare alternative graft constructs for all-inside anterior cruciate ligament (ACL) reconstruction in the event that the semitendinosus harvested is too narrow or too short to make a graft larger than 8 mm.

METHODS

Bovine extensor tendons were used to make 6 different 9-mm-diameter grafts: traditional 4-strand, anastomosis 4-strand, 6-strand, 3-strand, button-fixation 4-strand, and loop-and-tack 4-strand grafts. The grafts were then subjected to cyclic biomechanical testing followed by failure loading. Force at 3 and 5 mm of displacement and ultimate force were recorded for all grafts.

RESULTS

Compared with the traditional 4-strand graft, the only graft that showed significant biomechanical differences during the cyclic phase of testing was the button-fixation 4-strand graft, which was characterized by lower force at 3 mm of displacement (74 ± 34 N vs 122 ± 13 N, P = .004) and 5 mm of displacement (122 ± 35 N vs 172 ± 3 N, P = .006). During failure loading, ultimate force was significantly lower for both the 6-strand graft (491 ± 186 N, P = .041) and button-fixation 4-strand graft (326 ± 27 N, P < .001) than for the traditional 4-strand graft (778 ± 176 N). All other grafts were equivalent for the parameters tested.

CONCLUSIONS

The anastomosis 4-strand, 3-strand, and loop-and-tack 4-strand grafts do not biomechanically differ in cyclic loading and ultimate force from traditional 4-strand grafts. This study supports the use of anastomosis 4-strand, 3-strand, or loop-and-tack 4-strand grafts in the event that a traditional all-inside 4-strand graft cannot be prepared from a harvested semitendinosus tendon in ACL reconstruction.

CLINICAL RELEVANCE

This study tests and describes alternatives to the traditional 4-strand semitendinosus autograft for all-inside ACL reconstruction in the event that the harvested tendon is not adequate.

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.

Biomechanical and microbiological effects of local vancomycin in anterior cruciate ligament (ACL) reconstruction: a porcine tendon model

INTRODUCTION

Although there is increasing evidence for the successful use of local vancomycin applied by soaked compresses during ACL reconstruction, there are still little data on its microbiological and biomechanical effects. Furthermore, exact dosage of vancomycin with respect to tendon stability and microbiological effectivity is still unknown.

MATERIALS AND METHODS

63 porcine flexor digitorum profundus tendons were harvested under sterile conditions from fresh cadaver legs. After contamination with Staphylococcus epidermidis (S. epidermidis), tendons were wrapped into sterile compresses moistened with different concentrations of vancomycin for 10 or 20 min. Sterile sodium chloride was used for control. After treatment, tendons were rolled onto blood-agar plates to test for residual bacterial contamination and tested for maximum load and stiffness using a uniaxial testing device with cryo-clamps for tendon fixation. Agar plates were checked after 1 week of culture at 36 °C for signs of bacterial growth.

RESULTS

When applying vancomycin for only 10 min, bacterial contamination was found in all dosage groups ranging from 28.6% contamination (n = 2 of 7 tendons) when using 10 mg/ml up to 85.7% (n = 6 of 7 tendons) when using 1 mg/ml. Applying vancomycin-soaked compresses for 20 min, bacterial contamination was still found in the groups using 1 mg/ml and 2.5 mg/ml (contamination rate 85.7 and 42.9% respectively). When using 5 mg/ml and 10 mg/ml, no bacterial contamination could be perceived after 7 days of culture. With regard to biomechanical properties, no differences were found regarding maximum load or Young's modulus between groups.

CONCLUSIONS

This study showed no signs of biomechanical impairment of porcine flexor tendons after the use of vancomycin wraps with concentration ranging from 1 to 10 mg/ml for 10 or 20 min at a time zero testing. Contamination with S. epidermidis was cleansed in 100% of tendons when using at least 5 mg/ml of vancomycin for 20 min.

Screw oversizing for anterior cruciate ligament graft fixation in primary and enlarged tibial tunnels: A biomechanical study in a porcine model

BACKGROUND

Ideal diameter for tibial interference screw fixation of the anterior cruciate ligament (ACL) graft remains controversial. Tibial graft fixation with screws matching the tunnel diameter vs. one-millimetre oversized screws were compared.

METHODS

In 32 cadaveric porcine tibiae, bovine extensor tendons with a diameter of eight millimetres were fixed in (I) a primary ACL reconstruction scenario with eight-millimetre tibial tunnels (pACL), with eight-millimetre (pACL-8) vs. nine-millimetre (pACL-9) screws, and (II) a revision ACL reconstruction scenario with enlarged tunnels of 10 mm (rACL), with 10-mm (rACL-10) vs. 11-mm (rACL-11) screws. Specimens underwent cyclic loading with low and high load magnitudes followed by a load-to-failure test. Graft slippage and ultimate failure load were recorded.

RESULTS

In comparison with matched-sized screws (pACL-8), fixation with oversized screws (pACL-9) showed with significantly increased graft slippage during cyclic loading at higher load magnitudes (1.19 ± 0.23 vs. 1.98 ± 0.67 mm; P = 0.007). There were no significant differences between the two screw sizes in the revision scenario (rACL-10 vs. rACL-11; P = 0.38). Graft fixation in the revision scenario resulted in significantly increased graft slippage in comparison with fixation in primary tunnels at higher loads (pACL vs. rACL; P = 0.004). Pull-out strengths were comparable for both scenarios and all screw sizes (P > 0.316).

CONCLUSIONS

Matched-sized interference screws provided better ACL graft fixation in comparison with an oversized screw diameter. In revision cases, the fixation strength of interference screws in enlarged tunnels was inferior to the fixation strength in primary tunnels.

Evaluating different closed loop graft preparation technique for tibial suspensory fixation in ACL reconstruction using TightRope™

In most anterior cruciate ligament (ACL) reconstructions, grafts are fixed to the femoral side first followed by the tibial side. Various techniques have been reported to achieve optimal tension on the grafts, but once the grafts are fixed it is difficult to adjust graft tension further. To enable post fixation tension control we have invented a new graft configuration using an adjustable loop-device (TightRope^TM, Arthrex, FL, USA) on the tibial side. In this paper, biomechanical properties of this configuration using soft tissue were examined in terms of graft diameter and various suture techniques (referred to as base suture) to make a closed circle to support TightRope^TM.

Two experiments were conducted under different conditions. In each experiment, cyclic load, followed by a pull-to-failure load, was applied to the grafts and elongation and failure mode were recorded. (1) To evaluate the effects of diameter, 5.0 or 6.0 mm grafts were prepared by a single locking loop stitch as the base suture (SLL5, SLL6). (2) To evaluate different base sutures, 5.0 mm tendons were used, and grafts were prepared using five kinds of base sutures (SLL, ZLL: zigzag locking loop, DZLL: double zigzag locking loop, DK: double Krackow, DK w/o TR: double Krackow without TightRopeTM). In the first experiment, tearing was observed in 2 of 6 cases in the SLL5 test group, whereas no tearing was observed with SLL6. In the second experiment, no tearing was observed with DZLL or DK. Elongation was smaller in these two groups compared to the other groups. Mechanical strength decreases with a smaller graft diameter. Biomechanical properties differed with different base sutures and, among them, the double-zigzag-suture stitch and double Krackow provided less elongation and higher ultimate load in this graft configuration.

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.

Independent Suture Tape Reinforcement of Small and Standard Diameter Grafts for Anterior Cruciate Ligament Reconstruction: A Biomechanical Full Construct Model

PURPOSE

To compare the dynamic elongation, stiffness behavior, and ultimate failure load of standard with small diameter soft tissue grafts for anterior cruciate ligament (ACL) reconstruction with and without high-strength suture tape reinforcement.

METHODS

Both a tripled "small" diameter and a "standard" quadrupled tendon graft with and without suture tape reinforcement were tested using suspensory fixation (n = 8 each group). The suture tape was passed through the suspensory fixation button on the femur and tibia to ensure independent (safety belt) fixation from the graft in vitro. The testing of the constructs included position-controlled cyclic loading, force-controlled cyclic loading at 250 N and 400 N as well as pull to failure (50 mm/min).

RESULTS

Reinforcement of a small diameter graft significantly reduced dynamic elongation of 38% (1.46 ± 0.28 mm vs 2.34 ± 0.44 mm, P < .001) and 50% (2.55 ± 0.44 mm vs 5.06 ± 0.67 mm, P < .001) after the 250 N and 400 N load protocol, respectively. Reinforcement of a standard diameter tendon graft decreased dynamic elongation of 15% (1.59 ± 0.34 mm vs 1.86 ± 0.17 mm, P = .066) and 26% (2.62 ± 0.44 mm vs 3.55 ± 0.44 mm, P < .001). No significant difference was found between both reinforced models. The ultimate failure loads of small and standard diameter reinforced grafts were 1592 ± 105 N and 1585 ± 265 N, resulting in a 64% (P < .001) and 40% (P < .001) increase compared with their respective controls.

CONCLUSIONS

Independent suture tape reinforcement of soft tissue grafts for ACL reconstruction leads to significantly reduced elongation and higher ultimate failure load according to in vivo native ACL function data without stress-shielding the soft tissue graft.

CLINICAL RELEVANCE

If in vitro results are translational to human knees in vivo, the suture tape reinforcement technique for ACL reconstruction may decrease the risk of graft tears, particularly in the case of small diameter soft tissue grafts.

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.

Intraoperative Workflow for All-Inside Anterior Cruciate Ligament Reconstruction: An In Vitro Biomechanical Evaluation of Preconditioning and Knot Tying

PURPOSE

To evaluate and compare the effect of preconditioning according to intraoperative workflow on the elongation behavior of single-side and fully knotted all-inside anterior cruciate ligament (ACL) reconstruction configurations in a biomechanical in vitro study.

METHODS

Four full construct all-inside ACL reconstruction groups (n = 8 per group) were tested using porcine tibias and bovine tendons. Groups included both an all-inside configuration with one- (group 1) and both-side knotted adjustable loop-length devices (group 2), without and with performing intraoperative preconditioning (group 1-intraoperative preconditioned [IPC], group 2-IPC). Adjustable loop-length devices for control groups were knotted according to test configurations. Intraoperative preconditioning specimens were further precycled for 10 times at 0.5 Hz and manually retensioned before knotting. All groups underwent dynamic cycling in position and force control mode each for 1,000 cycles at 0.75 Hz according to in vitro loading parameters replicating the in vivo ACL environment. Finally, a load-to-failure test at 50 mm/min was performed.

RESULTS

Intraoperative preconditioning increases initial graft tension for single- (242 ± 22 N vs 174 ± 13 N; P < .0001) and both-side knotted configurations (225 ± 15 N vs 159 ± 10 N; P < .0001) compared with controls and allows maintained graft tension at higher levels until reaching the end of position-controlled cyclic loading. Furthermore, dynamic elongation is reduced for one- (1.93 ± 0.28 vs 0.76 ± 0.12; P < .0001) and both-side knotted (1.84 ± 0.20 vs 0.96 ± 0.32; P < .0001) configurations by 61% and 47%, respectively. No intergroup (group 1 vs group 2 and group 1-IPC vs group 2-IPC) statistically significant differences could be found between one- and both-side knotted configurations.

CONCLUSIONS

All-inside ACL reconstruction with preconditioning according to intraoperative workflow leads to a statistically significant improved mechanical behavior and may allow for optimizing initial graft tension and elongation for all-inside ACL reconstruction to reduce knee laxity. A single-side knotted configuration achieves similar stabilization strength to fully knotted constructs.

CLINICAL RELEVANCE

Graft insertion until tunnel docking increases the intratunnel graft portion that may optimize graft incorporation. Eliminating a suture knot stack may improve intraoperative workflow and reduce postoperative knot irritation.

The impact of different peripheral suture techniques on the biomechanical stability in flexor tendon repair

PURPOSE

Flexor tendon repair consists of circumferential peripheral sutures in combination with core sutures to avoid fraying and reduces the exposure of suture material on tendon surface. The peripheral suture adds up to a tenfold increase of the biomechanical stability compared to the core suture alone. The purpose of our study was to determine the most favourable peripheral repair technique for tendon repair.

METHODS

Seventy-two porcine flexor tendons underwent standardized tenotomy and repair using one of the following six methods (n = 12): simple-running (SR), simple-locking (SL), Halsted-mattress (HM), lin-locking (LL), Lembert-mattress (LM), and Silfverskiöld cross-stich (SCS) suture technique. The SL- suture was placed 2 mm; the HM, LM, SC, and LL suture were placed 5 mm from the tendon gap. The SR suture was placed 1, 2, and 3 mm from tendon ends; no additional core suture was applied. For cyclic testing (1000 cycles), elongation was calculated; for load to failure construct stiffness, yield load and maximum load were determined.

RESULTS

The mean cyclic elongation for all tested suture techniques was less than 2 mm; there was no significant difference between the groups regarding elongation as well as yield load. The HM, LM, SCS, and LL suture techniques presented significantly higher maximum loads compared to the SR- and SL-sutures. The 3 mm SR showed significantly higher maximum loads compared to the 2 and 1 mm SR.

CONCLUSIONS

Beside the distance from tendon gap, the type of linkage of the suture material across and beneath the epitendineum is important for biomechanical stability. Simple-running suture is easy to use, even with a slight increase of the distance from tendon gap significantly increases biomechanical strength. For future repairs of flexor tendon injuries, 3 mm stitch length is highly recommended for simple peripheral suture, while the Halsted-mattress suture unites the most important qualities: biomechanically strong, most part of suture material placed epitendinous, and not too complicated to perform.

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

BACKGROUND

Numerous needleless techniques for tendon graft fixation that feature several advantages have been reported. However, there are few studies that have compared the holding strength between the needleless techniques (rolling hitch and modified rolling hitch) and traditional suture methods.

QUESTIONS/PURPOSES

To compare the tendon graft-holding strength of the rolling hitch and modified rolling hitch with the Krackow stitch in an in vitro porcine biomechanical model.

METHODS

Thirty fresh-frozen porcine flexor profundus tendons were randomly divided into three groups of 10 specimens. The experimental procedure was designed to assess elongation of the suture-tendon construct across the needleless tendon-grasping techniques and the Krackow stitch. All suture configurations were completed with a braided nonabsorbable suture. Each tendon was pretensioned to 100 N for three cycles, cyclically loaded from 50 to 200 N for 200 cycles, and then finally loaded to failure. Elongation, load to failure, and mode of failure were recorded for each specimen.

RESULTS

Five of the 10 rolling hitch specimens failed during cyclic loading. With the numbers available, elongation after cyclic loading was not different among the successful rolling hitch specimens (19% [1.19 cm/6.17 cm] ± 6%), modified rolling hitch fixations (19% [1.11 cm/ 5.93 cm] ± 6%), and Krackow stitch fixations (26% [1.41 cm/5.43 cm] ± 6%); ultimate failure loads also were not different among the rolling hitch fixations (316 ± 35 N), modified rolling hitch fixations (342 ± 14 N), and Krackow stitches (327 ± 33 N) with the numbers available.

CONCLUSIONS

With the numbers available, the rolling hitch, modified rolling hitch, and Krackow stitch techniques were not different in terms of elongation after cyclic loading and to failure in this in vitro biomechanical evaluation.

CLINICAL RELEVANCE

Based on the biomechanical properties from this in vitro animal study, the modified rolling hitch may be an attractive alternative for tendon graft fixation in ligament-reconstruction surgery. Future studies might consider further evaluating these needleless techniques in a cadaver model, in an in vivo animal model, and in an intraarticular model in which the testing is performed in the presence of synovial fluid.