Sutures and suture anchors: update 2003

Purpose:The purpose of this study was to evaluate recently introduced sutures and suture anchors for single-pull load-to-failure strength and failure mode.Type of Study:Experimental laboratory biomechanical study.Methods:Using an established protocol in fresh porcine femurs, anchors were tested in diaphyseal cortex, metaphyseal cortex, and cancellous troughs after threading them with either steel sutures or strong synthetic material to reduce the likelihood of suture breakage as a mode of failure. An Instron machine (Instron, Canton, MA) applied tensile loads parallel to the axis of insertion at a rate of 12.5 mm/second until failure, and mean anchor failure strengths were calculated. Mode of failure was recorded (anchor pullout, suture eyelet cutout, or wire breakage). Anchors tested included the RotorloC (Smith & Nephew Endoscopy, Andover, MA), TwinFix Ti 3.5, TwinFix Ti 5.0, and TwinFix AB (Smith & Nephew Endoscopy), Super Revo and UltraSorb (Linvatec, Largo, FL), Duet (Bionx Implants, Blue Bell, PA), AlloAnchor RC (Regeneration Technologies, Alachua, FL), Opus Magnum anchor (Opus Medical, San Juan Capistrano, CA), and the BioCorkscrew 5.0 and BioCorkscrew 6.5 (Arthrex, Naples, FL). Sutures tested were No.2 and No. 5 Ethibond (Ethicon, Somerville, NJ), No. 2 Panacryl (Mitek, a division of Ethicon, Somerville, NJ), and Nos. 2, 5, and 2–0 Fiberwire (Arthrex, Naples, FL).Results:The sutures all broke in the midpoint of their tested strand away from the grips. The No. 2 Ethibond failed at a mean of 21 lb (92 N); No. 5 Ethibond failed at a mean of 44 lb (193 N); No. 2, No. 5, and No. 2–0 Fiberwire at means of 44 lb (188 N), 112 lb (483N), and 19 lb (82 N), respectively; and No. 2 Panacryl at a mean of 22 lb (99 N). The suture anchors all failed at levels higher than the associated sutures.Conclusions:Screw anchors showed higher load to failure values than nonscrew designs, and the new biodegradable anchors showed failure loads lower than the anchors. All anchors were stronger than the suture for which they are designed.     

Suture anchors--update 1999.

New suture anchors continue to become available. Our prior reports on the pullout strength of over 50 different anchors is supplemented by a similar test conducted on 25 additional new anchors. This anchor comparison, using an established protocol in fresh porcine femurs, recorded failure strength, failure mode (anchor pullout, suture eyelet cutout, or wire breakage), eyelet size, minor and major diameters, and drill hole sizes. These new anchors were tested in diaphyseal cortex, metaphyseal cortex, and a cancellous trough. Tensile stress parallel to the axis of insertion was applied at a rate of 12.5 mm/sec by an Instron 1321 until failure and mean anchor failure strengths were calculated. Anchors tested included DePuy 4.5 prototypes D1, D2 Catera 4.5, and D3; DePuy 3.5 prototypes D4- Catera 3.5, D5, and D6; Mainstay 2.7, 3.5, 4.5; ROC EZ 2.8, EZ 3.5, and XS 3.5; Ultrafix RC and Ultrafix MiniMite; 1.3 MicroMitek, Panalok 3.5, and Tacit 2.0; Umbrella Harpoon; PeBA 2.8, 4.0, 6.5; and Stryker 1.9, 2.7, 3.4, and 4.5 prototypes. Screw anchors still tend to have higher values, but for the newer nonscrew designs this distinction is less apparent. The new biodegradable anchors were all composed of poly L-lactic acid suggesting a trend away from other polymers, and these new biodegradable anchors showed load-to-failure strengths comparable to others in their class. All anchors were stronger than the suture for which they are designed to accommodate.     

Failure properties of suture anchors in the glenoid and the effects of cortical thickness

The ultimate pullout strength and fatigue properties of a screw-design suture anchor implanted in the anterior glenoid rim were investigated and compared with results from a nonscrew-design suture anchor. Twenty- two cadaveric glenoids were harvested and one to two anchors were implanted in the superior and inferior quadrants. Fifty-seven Statak 3.5 anchors (Zimmer, Warsaw, IN) were tested and compared with results obtained in a previous study on 50 Mitek GII anchors (Mitek Products, Inc, Westwood, MA). The specimens were mounted on an Instron fatigue testing machine (Instron Corp, Canton, MA) and cycled between preselected minimum and maximum loads until pullout. The Mitek GII maintained a higher pullout strength than the Statak 3.5 after cyclic loading. Cortical thickness at the implantation sites was measured, and found to decrease monotonically from superior to inferior positions. The ultimate pullout strength, and subsequently the fatigue life, of both types of suture anchors depended directly on cortical thickness. The significantly lower performance of both anchors when placed inferiorly emphasizes the importance of correct anchor selection, number, and placement in this region. All anchors settled during the first 10 to 100 cycles, resulting in partial exposure of the implant. Intraoperative cycling of the anchors before suture tying may be necessary to achieve complete settling and prevent subsequent loss of coaptation between capsule and glenoid. The study shows that for the anchors to last 1,000 cycles or more, less than 50% of the theoretical ultimate pullout strength should be applied cyclically. With aggressive early rehabilitation exercises, this significant decrease in fixation strength could shift reconstruction failure from suture breakage or soft tissue tearing to anchor pullout.Arthroscopy 1998 Mar;14(2):186-91     

Fatigue properties of suture anchors in anterior shoulder reconstructions: Mitek GII

Suture anchors have simplified anterior capsule labral reconstruction. During rehabilitation the shoulder goes through many repetitions of range of motion exercises. These exercises will repetitively submaximally load the anchor and in theory should reduce the pullout strength of the suture anchor. No published reports exist on the fatigue strengths and properties of one of the most commonly used anchors: Mitek GII suture anchors. Fifty trials of cyclic submaximal load were done on 22 cadaveric glenoids with an average age of 66.8 years (range, 40 to 90 years). At two to three different sites on the same specimen, the anchors were inserted according to manufacturer's specifications. The anchors were tested to failure on a Instron 1331 servohydraulic mechanical testing system at 2 Hertz sinusoidal loading pattern using steel sutures and a predetermined load. There were 22 (44%) tests performed in the superior quadrant and 28 (56%) tests in the inferior quadrant. All anchors pulled out, and no wires broke. There were statistically significant differences between the superior and inferior portion of the glenoid with regard to number of cycles to failure at a given maximum load. The anchors underwent an average of 6,220 cycles before pullout at an average load of 162 N (SD = 73 N). In the superior quadrant, the average ultimate pullout strength was 237 N (SD = 42 N), whereas in the inferior quadrant the average ultimate pullout strength was 126 N (SD = 36 N). Hence, the ultimate pullout strength of the Mitek GII anchor was significantly higher (P < .002) in the superior quadrant than in the inferior quadrant. Using a least squares regression analysis, it was possible to predict the fatigue life of the superiorly and inferiorly placed suture anchors over a wide range of cycles. The R-squared values for trendlines showed good reliability (superior R² = 0.55; inferior R² = 0.28). The fatigue life curves for the two different quadrants were normalized using the ultimate pullout strength. This new, universal curve predicts the fatigue life of the Mitek GII anchor as a percentage of the ultimate pullout strength for any selected location. For a clinically relevant number of cycles, no more than approximately 40% to 50% of the ultimate pullout strength of the suture anchor can be cyclically applied to the anchor to guarantee a life for the duration of rehabilitation. For the entire system, the inferiorly placed anchors dictate the amount of cyclically applied load the system can experience without failing, and rehabilitation should be adjusted accordingly.     

The twist-lock concept of tissue transport and suture fixation without knots: observations along the Hong Kong skyline

Purpose:To evaluate the load to failure and the mode of failure of a novel suture anchor construct that does not require knots (the “twist-lock” construct) and to compare it with a standard suture anchor construct (Corkscrew; Arthrex, Naples, FL).Type of Study:Biomechanical single-pull load-to-failure study comparing the twist-lock construct to the Corkscrew suture anchor construct.Methods:The twist-lock construct is a suture anchor system that does not use knots, instead using 3 consecutive twists between suture limbs to enhance internal interference between the suture limbs. This system maximizes internal interference by 2 mechanically verifiable friction-multiplier mechanisms: the cable friction effect and the wedge effect. After theoretically verifying the strength characteristics of the twist-lock system, the authors tested and compared its strength in vitro to that of a standard screw-type suture anchor system (Corkscrew). Unicellular polyurethane, which has been shown to accurately mimic the properties of cancellous bone, was used for implantation of suture anchors for the purpose of comparing the load to failure of 10 identical constructs in each of the 2 anchor systems. Axial single-pull loading to failure was performed with an Instron 5565 testing machine (Instron, Canton, MA).Results:The average load to failure for the twist-lock group was 137.2 N, and the average for the Corkscrew group was 123.0 N, a difference of 14.2 N. This study shows that the twist-lock anchors failed at a load that was 12% higher than that of the Corkscrew group (P = .02).Conclusion:The twist-lock system is a suture anchor system that achieves suture fixation of soft tissue to bone without the need to tie knots. It shows single-pull loads to failure that are significantly higher than those of a standard suture anchor system.     

Bone suture anchors versus the pullout button for repair of distal profundus tendon injuries: a comparison of strength in human cadaveric hands.

Avulsion or distal tendon laceration of flexor digitorum profundus (FDP) is classically repaired to the base of the distal phalanx via a pullout suture over a button. Bone suture anchors, used extensively in other surgical areas, have recently been proposed for reattachment of the FDP to the distal phalanx. The FDP tendons of the index, long, and ring fingers in 9 fresh frozen cadeveric hands were randomized to 1 of 3 repair techniques after simulated distal avulsion injuries. These were the pullout button using 3-0 monofilament nylon in a 2-strand Bunnell suture pattern, the 1.8 mm Mini QuickAnchor (Mitek Products, Norwood, MA) using 3-0 braided polyester in a 2-strand Bunnell suture pattern, and the Mitek micro anchor using 3-0 braided polyester with a modified 4-strand Becker suture pattern. Nine specimens were loaded to failure, noting maximum load and mode of failure. The 1.3 mm Micro QuickAnchor (Mitek) technique (69.6 +/- 10.8 N) was significantly stronger than the pullout button (43.3 +/- 4.8 N) or the Mini anchor technique (44.6 +/- 12.7 N). The Micro bone suture anchor provides a stronger tendon to bone repair than the pullout button or the Mini anchor. Given the disadvantages of the pullout button, the Micro bone suture anchor with the modified Becker technique is worth consideration as an alternative method to repair distal FDP avulsions.     

Suture anchor fixation strength in osteopenic versus non-osteopenic bone for rotator cuff repair

Introduction

Rotator cuff tears are increasing with age. Does osteopenic bone have an influence on the pullout strength of suture anchors?

Materials and methods

SPIRALOK 5.0 mm (DePuy Mitek), Super Revo 5 mm and UltraSorb (both ConMed Linvatec) suture anchors were tested in six osteopenic and six healthy human cadaveric humeri. Incremental cyclic loading was performed. The ultimate failure load, anchor displacement, and the mode of failure were recorded.

Results

In the non-osteopenic bone group, the absorbable SPIRALOK 5.0 mm achieved a significantly better pullout strength (274 N ± 29 N, mean ± SD) than the titanium anchor Super Revo 5 mm (188 N ± 34 N, mean ± SD), and the tilting anchor UltraSorb (192 N ± 34 N, mean ± SD). In the osteopenic bone group no significant difference in the pullout strength was found. The failure mechanisms, such as anchor pullout, rupture at eyelet, suture breakage and breakage of eyelet, varied between the anchors.

Conclusion

The present study demonstrates that, in osteopenic bone, absorbable suture anchors do not have lower pullout strengths than metal anchors. In normal bone, the bioabsorbable anchor in this study even outperformed the non-absorbable anchor.

     

Biomechanical testing of a new knotless suture anchor compared with established anchors for rotator cuff repair

Various suture anchors are available for rotator cuff repair. For arthroscopic application, a knotless anchor was developed to simplify the intra-operative handling. We compared the new knotless anchor (BIOKNOTLESStrade mark RC; DePuy Mitek, Raynham, MA) with established absorbable and titanium suture anchors (UltraSorbtrade mark and Super Revo 5mmtrade mark; ConMed Linvatec, Utica, NY). Each anchor was tested on 6 human cadaveric shoulders. The anchors were inserted into the greater tuberosity. An incremental cyclic loading was performed. Ultimate failure loads, anchor displacement, and mode of failure were recorded. The anchor displacement of the BIOKNOTLESStrade mark RC (15.3 +/- 5.3 mm) after the first cycle with 75 N was significantly higher than with the two other anchors (Super Revo 2.1 +/- 1.6 mm, UltraSorb: 2.7 +/- 1.1 mm). There was no significant difference in the ultimate failure loads of the 3 anchors. Although the Bioknotlesstrade mark RC indicated comparable maximal pullout strength, it bares the risk of losing contact between the tendon-bone-interface due to a significantly higher system displacement. Therefore, gap formation between the bone and the soft tissue fixation jeopardizes the repair. Bioknotlesstrade mark RC should be used in the lateral row only when a double row technique for rotator cuff repair is performed, and is not appropriate for rotator cuff repair if used on its own.     

Rotator cuff repair with bioabsorbable screws: An in vivo and ex vivo investigation

Purpose: The purpose of this study was to evaluate in vivo the clinical outcomes of rotator cuff repairs with bioabsorbable screws compared with metal suture anchors, and to compare the ex vivo initial load to failure of rotator cuff repairs using 3 different bioabsorbable screws, suture anchors, and transosseous sutures. Type of Study: In vivo clinical outcomes investigation, and ex vivo biomechanical study. Methods: Three cohorts of patients with rotator cuff tears that measured less than 4 cm², were sequentially repaired with Mitek Rotator Cuff QuickAnchors (Mitek Surgical Products, Norwood, MA) (n = 9), Arthrex Headed Bio-Corkscrews (n = 9) (Arthrex, Naples, FL), and Mitek Rotator Cuff QuickAnchors (n = 9). Patients were systematically assessed with a specific shoulder questionnaire and 23 shoulder tests performed preoperatively and at 1 and 6 weeks, 3 and 6 months, and 1 year postoperatively. A correlative ex vivo biomechanical study was performed on 53 ovine shoulders to evaluate the initial failure load properties of bioabsorbable screws compared with fixation with suture anchors and transosseous sutures. Results: In the in vivo portion of the study, the cohort treated with the Headed Bio-Corkscrew demonstrated no improvement on any measured parameter until 1-year after rotator cuff repair. In contrast, shoulders repaired with Mitek Rotator Cuff QuickAnchors demonstrated improved overall shoulder function as early as 6 weeks postoperatively (P =.002), had a better constant score at 1-year after repair (88 ± 9 v 73 ± 17; P =.016), and a lower rate of revision rotator cuff repair (P =.029). In the ex vivo portion of the study, the bioabsorbable headed screws, Headed Bio-Corkscrew (100 ± 30 N) and BioTwist (76 ± 35 N), had inferior initial failure load properties compared with suture anchors (140 ± 36 N) and transosseous sutures (147 ± 68 N). In contrast, the BioCuff (190 ± 56 N), a bioabsorbable implant that used a screw and serrated washer design, had equivalent initial failure load properties as the suture repairs. Conclusions: This investigation had poorer early outcomes, a lower shoulder functional score 1-year after repair, and a higher rate of repeat surgery in patients who had their rotator cuff repaired with a bioabsorbable screw than in patients who had their shoulders repaired with a standard metal suture anchor. Furthermore, the biomechanical testing demonstrated a lower tensile load to failure in the tendons repaired with a simple screw design compared to suture anchors with a mattress stitch. Of note, the implant that used a screw and washer design demonstrated a greater ability to resist initial tensile load.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 3 (March), 2003: pp 239–248     

Bearing area: A new indication for suture anchor pullout strength?

Studies performed to quantify the pullout strength of suture anchors have not adequately defined the basic device parameters that control monotonic pullout. The bearing area of a suture anchor can be used to understand and predict anchor pullout strength in a soft‐bone model. First, conical‐shaped test samples were varied in size and shape and tested for pullout in 5, 8, and 10 pcf sawbone models. Next, bearing area and pullout strength relationships developed from the test samples were validated against nine commercially available suture anchors, including the Mitek QuickAnchor and SpiraLok, Opus Magnum², ArthroCare ParaSorb, and Arthrex BioCorkscrew. The samples showed a direct correlation between bearing area and pullout strength. Increased insertion depth was a secondary condition that also increased pullout strength. The pullout strength for the suture anchors followed the predicted trends of conical devices based on their individual bearing areas. For the 5 and 8 pcf models, only two and three devices, respectively, fell outside the predicted pullout strength range by more than a standard deviation. The use of a synthetic sawbone model was validated against the pullout strength of an Arthrex Corkscrew in five fresh‐frozen cadaver humeral heads. The bearing area of a suture anchor can be used to predict the pullout strength independent of design in a soft‐bone model. This work helps provide a foundation to understand the principles that affect the pullout strength of suture anchors. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 1048–1054, 2009     

In vitro comparison of standard and knotless metal suture anchors

Purpose: Clinical experience after failed Knotless suture anchor (Mitek, Westwood, MA) fixations suggested that the Knotless anchor provides considerably less fixation stability than a standard metal anchor. The purpose of this study was to analyze soft tissue fixation to bone comparing a standard and a Knotless metal suture anchor. Type of Study: In vitro study. Methods: The Mitek GII and Mitek Knotless suture anchors were tested on 7 human cadaveric fresh-frozen glenoids. The anchors were inserted into the glenoid rims, and the sutures of the anchors were fixed to a metal hook attached to the cross-head of a testing machine. Cyclic loading was performed. The gap formation between the metal hook and the glenoid rim, the ultimate failure loads and the modes of failure were determined. Results: The mean gap formation was significantly greater for the Knotless anchor (3.8 ± 1.4 mm) than for the GII anchor (2.4 ± 0.5 mm) after 25 cycles with 50 N repeated load (P = .04). The largest gap of a Knotless fixation was 5.3 mm compared with 3.0 mm for the GII. The ultimate failure load was not significantly different for the Knotless anchor (179 N) and for the GII anchor (129 N). Both anchors failed by either rupture of the suture material or by pullout of the anchors. Conclusions: The GII anchor allows significantly less displacement than the Knotless anchor. Ultimate tensile strength and mode of failure are similar. Greater displacement results in larger gap formation between the soft tissue and the bone. This might weaken and jeopardize the repair. Clincial Relevance: If reattached soft tissues are subjected to postoperative loading, gap formation may result when using the Knotless anchor. For these conditions, suture fixation with knots may be used instead.     

A comparison of soft-tissue anchors in tendo achilles reattachment.

This prospective study evaluated four soft-tissue fixation modalities, used in seven different combinations, to reattach the tendo Achilles in 34 cadaveric specimens. Ultimate loads, elastic moduli, and modes of failure were evaluated by loading the specimen in a cantilevered fashion on an Instron. Mann-Whitney U tests were performed to compare the failure load data for statistical significance. Although the use of two Mitek SuperAnchors showed better load resistance than one anchor (p < .01), there was no significant improvement between using two or three anchors (one anchor 116 +/- 24 N, two anchors 234 +/- 21 N, three anchors 277 +/- 80 N). Two Bionx Bankart Tacks demonstrated no significant difference over using a single tack (one tack 178 +/- 57 N, two tacks 214 +/- 86 N). No statistical difference was observed between the screw and washer systems (screw with polyacetal resin washer 307 +/- 80 N, screw with metal washer 290 +/- 81 N). Both screw and washer systems did show greater stability when compared with a single Mitek SuperAnchor (p < .01) or a single Bionx Bankart Tack (p < .05). Similar analyses using the Mann-Whitney U tests were performed on the elastic modulus data. Analysis of the displacement data among all groups showed no statistical difference. Observations of the mode of failure exhibited 86% of Mitek SuperAnchor failed secondary to suture, and 70% of the Bionx Bankart Tack and 90% of the screw and washer systems failed because of the tendon shearing around the fixation. The comparisons of cost-effectiveness among the fixations showed the Synthes screw and polyacetal resin spiked washer to have the lowest cost to load ratio ($0.15/N).     

A novel, resorbable suture anchor: pullout strength from the human cadaver greater tuberosity.

The pullout strength of a collagen bone anchor that creates interference fixation as the result of radial swelling on hydration was compared with a Mitek rotator cuff anchor after insertion into the greater tuberosity of human cadaver humeri. Bones were fully hydrated at 37 degrees C. Stiffness, peak load, and the mode of failure were recorded. Real and apparent bone densities were measured. Peak load for the collagen anchor at 15 minutes (121.0N +/- 81.3N) was greater than at 2 minutes (60.5N +/- 38.5N) after insertion (P <.05). At between 5 and 60 minutes after insertion, peak loads for the Mitek and the collagen anchors did not differ. After 30 minutes from insertion, the mode of failure of the collagen anchor changed from pullout with minor body damage to pullout with major body damage. Peak load at pullout correlated with bone density for the Mitek (P <.05, r = 0.516) but for the collagen bone anchor appeared unaffected by bone density.     

Fixation of tendon grafts for collateral ligament reconstructions: a cadaveric biomechanical study

PURPOSE: To compare the biomechanical properties of 4 methods of fixation of tendon grafts to bone as used for ligament reconstructions. METHODS: Thirty-two metacarpals were harvested from fresh-frozen cadavers and stripped of soft tissue. Flexor tendons were harvested from the same cadavers and cut into 2-mm-wide strips. Each tendon was fixed to a metacarpal head at the site of origin of a collateral ligament. Four different methods of fixation were tested. In group 1 the tendon was fixed to the bone with a 4.0-mm Arthrex bio-tenodesis interference screw (Arthrex, Inc., Naples, FL). In group 2 the tendon was passed through a bone tunnel and fixed with a 3.2-mm mini-Acutrak screw (Acumed, LLC, Hillsboro, OR) that was inserted in interference mode. In group 3 the tendon was passed through a bone tunnel and fixed with sutures tied over a polyethylene button. In group 4 the tendon was fixed with a mini-Mitek bone suture anchor (Mitek Worldwide, Norwood, MA). All specimens were clamped into a linear loading machine and loaded until failure. Statistical analysis was performed by 1-way analysis of variance testing. RESULTS: The differences in maximal tensile strength and stiffness were statistically significant when comparing any 2 groups. The Arthrex biotenodesis interference screw was the strongest and stiffest fixation method, followed by the Acutrak screw inserted in interference mode. Next was the suture tied over a button method. The mini-Mitek bone suture anchor was the weakest. CONCLUSIONS: Interference screw fixation of tendons to bone has statistically significant higher pullout strength and stiffness than 2 other commonly used fixation methods. The use of interference screws for fixation of tendon grafts to bone for hand ligament reconstructions is a promising new surgical technique.     

Failure of suture material at suture anchor eyelets

Purpose: In the repair of soft tissue to bone using suture anchors, failure of the suture material can occur at the anchor eyelet. This study examines the load strength at which suture material fails with different metallic suture anchor eyelets. Type of study: Biomechanical study. Methods: Suture material (Ethibond No. 2, Ethicon, Norderstedt, Germany) was pulled out from 22 metallic suture anchor models at 60 mm/min, and tensile load at failure and failure mode were recorded. Tests were performed either by simultaneous pulling on 2 suture limbs in 3 different directions (straight, at 45°, and at 45° rotated by 90° to the suture anchor axis) or by pulling on 1 suture limb while measuring the resulting force on the second limb. All tests were performed until suture failure. Pulling was performed in single tests on an Instron materials testing machine (High Wycombe, UK), with the anchors held by a vise. Results: In all cases, the suture failed at the anchor eyelet. Failure load at straight loading ranged from 116 ± 5 N to 226 ± 5 N and from 69 ± 5 N to 193 ± 7 N when loaded at an angle of 45°. The best results were found with the Statak 5.2-mm (Zimmer, Warsaw, IN): 177 N; Corkscrew 6.5-mm anchor (Arthrex, Naples, FL): 174 N; and PeBA 4.0-mm anchor (OBL Orthopaedic Biosystems, Scottsdale, AZ): 169 N. With each eyelet, sutures failed preferentially in 1 direction, depending on the presence of sharp edges. Conclusions: Suture material can be cut at suture anchor eyelets. Failure load depends on sharp edges on the eyelet and occurs at forces up to 73% below the breaking strength of the suture material on a smooth hook. Anchors with suture-protecting channels are particularly sensitive to the orientation in which the sutures are loaded.     

Suture anchor failure strength—An in vivo study

Suture anchors are increasingly used to secure tendons or ligaments to bone. These devices are applicable for arthroscopic shoulder stabilization and rotator cuff repair. This study reports the in vivo characteristics of four anchors, including one absorbable anchor composed of poly-L-lactic acid. Failure strength and method of failure were recorded for these anchors as a function of time. Samples of four anchors [Mitek G2, Zimmer Statak, Acufex TAG wedge, and the absorbable Arthrex expanding suture plug (ESP)] were implanted into ram femurs and harvested at intervals. Each bone-anchor-suture system was stressed to failure. The failure force and failure method was recorded. Mitek G2 and Statak suture anchors failed consistently at 30 pounds by suture breakage. They had no implantation difficulties. The TAG wedge exhibited suture pull-out and implant flipping at insertion. The TAG wedge failed by suture cut-out, anchor pull-out, and suture breakage. Its average failure strength was initially 16 pounds, but increased to 28 pounds at 2 weeks and reached the 30-pound level by 4 weeks. The ESP poly-L-lactic acid anchors experienced implantation breakage in 20% because of their greater length and composition. At pull-out testing, the ESP failed by suture cut-out, anchor pull-out, and suture breakage. Failure strength was initially 27 pounds, was 17 pounds at 2 weeks, and increased to 30 pounds by 6 weeks. The absorbable ESP does not have initial pull-out strength comparable with the Mitek and Statak suture anchors but does achieve this strength by 6 weeks. This information should provide insight about the suitability of these suture anchors in the clinical setting.     

Repair of central slip avulsions using Mitek Micro Arc bone anchors. An in vitro biomechanical assessment

In this study we evaluated the pullout strength of the Mitek Micro Arc anchor for the reconstruction of central slip avulsions at the proximal interphalangeal joint of the finger. Forty paired fresh frozen cadaver fingers were randomized into treatment (anchor) and control groups (horizontal mattress repair) and subjected to tensile loading to failure. The mean (SD) failure loads of the repairs were: Mitek repair group 22.3 (4.7) N, and control group 24.7 (5.5) N. There were no statistically significant differences between the failure loads or the failure mechanisms of the two repairs. The pullout strength of the isolated anchor-bone complex was evaluated by refitting five anchors with stainless steel wire. The mean failure load of the isolated anchor was 400% higher than the tendon-suture-anchor complex, indicating that the weakest link of the system is not the bone-anchor interface.     

Bone suture anchor fixation in the lower extremity: a review of insertion principles and a comparative biomechanical evaluation

BACKGROUND: Suture anchors have been developed for the fixation of ligaments, capsules, or tendons to bone. These devices have led to improved fixation, smaller incisions, earlier limb mobility, and improved outcomes. They were originally developed for use in shoulder reconstructions but are now used in almost all extremities. In the lower leg they are used in the tibia, the talus, the calcaneus, tarsal bones, and phalanges. Nevertheless, techniques for insertion and mechanisms of failure are not well described. METHODS: Five suture anchors were studied to determine the pullout strength in four distal cadaver femurs and four proximal cadaver tibias from 55- and 62-year-old males. Eight hundred ninety Newton line was used, testing the anchors to failure with an Instron testing device (Instron, Norwood, MA). The anchor devices were inserted randomly and tested blindly (12 tests per anchor device, 60 tests in all). RESULTS: Two anchors in each group tested failed at low loads. Both types of plastic anchors had failures at the eyelet. Average pullout strength varied from 85.4 to 185.6 N. CONCLUSIONS: Insertion techniques are specific for each device, and they must be followed for optimal fixation. In this study, in all five groups of anchors tested two of the 12 anchors in each group failed with minimal force. On the basis of this finding we recommend that, if suture anchor fixation is necessary, at least two anchors should be used. Since there appears to be a percentage of failure in all devices, the second anchor can serve as a backup. It is imperative that surgeons be familiar with the insertion techniques of each device before use.     

Über die Primärfestigkeit konventioneller und alternativer Nahttechniken der RotatorenmanschetteEine biomechanische Untersuchung

The aim of this biomechanical study was to evaluate rotator cuff repair strength using different suture anchor techniques compared to conventional repair, taking into consideration the native strength of the supraspinatus tendon. Therefore, a defined defect of the supraspinatus was created in 50 freshly frozen cadaver specimen (group size n = 10; median age at death: 56 years). Five methods were employed for cuff repair: standard transosseous suture, modified transosseous suture with patch augmentation and three suture anchors (Acufex Wedge TAG, Acufex Rod TAG und Mitek GII). The maximum tensile load of the five techniques was: standard transosseous suture, 410 N; modified transosseous suture, 552 N; Wedge TAG, 207 N; Rod TAG, 217 N; Mitek GII, 186 N. The difference between the suture anchor and standard techniques were highly significant (P < 0.001). In this series, the Mitek Gll anchor showed the lowest anchor dislocation rate at 3% (n = 1). The Wedge TAG system had a dislocation rate of 27% (n = 8) and the Rod TAG system 43% (n = 13). Suture anchor techniques revealed about 20%, the standard technique 34% and its modification 60% of the hypothetically calculated native tendon strength. Compared to conventional transosseous suture techniques, the use of the suture anchors tested in this series does not significantly increase the primary fixation strength of rotator cuff repair. The metallic implant with two barbs (Mitek GII) seems to be superior to the polyacetal anchors when inserted into the spongiform bone of the greater tubercle. The considerably weaker repair strength needs to be taken into consideration in postoperative patient rehabilitation, especially after the use of suture anchors.     

Cyclic loading of rotator cuff repairs: A comparison of bioabsorbable tacks with metal suture anchors and transosseous sutures

Purpose: The purposes of the study were (1) to compare rotator cuff repair strengths after cyclic loading of 2 bioabsorbable nonsuture-based tack-type anchors, transosseous sutures, and a metal suture-based anchor, and (2) to correlate bone mineral density with mode of failure and cycles to failure. We hypothesized that specimens with a lower bone density would fail through bone at a lower number of cycles independent of the method of cuff fixation. Type of Study: Ex vivo biomechanical study. Methods: Standardized full-thickness rotator cuff defects were created in 30 fresh-frozen cadaveric shoulders that were randomized to 1 of 4 repair groups: transosseous sutures; Mitek Super suture anchors (Mitek Surgical Products, Westwood, MA); smooth bioabsorbable 8-mm Suretacs (Acufex, Smith & Nephew Endoscopy, Mansfield, MA); or spiked bioabsorbable 8-mm Suretacs (Acufex). All repairs were cyclically loaded from 10 to 180 N; the numbers of cycles to 50% (gap, 5 mm) and 100% (gap, 10 mm) failure were recorded. Results: In comparing the repair groups, we found only 1 significant difference: the number of cycles to 100% failure was significantly higher (P <.05) for the smooth bioabsorbable tack than for the transosseous suture group. There were no statistically significant (P ≤.05) differences in bone mineral densities with regard to each specimen’s mode of failure. Conclusions: Our results suggested that immediate postoperative fixation provided by bioabsorbable tacks was similar to that provided by Mitek anchors and more stable than that provided by transosseous sutures. Therefore, the immediate postoperative biomechanical strength of bioabsorbable tacks seems comparatively adequate for fixation of selected small rotator cuff tears. However, additional evaluation in an animal model to examine degradation characteristics and sustained strength of repair is recommended before clinical use.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 17, No 4 (April), 2001: pp 360–364