Suture anchor strength revisited

The rapid proliferation of suture anchors continues. Our prior report on the pullout strength of 14 different anchors is supplemented by a similar test conducted on 8 additional anchors. Comparative data on modes of failur and failure strengths (ultimate loads to failure) for these new devices are compared statistically with the previously tested anchors. In a fresh never-frozen porcine femur model, 10 samples of each of the additional anchors tested were threaded with stainless steel sutures and inserted into three different test areas (diaphyscal cortex, metaphyseal cortex, and a cancellous trough). Tensile stress parallel to the axis of insertion was applied at a rate of 12.5 mm/s by an Instron 1321 testing machine (Instron Corp., Canton, MA) until failure and mean anchor failure strengths calculated. The anchors tested were the MItek G2 as a control, miniMitek, Mitek Superanchor, Mitek Rotator Cuff anchor (Mitek Products, Westwood, MA), Innovasive Devices Radial Osteal Compression device (Innovasive Devices, Hopkinton, MA), Arthrex Fastak (Arthrex Inc, Naples, FL), Arthrotek miniHarpoon (Arthrotek, Warsaw, IN), Orthopedic Biosystems PeBA 3 and PeBA 5 (Orthopedic Biosystems, Scottsdale, AZ), and AME 5.5 screw (American Medical Electronics, Richardson, TX). Failure mode (anchor pullout, suture eyelet cut out, or wire breakage) was generally consistent for each anchor type. The size of insertion hole is clinically important and each anchor's performance was evaluated as a function of is minor diameter or drill hole. For screw anchors, the larger the minor diameter of the screw, the higher the mean failure strengthsin all three test areas (P = .001). However, larger drill holes for non-screw anchors resulted in lower mean failure strengths in cancellous bone (P = .03) and diaphyseal cortex (P < .005).     

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     

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     

Button Fixation Technique for Achilles Tendon Reinsertion: A Biomechanical Study

Chronic insertional tendinopathy of the Achilles tendon is a frequent and disabling pathologic entity. Operative treatment is indicated for patients for whom nonoperative management has failed. The treatment can consist of the complete detachment of the tendon insertion and extensive debridement. We biomechanically tested a new operative technique that uses buttons for fixation of the Achilles tendon insertion on the posterior calcaneal tuberosity and compared it with 2 standard bone anchor techniques. A total of 40 fresh-frozen cadaver specimens were used to compare 3 fixation techniques for reinserting the Achilles tendon: single row anchors, double row anchors, and buttons. The ultimate loads and failure mechanisms were recorded. The button assembly (median load 764 N, range 713 to 888) yielded a median fixation strength equal to 202% (range 137% to 251%) of that obtained with the double row anchors (median load 412 N, range 301 to 571) and 255% (range 213% to 317%) of that obtained with the single row anchors (median load 338 N, range 241 to 433N). The most common failure mechanisms were suture breakage with the buttons (55%) and pull out of the implant with the double row (70%) and single row (85%) anchors. The results of the present biomechanical cadaver study have shown that Achilles tendon reinsertion fixation using the button technique provides superior pull out strength than the bone anchors tested.     

Mechanical testing of absorbable suture anchors

Purpose: Absorbable suture anchors offer great advantages but are made of mechanically weak material. The weakest link in the fixation of soft tissue to bone may therefore be the anchor itself. In this study, several commercially available anchors were mechanically tested in vitro. Type of study: Biomechanical bench study. Methods: Twelve absorbable suture anchor models were implanted into an artificial test bone according to the recommended technique. Testing temperature was 37°C ± 1°C. The anchors were loaded with an Instron testing machine with the suture material (USP No. 2, Ethibond, Ethicon, Somerville, NJ) in line with the anchor axis, with and without previous abrasion of the suture at the eyelet. Tensile load at failure and failure mode were recorded. To test creep behavior, a permanent load of 100 N was applied to the anchors, and time to failure was recorded. Suture anchor weight and crystallinity were analyzed. Results: Mean failure load on tensile testing using a cross-head speed of 60 mm/min ranged from 124 to 244 N. Failure modes were eyelet failure in 5 cases, suture failure in 6 cases, and anchor pullout in 1 case. In creep testing, eyelet failure occurred in 8 anchor models after a mean duration of 0.5 to 99 hours; 3 anchor models remained intact after 300 hours, and 1 anchor model failed by pullout of the test sample. Crystallinity ranged from 0% (amorphous) to 57.2%; anchor weight ranged from 0.036 to 0.161 g. Mechanical properties did not correlate with crystallinity but with anchor weight. Abrasion of the suture material at the eyelet had little effect on failure load. Conclusions: At 37°C, structural failure (breaking) of absorbable suture anchors may occur if loaded to the mechanical limit. Absorbable anchors are particularly sensitive to static, long-term loading.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 2 (February), 2003: pp 188–193     

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.     

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.     

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.     

Fixation of calcaneal avulsion fractures using screws with and without suture anchors: a biomechanical investigation

BACKGROUND: Lag screw fixation commonly is used to treat avulsion fractures of the posterior calcaneal tuberosity, but this method may not offer reliable fixation. This study compared the strength to failure of lag screws compared to lag screw fixation augmented with suture anchors in these fractures. METHODS: The calcanei and Achilles tendons of 12 fresh lower extremity cadaver matched pairs were dissected and removed. An oblique osteotomy was created in the calcaneus, and two 4.0-mm lag screws were placed nearly perpendicular to the plane of the fracture in the dorsal aspect of the calcaneus with 30 degrees of divergence between them. In the contralateral specimen, the same procedure was done, but with two suture anchors placed 1.5 to 2 mm distal to the osteotomy. A zigzag suture technique through the Achilles tendon was used. The specimens were mounted and placed in a load frame for monotonic loading to failure. A paired Student t-test and a Pearson correlation were used to analyze the data (p 相似文献   

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.     

Biomechanic comparison of the Teno Fix tendon repair device with the cruciate and modified Kessler techniques

PURPOSE: To compare the mechanical behavior of a novel internal tendon repair device with commonly used 2-strand and 4-strand repair techniques for zone II flexor tendon lacerations. METHODS: Thirty cadaveric flexor digitorum profundus tendons were randomized to 1 of 3 core sutures: (1) cruciate locked 4-strand technique, (2) modified Kessler 2-strand core suture technique, or (3) Teno Fix multifilament wire tendon repair device. Each repair was tested in the load control setting on a Instron controller coupled to an MTS materials testing machine load frame by using an incremental cyclic linear loading protocol. A differential variable reluctance transducer was used to record displacement across the repair site. Cyclic force (n-cycles) to 1-mm gap and repair failure was recorded using serial digital photography. RESULTS: There was no significant difference in differential variable reluctance transducer displacement between the cruciate, modified Kessler, and Teno Fix repairs. The cruciate repair had greater resistance to visual 1-mm repair-site gap formation and repair-site failure when compared with the Kessler and Teno Fix repairs. No significant difference was found between the modified Kessler repair and the Teno Fix repair. In all specimens, the epitenon suture failed before the core suture. Repair failure occurred by suture rupture in the 7 cruciate specimens that failed, with evidence of gap formation before failure. Seven of 10 modified Kessler repairs failed by suture rupture. All of the Teno Fix repairs failed by pullout of the metal anchor. CONCLUSIONS: The Teno Fix repair system did not confer a mechanical advantage over the locked cruciate or modified Kessler suture techniques for zone II lacerations in cadaveric flexor tendons during cyclic loading in a linear testing model. This information may help to define safe boundaries for postoperative rehabilitation when using this internal tendon repair device.     

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.     

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.     

Biomechanical evaluation of open suture anchor fixation versus interference screw for biceps tenodesis

Biceps tenodesis provides reliable pain relief for patients with biceps tendon abnormality. Previous cadaver studies have shown that, for biceps tenodesis, an interference screw provides biomechanical strength to failure superior to that of suture anchors. This finding has led some providers to conclude that screw fixation for biceps tenodesis is superior to suture anchor fixation. The purpose of the current study was to test the hypothesis that the strength of a 2-suture-anchor technique with closing of the transverse ligament is equal to that of interference screw fixation for biceps tenodesis.In 6 paired, fresh-frozen cadaveric shoulder specimens, we excised the soft tissue except for the biceps tendon and the transverse ligament. We used 2 different methods for biceps tenodesis: (1) suture anchor repair with closing of the transverse ligament over the repair, and (2) interference screw fixation of the biceps tendon in the bicipital groove. Each specimen was preloaded with 5 N and then stretched to failure at 5 mm/sec on a materials testing machine. The load-to-failure forces of each method of fixation were recorded and compared. Mean loads to failure for the suture anchor and interference screw repairs were 263.2 N (95% confidence interval [CI], 221.7-304.6) and 159.4 N (95% CI, 118.4-200.5), respectively. Biceps tenodesis using suture anchors and closure of the transverse ligament provided superior load to failure than did interference screw fixation. This study shows that mini-open techniques using 2 anchors is a biomechanically comparable method to interference fixation for biceps tendon tenodesis.     

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.     

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.     

Editorial Commentary: Biomechanics of All Suture Anchors: What We Know So Far

All suture anchors (ASAs) have proven valuable for soft tissue to bone fixation. They have a small footprint and can be inserted in tight spaces where little bone is available. Additionally, more ASAs can be inserted in the same amount of bone than their larger predecessors, and this may improve the overall biomechanics of the repair construct through load sharing at multiple points of fixation. ASAs are more dependent on the cortical bone than the cancellous bone where they are inserted for fixation. Decortication of this bone should be minimized or avoided, and deployed anchors should be seated to the cortical bone as much as possible at the time of insertion to avoid later settling with cyclic loading. In anchor biomechanical studies, it is important to look at gap formation with cyclic loading. This biomechanical property is clinically more significant than catastrophic failure because of anchor pullout or suture breakage, which is uncommon. Finally, regarding shoulder rotator cuff surgery, biological (healing) is our greatest challenge; in general, anchor fixation strength is adequate.     

Biomechanical Comparison of Knotless Suture Anchor Versus Percutaneous End-to-End Technique for Mid-Substance Achilles Tendon Rupture Repair

Percutaneous Achilles tendon repairs can be performed with 2 distal fixation techniques: knotless suture anchor repair (KL) or percutaneous end-to-end repair (ETE). There is a paucity of literature comparing the biomechanical strength of these 2 distal fixation techniques. The aim of this study was to compare the strength of KL and ETE repairs using flat-braided suture for mid-substance Achilles tendon rupture during simulated progressive rehabilitation. Nine matched pairs of fresh-frozen below-knee cadaveric extremities were randomly assigned into these 2 repair groups. Each specimen was tested in 2 parts sequentially; Part I simulating passive ankle range of motion (cyclic: 20N-100N), and Part II simulating ambulation in a walking boot (cyclic: 20N-190N). The number of cycles, gap displacement, and the mode of failure were recorded for each repair. Achilles tendon repairs using the percutaneous methods of ETE and KL techniques showed no significant difference in the number of cycles to clinical failure, mean gap displacement, or overall failure rate. During Part I, the survival rate in terms of clinical failure for KL and ETE groups was 8 of 9 repairs and 7 of 9 repairs, respectively. During Part II, all repairs experienced clinical failure in both groups. Five repairs in the KL group experienced suture anchor pull out from the calcaneus, and 3 repairs failed at suture-tendon interface. Four repairs in the ETE group failed due to knot slippage and 5 repairs failed at suture-tendon interface. Both techniques are viable options in treating acute mid-substance Achilles tendon ruptures.     

Cyclic testing of pullout sutures and micro-mitek suture anchors in flexor digitorum profundus tendon distal fixation

PURPOSE: Little data exist comparing the strength of traditional methods of fixation in a flexor digitorum profundus tendon with the use of a suture anchor. In vitro cyclic testing simulating a passive mobilization protocol was used to compare the repair of a flexor digitorum profundus tendon using a single micro-Mitek anchor (Mitek, Westwood, MA) or a modified Bunnell 2-strand pullout technique using a monofilament or a braided polyester suture. METHODS: Twenty-four fresh-frozen cadaveric fingers were divided randomly into 4 repair groups (n = 6 each): a micro-Mitek with a 3-0 braided polyester suture or a 3-0 monofilament suture, or a modified Bunnell technique with a 3-0 braided polyester suture or a 3-0 monofilament suture. After repair the specimens were loaded cyclically from 2 to 15 N at 5 N/s, for a total of 500 cycles. Gap formation at the tendon-bone interface was assessed every 100 cycles. Samples were tested to failure at the completion of 500 cycles. RESULTS: No specimens failed catastrophically during cyclic testing. A significantly greater gap formed using the monofilament sutures compared with the braided polyester sutures with both repair techniques. Load to failure in the modified Bunnell technique was superior to the micro-Mitek with both suture types. The modified Bunnell technique using a braided polyester suture was superior to the monofilament suture whereas the suture type did not alter the properties of the micro-Mitek repair. CONCLUSIONS: Significant gap formation with the use of a monofilament suture may be of concern. The use of a braided polyester suture when removal of the pullout suture is required as in the Bunnell technique also needs to be considered.     

The effect of suture anchor design and orientation on suture abrasion: An in vitro study

Purpose: To evaluate the effects of suture anchor design and orientation on suture abrasion in a cyclic model. Type of Study: In vitro. Methods: Biomechanical studies have shown suture breakage to be a predominant mode of failure in a suture anchor repair construct. It is possible that suture abrasion during knot tying or in vivo cyclic loading may contribute to early failure. This study specifically investigates suture abrasion caused by 17 commonly used suture anchors and demonstrates the effects of suture anchor angulation and rotation on suture abrasion. To eliminate target tissue as a source of failure, all anchors were implanted into a solid block of sawbones material and tested with No. 2 Ethibond Excel sutures (Ethicon, Somerville, NJ). The testing model focused on 3 variables: suture anchor type, suture pull angle (SA) and angle of anchor rotation (RA). Abrasion testing was then performed on a servohydraulic materials testing system by continually cycling the suture back and forth through each anchor with an excursion of 4 cm at a rate of 0.5 Hz under a load of 10 N until suture failure occurred. Results: Sutures performed significantly better when cycled in line with the anchor at 0° SA with 0° RA than they did at 45° SA with 0° RA or 45° SA with 90° RA. We found no significant difference between anchors tested at 45° SA with 0° RA and 45° SA with 90° RA. For tests performed using metallic suture anchors, all constructs failed by fraying of the suture. Constructs using biopolymer anchors and nonabsorbable polymeric anchors experienced a mixture of suture and anchor eyelet failures. Conclusions: In addition to the statistically significant detrimental effects of suture anchor angulation and rotation on suture abrasion, suture anchor eyelet design may also influence suture abrasion. Surgeons should be aware of the effects of anchor angulation, suture position in the eyelet, and design and composition of the eyelet to maximize the durability of the construct.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 3 (March), 2003: pp 274–281