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    Biomechanical Analysis of Pullout Strengths of Rotator Cuff and Glenoid Anchors: 2011 Update
    (W B Saunders Co-Elsevier Inc, 2011) Barber, F. Alan; Herbert, Morley A.; Hapa, Onur; Rapley, Jay H.; Barber, Cameron A. K.; Bynum, James A.; Hrnack, Scott A.
    Purpose: To evaluate the biomechanical and design characteristics of newer suture anchors. Methods: Suture anchors were tested in fresh porcine metaphyseal cortex and cancellous troughs by use of an established protocol. A mechanical testing machine applied tensile loads parallel to the axis of insertion at 12.5 mm/s until failure, and mean anchor failure strengths were calculated. The mode of failure was recorded. Rotator cuff anchors tested included the Doubleplay and Opus SpeedScrew (ArthroCare Sports Medicine, Sunnyvale, CA); PEEK Intraline and PEEK Zip (Stryker, San Jose, CA); Paladin, SuperRevo FT, and CrossFT (ConMed Linvatec, Largo, FL); Piton (Tornier, Warsaw, IN); Ti Screw, ALLthread PEEK, LactoScrew, ALLthread Ti, and ALLthread PEEK knotless (Biomet Sports Medicine, Warsaw, IN). Glenoid anchors included the Gryphon BR P (DePuy-Mitek, Raynham, MA) and JuggerKnot 1.4 (Biomet Sports Medicine). Results: Mean cortical failure loads for cuff anchors were as follows: Doubleplay 5.0, 279 N; Doubleplay 6.5, 338 N; Opus SpeedScrew 5.5, 356 N; Opus SpeedScrew 6.5, 336 N; PEEK Intraline 5.5, 263 N; PEEK Intraline 6.5, 344 N; PEEK Zip 5.5, 435 N; PEEK Zip 6.5, 502 N; Paladin 5.0, 500 N; Paladin 6.5, 521 N; SuperRevo FT, 496 N; CrossFT, 569 N; Piton, 379 N; Ti Screw 5.0, 457 N; Ti Screw 6.5, 443 N; ALLthread PEEK 5.5, 476 N; LactoScrew 5.5, 403 N; ALLthread Ti 5.0, 526 N; ALLthread Ti 6.5, 653 N; and ALLthread PEEK knotless, 441 N). Mean cortical failure loads for glenoid anchors were 161 N for Gryphon BR P and 239 N for JuggerKnot 1.4. Mean cancellous bone failure loads for cuff anchors were Doubleplay 5.0, 263 N; Doubleplay 6.5, 340 N; Opus SpeedScrew 5.5, 356 N; Opus SpeedScrew 6.5, 344 N; PEEK Intraline 5.5, 274 N; PEEK Intraline 6.5, 327 N; PEEK Zip 5.5, 401 N; PEEK Zip 6.5, 396 N; Paladin 5.0, 427 N; Paladin 6.5, 491 N; SuperRevo FT, 483 N; CrossFT, 547 N; Piton, 365 N; Ti Screw 5.0, 420 N; Ti Screw 6.5, 448 N; ALLthread PEEK 5.5, 475 N; LactoScrew 5.5, 435 N; ALLthread Ti 5.0, 512 N; ALLthread Ti 6.5, 612 N; and ALLthread PEEK knotless, 466 N). Mean cancellous failure loads for glenoid anchors were 117 N for Gryphon BR P and 194 N for JuggerKnot 1.4. None of the anchors had pullout as the predominant failure mode. Eyelet failure was the predominant failure mode for Doubleplay, Opus SpeedScrew, PEEK Intraline, Gryphon BR P, ALLthread Ti 6.5, ALLthread PEEK 5.5, and LactoScrew. Conclusions: Failure load was not dependent on anchor location (cancellous or cortical bone) (P = .58) but was dependent on anchor type (cuff anchor or glenoid anchor) (P < .001). Clinical Relevance: Whereas larger fully threaded screw anchors designed for rotator cuff repair showed higher failure strengths than smaller non-screw anchors designed for glenoid repairs (P < .05), the larger version of a screw anchor for a cuff repair did not provide a statistically greater failure load than the smaller screw anchor.
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    Comparative Testing by Cyclic Loading of Rotator Cuff Suture Anchors Containing Multiple High-Strength Sutures
    (W B Saunders Co-Elsevier Inc, 2010) Barber, F. Alan; Hapa, Onur; Bynum, James A.
    Purpose: To compare isolated medial-row with isolated lateral-row anchor performance by use of cyclic loading followed by destructive testing in an in vitro cadaveric model. Methods: Using 16 human cadaveric humeri without tendons, we rotated 4 medial-row (Bio-Corkscrew FT [Arthrex, Naples FL], CrossFT PK [ConMed Linvatec, Largo, FL], TwinFix PK FT [Smith & Nephew Endoscopy, Andover, MA], and Healix PK [DePuy Mitek, Raynham, MA]) and 4 lateral-row (PopLok PK [ConMed Linvatec], PEEK [polyetheretherketone] PushLock [Arthrex], Footprint PEEK [Smith & Nephew Endoscopy], and Versalok [DePuy Mitek]) anchors among different medial (articular cartilage edge) and lateral greater tuberosity sites (anterior, central, posterior). All medial anchors were inserted into the humeral head at an angle no greater than 45 degrees. All lateral anchors were inserted over the top, nearly planar to the superior humeral surface. After preloading, the constructs were cycled 500 times from 10 to 60 N at 1 Hz with the loads applied to the accompanying sutures. Those constructs surviving cycling were destructively tested. Cyclic displacement, ultimate load, and failure mode were recorded. Results: In this laboratory setting, most displacement occurred in the first 100 cycles except for the Footprint anchor. Lateral-row anchors had greater mean displacements (2.6 mm) than medial-row anchors (1.2 mm) at 100 cycles and between 100 and 500 cycles (1.8 mm v 0.75 mm). Lateral-row anchors also had more total displacement (4.4 mm) than medial-row anchors (1.9 mm). A 5-mm displacement gap, defined as failure, was not seen in the Bio-Corkscrew FT, TwinFix PK FT, and Versalok anchors. Ultimate failure loads ranged from 163 N (Footprint) to 308 N (Versalok) (P < .05). The principal failure mode was anchor pullout, followed by eyelet breakage. Medial-row eyelet failures only occurred after 500 cycles at loads higher than each anchor's mean failure load. Eyelet failure for lateral-row anchors occurred before 500 cycles and at failure loads lower than each anchor's mean. Conclusions: Lateral row anchors benefit from medial row anchors for their security, and because of design differences demonstrate more displacement. When lateral-row anchors fail at the eyelet, it is at lower failure loads, while if medial-row anchors fail at the eyelet, it is at higher loads. Clinical Relevance: Anchors designed to function as lateral-row fixation provide fixation strength inferior to that of medial-row anchors and are more likely to be subject to suture slippage.