Comparative testing by cyclic loading of rotator cuff suture anchors containing multiple high-strength sutures

Abstract

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.