Biomechanical Stability of Knotless Suture Anchors Used in Rotator Cuff Repair in Healthy and Osteopenic Bone

Purpose: The primary stability of 5 new knotless suture anchors was compared in healthy and osteopenic humeri by use of the following anchor systems: Opus Magnum 2 (ArthroCare, Austin, TX), PushLock (Arthrex, Naples, FL), SwiveLock (Arthrex), Kinsa RC (Smith & Nephew, London, England), and Versalok (DePuy Mitek, Raynham, MA). Methods: Twenty healthy and 20 osteopenic, macroscopically intact humeri with mean ages of 47 and 72 years, respectively, and mean bone mineral densities of 139.8 mg of calcium hydroxyapatite (Ca2+-HA) per milliliter and 51.8 mg of calcium hydroxyapatite per milliliter, respectively, were used. Cyclic loading was performed to simulate postoperative conditions. The maximum failure load (F-max), the system displacement, and the modes of failure were recorded. Results: SwiveLock had the highest mean Fmax in healthy humeri, followed by Versalok, PushLock, Kinsa RC, and Opus Magnum 2, with SwiveLock and Versalok being statistically superior to Opus Magnum 2. In osteopenic humeri Versalok had the highest mean F-max, followed by Opus Magnum 2, SwiveLock, Kinsa RC, and PushLock, with no significant differences between all tested anchors. The Versalok anchor showed the shortest system displacement in healthy humeri, with 1.06 mm, and in osteopenic humeri, with 1.47 mm. In healthy humeri the system displacement of all anchors lay under the clinical failure threshold of 5 mm. In osteopenic humeri the PushLock clearly exceeded the clinical failure threshold, with 16.11 mm, whereas the other anchors were notably below the 5-mm threshold, with solitary measurements exceeding it. Conclusions: Every tested anchor presented different problems that may lead to premature failure of the rotator cuff reconstruction. Knotless suture anchors show differences in primary stability depending on the bone quality of the greater tuberosity, the anchorage mechanism in the bone, the suture-retaining mechanism, and the anchor design. Nevertheless, cortical screw type and subcortical wedging anchors tend to show better primary stability than other designs. Clinical Relevance: Anchor design and bone quality play important roles in the stability of the rotator cuff repair.