The interrelation of trabecular microstructural parameters of the greater tubercle measured for different species.

In the present study the trabecular microstructural parameters (bone volume fraction, trabecular thickness, trabecular separation, trabecular number, connectivity density, degree of anisotropy, and structure model index) of the greater tubercle of the humeral head were measured for human healthy, human osteopenic, ovine, bovine, and porcine bones using micro-computed tomography. Except for trabecular thickness and degree of anisotropy the values of the trabecular microstructural parameters generally differed significantly between species. Thus, only the species for which the implant is designed should be used for in vitro mechanical tests on the stability of implants in trabecular bone. Multivariate regression analysis showed that the microstructural parameters have similar principal interrelations in all species. The most significant relations were found between trabecular thickness and bone volume fraction (median (over all species) p < 0.001), trabecular number and bone volume fraction (p = 0.001), the structural change from plates to rods and bone volume fraction (p < 0.001) as well as between connectivity density and trabecular number (p < 0.001). Trabecular thickness, trabecular number, and the structural change from plates to rods each contributed to the bone volume fraction approximately to the same extent. Based on the similar principal interrelations of the trabecular microstructural parameters found in all investigated species the design of trabecular microstructure in the greater tubercle follows similar phenomenological mechanisms in all species. Thus, in vivo experiments on trabecular bone healing and osteoporosis research for application in humans can be conducted in ovine, bovine, or porcine species.

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 F(max) 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.