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Purpose: To investigate the metal screw-in anchor failure mode and load to failure for 2 different eyelet alignments after anchor insertion in ovine humeri. Methods: Sixteen ovine humeri were dissected, and a 5-mm metal anchor with 2 nonabsorbable polyblend polyethylene sutures was inserted into them in the proximal position of the greater tuberosity. The alignment of the anchors after insertion was adjusted to make 2 test groups, each with 8 specimens: In group 1, the anchor eyelets were malpositioned, whereas in group 2, the anchor eyelets were aligned according to the manufacturer's instructions. After insertion, cyclic tests from 10 N to 180 N were performed with a frequency of 1 Hz for 200 cycles; specimens were then loaded to failure to evaluate the maximum load of the system and observe the associated failure mode. Results: The mean ultimate failure load in group 2 was not significantly different from that in group 1 (P ¼ .472). Conclusions: For metallic screw-in suture anchors, the alignment of the eyelet does not change the failure mode and the load to failure after cyclic loading of the bone-anchor-suture system in ovine humeri. Clinical Relevance: Our results indicate that on the basis of this anchor model, the position of the eyelet in the greater tuberosity does not interfere directly with the biomechanical performance of the system.
Objective: The aim of this study was to develop and evaluate a new benchtop test method to measure the potential migration of intervertebral body fusion devices (IBFDs) of different designs. Methods: A new benchtop test method was proposed to evaluate the migration resistance of intervertebral cages under cyclic loads, which is based on movements and flexion-extension loads experienced by the lumbar spine. The IBFD migration behavior under four test setups was investigated by controlled replicates of the test combining two loading configurations and two foam block densities for the bone substitute material. Additionally, the use of two distinct displacement measurement systems, one optical (OptiTrack) and another involving contact (linear variable differential transformer [LVDT]), was evaluated to measure the posterior-anterior movement of the IBFD during testing. Results: The results obtained by applying the new benchtop method indicate that the different test setups can influence the direction and magnitude of the resulting migration of the intervertebral cages, while the two measurement systems provided similar results. Conclusions: The proposed benchtop methodology is able to perform evaluation of IBFD. The use of foam block grade 15 and a test setup with eccentric anterior positioning results in migrations measurable using LVDT or OptiTrack, allowing comparisons between different IBFD designs. The method could be improved to more accurately mimic the movements that cause the migration of IBFD.
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