School of Mechanical Medical and Process Engineering, Queensland University of Technology, Gardens Point Campus, P'Block, Level 7, Room 717, Brisbane, QLD, 4000, Australia.
Medical Devices Research Institute, College of Science and Engineering, Flinders University, Adelaide, SA, Australia.
J Orthop Surg Res. 2024 Mar 12;19(1):180. doi: 10.1186/s13018-024-04652-9.
Reverse Shoulder Arthroplasties (RSA) have become a primary choice for improving shoulder function and pain. However, the biomechanical failure mechanism of the humeral component is still unclear. The present study reports a novel protocol for microstructural imaging of the entire humerus implant under load before and after fracture.
A humerus specimen was obtained from a 75-year-old male donor. An expert surgeon implanted the specimen with a commonly used RSA implant (Aequalis reversed II, Stryker Orthopaedics, USA) and surgical procedure. The physiological glenohumeral contact force that maximized the distal implant migration was selected from a public repository ( orthoload.com ). Imaging and concomitant mechanical testing were performed using a large-volume micro-CT scanner (Nikon XT H 225 ST) and a custom-made compressive stage. Both when intact and once implanted, the specimen was tested under a pre-load and by imposing a constant deformation causing a physiological reaction load (650 N, 10 degrees adducted). The deformation of the implanted specimen was then increased up to fracture, which was identified by a sudden drop of the reaction force, and the specimen was then re-scanned.
The specimen's stiffness decreased from 874 N/mm to 464 N/mm after implantation, producing movements of the bone-implant interface consistent with the implant's long-term stability reported in the literature. The micro-CT images displayed fracture of the tuberosity, caused by a combined compression and circumferential tension, induced by the distal migration of the implant.
The developed protocol offers detailed information on implant mechanics under load relative to intact conditions and fracture, providing insights into the failure mechanics of RSA implants. This protocol can be used to inform future implant design and surgical technique improvements.
反肩置换术（RSA）已成为改善肩部功能和缓解疼痛的主要选择。然而，肱骨部件的生物力学失效机制仍不清楚。本研究报告了一种新颖的协议，用于在骨折前后在负载下对整个肱骨植入物进行微观结构成像。
从一名 75 岁男性供体中获得肱骨标本。一位专家外科医生使用一种常用的 RSA 植入物（Aequalis 反 II，Stryker Orthopaedics，美国）和手术程序植入标本。从公共存储库（orthoload.com）中选择最大程度地增加远端植入物迁移的生理盂肱接触力。使用大容量微 CT 扫描仪（尼康 XT H 225 ST）和定制的压缩台进行成像和伴随的机械测试。在完整状态和植入状态下，标本均在预载下进行测试，并施加导致生理反应负载的恒定变形（650 N，10 度内收）。然后将植入物标本的变形增加到骨折，通过突然降低反作用力来识别骨折，然后对标本进行重新扫描。
植入后标本的刚度从 874 N/mm 降低到 464 N/mm，产生了与文献中报道的植入物长期稳定性一致的骨-植入物界面运动。微 CT 图像显示了由于植入物远端迁移引起的压缩和周向张力联合作用导致的结节骨折。
所开发的协议提供了有关植入物在负载下相对于完整状态和骨折的力学的详细信息，为 RSA 植入物的失效力学提供了深入了解。该协议可用于为未来的植入物设计和手术技术改进提供信息。
