Abstract
The recent reverse total shoulder arthroplasty (TSA) implant designs employ shorter humeral component stems; some designs even eliminate the stem completely. The short stem provides several advantages: preserved bone, less stress shielding, ease of revision surgery, and freedom of humeral component location due to the minimal stem length and non-complex shape. However, due to the reduction in contact surface and frictional fixation, this stemless design may cause failure of the implant, especially during early stages following surgery. In this study, the effect of fin shape and fin length of stemless humeral components were investigated, and hypothesis was that stress and micromotion would decrease as the ratio of fin length to baseplate radius increases and the overall size of the humerus component increased. 15 different 3D models of stemless humeral components, 5 different lengths and 3 different shapes, within reverse TSA systems were developed. Each humerus component was analyzed using finite element analysis (FEA) to investigate the effects of stem length and fin shape on the initial stability of the component. The highest stress and micromotion were observed at the shortest fin length; lowest stress and micromotion were found at the longest fin length. Results suggest that the length of the fin affects the stress at the bone as well as the amount of micromotion; 20–30% longer fin length than baseplate radius would be ideal for the stemless humeral component design. However, the various fin shapes showed mixed effects on the results and further investigation is required.
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This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), which is funded by the Ministry of Education (NRF-2017R1D1A3B04033410).
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Tae Soo Bae is an Associate Professor in the Department of Biomedical Engineering, Jungwon University in Korea. His research interests include musculoskeletal dynamics and surgical navigation in orthopedic & rehabilitation research and other physics-based simulations related to biomedical devices.
Erin E. Ritzer is a former B.S. student in Biomedical Engineering at Robert Morris University. Her research interests include orthopedic biomechanics and computer simulations. Currently she is a student at LECOM Medical School, FL, USA.
Woong Cho is a Ph.D. candidate in Mechanical Engineering Department, Korea University. His interest is mechanical engineering design, motion analysis and medical device.
Won Joo is an Associate Professor in the Department of Engineering at Robert Morris University in PA, USA. His research interests include musculoskeletal biomechanics, damage and fracture mechanics of solid, orthopedic implant, and additive manufacturing of medical devices.
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Bae, T.S., Ritzer, E.E., Cho, W. et al. Effect of fin length and shape of stemless humeral components in a reverse shoulder implant system: a FEA study. J Mech Sci Technol 35, 417–422 (2021). https://doi.org/10.1007/s12206-020-1241-x
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DOI: https://doi.org/10.1007/s12206-020-1241-x