Razfar Najmeh, Reeves Jacob M, Langohr Daniel G, Willing Ryan, Athwal George S, Johnson James A
Department of Biomedical Engineering, Western University, London, ON, Canada; Roth|McFarlane Hand and Upper Limb Centre, St. Joseph's Health Centre, London, ON, Canada; Department of Mechanical Engineering, Western University, London, ON, Canada.
Roth|McFarlane Hand and Upper Limb Centre, St. Joseph's Health Centre, London, ON, Canada; Department of Mechanical Engineering, Western University, London, ON, Canada.
J Shoulder Elbow Surg. 2016 Jul;25(7):1076-83. doi: 10.1016/j.jse.2015.11.011. Epub 2016 Jan 22.
The stem lengths of humeral components used in shoulder arthroplasty vary; however, the literature on these devices is limited. This finite element study investigates the effect of humeral component length on stresses in the proximal humerus.
Intact and 3 reconstructed (standard length, short, and stemless implants) finite element models were created from shoulder computed tomography scan data (N = 5). Loading was simulated at varying abduction angles (15°, 45°, and 75°). The average bone stress (represented as a percentage of intact values) was reported at 8 transverse slices. In addition, the overall average change in cortical and trabecular bone stresses was quantified.
Cortical bone stresses in the most proximal slice for the standard (58% ± 12%) and short (78% ± 10%) stem models were significantly reduced compared with the intact (100%) and stemless (101% ± 6%) models (P = .005). These reductions persisted in the second cortical slice for the standard stem compared with the intact, stemless, and short models (P = .025). Interestingly, stresses in the trabecular bone within these proximal slices were significantly elevated when stemless implants were used compared with all other implants (P < .001), regardless of abduction angle.
Reducing stem length produced humeral stresses that more closely matched the intact stress distribution in proximal cortical bone. Opposing trends presented in the proximal trabecular bone, probably because of differences in load transfer when shorter stems are used. Accordingly, the results suggest that implant stem length is 1 variable that can be modified in an attempt to better mimic intact bone stresses during humeral component insertion, provided stem fixation is adequate.
肩关节置换术中使用的肱骨假体柄长度各异，但关于这些假体的文献有限。本有限元研究探讨了肱骨假体柄长度对肱骨近端应力的影响。
利用肩部计算机断层扫描数据（N = 5）创建完整的和3个重建的（标准长度、短柄和无柄假体）有限元模型。在不同外展角度（15°、45°和75°）下模拟加载。报告8个横向切片处的平均骨应力（以完整值的百分比表示）。此外，对皮质骨和小梁骨应力的总体平均变化进行了量化。
与完整模型（100%）和无柄模型（101%±6%）相比，标准柄（58%±12%）和短柄（78%±10%）模型最近端切片处的皮质骨应力显著降低（P = 0.005）。与完整模型、无柄模型和短柄模型相比，标准柄模型第二个皮质切片处的应力持续降低（P = 0.025）。有趣的是，无论外展角度如何，使用无柄假体时，这些近端切片内小梁骨的应力与所有其他假体相比均显著升高（P < 0.001）。
缩短假体柄长度会使肱骨应力更接近近端皮质骨的完整应力分布。近端小梁骨呈现相反趋势，可能是因为使用较短假体柄时载荷传递存在差异。因此，结果表明，在假体柄固定充分的情况下，假体柄长度是一个可以调整的变量，旨在肱骨假体植入过程中更好地模拟完整骨应力。
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