Department of Orthopedic Surgery, Rush University Medical Center, Chicago, Illinois, USA.
Bone Joint J. 2020 Jul;102-B(7_Supple_B):33-40. doi: 10.1302/0301-620X.102B7.BJJ-2019-1678.R1.
The aim of this study was to develop a novel computational model for estimating head/stem taper mechanics during different simulated assembly conditions.
Finite element models of generic cobalt-chromium (CoCr) heads on a titanium stem taper were developed and driven using dynamic assembly loads collected from clinicians. To verify contact mechanics at the taper interface, comparisons of deformed microgroove characteristics (height and width of microgrooves) were made between model estimates with those measured from five retrieved implants. Additionally, these models were used to assess the role of assembly technique-one-hit versus three-hits-on the taper interlock mechanical behaviour.
The model compared well to deformed microgrooves from the retrieved implants, predicting changes in microgroove height (mean 1.1 μm (0.2 to 1.3)) and width (mean 7.5 μm (1.0 to 18.5)) within the range of measured changes in height (mean 1.4 μm (0.4 to 2.3); p = 0.109) and width (mean 12.0 μm (1.5 to 25.4); p = 0.470). Consistent with benchtop studies, our model found that increasing assembly load magnitude led to increased taper engagement, contact pressure, and permanent deformation of the stem taper microgrooves. Interestingly, our model found assemblies using three hits at low loads (4 kN) led to decreased taper engagement, contact pressures and microgroove deformations throughout the stem taper compared with tapers assembled with one hit at the same magnitude.
These findings suggest additional assembly hits at low loads lead to inferior taper interlock strength compared with one firm hit, which may be influenced by loading rate or material strain hardening. These unique models can estimate microgroove deformations representative of real contact mechanics seen on retrievals, which will enable us to better understand how both surgeon assembly techniques and implant design affect taper interlock strength. Cite this article: 2020;102-B(7 Supple B):33-40.
本研究旨在开发一种新的计算模型，以估计不同模拟装配条件下的头部/柄锥机械性能。
开发了通用钴铬（CoCr）头在钛柄锥上的有限元模型，并使用从临床医生收集的动态装配载荷进行驱动。为了验证锥面接口的接触力学，对模型估计值与从五个回收植入物测量的变形微槽特征（微槽高度和宽度）进行了比较。此外，还使用这些模型评估了装配技术（一击与三击）对锥面互锁机械性能的影响。
该模型与从回收植入物中得到的变形微槽吻合良好，预测了微槽高度（平均 1.1μm（0.2 至 1.3））和宽度（平均 7.5μm（1.0 至 18.5））的变化，变化范围与测量的微槽高度变化一致（平均 1.4μm（0.4 至 2.3）；p=0.109）和宽度（平均 12.0μm（1.5 至 25.4）；p=0.470）。与台式研究一致，我们的模型发现，增加装配载荷大小会导致锥面接合、接触压力和柄锥微槽的永久变形增加。有趣的是，我们的模型发现，在低载荷（4kN）下，使用三次撞击的装配比相同大小的单次撞击的装配在整个柄锥上导致的锥面接合、接触压力和微槽变形更小。
这些发现表明，与一次坚固的撞击相比，在低载荷下增加装配次数会导致锥面互锁强度降低，这可能受到加载速率或材料应变硬化的影响。这些独特的模型可以估计与实际回收中所见的真实接触力学相对应的微槽变形，这将使我们能够更好地理解手术医生的装配技术和植入物设计如何影响锥面互锁强度。
