Institute of Biomechanics, TUHH Hamburg University of Technology, Hamburg, Germany.
PLoS One. 2024 May 17;19(5):e0303682. doi: 10.1371/journal.pone.0303682. eCollection 2024.
The implantation of uncemented prostheses requires the application of sufficient forces to achieve a press-fit of the implant in the bone. Excessive forces have to be omitted to limit bone damage. Force measurements along the force transmission path between mallet and implant are frequently used to investigate this trade-off. Placing a load cell at a position of interest (PoI), which might be the implant bone interface or the head taper junction, is technically challenging or even impossible so that nearby positions are chosen. Thus, a certain inertia and stiffness remain between the PoI and the sensor, and consequently the measured dynamic forces differ from those at the PoI. This experimental and numerical study aimed to investigate the amount of force reduction along the transmission path while joining femoral heads to stem tapers. Forces were measured in vitro at the tip of the mallet, directly above the polymer tip of the impactor and below the stem taper. Springs and masses were used to represent the responding tissue of a patient. A semi-empirical numerical model of the force transmission path was developed and validated in order to simulate a larger range of responding tissue properties than experimentally possible and to investigate the influence of different surgical instruments. A distinct attenuation was observed since the peak forces at the impactor reached 35% of the applied peak forces and 21% at the stem taper, respectively. The force curves were replicated with a median root mean square error of 3.8% of the corresponding mallet blow for the impactor and 3.6% for the stem. The force measurement position and the used surgical instruments have a strong influence on the measured forces. Consequently, the exact measurement conditions with regard to sensor positioning and used surgical instruments have to be specified and hence only studies with similar setups should be compared to avoid misestimation of the forces at the PoI. The proposed dynamic numerical model is a useful tool to calculate the impact of the chosen or changed mechanical parameters prior to executing experiments and also to extrapolate the effect of changing the applied forces to the resulting forces at the PoI.
骨水泥型假体的植入需要施加足够的力以实现假体与骨之间的压配。为了限制骨损伤，必须避免过大的力。因此，人们经常沿力传递路径在感兴趣的位置（PoI）测量力，该位置可能是假体与骨的界面或头部锥度连接点。然而，在这些位置安装力传感器在技术上具有挑战性，甚至是不可能的，因此选择了附近的位置。因此，在 PoI 和传感器之间仍然存在一定的惯性和刚度，并且所测量的动态力与 PoI 处的力不同。本实验和数值研究旨在研究在将股骨头连接到柄锥时沿传递路径的力减小量。在体外，在冲击锤的尖端、冲击器聚合物尖端的正上方和柄锥下方测量力。使用弹簧和质量来代表患者的反应组织。开发并验证了力传递路径的半经验数值模型，以便模拟比实验可能的更大范围的反应组织特性，并研究不同手术器械的影响。由于冲击器上的峰值力达到施加的峰值力的 35%，而在柄锥处则达到 21%，因此观察到明显的衰减。力曲线的复制中位数均方根误差为冲击器对应锤击的 3.8%，柄锥为 3.6%。力测量位置和使用的手术器械对测量力有很大影响。因此，必须指定传感器定位和使用的手术器械的精确测量条件，因此，只有具有相似设置的研究才能进行比较，以避免对 PoI 处的力产生错误估计。所提出的动态数值模型是在执行实验之前计算所选或更改的机械参数的影响以及推断施加力的变化对 PoI 处的结果力的有用工具。
