Lee Winson C C, Doocey Jacinta M, Brånemark Rickard, Adam Clayton J, Evans John H, Pearcy Mark J, Frossard Laurent A
School of Engineering Systems, Queensland University of Technology, Brisbane, Australia.
Clin Biomech (Bristol). 2008 Dec;23(10):1243-50. doi: 10.1016/j.clinbiomech.2008.06.012. Epub 2008 Sep 21.
The direct anchorage of lower-limb prosthesis to the bone has been shown to be an excellent alternative for amputees experiencing complications in using a conventional prosthetic socket. During rehabilitation phase, amputees are asked to apply static loading on the abutment perpendicular to a weigh scale to prepare the bone to tolerate the forces likely to be developed during walking. The weigh scale measures only the vertical force. A different loading protocol can affect the bone-implant interface stresses and the outcome of the rehabilitation.
This study developed a Finite Element model to study the stresses in the bone adjacent to the implant. Three loading conditions were applied based on the experimentally measured load: (1) vertical force applied along the long axis of the limb, corresponding to the load clinically prescribed in the weight bearing exercise; (2) loads applied on the three axes, corresponding to the "true" load measured simultaneously by a tri-axial load transducer during the same exercise; and (3) loads experienced during independent walking.
The model revealed that the weigh scale might in fact be applying much higher and less uniform stresses on the bone than expected. During walking, high stress occurred at various locations of the implanted region, which was different from the patterns of stress distribution during weight bearing exercises.
The difference in stress among three loading conditions implies that tri-axial load should be monitored during the weight bearing exercises and carefully prescribed.
对于在使用传统假肢接受腔时出现并发症的截肢者，下肢假肢直接与骨骼固定已被证明是一种极佳的替代方案。在康复阶段，要求截肢者在与体重秤垂直的基台上施加静态负荷，以使骨骼适应行走过程中可能产生的力量。体重秤仅测量垂直力。不同的负荷方案会影响骨植入物界面应力以及康复效果。
本研究建立了一个有限元模型来研究植入物附近骨骼中的应力。基于实验测量的负荷施加了三种负荷条件：(1) 沿肢体长轴施加垂直力，对应于负重锻炼中临床规定的负荷；(2) 在三个轴上施加负荷，对应于在同一项锻炼中由三轴负荷传感器同时测量的“真实”负荷；(3) 独立行走时承受的负荷。
该模型显示，体重秤实际上可能在骨骼上施加比预期更高且更不均匀的应力。在行走过程中，植入区域的不同位置会出现高应力，这与负重锻炼期间的应力分布模式不同。
三种负荷条件下的应力差异表明，在负重锻炼期间应监测三轴负荷并谨慎规定。
