University of Southampton, Southampton, UK.
J Biomech. 2012 Feb 23;45(4):719-23. doi: 10.1016/j.jbiomech.2011.11.042. Epub 2012 Jan 10.
Acetabular cup loosening is a late failure mode of total hip replacements, and peri-prosthetic bone deterioration may promote earlier failure. Preservation of supporting bone quality is a goal for implant design and materials selection, to avoid stress shielding and bone resorption. Advanced polymer composite materials have closer stiffness to bone than metals, ceramics or polymers, and have been hypothesised to promote less adverse bone adaptation. Computer simulations have supported this hypothesis, and the present study aimed to verify this experimentally. A composite hemi-pelvis was implanted with Cobalt Chromium (CoCr), polyethylene (UHMWPE) and MOTIS(®)carbon-fibre-reinforced polyether etherketone (CFR-PEEK) acetabular cups. In each case, load was applied to the implanted pelvis and Digital Image Correlation (DIC) was used for surface strain measurement. The test was repeated for an intact hemi-pelvis. Trends in implanted vs. intact bone principal strains were inspected to assess the average principal strain magnitude change, allowing comparison of the potential bone responses to implantation with the three cups. The CFR-PEEK cup was observed to produce the closest bone strain to the intact hip in the main load path, the superior peri-acetabular cortex (+12% on average, R(2)=0.84), in comparison to CoCr (+40%, R(2)=0.91) and UHWMPE cups (-26%, R(2)=0.94). Clinical observations have indicated that increased periacetabular cortex loading may result in reduced polar cancellous bone loading, leading to longer term losses in periprosthetic bone mineral density. This study provides experimental evidence to verify previous computational studies, indicating that cups produced using materials with stiffness closer to cortical bone recreate physiological cortical bone strains more closely and could, therefore, potentially promote less adverse bone adaptation than stiffer press-fitted implants in current use.
髋臼杯松动是全髋关节置换术的晚期失效模式，而假体周围骨恶化可能会导致更早的失效。保持支撑骨的质量是植入物设计和材料选择的目标，以避免应力屏蔽和骨吸收。先进的聚合物复合材料的刚度比金属、陶瓷或聚合物更接近骨骼，并且假设它们可以促进较少的不利骨骼适应。计算机模拟支持了这一假设，本研究旨在通过实验验证这一假设。用钴铬（CoCr）、超高分子量聚乙烯（UHMWPE）和 MOTIS(®)碳纤维增强聚醚醚酮（CFR-PEEK）髋臼杯植入复合半骨盆。在每种情况下，都将载荷施加到植入的骨盆上，并使用数字图像相关（DIC）进行表面应变测量。重复测试完整的半骨盆。检查植入骨与完整骨主应变之间的趋势，以评估平均主应变幅度的变化，从而比较三种髋臼杯植入物对骨骼的潜在反应。与 CoCr（+40%，R(2)=0.91）和 UHMWPE 杯（-26%，R(2)=0.94）相比，CFR-PEEK 杯在主要载荷路径中观察到与完整髋关节最接近的骨应变，即髋臼周围上皮质（平均+12%，R(2)=0.84）。临床观察表明，增加髋臼周围皮质的负荷可能导致极皮质骨负荷减少，从而导致假体周围骨矿物质密度的长期损失。本研究提供了实验证据，验证了先前的计算研究，表明使用与皮质骨刚度更接近的材料制造的髋臼杯更能重现生理皮质骨应变，因此可能比目前使用的刚度更大的压配合植入物更能促进较少的不利骨骼适应。
