Beulah Pearline, Sivarasu Sudesh, Mathew Lazar
School of Biosciences and Technology, Vellore Institute of Technology University, Vellore, India.
J Long Term Eff Med Implants. 2009;19(4):271-8. doi: 10.1615/jlongtermeffmedimplants.v19.i4.40.
The major causes for revision surgery after total hip arthroplasty are aseptic loosening, dislocation, wear, design factors, stress shielding on the bone, and mechanical and biological factors. A material with toughness and high wear properties is essential for a good hip implant because these implants fail due to design. Stress shielding is found to be the major cause for the failure of hip implants, and can lead to the implant needing to be replaced or revised, which is painful for the patient and costly for the health care industry. The hip stem designs developed by various manufacturers are solid stems with indentations; stems with collars; collarless, tapered stems; and teardrop-shaped, polished stems without indentations. They are found to have a greater rigidity, and therefore they transfer less load proximally, which results in high proximal stress shielding of the proximal femur. A stem of low stiffness alone would not suffice in achieving a reduced or optimal stress shielding. The existing design proposals to minimize the effect of stress shielding are focused on the use of lightweight materials, composite materials, circular and longitudinal hole patterns, and different hollow-bore depths. A skeletal hip implant with varying cross-sections was designed and finite-element analysis was performed. The skeletal hip implant with a hexagonal cross-section was optimized based on the mass of the implant and the load-bearing capacity. This lightweight, novel design ameliorates implant fixation, minimizes stress shielding, enhances the longevity of the implant, and offers better mobility to the patient.
全髋关节置换术后翻修手术的主要原因包括无菌性松动、脱位、磨损、设计因素、骨应力遮挡以及机械和生物学因素。对于优质的髋关节植入物而言，具有韧性和高耐磨性能的材料至关重要，因为这些植入物可能因设计问题而失效。应力遮挡被发现是髋关节植入物失败的主要原因，可能导致植入物需要更换或翻修，这对患者来说很痛苦，对医疗行业来说成本也很高。各制造商开发的髋关节柄设计包括带凹痕的实心柄、带颈圈的柄、无颈圈的锥形柄以及无凹痕的泪滴形抛光柄。这些设计被发现具有更高的刚性，因此它们向近端传递的负荷较小，这导致股骨近端出现高度的近端应力遮挡。仅使用低刚度的柄不足以实现降低或优化应力遮挡的效果。现有的旨在最小化应力遮挡影响的设计方案主要集中在使用轻质材料、复合材料、圆形和纵向孔图案以及不同的空心孔深度。设计了一种具有不同横截面的骨骼式髋关节植入物并进行了有限元分析。基于植入物的质量和承重能力对具有六边形横截面的骨骼式髋关节植入物进行了优化。这种轻质的新颖设计改善了植入物的固定，最小化了应力遮挡，提高了植入物的使用寿命，并为患者提供了更好的活动能力。
