Lacroix D, Murphy L A, Prendergast P J
Department of Mechanical Engineering, Trinity College, Dublin, Ireland.
J Biomech Eng. 2000 Aug;122(4):430-6. doi: 10.1115/1.1286318.
Glenoid component loosening is the dominant cause of failure in total shoulder arthroplasty. It is presumed that loosening in the glenoid is caused by high stresses in the cement layer. Several anchorage systems have been designed with the aim of reducing the loosening rate, the two major categories being "keeled" fixation and "pegged" fixation. However, no three-dimensional finite element analysis has been performed to quantify the stresses in the cement or to compare the different glenoid prosthesis anchorage systems. The objective of this study was to determine the stresses in the cement layer and surrounding bone for glenoid replacement components. A three-dimensional model of the scapula was generated using CT data for geometry and material property definition. Keeled and pegged designs were inserted into the glenoid, surrounded by a 1-mm layer of bone cement. A 90 deg arm abduction load with a full muscle and joint load was applied, following van der Helm (1994). Deformations of the prosthesis, stresses in the cement, and stresses in the bone were calculated. Stresses were also calculated for a simulated case of rheumatoid arthritis (RA) in which bone properties were modified to reflect that condition. A maximum principal stress-based failure model was used to predict what quantity of the cement is at risk of failure at the levels of stress computed. The prediction is that 94 percent (pegged prosthesis) and 68 percent (keeled prosthesis) of the cement has a greater than 95 percent probability of survival in normal bone. In RA bone, however, the situation is reversed where 86 percent (pegged prosthesis) and 99 percent (keeled prosthesis) of the cement has a greater than 95 percent probability of survival. Bone stresses are shown to be not much affected by the prosthesis design, except at the tip of the central peg or keel. It is concluded that a "pegged" anchorage system is superior for normal bone, whereas a "keeled" anchorage system is superior for RA bone.
肩胛盂组件松动是全肩关节置换术失败的主要原因。据推测，肩胛盂的松动是由骨水泥层中的高应力引起的。为了降低松动率，已经设计了几种锚固系统，主要分为“带龙骨”固定和“带栓”固定两类。然而，尚未进行三维有限元分析来量化骨水泥中的应力或比较不同的肩胛盂假体锚固系统。本研究的目的是确定肩胛盂置换组件骨水泥层及周围骨骼中的应力。利用CT数据生成肩胛骨的三维模型，用于定义几何形状和材料属性。将带龙骨和带栓设计的假体植入肩胛盂，周围有一层1毫米厚的骨水泥。按照范德·赫尔姆（1994年）的方法，施加90度手臂外展负荷，并施加完整的肌肉和关节负荷。计算假体的变形、骨水泥中的应力和骨骼中的应力。还针对类风湿性关节炎（RA）的模拟病例计算了应力，其中修改了骨骼属性以反映该病症。使用基于最大主应力的失效模型来预测在计算的应力水平下有多少骨水泥有失效风险。预测结果是，在正常骨骼中，94%（带栓假体）和68%（带龙骨假体）的骨水泥有超过95%的存活概率。然而，在RA骨骼中，情况相反，86%（带栓假体）和99%（带龙骨假体）的骨水泥有超过95%的存活概率。除了在中央栓或龙骨的尖端外，骨骼应力显示受假体设计的影响不大。结论是，“带栓”锚固系统在正常骨骼中更具优势，而“带龙骨”锚固系统在RA骨骼中更具优势。
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