Completo A, Pereira J, Fonseca F, Ramos A, Relvas C, Simões J
Mechanical Engineering Department, University of Aveiro, Portugal.
Clin Biomech (Bristol). 2011 Dec;26(10):990-7. doi: 10.1016/j.clinbiomech.2011.06.008. Epub 2011 Jul 8.
Numerous models of elbow prostheses are being used and can be divided into two categories: one being a semi-constrained, linked type; and the other being non-constrained, unlinked type. Recent reports of National Elbow Arthroplasty Registers reveal no significant differences in the survival rates between linked and unlinked prosthesis brands, and the main cause appointed for revision for both types is loosening. Some previous biomechanical studies confirm the presence of abnormal bone stresses for the linked type, which can be associated with the risk of loosening. However for the unlinked type, biomechanical studies are not available that corroborate a loosening risk. It seems, that issue has not yet been fully answered and requires further analysis.
Cortex strains adjacent to the elbow joint were measured with strain gauges in synthetic humeri and ulnae, before and after replacement. To assess cancellous bone strains and cement stresses around the implant finite element models validated relative to measured strains were used.
Bone strains adjacent to the implant tip increased several times in the humerus and ulna. At the epiphyseal regions a generalised cancellous bone strain reduction was observed for both humerus and ulna relatively to the intact bones.
The unlinked elbow prostheses can be associated with the risk of bone fatigue failure by overload, particularly in the ulna, and bone resorption by stress-shielding at the epiphyseal regions. The identical structural behaviour relative to linked prostheses associated with the same loosening risks corroborates the results of recent arthroplasty published register reports.
目前正在使用多种类型的肘关节假体，可分为两类：一类是半限制型、链式假体；另一类是非限制型、非链式假体。国家肘关节置换登记处最近的报告显示，链式和非链式假体品牌的生存率没有显著差异，两种类型假体翻修的主要原因都是松动。此前的一些生物力学研究证实，链式假体存在异常骨应力，这可能与松动风险有关。然而，对于非链式假体，尚无生物力学研究证实其存在松动风险。看来，这个问题尚未得到充分解答，需要进一步分析。
在置换前后，用应变片测量合成肱骨和尺骨中肘关节附近的皮质骨应变。为了评估植入物周围的松质骨应变和骨水泥应力，使用了相对于测量应变进行验证的有限元模型。
植入物尖端附近的肱骨和尺骨骨应变增加了几倍。在骨骺区域，相对于完整骨骼，肱骨和尺骨的松质骨应变普遍降低。
非链式肘关节假体可能与因过载导致的骨疲劳失效风险相关，尤其是在尺骨，以及骨骺区域因应力遮挡导致的骨吸收风险相关。与链式假体相同的结构行为以及相同的松动风险证实了最近关节置换登记报告的结果。
