单髁置换股骨假体不同放置位置的生物力学效应

Biomechanical effects of different placement of femoral prosthesis in unicompartmental knee arthroplasty

背景:单髁置换手术的高翻修率是亟待解决的问题,翻修原因多为假体松动、聚乙烯磨损和健侧间室关节炎进展等术后并发症,而上述并发症与假体对位不良引起的关节内应力异常密切相关。目的:研究内侧固定平台单髁置换过程中股骨假体不同内外翻角度对聚乙烯上表面、外侧间室软骨表面及胫骨假体下松质骨表面应力大小和分布的影响。方法:利用放射学技术和三维扫描技术获得膝关节和单髁假体的数字化影像,通过mimics、Ansys workbench等软件建立正常膝关节模型并验证其有效性。在Ansys workbench软件中模拟单髁置换手术,将假体进行适当定位,并改变股骨假体位置,建立股骨假体内、外翻0°,3°,6°,9°,12°共9种工况,观察各工况中聚乙烯上表面、外侧间室软骨表面及胫骨假体下松质骨表面应力大小和分布的变化规律。结果与结论:(1)在膝关节伸直位静态载荷下,聚乙烯上表面的应力随假体内外翻角度的增大而增大,外翻时的增幅更大;聚乙烯上表面的应力分布在内翻时向内移,在外翻时向外移;(2)外侧间室软骨表面的应力在内翻时增大、外翻时减小;(3)胫骨假体下松质骨表面的应力集中在沟槽中,内外翻时应力均增大,外翻时的增幅更大;(4)从内翻到外翻的过程中载荷逐渐向内侧间室转移;(5)各结构中聚乙烯上表面的应力最大,其中股骨假体内、外翻≥6°的应力值显著高于标准位置(内、外翻0°)。

BACKGROUND:Most of the revision causes of unicompartmental knee arthroplasty are postoperative complications,such as prosthesis loosening,polyethylene wear and progression of uninvolved compartment arthritis,which are linked to the abnormal intra-articular stress caused by the malposition of the prosthesis.OBJECTIVE:To study the effects of different positions of the femoral prosthesis on the stress magnitude and distribution of polyethylene surface,articular cartilage surface,and cancellous bone surface during unicompartmental knee arthroplasty.METHODS:The digital image of the knee joint and prosthesis was obtained using radiological technologies and three-dimensional scanning techniques.A normal knee model was developed and validated using mimics and Ansys workbench software.Unicompartmental knee arthroplasty was simulated in Ansys Workbench software.The prosthesis was positioned appropriately and the femoral prosthesis was requisitioned.Nine working conditions were established at the 0°,3°,6°,9°,and 12°of femoral prosthesis varus and valgus to observe the changes in stress and distribution of polyethylene surface,articular cartilage surface and cancellous bone surface in each model.RESULTS AND CONCLUSION:(1)The stress on the upper surface of polyethylene increased with the increase of the valgus and varus angle in the prosthesis under static load of knee joint extension,and the increase range was large during valgus.The stress distribution on the upper surface of polyethylene shifts was inward during varus and outward during valgus.(2)The stress on the articular cartilage surface increased during varus and decreased during valgus.(3)The stress on the surface of cancellous bone was concentrated in the grooves,and the stress was increased during valgus and varus,and greater during valgus.(4)As move from varus to valgus,the load shifted to the medial side of the knee.(5)Among all the structures,the stress on the upper surface of polyethylene prosthesis was the highest,and the stress value at≥6°of valgus and valgus of femoral prosthesis was significantly higher than that at the standard position(0°valgus and valgus).