Bobyn J D, Mortimer E S, Glassman A H, Engh C A, Miller J E, Brooks C E
Montreal General Hospital, Quebec, Canada.
Clin Orthop Relat Res. 1992 Jan(274):79-96.
Experimental canine model studies of stiff versus flexible, fully porous-coated, metallic femoral stems (differing by three- to fivefold in stiffness characteristics) revealed markedly different resorptive bone remodeling patterns. The flexible stem resulted in about 30% more cortical bone retention adjacent to the implant at one-year postimplantation and larger differences in dogs killed two and three years after surgery. Strain-gauge studies confirmed that there are differences in cortical bone strains with the two stem designs, the flexible stem producing a more uniform and more nearly normal strain distribution medially. Differences in cortical bone remodeling were quantified using dual energy X-ray absorptiometry (DEXA). The bone mineral content in femora with the flexible stem decreased less than 20%, compared to normal. At three years postimplantation, the bone mineral content of the femora with the stiff stem was about 50% that of the femora with the flexible stem. Clinically, DEXA revealed that 5%-15% changes in bone mineral density at various periimplant sites were common within the first two years after surgery; these changes were not usually evident roentgenographically. Serial roentgenographically distinct bone resorption was usually associated with bone mineral density changes of 20%-50%. Five- to 13-year roentgenographic follow-up observations of 213 cases with the Anatomic Medullary Locking prosthesis showed that pronounced bone resorption occurred in 33% of patients. Larger stems (greater than 13 mm in diameter) and stems with extensive porous coating had a significantly higher incidence of pronounced bone resorption than smaller stems and those with proximal coating. The stiffness characteristics of the human femur were established as a function of canal size and compared with those of noncemented hip prostheses. Increased mechanical compatibility was found for stems made of titanium alloy and with design features that reduce cross-sectional area and moment of inertia. Clinical data suggest that to reduce the likelihood of pronounced bone resorption, it would be beneficial for the implant to possess a bending stiffness of about one half to one third that of the human femur.
对刚性与柔性、全多孔涂层金属股骨柄（刚度特性相差三到五倍）进行的犬类实验模型研究显示，骨吸收重塑模式明显不同。柔性股骨柄在植入后一年时，其邻近植入物处保留的皮质骨比刚性股骨柄多约30%，在术后两年和三年处死的犬中差异更大。应变片研究证实，两种股骨柄设计的皮质骨应变存在差异，柔性股骨柄在内侧产生更均匀且更接近正常的应变分布。使用双能X线吸收法（DEXA）对皮质骨重塑差异进行了量化。与正常情况相比，植入柔性股骨柄的股骨骨矿物质含量减少不到20%。植入三年后，植入刚性股骨柄的股骨骨矿物质含量约为植入柔性股骨柄的股骨的50%。临床上，DEXA显示，术后头两年内，植入物周围不同部位的骨矿物质密度变化5%-15%很常见；这些变化通常在X线片上不明显。X线片上连续出现的明显骨吸收通常与骨矿物质密度20%-50%的变化相关。对213例使用解剖型髓内锁定假体的患者进行5至13年的X线随访观察发现，33%的患者出现明显骨吸收。直径较大（大于13毫米）和多孔涂层广泛的股骨柄，其明显骨吸收的发生率显著高于较小的股骨柄和近端涂层的股骨柄。确定了人类股骨的刚度特性是髓腔大小的函数，并与非骨水泥型髋关节假体的刚度特性进行了比较。发现钛合金制成的、具有减小横截面积和惯性矩设计特征的股骨柄机械兼容性更高。临床数据表明，为降低明显骨吸收的可能性，植入物的弯曲刚度约为人股骨弯曲刚度的二分之一到三分之一可能有益。
