O'Connor D O, Burke D W, Jasty M, Sedlacek R C, Harris W H
Orthopaedic Biomechanics Laboratory, Massachusetts General Hospital, Boston 02114, USA.
J Orthop Res. 1996 Sep;14(5):769-77. doi: 10.1002/jor.1100140514.
The strains in the cement mantle surrounding the cemented femoral component of a total hip replacement were measured in vitro, using strain gauges embedded within the cement mantle adjacent to the femoral component in femurs from cadavers under physiologic loads simulating both single-limb stance and stair-climbing. Cement strains in the most proximal portion of the cement mantle were measured with and without full contact of the collar of the femoral stem on the cortex of the medial portion of the femoral neck during both loading conditions. To our knowledge, these are the first studies to contrast by direct measurement the strain profile in the cement mantle of a cemented femoral component under simulated stair-climbing with that occurring under simulated single-limb stance. They extend the findings from finite element analyses and from clinical specimens retrieved at autopsy in identifying those regions of the cement mantle most likely to fail. At two specific foci, the magnitude of the strain in the cement mantle approaches values that could lead to early fatigue failure of the cement. The two regions in which the strains were highest (greater than 1,000 microstrain) were the most proximal portions of the cement mantle and near the tip of the femoral component. Although these two regions are recognized areas of high strain and also common sites of cement debonding and cement mantle failure, the strain-gauge studies showed that the magnitude of cement strains in the proximal portion of the cement mantle were highest during stair-climbing; in contrast, high strains at the tip region occurred in both gait and stair-climbing. Contact between the collar and the medial portion of the femoral neck reduced the strain in the proximal portion of the cement mantle not only in single-limb stance but in stair-climbing as well. The level of strain recorded in these studies for a simulated person weighing 115 pounds (52 kg) could lead to cement fracture during extended in vivo service life of a cemented femoral component, from either single-limb stance or stair-climbing. This risk would be increased if a void or defect existed in the cement mantle at these sites. Moreover, the increase in strain in the cement mantle was linear with increases in body weight between 100 and 200 pounds (45 and 91 kg) of spinal load, indicating that strains in a heavy patient could readily exceed the fatigue limit of the cement, particularly if a stress riser such as a pore in the cement or a sharp corner of the prosthesis were present. These data reemphasize the need to continue efforts to develop methods to strengthen bone cement and to reduce those factors that increase the strain in the cement mantle of cemented femoral components of total hip arthroplasty, particularly proximally and near the tip.
在体外测量了全髋关节置换术中骨水泥固定股骨部件周围骨水泥壳内的应变，使用埋入尸体股骨中与股骨部件相邻的骨水泥壳内的应变片，在模拟单腿站立和爬楼梯的生理负荷下进行测量。在两种负荷条件下，测量了股骨颈内侧皮质上股骨柄颈圈完全接触和未完全接触时骨水泥壳最近端部分的水泥应变。据我们所知，这些是首次通过直接测量对比模拟爬楼梯和模拟单腿站立时骨水泥固定股骨部件的骨水泥壳内应变情况的研究。它们扩展了有限元分析和尸检时获取的临床标本的研究结果，以确定骨水泥壳中最可能失效的区域。在两个特定部位，骨水泥壳内的应变大小接近可能导致骨水泥早期疲劳失效的值。应变最高（大于1000微应变）的两个区域是骨水泥壳的最近端部分和股骨部件尖端附近。尽管这两个区域是公认的高应变区域，也是骨水泥脱粘和骨水泥壳失效的常见部位，但应变片研究表明，在爬楼梯时骨水泥壳近端部分的骨水泥应变大小最高；相比之下，尖端区域在步态和爬楼梯时都会出现高应变。颈圈与股骨颈内侧部分之间的接触不仅在单腿站立时，而且在爬楼梯时都降低了骨水泥壳近端部分的应变。这些研究中记录的模拟体重115磅（52千克）的人的应变水平，可能会导致骨水泥固定股骨部件在体内延长使用寿命期间，因单腿站立或爬楼梯而发生骨水泥骨折。如果这些部位的骨水泥壳存在空隙或缺陷，这种风险将会增加。此外，在100至200磅（45至91千克）脊柱负荷下，骨水泥壳内的应变增加与体重增加呈线性关系，这表明体重较重的患者的应变很容易超过骨水泥的疲劳极限，特别是如果存在诸如骨水泥中的孔隙或假体尖锐角等应力集中源。这些数据再次强调，需要继续努力开发加强骨水泥的方法，并减少增加全髋关节置换术中骨水泥固定股骨部件骨水泥壳内应变的因素，特别是在近端和尖端附近。
