Yamaguchi M, Bauer T W, Hashimoto Y
Department of Anatomic Pathology, The Cleveland Clinic Foundation, Ohio 44195, USA.
J Bone Joint Surg Am. 1997 Oct;79(10):1539-44. doi: 10.2106/00004623-199710000-00011.
The wear of polyethylene acetabular components is an important issue in total hip arthroplasty. The amount of wear has been measured in many studies, but few have addressed other mechanical aspects of wear in vivo. We used the shadowgraph method to measure the wear vectors in 104 retrieved acetabular cups that had been made by a single manufacturer, and we identified more than one wear vector in thirty-one cups (30 per cent). We hypothesized that the most likely explanation of multiple wear vectors was loosening of the acetabular implant with a change in the orientation of the implant in the pelvis. To test this hypothesis, we estimated the extent of motion of the cup in situ on the basis of differences in angles measured from serial radiographs of sixteen hips. We then used linear transformation of the three-dimensional vectors to compare the wear directions measured in the retrieved implants with the wear directions predicted from the radiographs. The change in wear direction predicted on the basis of in vivo motion of the cup never corresponded to the actual difference between wear vectors in the retrieved implants. Our results suggest that multiple wear vectors may be commonly found in retrieved implants, but loosening of the acetabular cup does not account for the multiple vectors. Additional observations suggest that impingement between the edge of the acetabular cup and the femoral component may be associated with multiple wear vectors. These results have implications for the investigation of the general mechanisms of wear in vivo and suggest that clinical or wear-testing scenarios that assume a single direction of wear may underestimate the over-all amount of volumetric wear.
聚乙烯髋臼部件的磨损是全髋关节置换术中的一个重要问题。许多研究都对磨损量进行了测量，但很少有研究涉及体内磨损的其他力学方面。我们使用阴影图法测量了104个由单一制造商生产的回收髋臼杯的磨损矢量，在31个杯子（30%）中发现了不止一个磨损矢量。我们假设多个磨损矢量最可能的解释是髋臼植入物松动并伴有植入物在骨盆中方向的改变。为了验证这一假设，我们根据从16例髋关节的系列X线片中测量的角度差异估计了髋臼杯在原位的运动程度。然后，我们使用三维矢量的线性变换来比较回收植入物中测量的磨损方向与根据X线片预测的磨损方向。根据髋臼杯的体内运动预测的磨损方向变化从未与回收植入物中磨损矢量的实际差异相对应。我们的结果表明，回收植入物中可能普遍存在多个磨损矢量，但髋臼杯的松动并不能解释这些多个矢量。其他观察结果表明，髋臼杯边缘与股骨部件之间的撞击可能与多个磨损矢量有关。这些结果对体内磨损一般机制的研究具有启示意义，并表明假设单一磨损方向的临床或磨损测试方案可能会低估总体积磨损量。
