Woolson S T, Milbauer J P, Bobyn J D, Yue S, Maloney W J
Stanford University Hospital, California, USA.
J Bone Joint Surg Am. 1997 Dec;79(12):1842-8. doi: 10.2106/00004623-199712000-00010.
Ten patients who had had a total hip replacement with a forged cobalt-chromium-molybdenum femoral prosthesis (Precoat or Precoat Plus) inserted with cement were seen with a fatigue fracture of the stem an average of fifty months (range, nineteen to seventy-four months) postoperatively. The average age of the patients was sixty-one years (range, forty-three to seventy-three years), and the average weight was ninety-six kilograms (range, seventy to 130 kilograms). Eight patients had had a primary total hip replacement, and two had had a revision; all of the acetabular components had been inserted without cement. Radiographs that had been made before the fracture were available for four of the eight hips that had had a primary replacement; all four had radiographic evidence of debonding of the cement mantle from the proximal end of the stem. This probably caused exaggerated cantilever bending stresses on the proximal aspect of the stem as the distal end of the stem was well fixed. The radiographs of both hips that had had a revision demonstrated a non-union of the greater trochanter, which had resulted in separation at the cement-bone interface at the proximal portion of the femur before the fracture. Scanning electron micrographs of five of the ten fractured prostheses demonstrated a fatigue fracture that began near the anterolateral corner of the prosthesis, through characters that had been etched on the implant with a laser. Metallurgical analysis indicated subsurface voids or inclusions, or both, immediately under the region that had been etched. This finding is consistent with thermal changes to the microstructure of the alloy that probably caused a focal reduction in the material strength. A high proportion (seven) of the ten stems had a poor cement mantle. Also, of the seven small stems that were used, six had been implanted in patients who weighed more than eighty kilograms, so there was relative undersizing of the prostheses. Early debonding of the proximal end of a Precoat femoral prosthesis from the cement mantle may occur as a result of a thin cement mantle, leading to loosening and possibly to early fatigue fracture of the stem if the distal portion of the stem remains solidly fixed in the distal portion of the cement column. On the basis of our experience, we recommend that patients who have radiographic evidence of a debonded Precoat femoral component should be informed of the risk of fatigue fracture of the stem and be followed closely even though there may be no symptoms of loosening of the femoral component.
10例采用骨水泥植入锻造钴铬钼股骨假体（Precoat或Precoat Plus）进行全髋关节置换术的患者，术后平均50个月（范围19至74个月）出现假体柄疲劳骨折。患者平均年龄61岁（范围43至73岁），平均体重96千克（范围70至130千克）。8例患者接受初次全髋关节置换术，2例接受翻修手术；所有髋臼组件均未使用骨水泥植入。8例初次置换的髋关节中有4例在骨折前有X线片，所有4例均有骨水泥壳从假体柄近端脱粘的X线证据。这可能导致假体柄近端出现过度的悬臂弯曲应力，因为假体柄远端固定良好。2例翻修髋关节的X线片显示大转子不愈合，这导致骨折前股骨近端骨水泥与骨界面分离。10个骨折假体中的5个的扫描电子显微镜图像显示疲劳骨折始于假体前外侧角附近，穿过用激光蚀刻在植入物上的标记。金相分析表明在蚀刻区域正下方存在表面下孔隙或夹杂物，或两者皆有。这一发现与合金微观结构的热变化一致，这可能导致材料强度局部降低。10个假体柄中有很大比例（7个）的骨水泥壳质量差。此外，在使用的7个小号假体柄中，有6个植入了体重超过80千克的患者体内，因此假体相对尺寸过小。Precoat股骨假体柄近端与骨水泥壳早期脱粘可能是由于骨水泥壳薄所致，如果假体柄远端牢固固定在骨水泥柱远端，则会导致松动，并可能导致假体柄早期疲劳骨折。根据我们的经验，我们建议，即使股骨组件可能没有松动症状，但对于有Precoat股骨组件脱粘X线证据的患者，应告知其假体柄疲劳骨折的风险，并密切随访。
