Misconceptions (2): Turnover is always higher in cancellous than in cortical bone
Misconceptions (2): Turnover is always higher in cancellous than in cortical bone
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DOI：
10.1016/s8756-3282(02)00735-4
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发表时间：
2002-06-01
期刊：
影响因子：
4.1
通讯作者：
Parfitt, AM
中科院分区：
文献类型：
--
作者：
Parfitt, AM
自从人们普遍认识到骨可以发生周转以来，28经常毫无保留地断言松质骨的周转率高于皮质骨。例如：“皮质骨和新陈代谢更活跃的松质骨的差异往往是……”13；松质骨..。新陈代谢活性是皮质骨的八倍。在代谢方面，松质骨比皮质骨更活跃，前者的年周转率约为20%至30%，后者的年周转率约为3%至10%。2“松质骨约占骨骼质量的20%，占总周转率的80%，而占骨骼80%的皮质仅占总周转率的20%。”5在此，我确切地阐明了这种信念的含义，追溯其起源，定义其成立的情况，并指定必要的条件，这些条件总是被省略。但首先，我必须确切地解释一下什么是“骨周转”。科学语言经常取常用的词语，并为不同的目的重新定义它们，但骨生理学中“周转”的含义与它的日常含义完全相同，那就是替代。企业的人事经理是指员工的周转率，店主是商品的周转率。在这两种情况下，周转率都以每单位时间占总时间的比例(通常是小数或百分比)表示，前者可能是一年，后者可能是一周。营业额的互换总是有一段时间的。例如，如果收银员的流动率为50%/年，他们的平均雇佣年限将为2年，尽管他们的个人长度可能会有很大的差异。在日常使用中，周转最常见的是人或物。骨骼是一种连续的材料，而不是离散实体的集合，但在其他方面，它的周转率是以完全相同的方式定义的-它指的是单位时间的比例体积替换，通常表示为百分比/年。如前所述，周转率的倒数是一段时间；如果骨周转率为10%/年，那么每部分骨的平均寿命为10年，尽管它们的个体寿命可能有很大的差异。14.
Since it became generally recognized that bone is subject to turnover, 28 it has often been asserted without qualification that cancellous bone has higher turnover than cortical bone. For example:“Much is often made of differences in cortical and metabolically more active cancellous bone...” 13;“... trabecular bone... is eight times more metabolically active than cortical bone” 29;“... trabecular bone is metabolically more active than cortical bone, with an annual turnover of approximately 20% to 30% for the former and 3% to 10% for the latter” 2; and “the cancellous bone, which represents about 20% of the skeletal mass, makes up 80% of the turnover, while the cortex, which represents 80% of the bone, makes up only 20% of the turnover.” 5 Herein, I clarify exactly what such a belief implies, trace its origins, define the circumstances in which it is true, and specify the necessary qualifications, which are invariably omitted. But first I must explain precisely what is meant by “bone turnover.” The language of science frequently takes words in common use and redefines them for a different purpose, but the meaning of “turnover” in bone physiology is exactly the same as its everyday meaning, which is replacement. The personnel manager of a business refers to the turnover of employees and the owner of a store to the turnover of items of merchandise. In both cases, the rate of turnover is expressed as a proportion of the total (usually a decimal fraction or a percentage) per unit of time, which could be a year in the former case or a week in the latter. The reciprocal of turnover is always a period of time. For example, if the turnover of checkout clerks is 50%/year, their average length of employment will be 2 years, although their individual lengths may vary over a wide range. In everyday use, turnover is most often of people or things. Bone is a continuous material rather than an assemblage of discrete entities, but otherwise its turnover is defined in exactly the same way—it refers to proportional volume replacement per unit time, usually expressed as percent/year. As before, the reciprocal of turnover is a period of time; if bone turnover is 10%/year, then the mean lifetime of each moiety of bone is 10 years, although their individual lifetimes may vary over a wide range. 14