软骨终板的功能
1.保护椎体:软骨终板由透明软骨构成,位于椎体上、下面,其大小和形状与上、下相连的椎体相当,厚约1mm,这种椎体上、下无血管软骨终板如同膝关节、髋关节的关节软骨,可以承受压力保护椎体,防止椎体遭受压力而受损,只要软骨终板保持完整,椎体不会因压力而发生吸收现象。
2.固定髓核,防止髓核向椎体内突出:
在静载荷作用下,椎体终板首先发生破坏,这说明终板是一个较为薄弱的结构。脊柱软骨终板破裂多发生于胸腰椎软骨板中部,髓核向椎体松质骨内突出,形成Schmorl结节。完整无损的软骨终板是不会出现Schmorl结节的。
3.软骨终板具有半渗透膜作用:椎体与椎间盘之间的液体、营养的交换,髓核代谢物质的传递都是通过软骨终板进行的。髓核的营养经软骨终板渗透,后者与椎体松质骨密切相连,其间无皮质骨相隔。椎体的松质骨有丰富血供,尤其是软骨终板的中心部位渗透性更强,在人体活动和负重情况下,更有利于软骨终板弥散过程的完成,使椎体内的液体流出流进,营养物质和代谢产物顺利进行交换。所以当直立时髓核内压力加大,液体自髓核渗透出,卧位时,压力消除,肌肉张力减少,液体又经软骨终板渗透至髓核。
4.缓冲压力。
5.保护椎间盘结构、维持椎间盘的功能:软骨终板与纤维环一起固定髓核,使髓核发挥其功能。另外,椎间盘的弹性及张力取决于软骨终板的通透性和髓核的渗透性。椎间盘的吸液性如发生改变,不仅影响椎间盘的稳定性,而且可使椎间盘发生变性。在机体生长发育和老化过程中,椎间盘中央部位细胞和基质最关键的变化是营养供应减少。椎间盘细胞的营养物质依靠纤维环外周和椎体内血管通过基质弥散供应。在生长过程中,椎间盘体积增大、机体老化过程中供应椎间盘周围的动脉数量减少、软骨终板逐渐钙化,这些改变妨碍了营养物质的供应和废物的清除。另外,有人研究认为正常椎间盘中除软骨终板含有少许活性蛋白酶外,在髓核和纤维环中并没有发现此酶的存在,此酶被软骨终板阻隔于椎体内,当软骨终板退变变薄时,此酶经软骨终板进入髓核和纤维环,使弹性蛋白降解,并分解蛋白多糖和胶原纤维,从而使椎间盘发生退变。在上述3个变化中,软骨终板钙化的影响尤为重要,因为椎间盘营养是通过软骨终板中央部位的弥散而摄取的。
(郭义柱)
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