Boyde A, Firth E C
Biophysics, Centre for Oral Growth and Development, St Barts and The London School of Medicine and Dentistry, Queen Mary University of London, Whitechapel, London E11BB, England.
N Z Vet J. 2005 Apr;53(2):123-32. doi: 10.1080/00480169.2005.36489.
To characterise and explain the increase in density evident by computerised tomography (CT) and radiography in companion studies as a response to training, in bone in the palmar and dorsal regions of the condyles of the third metacarpal bone (Mc3) of 2-year-old Thoroughbred horses.
Compositional back-scattered electron (BSE) imaging in scanning electron microscopy (SEM) and confocal scanning laser microscopy (CSLM) were conducted on polymethyl methacrylate (PMMA)-embedded mediolateral slices of the right distal Mc3 from seven 2-year-old Thoroughbred horses trained on a racetrack and seven untrained horses kept at pasture. One left Mc3 from each group was studied in transverse section planes. This study focussed on regions of Mc3 found to differ in density between the trained and untrained horses in companion studies using CT and radiography.
The increase of bone density in the condyles of Mc3 in trained horses compared with untrained horses occurred, without prior osteoclastic resorption, via the deposition of new bone on pre-existing internal surfaces. Within prior marrow spaces of cancellous bone, there was also rapid formation of immature strands and fronds of bone which were more cellular and mineralised, and more lamellar bone tissue was deposited on these new scaffolding elements in the trained horses. Both resulted in increased bone volume fraction (BVF). The microscopic mineralisation density of the bulk of the new tissue was lower than in pre-existing bone, and CT and radiography underestimated the increase in BVF. The new tissue was thus probably less stiff at the microscopic scale than pre-existing bone, though its addition would stiffen the global structure.
In Mc3 of all the trained horses, there were obvious differences in microscopic structure compared with those from the untrained horses. Moderate, industry-standard levels of exercise used to prepare young horses for racing induced the formation of new bone in non-bone spaces in bone tissue, such that the bone organ should better withstand later increased levels of exercise.
在两项配套研究中，通过计算机断层扫描（CT）和X线摄影发现，2岁纯种马第三掌骨（Mc3）掌侧和背侧髁部的骨密度因训练而增加，本研究旨在对这一现象进行特征描述并解释其原因。
对7匹在赛道上训练的2岁纯种马和7匹在牧场饲养的未经训练的马，取其右侧Mc3远端的内外侧切片，用聚甲基丙烯酸甲酯（PMMA）包埋后，进行扫描电子显微镜（SEM）中的成分背散射电子（BSE）成像和共聚焦扫描激光显微镜（CSLM）检查。每组取1根左侧Mc3进行横断面研究。本研究聚焦于在CT和X线摄影的配套研究中发现的训练马和未训练马之间骨密度存在差异的Mc3区域。
与未训练的马相比，训练马的Mc3髁部骨密度增加，且无先前破骨细胞吸收的情况，是通过在已有内表面上新骨的沉积实现的。在先前松质骨的骨髓腔内，还迅速形成了不成熟的骨小梁和骨片，这些骨小梁和骨片细胞更多、矿化程度更高，并且在训练马中，更多的板层骨组织沉积在这些新的支架结构上。两者均导致骨体积分数（BVF）增加。大部分新组织的微观矿化密度低于已有骨，CT和X线摄影低估了BVF的增加。因此，尽管新组织的添加会使整体结构变硬，但在微观尺度上，新组织可能比已有骨的硬度更低。
所有训练马的Mc3与未训练马相比，微观结构存在明显差异。用于让幼马为比赛做准备的适度的、行业标准水平的运动，会诱导骨组织中非骨空间形成新骨，从而使骨骼器官能更好地承受后期增加的运动水平。
