Faculty of Veterinary Science, Equine Centre, University of Melbourne, 250 Princes Hwy, Werribee, Victoria 3030, Australia.
Osteoporos Int. 2013 Jul;24(7):2043-8. doi: 10.1007/s00198-013-2291-z. Epub 2013 Feb 1.
Bone remodelling is inhibited by high repetitive loading. However, in subchondral bone of racehorses in training, eroded surface doubled in association with fatigue fracture and there was greater surrounding trabecular bone volume suggesting trabecular modelling unloads the bone focally, allowing damage repair by remodelling.
Remodelling replaces damaged bone with new bone but is suppressed during high magnitude repetitive loading when damage is most likely. However, in cortical bone of racehorses, at sites of fatigue fracture, focal porosity, consistent with remodelling, is observed in proportion to the extent of surrounding callus. Focal areas of porosity are also observed at sites of fatigue damage in subchondral bone. We hypothesised that fatigued subchondral bone, like damaged cortical bone, is remodelled focally in proportion to the modelling of surrounding trabecular bone.
Eroded and mineralizing surfaces and bone area were measured using backscattered scanning electron microscopy of post-mortem specimens of the distal third metacarpal bone in 11 racehorses with condylar fractures (cases) and eight racehorses in training without fractures (controls).
Cases had a two-fold greater eroded surface per unit area at the fracture site than controls (0.81 ± 0.10 vs. 0.40 ± 0.12 mm(-1), P = 0.021) but not at an adjacent site (0.22 ± 0.09 vs. 0.30 ± 0.11 mm(-1), P = 0.59). Area fraction of surrounding trabecular bone was higher in cases than controls (81 ± 2 vs. 72 ± 2 %, P = 0.0020) and the eroded surface at the fracture site correlated with the surrounding trabecular area (adjusted R (2) = 0.63, P = 0.0010).
In conclusion, exercise-induced inhibition of remodelling is offset at sites of fatigue fracture. Modelling of trabecular bone may contribute to unloading these regions, allowing repair by remodelling.
高重复加载会抑制骨重塑。然而，在训练中的赛马的软骨下骨中，侵蚀表面增加了一倍，与疲劳性骨折有关，并且周围的小梁骨体积更大，这表明小梁重塑使骨局部卸载，从而通过重塑进行损伤修复。
重塑用新骨替代受损的骨，但在高幅度重复加载时会受到抑制，因为此时最有可能发生损伤。然而，在赛马的皮质骨中，在疲劳性骨折部位，与周围骨痂成比例地观察到焦点多孔性，这与重塑一致。在软骨下骨的疲劳性损伤部位也观察到焦点区域的多孔性。我们假设，像受损的皮质骨一样，疲劳性软骨下骨是局部成比例地重塑的，与周围小梁骨的重塑成比例。
使用 11 匹患有髁部骨折（病例）和 8 匹没有骨折（对照）的训练中的赛马的远三掌骨骨的死后标本的背散射电子显微镜，测量侵蚀和矿化表面以及骨面积。
病例组在骨折部位的单位面积的侵蚀表面是对照组的两倍（0.81 ± 0.10 对 0.40 ± 0.12 mm（-1），P = 0.021），但在相邻部位则不然（0.22 ± 0.09 对 0.30 ± 0.11 mm（-1），P = 0.59）。病例组的周围小梁骨的面积分数高于对照组（81 ± 2%对 72 ± 2%，P = 0.0020），并且骨折部位的侵蚀表面与周围小梁骨面积相关（调整 R（2）= 0.63，P = 0.0010）。
总之，运动引起的重塑抑制在疲劳性骨折部位得到缓解。小梁骨的重塑可能有助于使这些区域卸载，从而通过重塑进行修复。
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